zzzzq) Powerpoint Immunity Parts 1-3

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Where are pattern recognition receptors (PRR), the best-described of which are toll-like receptors (TLR), found ?

Macrophages and dendritic cells also have special receptors known as pattern recognition receptors (PRR), the best-described of which are toll-like receptors (TLR). PRRs are able to recognize the category of the invader (bacterium, virus, fungus, or parasite). This allows for the production of appropriate cytokines to recruit the right type of immune cells; each immune cell has different weapons that can target particular groups of pathogens.

Into which types of cells do myeloid stem cells differentiate ?

Myeloid stem cells differentiate into four types of leukocytes (neutrophils, eosinophils, basophils, and monocytes). Via another developmental pathway, myeloid cells also differentiate into mast cells and dendritic cells. Macrophages differentiate from monocytes

Describe clonal selection.

Once an antigen receptor binds its anti- gen, the selected cell divides into a clone of effector cells and memory cells specific for that antigen.

26. What is the major cell type involved in graft rejection?

Rejection of tissue transplants is initiated by MHC proteins on the transplanted cells and is mediated mainly by cytotoxic T cells.

Which characterizes antigenic determinants? Please choose the correct answer from the following choices, and then select the submit answer button. Specific regions on antigens are recognized by the immune system. They are also called antibodies. Each antigenic molecule has one, and only one, antigenic determinant. They are usually phospholipids. Multiple, different antibodies bind to a single one.

The correct answer is: Specific regions on antigens are recognized by the immune system.

When would a B cell present an antigen on an MHC I protein? Please choose the correct answer from the following choices, and then select the submit answer button. When the B cell is infected with a virus After stimulation by cytokines As part of the effector phase of any immune response After activation by a TH cell After ingesting a pathogen in a phagosome

The correct answer is: When the B cell is infected with a virus

When a patient comes into a clinic with allergies, a doctor will often recommend antihistamines. When a person takes antihistamines, he or she is trying to prevent Please choose the correct answer from the following choices, and then select the submit answer button. mast cell activity. T cells from producing antibody. macrophages from completing phagocytosis. neutrophils from degranulating. B cells from killing target cells.

The correct answer is: mast cell activity.

3. Name the three cell types that function as phagocytes.

The main cells that function as phagocytes are the neutrophils, monocytes, macrophages, and dendritic cells. These cells also secrete many inflammatory mediators.

3. Which cells are considered a) granulocytes? b) Which are considered agranulocytes?

a) Granulocytes include neutrophils, eosinophils, and basophils. b) Agranulocytes include B- and T-cells (lymphocytes) and monocytes (macrophages).

1. Which of the following is an opsonin? a. IL-2 b. C1 protein c. C3b protein d. C-reactive protein e. membrane attack complex

13. Plasma cells are a. the same as memory cells. b. formed from blood plasma. c. B cells that are actively secreting antibody. d. inactive T cells carried in the plasma._.-

20. A child with severe combined immunodeficiency will have low or absent amounts of a. antibodies. b. B cells. c. cell-mediated immunity. d. T cells. e. All of these are correct.

humoral immunity is called humoral - why ?

http://www.differencebetween.net/science/difference-between-humoral-and-cell-mediated-immunity/

Compare and contrast B- and T-cells: 1. B-cell site of development? 2. T-cell " " " ? 3. B-cell site of Maturation ? 4. T-cell site of Maturation ? 5. B-cell major function ? 6. T-cell " " " ? 7. B-cell specific or non-specific ? 8. T-cell specific or non-specific ? 9. B-cell Humoral or cell-mediated ? 10. T-cell Humoral or cell-mediated ?

1. Bone marrow 2. " " 3. Bone marrow but activated in spleen or lymph node 4. Thymus 5. Produce antibodies 6. Coordinate immune system and directly kill infected cells 7. Specific 8. " 9. Humoral 10. Cell-mediated

25. What is the major defect in AIDS, and what causes it?

AIDS is caused by a retrovirus that destroys helper T cells and therefore reduces the body's ability to resist infection and cancer.

Activated complement proteins cause a) Direct destruction of invading microbes by membrane attack complex b) Enhancement of phagocytosis (opsonization) c) Vasodilation and increased permeability of capillaries and venules to proteins d) Chemotaxis

All are true

1. Which of these is not part of insect immunity? (A) enzyme activation of pathogen-killing chemicals (B) activation of natural killer cells (C) phagocytosis by hemocytes (D) production of antimicrobial peptides

4. Which of the following statements is not true? (A) An antibody has more than one antigen-binding site. (B) A lymphocyte has receptors for multiple different antigens. (C) An antigen can have different epitopes. (D) A liver or muscle cell makes one class of MHC molecule.

5. Which of the following should be the same in identical twins? (A) the set of antibodies produced (B) the set ofMHC molecules produced (C) the set of T cell antigen receptors produced (D) the set of immune cells eliminated as self-reactive

How do antibodies become specific for a given antigen?

B-cells originally mature in the bone marrow and have some specificity at that point; however, antibodies that can respond to a given antigen undergo hypermutation, or rapid mutation of their antigen-binding sites. Only those B-cells that have the highest affinity for the antigen survive and proliferate, increasing the specificity for the antigen over time.

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Histamine causes inflammation by inducing ___________ and the movement of fluid and cells from the bloodstream into tissues.

Histamine causes inflammation by inducing vasodilation and the movement of fluid and cells from the bloodstream into tissues.

365. The specificity of an antibody is determined by (A) random gene rearrangements within B-cell progenitors. (B) antigenic selection of B-cell clones within the bone marrow. (C) clonal selection by macro phages within the bone marrow. (D) B-cell response within lymph nodes. (E) B-cell encounters with foreign antigens.

(A) During hematopoiesis, progenitor lymphocytes undergo random gene rearrangements. This randomly rearranged DNA then codes for the receptor that determines the antigen specificity for that individual cell, which will be different from that for every other cell.

347. Which of the following is NOT descriptive of immunoglobulins? (A) They are composed of three alpha-chains and one Beta-chain. (B) They are glycoproteins found in the blood. (C) They are produced in large quantities by plasma cells. (D) They are glycoproteins found in lymph. (E) They neutralize toxins by binding to complementary regions.

(A) Immunoglobulin is another name for an antibody. Once these glycoproteins are synthesized in lymph tissues, they circulate firstihrough the lymph, then through the blood. While they are composed of four protein chains, these are identified as two light chains and two heavy chains bound together by disulfide bridges.

348. The primary lymphoid organs include (A) the thymus and bone marrow. (B) lymph nodes and nodules:' (C) the spleen and thymus. (D) lymph nodes, follicles, and nodules. (E) bone marrow and the thyroid.

(A) The immune system is divided into primary and secondary lymphoid organs or tissues. The primary organs are responsible for generating and screening the cells of the immune system. The organs responsible for initially manufacturing these cells are the thymus and the bone marrow.

355. After antigenic stimulation, a specific B-cell (A) will undergo lymphoproliferation, then differentiation. (B) will start to produce membrane-bound antibodies. (C) will differentiate into a plasma cell. (D) will start the manufacture of antibodies for secretion. (E) will differentiate into a memory cell.

(A) When a foreign antigen binds to the surface-bound antibody, it activates the B-cell response. First, the cell undergoes Iymphoproliferation, producing a clone of cells, all producing the same antibody. Second, these cells all shift to manufacturing secreted antibodies. Some of these cells become memory cells, and the remainder of the activated cells will differentiate into antibody factories known as plasma cells.

352. Which of the following is NOT a primary function of the lymph system? (A) Maintaining proper fluid balance (B) Production of antibodies (C) Transport of large triglycerides (D) Movement of materials from the tissues to the blood (E) Transport of proteins

(B) The only thing listed that the lymph does not do is to produce antibodies, as that is done by B-cells and plasma cells congregated in the lymphoid tissues that they pass through.

345. The cell type that carries the greatest responsibility for phagocytic protection of the body is the (A) lymphocyte. (B) neutrophil. (C) macrophage. (D) eosinophil. (E) erythrocyte.

(B) Neither erythrocytes nor lymphocytes are phagocytic. The three remaining choices are, but eosinophils are only slightly so, and they are few in number. While macrophages are larger than neutrophils and are each capable of phagocytosing more per cell, they are outnumbered by neutrophils by more than 3:1.

363. Which chemical would interfere with the purpose of platelets? (A) SRS-A (B) Histamine (C) Heparin (D) Plasminogen (E) Serotonin

(C) Platelets, also known as thrombocytes because of their role in forming a thrombus (blood clot), are degenerate cell fragments found throughout the blood. Heparin is an anti-coagulant whose presence leads to the inactivation of thrombin, thus preventing effective clot formation.

343. Of the following, which is the smallest and simplest of the immune components? (A) Lymph node (B) Thymus (C) Lymph follicle (D) Lymph nodule (E) Spleen

(C) The immune system is composed of primary and secondary lymphoid organs. The thymus (a primary organ) and the spleen (a secondary organ) are the organs that are the largest of the group. Lymph nodes are the next smaller in size and are more complex and organized than the other two. Of the remaining two, lymph nodules are collections of lymph follicles.

366. The lymph system connects to the circulatory system (A) within the spleen. (B) in lymph nodes. (C) at the vena cava. (D) at the capillaries in various somatic tissues. (E) within the lungs.

(C) The lymph system has no pump, and lymph moves slowly from the tissues through the ducts, passing through lymph nodules and nodes that provide immune surveillance by constantly searching for foreign proteins draining from the tissues. This fluid reenters the circulatory system when the lymph fluid is dumped back into the circulatory system at the vena cava.

371. Which of the following least distinguishes the primary immune response from the secondary immune response? (A) A difference in time when a maximum response is presented (B) Which antibody class is predominant (C) Which antigen is used to stimulate the responses (D) The level of the antibody response (E) The role of memory cells in generating the response

(C) The primary immune response occurs following a first-time exposure to an antigen and is characterized by low levels of IgM production. The secondary response is characterized by a higher production of IgG and the subsequent production of memory cells. What doesn't seem to matter is the specific antigen; only the level and duration of exposure determines which response will be observed.

351. Elimination of cancer cells is the responsibility of (A) T-helper cells. (B) macrophages. (C) T CTL cells. (0) antibodies. (E) complement.

(C) When a cell becomes cancerous, it usually starts to express proteins that are nor- mally not expressed by normal cells, and these can stimulate a specific immune response. The effector cells that attack cancer cells by inducing apoptosis are known as cytotoxic T -lyrnphocytes, or T CTL cells.

364. Hematopoiesis is a process that occurs in (A) the spleen. (B) the thymus. (C) lymph nodes. (D) bone marrow. (E) areas of infection.

(D) Hematopoiesis is the process of making blood, specifically the cellular compo- nents. Other than the red blood cells, all of these cells are leukocytes associated with some aspect of body defense. The thymus is a primary lymphoid organ, but the T-cells that are there migrated there during gestation from the actual site of hematopoiesis, the bone marrow.

354. Erythrocytes are best described as (A) leukocytes that carry oxygen. (B) thrombocytes that contain iron. (C) bone marrow-derived cells that carry nutrients. (D) lymphocytelike cells that carry CO2, (E) degenerate cells that contain hemoglobin.

(E) Bone marrow stem cells initially differentiate into myeloid and lymphoid progenitor cells. Erythroid progenitor cells then degenerate into erythrocytes (or red blood cells).

362. Of the following, which is NOT an autoimmune disorder? (A) Type I diabetes (B) Rheumatoid arthritis (C) Hemolytic anemia (D) Pernicious anemia (E) Type II diabetes

(E) An autoimmune disorder occurs when one's immune system attacks one's own body and produces damage. Type II diabetes can be caused by several things, including loss of sensitivity to insulin or its insufficient production, but none are classed as autoimmunity.

353. The proper sequence of actions that bring phagocytic cells from circulation in the blood into infected tissues is (A) tight binding, rolling adhesion, diapedesis, migration. (B) diapedesis, rolling adhesion, migration, tight binding. (C) migration, rolling adhesion, diapedesis, tight binding. (D) tight binding, diapedesis, migration, rolling adhesion. (E) rolling adhesion, tight binding, diapedesis, migration.

(E) Macrophages flowing through the blood bounce into ligands and begin to mar- ginate, first slowly as a rolling adhesion, then with the cells becoming more firmly attached by tighter binding with additional molecules. Once they are stopped, the cells enter the tissues by going between adjacent endothelial cells (diapedesis). Once there, they migrate through the tissues toward the infected area following a Signal gradient.

358. What substance dilates blood vessels, increases tissue pressure, and can induce hypovolemic shock? (A) SRS-A (B) gamma-interferon (C) IL-2 (D) CD4 (E) Histamine

(E) SRS-A (slow-reacting substance of anaphylaxis) does produce a systemic response, but, as its name implies, it does so slowly and causes sustained broncoconstriction. Histamine, on the other hand, produces all of the effects listed.

369. Which of the following antibody classes provides the best protection against microbial invasion through the intestinal mucosa? (A) IgM (B) IgD (C) IgG (D) IgE (E) IgA

(E) The primary antibody type in respiratory and intestinal secretions is manufactured just inside the epithelial layer of these tissues. These are then attached to a special protein called a secretory component that escorts these IgA antibodies through the epithelial cells and into the mucus, where they neutralize invaders before they have a chance to get inside the body.

346. Which of the following best distinguishes serum from plasma? (A) Serum has a higher concentration of proteins than plasma. (B) Plasma contains a higher percentage of erythrocytes than serum. (C) Plasma is the same thing as whole blood, while serum lacks the cellular components. (D) Where plasma contains antibodies, serum contains only the alpha- and Beta-globulins. (E) Serum is the same thing as plasma, but lacks clotting proteins.

(E) If blood is withdrawn from the body, it immediately begins to clot. The straw- colored liquid that remains is called serum. However, if the blood is drawn into a tube containing an anticoagulant, the clotting proteins remain in the fluid phase. After the cells settle, the straw-colored liquid that remains is called plasma. Serum is plasma with the clotting proteins removed.

6. Which of the following is an example of adaptive immunity? A. PRRs recognize that a pathogen is an invasive parasite and eosinophils are recruited to the area. B. Complement is activated, causing osmotic instability in a bacterium. C. Memory B-cells generated through vaccination are activated when their antigen is encountered. D. Dendritic cells sample bacteria within a laceration and travel to the lymph nodes to present the antigen.

C Adaptive immunity involves the activation of B-cells and T-cells specific to the encountered antigen. Any choice that conforms to this paradigm will be correct. Choice (C) indicates that B-cells are activated. Pattern recognition receptors, or PRRs, in choice (A) recognize patterns common to certain pathogens, but do not identify the specific pathogen. Complement is an example of a blood-borne nonspecific defense against bacteria, eliminating choice (B). Dendritic cells traveling to the lymph nodes in choice (D) are a part of the interaction between the innate and adaptive immune systems, but the dendritic cells themselves are nonspecific.

9. What is the response of the immune system to downregulation of MHC molecules on somatic cells? A. B-cells are activated and antibodies are released. B. T-cells are activated, resulting in a cytotoxic response. C. Natural killer cells induce apoptosis of affected cells. D. Macrophages engulf the pathogen and display its antigens.

C Healthy cells exhibit MHC class I molecules. Natural killer cells monitor the expression of MHC molecules on the sur- face of cells. Viral infection and cancer often cause a reduction in the expression of MHC class I molecules on the cell surface. Natural killer cells detect this lack of MHC and induce apoptosis in the affected cells.

11. Lymphoma is cancer of the cells of the lymphoid lineage. These cells often reside within lymph nodes. What type of cell is NOT likely to cause a lymphoma? A. CDS+ T-cells B. B-cells C. Macrophages D. Th1 cells

C Lymphocytes arise from the lymphoid lineage, which includes B-cells and T-cells. Thus, all types of B- and T-cells are capable of causing lymphoma. Macrophages, however, are not lymphocytes and are not likely to cause lymphoma.

Cytotoxic Immunity Whereas humoral immunity is based on the activity of B-cells, cell-mediated im- munity involves the T-cells. T-cells mature in the thymus, where they undergo both positive and negative selection. Positive selection refers to maturing only cells that can respond to the presentation of antigen on MHC (cells that cannot respond to MHC undergo apoptosis because they will not be able to respond in the periphery). Negative selection refers to causing apoptosis in cells that are self-reactive (activated by proteins produced by the organism itself). The maturation of T-cells is facilitated by thymosin, a peptide hormone secreted by thymic cells. Once the T-cell has left the thymus, it is mature but naive. Upon exposure to antigen, T-cells will also undergo clonal selection so that only those with the highest affinity for a given antigen proliferate. There are three major types of T-cells: helper T-cells, suppressor T-cells, and killer (cytotoxic) T-cells. Helper T-cells (Th), also called CD4+ T-cells, coordinate the immune response by secreting chemicals known as Iymphokines. These molecules are capable of recruiting other immune cells (such as plasma cells, cytotoxic 'l-cells, and macrophages) and increasing their activity. The loss of these cells, as occurs in human immunodeficiency virus (HIV) infection, pre- vents the immune system from mounting an adequate response to infection; in advanced HIV infection, also called acquired immunodeficiency syndrome (AIDS), even weak pathogens can cause devastating consequences as oppor- tunistic infections. CD4+ T-cells respond to antigens presented on MHC-II molecules. Because MHC-II presents exogenous antigens, CD4+ T-cells are most effective against bacterial, fungal, and parasitic infections.

CD4+ T-cells are better at fighting extracellular infections, while CD8+ T-cells are better at targeting intracel- lular infections.

What are the three main effects circulating antibodies can have on a pathogen?

Circulating antibodies can mark a pathogen for destruction by phagocytic cells (opsonization), cause agglutination of the pathogen in insoluble complexes that can be taken up by phagocytic cells, or can neutralize the pathogen by preventing its ability to invade tissues.

Which statement is false? Please choose the correct answer from the following choices, and then select the submit answer button. Phagocytes can move both within blood vessels and outside blood vessels. In their innate defense role, natural killer cells lyse cancerous cells and virus-infected cells. Phagocytes engulf and then kill pathogens using defensins, reactive oxygen-containing molecules, and nitric oxide. Interacting with adaptive defense mechanisms, natural killer cells lyse antibody-labeled target cells. Defensins attach to the surface of a pathogen, which helps phagocytes destroy the pathogen.

Correct: Defensins attach to the surface of a pathogen, which helps phagocytes destroy the pathogen.

8. Where are most self-reactive T-cells eliminated? A. Spleen B. Lymph nodes C. Bone marrow D. Thymus

D T-cells mature in the thymus, where they are "educated." This education involves the elimination of T-cells with improper binding to MHC-antigen complexes (positive selection) and self-reactive T-cells (negative selection). Thus, self-reactive T-cells are eliminated in the thymus

5. Which of the following is NOT an example of a nonspecific defense mechanism? A. Skin provides a physical barrier against invasion. B. Macrophages engulf and destroy foreign particles. C. An inflammatory response is initiated in response to physical damage. D. Cytotoxic T-cells destroy cells displaying foreign antigens.

D The body employs a number of nonspecific defense mechanisms against foreign invasion. The skin and mucous membranes provide a physical barrier against bacterial invasion. In addition, sweat contains enzymes that attack bacterial cell walls. Certain passages, such as the respiratory tract, are lined with ciliated mucus-coated epithelia, which filter and trap foreign particles. Macrophages engulf and destroy foreign particles. The inflammatory response is initiated in response to physical damage. The only choice that is not a nonspecific defense mechanism is choice (D), the correct answer. Cytotoxic T-cells are involved in (specific) cell-mediated immunity.

12. Upon encountering an antigen, only T-cells with a specific T-cell receptor are activated. This is an example of: A. innate immunity. B. a cytotoxic T-cell response. C. humoral immunity D. clonal selection.

D When the adaptive immune system encounters an antigen, only the cells with receptors (antibodies or T-cell receptors) specific to that antigen are activated. This is known as clonal selection. While a T-cell response may be a cytotoxic response, it could also be the activation of helper T-cells; plus, this does not explain the specificity of the response, eliminating choice (B).

What are the differences between MHC-I and MHC-II? • MHC-I: • MHC-II:

MHC-I is found in all nucleated cells and presents proteins created within the cell (endogenous antigens); this can allow for detection of cells infected with intracellular pathogens (especially viruses). MHC-II is only found in antigen- presenting cells and presents proteins that result from the digestion of extracellular pathogens that have been brought in by endocytosis (exogenous antigens).

Suppressor or regulatory T-cells (Treg) also express CD4, but can be differentiated from helper T-cells because they also express a protein called Foxp3. These cells help to tone down the immune response once infection has been adequately contained. These cells also turn off self-reactive lymphocytes to prevent autoimmune diseases: this is termed self-tolerance.

Many suppressor T-cells were formerly self-reactive T-cells that have been turned off. When a suppressor T-cell inactivates another lymphocyte, it can either target it for destruction or promote its conversion into another suppressor T-cell.

5. Which cells account for the fact that the secondary response to a pathogen is much more rapid and robust than the primary response?

Memory cells allow the immune system to carry out a much more rapid and robust secondary response.

"CD" in immunology stands for cluster of differentiation and includes cell-surface markers that can be detected by the lab technique called flow cytometry; these markers give an indication of the types of leukocytes under investigation, how many are present, and in what state of maturity they are. CD4+ T-cells are better at fighting extracellular infections, while CD8+ T-cells are better at targeting intracel- lular infections.

Mnemonic CD x MHC=8 CD4+ cells respond to MHC-ll (4 x 2 = 8) CD8+ cells respond to MHC-I (8 x 1 = 8)

6. What triggers the alternative pathway for complement activation? What functions does complement have in inflammation and cell killing?

One group of inflammatory mediators—the complement family of plasma proteins activated during nonspecific inflammation by the alternative complement pathway—not only stimulates many of the steps of inflammation but mediates extracellular killing via the membrane at tack complex. The family of plasma proteins known as complement provides another means for extracellular killing of pathogens without prior phagocytosis. Certain complement proteins are always circulating in the blood in an inactive state. Upon activation of a complement protein in response to infection or cell damage, a cascade occurs so that this active protein activates a second complement protein, which activates a third, and so on. In this way, multiple active complement proteins are generated in the extracellular fluid of the infected area from inactive complement molecules that have entered from the blood. Because this system consists of at least 30 distinct proteins, it is extremely complex, and we will identify the functions of only a few of the individual complement proteins. The central protein in the complement cascade is C3. Activation of C3 initiates a series of events. The first is the depo- sition of C3b, a component of C3, on the microbial surface. C3b acts as an opsonin that is recognized by receptors on phagocytes targeting the pathogen for destruction, as shown for a bacterium in Figure 18.6. C3b is also part of a proteolytic enzyme that amplifies the complement cascade and leads to the downstream development of a multiunit protein called the membrane attack complex (MAC). The MAC embeds itself in the bacterial plasma membrane (or virus protein coat) and forms porelike channels in the membrane, making it leaky. Water, ions, and small molecules enter the microbe, which disrupts the intracellular environment and kills the microbe. In addition to supplying a means for direct killing of patho- gens, the complement system serves other important functions in inflammation (Figure 18.7). Some of the activated complement molecules along the cascade cause, either directly or indirectly (by stimulating the release of other inflammatory mediators), vasodilation, increased microvessel permeability to protein, and chemotaxis. As we will see later, antibodies, a class of pro- teins secreted by certain lymphocytes, are required to activate the very first complement protein, C1, in the full sequence known as the classical complement pathway. However, lymphocytes are not involved in nonspecific inflamma- tion, our present topic. How, then, is the complement sequence ini- tiated during nonspecific inflammation? The answer is that there are at least two other means of activating complement, including one called the alternative complement pathway, one that is not antibody dependent and that bypasses C1. The alternative pathway is initiated as the result of interactions between carbohydrates on the surface of the microbes and inactive complement molecules beyond C1. These interactions lead to the formation of active C3b, the opsonin described in the previous paragraph, and the acti- vation of the subsequent complement molecules in the pathway. However, not all microbes have a surface conducive to initiating the alternative pathway. Function of complement C3b as an opsonin: One portion of C3b binds nonspecifically to carbohydrates on the surface of the bacterium, whereas another portion binds to specific receptor sites for C3b on the plasma membrane of the phagocyte.

For each of the lymphocytes listed below, what are its main functions? • Plasma cell: • Memory B-cell: • Helper T-cell: • Cytotoxic T-cell: • Suppressor (regulatory) T-cell: • Memory T-cell:

Plasma cells form from B-cells exposed to antigen and produce antibodies. Memory B-cells also form from B-cells exposed to antigen and lie in wait for a second exposure to a given antigen to be able to mount a rapid, robust response. Helper T-cells coordinate the immune system through lymphokines and respond to antigen bound to MHC-II. Cytotoxic T-cells directly kill virally infected cells and respond to antigen bound to MHC-I. Suppressor (regulatory) T-cells quell the immune response after a pathogen has been cleared and promote self-tolerance. Memory T-cells, like memory B-cells, lie in wait until a second exposure to a pathogen to be able to mount a rapid, robust response.

What is meant by positive and negative selection? • Positive selection: • Negative selection:

Positive selection occurs when T-cells in the thymus that are able to respond to antigen presented on MHC are allowed to survive (those that do not respond undergo apoptosis). Negative selection occurs when T-cells that respond to self-antigens undergo apoptosis before leaving the thymus.

3. For each of the noncellular nonspecific immune defenses listed below, provide a brief description of its immunologic function: ° Skin: ° Defensins: ° Lysozyme: ° Mucus: ° Stomach acid: ° Normal gastrointestinal flora: ° Complement:

Skin provides a physical barrier and secretes antimicrobial enzymes. Defensins are examples of antibacterial enzymes on the skin. Lysozyme is antimicrobial and is present in tears and saliva. Mucus is present on mucous membranes and traps incoming pathogens; in the respiratory system, cilia propel the mucus upward so it can be swallowed or expelled. Stomach acid is an antimicrobial mechanism in the digestive system. The normal gastrointestinal flora provides competition, making it hard for pathogenic bacteria to grow in the gut. Complement is a set of proteins in the blood that can create holes in bacteria.

Autoimmune diseases can result in destruction of tissues, causing various deficiencies. Type I diabetes mellitus results from autoimmune destruction of the beta-cells of the pancreas. This results in an inability to produce insulin, characterized by high blood sugars and excessive utilization of fats and proteins for energy. Other examples of autoimmune diseases include multiple sclerosis, myasthenia gravis, psoriasis, systemic lupus erythematosus, rheumatoid arthritis, Graves' disease, and Guillain-Barre syndrome.

B-cells mature in the bone marrow. T-cells mature in the thymus. T or F ?

Cytotoxic T-cells (Tc or CTI, for cytotoxic T-Iymphocytes), also called CD8+ T-cells, are capable of directly killing virally infected cells by injecting toxic chemicals that promote apoptosis into the infected cell. CD8+ T-cells respond to antigens presented on MHC-I molecules. Because MHC-I presents endogenous antigens, CD8+ T-cells are most effective against viral (and intracellular bacterial or fungal) infections.

Eosinophils contain bright red-orange granules and are primarily involved in allergic reactions and invasive parasitic infections. Upon activation, eosinophils release large amounts of histamine, an inflammatory mediator. This results in vasodilation and increased leakiness of the blood vessels, allowing additional immune cells (especially macrophages and neutrophils) to move out of the blood- stream and into the tissue. Inflammation is particularly useful against extracel- lular pathogens, including bacteria, fungi, and parasites.

Finally, basophils contain large purple granules and are involved in allergic re- sponses. They are the least populous leukocyte in the bloodstream under normal conditions. Mast cells are closely related to basophils, but have smaller granules and exist in the tissues, mucosa, and epithelium. Both basophils and mast cells release large amounts of histamine in response to allergens, leading to inflamma- tory responses.

MHC class II molecules are mainly displayed by professional antigen-presenting cells like macrophages. Remember that these phagocytic cells pick up pathogens from the environment, process them, and then present them on MHC-II. An antigen is a substance (usually a pathogenic protein) that can be targeted by an antibody. While antibody production is the domain of the adaptive immune system, it is important to understand that cells of the innate immune system also present antigens. Because these antigens originated outside the cell, this pathway is often called the exogenous pathway. The presentation of an antigen by an immune cell may result in the activation of both the innate and adaptive immune systems. Professional antigen-presenting cells include mac- rophages, dendritic cells in the skin, some B-cells, and certain activated epithelial cells.

Natural Killer Cells In the arms race between the human immune system and pathogens, some pathogens have found ways to avoid certain defenses. For example, some viruses cause downregulation of MHC molecules, making it harder for T-cells to recognize the presence of an infection. Natural killer (NK) cells, a type of nonspecific lymphocyte, are able to detect the downregulation of MHC and induce apoptosis in these virally infected cells. Cancer cells may also down- regulate MHC production, so NK cells also offer protection from the growth of cancer as well.

Neutrophils are the most populous leukocyte in blood and are very short-lived (a bit more than five days). These cells are phagocytic, like macrophages, and target bacteria. Neutrophils can literally follow bacteria using chemotaxis-the sensing of certain products given off by bacteria and migration of neutrophils to follow these products back to the source (the bacterium itself). Neutrophils can also detect bacteria once they have been opsonized (marked with an antibody from a B-cell). Other cells, like natural killer cells, macrophages, monocytes, and eosinophils, also contain receptors for antibodies and can attack opsonized bacteria. Dead neutrophil collections are responsible for the formation of pus during an infection.

The G I tract of a newborn baby is particularly susceptible to infection because the newborn's immune system is underdeveloped and the GI tract is not yet colonized. Breast milk contains a family of antibodies that are particularly effective on mucosal surfaces and helps to defend newborn babies against gastrointestinal infections.

Briefly describe the Complement system

The complement system consists of a number of proteins in the blood that act as a nonspecific defense against bacteria. Complement can be activated through a classical pathway (which requires the binding of an antibody to a pathogen) or an alternative pathway (which does not require antibodies). The complement proteins punch holes in the cell walls of bacteria, making them osmotically unstable. Despite the association with antibodies, complement is considered a nonspe- cific defense because it cannot be modified to target a specific organism over others.

Refer to the figure showing the adaptive immune system. (Click image to enlarge.) When a patient receives a kidney transplant, the patient will likely be given a drug to prevent rejection of the transplanted organ. The effect of the drug will have to result in an interruption in the action of which component to achieve this effect? Please choose the correct answer from the following choices, and then select the submit answer button. 1 3 only Both 3 and 5 4 5 only

The correct answer is: 4

What typically prompts a naïve B cell to develop into a plasma cell that secretes antibodies? Please choose the correct answer from the following choices, and then select the submit answer button. A cytotoxic T cell interacts with the B cell. A T-helper cell with the same specificity binds to the antigen. Chemical signals are sent from other plasma cells with the same specificity. Chemical signals are sent from memory cells. Adjacent B cells secrete stimulatory antibodies.

The correct answer is: A T-helper cell with the same specificity binds to the antigen.

Which statement about animal defense systems is true? Please choose the correct answer from the following choices, and then select the submit answer button. During the effector phase of a defensive response, an effector discriminates between self and nonself. Innate defenses act slowly. Innate defenses evolved after adaptive defenses. Animal defense systems are based on differentiating between self and nonself molecules. During the activation phase of a defensive response, cells and molecules destroy the invader.

The correct answer is: Animal defense systems are based on differentiating between self and nonself molecules.

Which statement is correct? Please choose the correct answer from the following choices, and then select the submit answer button. Some cells within a T cell clone differentiate into memory cells, which include cytotoxic T cells, T-helper cells, and plasma cells. Antibodies present antigens to T cells. Contact with a specific MHC-antigen complex activates a T cell, causing it to form a clone. T-helper cells lyse mutated cells and virus-infected cells. Cytotoxic T cells coordinate humoral and cellular immune responses.

The correct answer is: Contact with a specific MHC-antigen complex activates a T cell, causing it to form a clone.

The correct answer is: Defensins attach to the surface of a pathogen, which helps phagocytes destroy the pathogen.

Which pair is most appropriately matched? Please choose the correct answer from the following choices, and then select the submit answer button. Variable region - antibody binding site Disulfide bonds - join heavy and light chains Toll-like receptors - immunoglobulin IgA - allergic responses Constant region - antigen binding site

The correct answer is: Disulfide bonds - join heavy and light chains

Which defense mechanism would a pathogen on your skin encounter? Please choose the correct answer from the following choices, and then select the submit answer button. Pathogenesis-related (PR) proteins Complement proteins Dry environment Mucus Defensins

The correct answer is: Dry environment

Which statement is true? Please choose the correct answer from the following choices, and then select the submit answer button. Autoimmunity always results from a reaction to self antigens by the cellular, but not the humoral, immune system. Type I diabetes is an autoimmune disease that results in cells losing their ability to respond to insulin. Failure of clonal deletion is a potential cause of autoimmunity. Systemic lupus erythematosis is an immune deficiency disorder in which B cells lose the ability to give rise to plasma cells. People with rheumatoid arthritis have an excess of a protein that blocks T cells from reacting to self antigens.

The correct answer is: Failure of clonal deletion is a potential cause of autoimmunity.

Patients infected with HIV are susceptible to a variety of infections because Please choose the correct answer from the following choices, and then select the submit answer button. the virus produces cell surface receptors that bind to pathogens, making it easier for those pathogens to be infective. the synthesis of a DNA copy of the viral genome makes a person susceptible to infection. HIV destroys B cells, so antibodies cannot be made in response to invading pathogens. HIV attacks and destroys the TH cells, which are central to mounting an effective immune response. HIV mutates the B cells, so they cannot make the huge array of antibodies needed for an effective immune response.

The correct answer is: HIV attacks and destroys the TH cells, which are central to mounting an effective immune response.

If you were to design a vaccine to prevent infection from a mucosal pathogen such as Vibrio cholerae, which antibody class do you think would be most effective in preventing colonization in the intestinal tract? Please choose the correct answer from the following choices, and then select the submit answer button. IgA IgD IgE IgG IgM

The correct answer is: IgA

Which class of antibodies is the first released by B cells during a primary immune response? Please choose the correct answer from the following choices, and then select the submit answer button. IgG IgD IgM IgE IgA

The correct answer is: IgM

Which characterizes fever? Please choose the correct answer from the following choices, and then select the submit answer button. It decreases lymphocyte production. It is produced in response to histamine released by phagocytes. It is controlled by cytokines signaling the spinal cord. It can inhibit growth of pathogens. It decreases phagocytosis.

The correct answer is: It can inhibit growth of pathogens.

Which statements about human immunodeficiency virus (HIV) is true? Please choose the correct answer from the following choices, and then select the submit answer button. It is transmitted primarily through insect bites. It is a retrovirus that causes autoimmune deficiency syndrome (AIDS). It causes an immediate condition after infection known as Kaposi's sarcoma. It targets T-helper cells, which are involved with both cellular and humoral immune responses. The onset of its symptoms occurs at the set point.

The correct answer is: It targets T-helper cells, which are involved with both cellular and humoral immune responses.

Which statement is true? Please choose the correct answer from the following choices, and then select the submit answer button. MHC proteins are glycoproteins secreted into the extracellular space and then circulated in the blood. MHC proteins make it possible for T cell receptors to distinguish between self and nonself antigens. Different people usually have similar MHC genotypes. With only six different genetic loci for MHC proteins, humans have a small number of possible allele combinations. There are five different classes of MHC proteins, each with a slightly different function.

The correct answer is: MHC proteins make it possible for T cell receptors to distinguish between self and nonself antigens.

Which statement is true? Please choose the correct answer from the following choices, and then select the submit answer button. Nonself substances are major histocompatibility proteins that have been altered by T cells. Prostaglandins are a type of cytokine involved in dilating blood vessels during inflammation. Interferons help defend against viral pathogens by binding to the virus and causing it to lyse. Major histocompatibility complex II proteins occur on the surfaces of a broader range of cell types than major histocompatibility complex I proteins. Major histocompatibility complex proteins are used in identifying self from nonself substances.

The correct answer is: Major histocompatibility complex proteins are used in identifying self from nonself substances.

Which statement is true? Please choose the correct answer from the following choices, and then select the submit answer button. Dendritic cells are white blood cells that develop into microorganism-engulfing macrophages and monocytes, which present antigens to T cells. T cells are lymphocytes that produce antibodies, and B cells are lymphocytes that regulate activities of other white blood cells. Lymphocytes are restricted to lymph. Red blood cells develop from white blood cells. Mast cells and basophils are white blood cells that release histamine.

The correct answer is: Mast cells and basophils are white blood cells that release histamine.

Which list shows the correct components in the correct order for initiation of the inflammatory response? Please choose the correct answer from the following choices, and then select the submit answer button. Eosinophils; defensins; histamine release; lymphocytes Mast cells; histamine release; complement proteins; phagocytes Mast cells; histamine release; lymphocytes Monocytes; complement proteins; mast cells; histamine release Phagocytes; complement proteins; mast cells

The correct answer is: Mast cells; histamine release; complement proteins; phagocytes

Which statement about antibodies is correct? Please choose the correct answer from the following choices, and then select the submit answer button. Most antigens have a single antigenic determinant recognized by different antibodies made by different clones of B cells. A monoclonal antibody is specific for several different epitopes. An antigen always contains one, and only one, epitope. The specificity of antibodies prevents them from being useful in scientific experiments. Monoclonal antibodies can be produced artificially and used for diagnostic purposes.

The correct answer is: Monoclonal antibodies can be produced artificially and used for diagnostic purposes.

Which statement is true? Please choose the correct answer from the following choices, and then select the submit answer button. Natural killer cells are a type of white blood cell that kills virus-infected cells. Phagocytes are smaller than lymphocytes. The two major families of white blood cells are phagocytes and leukocytes. Lymphocytes include B cells and macrophages. Red blood cells have an innate immune defense function.

The correct answer is: Natural killer cells are a type of white blood cell that kills virus-infected cells.

Which statement is true? Please choose the correct answer from the following choices, and then select the submit answer button. Platelets release histamine that stimulates endothelial cells to divide, helping the wound to heal. The inflammatory response is confined to the skin. Phagocytes are responsible for much of the healing that occurs with inflammation. Pus is produced during an inflammatory response that is inappropriately strong. Mast cells release prostaglandins, which ease the pain of inflammation.

The correct answer is: Phagocytes are responsible for much of the healing that occurs with inflammation.

Which characterizes antibodies in the class IgA? Please choose the correct answer from the following choices, and then select the submit answer button. Found primarily free in blood plasma Prevent attachment of pathogens to epithelial cells of mucous membranes Protect epidermal cells of the skin Bind to mast cells Have monomer structure

The correct answer is: Prevent attachment of pathogens to epithelial cells of mucous membranes

When the sea urchin genome was sequenced, researchers concluded that this invertebrate has an exceptionally strong immune system. Which is the most likely observation that led researchers to this conclusion? Please choose the correct answer from the following choices, and then select the submit answer button. Sea urchins have more types of MHC proteins than humans. Sea urchins make more antibodies than humans do. Sea urchins make a compound with antimicrobial properties that lyses bacteria. Sea urchins have many more Toll-like receptors than humans. Sea urchins do not have clonal deletion of B cells, so they can respond to more different types of pathogens.

The correct answer is: Sea urchins have many more Toll-like receptors than humans.

A researcher is investigating which time of year birds are exposed to the West Nile Virus (WNV), so she places a cage full of lab-reared (and therefore unexposed) birds near a marsh full of mosquitoes suspected of carrying WNV. Her lab technician tests the birds' blood for anti-WNV antibodies three times per year. Eventually they find a large amount of IgG but almost no IgM. Which is the best conclusion the researcher can reach from these data? Please choose the correct answer from the following choices, and then select the submit answer button. Birds are not susceptible to WNV. WNV does not stimulate IgM production. Birds are incapable of producing IgM. Her media are contaminated. She needs to sample more frequently because she missed the period of IgM production.

The correct answer is: She needs to sample more frequently because she missed the period of IgM production.

Refer to the figure showing the adaptive immune system. (Click image to enlarge.) The cell labeled 2 is a _______ and the cell labeled 3 is a _______ cell. Please choose the correct answer from the following choices, and then select the submit answer button. T-helper cell; B macrophage; memory cytotoxic T cell; memory B cell; T memory cell; plasma

The correct answer is: T-helper cell; B

Refer to the figure showing the body's reaction to a splinter. Once the substance labeled A is released, which will be the next event in the inflammatory response? (Click image to enlarge.) The complement proteins labeled A will induce phagocytes to leave the blood vessel. The histamines labeled A will cause the blood vessel in the area to dilate and become leaky. The lysozyme labeled A will lyse the bacteria in the wound. The interferon labeled A will cause macrophages in the area to kill the bacteria. The growth factors labeled A will cause cell division in the skin for healing.

The correct answer is: The histamines labeled A will cause the blood vessel in the area to dilate and become leaky.

Which statement is true? Please choose the correct answer from the following choices, and then select the submit answer button. T-helper cells are part of the humoral but not the cellular immune response. The humoral and cellular immune responses can operate simultaneously. The humoral immune response is directed at antigens that have become established within cells. Cytotoxic T cells perform critical functions in the humoral immune response, and B cells produce antibodies in the humoral immune response. The humoral immune response produces antigens, and the cellular immune response can destroy bacteria.

The correct answer is: The humoral and cellular immune responses can operate simultaneously.

Which statement is correct? Please choose the correct answer from the following choices, and then select the submit answer button. An immunoglobulin molecule has only one antigen binding site. The variable region of a light chain and the variable region of a heavy chain form an antigen binding site of an immunoglobulin. Antibodies are trivalent. Because each antibody binds only one antigen molecule at once, antibodies are unable to form large complexes. An immunoglobulin is made up of four antibody proteins.

The correct answer is: The variable region of a light chain and the variable region of a heavy chain form an antigen binding site of an immunoglobulin.

Which characterizes antibodies? Please choose the correct answer from the following choices, and then select the submit answer button. They bind to molecules that identify self. They present antigen to T-helper cells. They are secreted as multiple copies when an antigen invades the body for the first time and binds to a B cell receptor. They occur in blood but not lymph. They are produced by cytotoxic T cells.

The correct answer is: They are secreted as multiple copies when an antigen invades the body for the first time and binds to a B cell receptor.

Which statement about antibodies in the class IgE is true? Please choose the correct answer from the following choices, and then select the submit answer button. They are secreted by mast cells in skin. They differ extensively in amino acid sequences of constant regions. They are found primarily in saliva and tears. They have the same general structure as antibodies in class IgA. They bind to basophils and mast cells, ultimately triggering release of histamine.

The correct answer is: They bind to basophils and mast cells, ultimately triggering release of histamine.

Which characterizes class I MHC proteins? Please choose the correct answer from the following choices, and then select the submit answer button. They are found only on the surface of macrophages and dendritic cells. They are recognized and bound by the surface protein CD4 on cytotoxic T cells. They have an antibody-binding site that activates the humoral immune response. They bring fragments of degraded intracellular proteins to the plasma membrane. They are used to present antigens to T-helper cells.

The correct answer is: They bring fragments of degraded intracellular proteins to the plasma membrane.

Which statement about antibodies in the class IgG is true? Please choose the correct answer from the following choices, and then select the submit answer button. They are made in greater quantity during a primary immune response than during a secondary immune response. They have a pentamer structure. They cross the placenta and provide passive immunity to fetus. They are the least abundant immunoglobulins in the blood. They are found primarily in saliva and tears.

The correct answer is: They cross the placenta and provide passive immunity to fetus.

Which statement about cytotoxic T (TC) cells is true? Please choose the correct answer from the following choices, and then select the submit answer button. They release cytokines that activate B cells. They attack pathogens by binding to cell surface antigens on those pathogens. They destroy host cells that are infected with a virus. They destroy pathogens by engulfing them. They stimulate the classical complement pathway.

The correct answer is: They destroy host cells that are infected with a virus.

Which characterizes complement proteins? Please choose the correct answer from the following choices, and then select the submit answer button. They cause lysozyme to lyse invading cells such as bacteria. They make up a group of just three different proteins that act in a cascade. They are a component of the innate immune response but not the adaptive immune response. They bind to antibodies but not antigens. They help to activate the inflammatory response.

The correct answer is: They help to activate the inflammatory response.

Which feature is characteristic of innate defenses? Please choose the correct answer from the following choices, and then select the submit answer button. They take days or weeks to develop. They are found only in vertebrates. They recognize specific pathogens. They include barriers such as the skin. They last longer than adaptive defenses.

The correct answer is: They include barriers such as the skin.

Which characterizes interferons? Please choose the correct answer from the following choices, and then select the submit answer button. They lyse virus-infected cells. They are involved in innate but not adaptive defense responses. They inhibit viral reproduction in neighboring cells, should they become infected. They are antibody signaling proteins. They are produced by natural killer cells.

The correct answer is: They inhibit viral reproduction in neighboring cells, should they become infected.

Which characterizes plasma cells? Please choose the correct answer from the following choices, and then select the submit answer button. They secrete large quantities of antibody protein that a precursor cell synthesized. They have few ribosomes. They have a relatively low amount of endoplasmic reticulum. They secrete antibodies unique to each individual cell. They originate from a parent B cell.

The correct answer is: They originate from a parent B cell.

Which characterizes class II MHC proteins? Please choose the correct answer from the following choices, and then select the submit answer button. They are found on surfaces of T cells and macrophages. They bring fragments of degraded intracellular proteins to the plasma membrane. They present fragments of degraded extracellular proteins to T-helper cells. They are recognized and bound by the surface protein CD8 on cytotoxic T cells. They have an antibody-binding site that activates the humoral immune response.

The correct answer is: They present fragments of degraded extracellular proteins to T-helper cells.

Which characterizes immediate hypersensitivity? Please choose the correct answer from the following choices, and then select the submit answer button. Some cases can be treated using desensitization, whereby small amounts of allergen are injected to stimulate a response from cytotoxic T cells. Antigen-presenting cells pick up the antigen and initiate a T cell response. Upon first exposure to the antigen, B cells make large amounts of IgA antibodies, which bind to basophils and mast cells. Upon subsequent exposures to the antigen, mast cells and basophils release large amounts of histamine. It does not include food allergies.

The correct answer is: Upon subsequent exposures to the antigen, mast cells and basophils release large amounts of histamine.

Which statement is false? Please choose the correct answer from the following choices, and then select the submit answer button. Vaccination generates memory cells. Vaccination initiates a primary immune response but does not cause disease. Heat-killed pathogens can be injected as a vaccination against certain diseases. Before a virus is included in a vaccine, it is modified to make it inactive or less virulent. Vaccination introduces antibodies into the body in a form that does not cause disease.

The correct answer is: Vaccination introduces antibodies into the body in a form that does not cause disease.

HIV targets CD4-expressing T cells. One of the long-term results of this is Please choose the correct answer from the following choices, and then select the submit answer button. an increase in the ability of macrophages to recognize specific antigenic determinants. a decrease in the ability of B cells to produce memory B cells. an increase in T-helper cells. loss of the gene coding for CD4. an increase in class II MHC proteins.

The correct answer is: a decrease in the ability of B cells to produce memory B cells.

An autoimmune disease is Please choose the correct answer from the following choices, and then select the submit answer button. active when organ transplantation is successful. always caused by viruses. a response in which the immune cells attack the body's own tissues. a result of the destruction of the immune system. inflammation that is always targeted to a specific location in the body.

The correct answer is: a response in which the immune cells attack the body's own tissues.

The fact that B cells and T cells are both clonally selected means that Please choose the correct answer from the following choices, and then select the submit answer button. each individual can form many different antibodies, but only one type of T cell receptor. there are five different types of immunoglobulin. each B cell or T cell produces only one kind of antibody. B cell lymphocytes change their antibody specificity to match a newly discovered antigen, and then undergo mitosis to form a clone of plasma cells. antibodies and T cell receptors are made before exposure to antigen.

The correct answer is: antibodies and T cell receptors are made before exposure to antigen.

Normal microbial flora in the body Please choose the correct answer from the following choices, and then select the submit answer button. are bacteria and fungi that naturally occupy the human body without causing disease. are pathogens that normally cause infection. form an adaptive defense because they compete with particular pathogens for resources. are unable to compete with pathogens for space and nutrients. are excluded from the skin by innate immune defenses.

The correct answer is: are bacteria and fungi that naturally occupy the human body without causing disease.

Toll-like receptors Please choose the correct answer from the following choices, and then select the submit answer button. are found in vertebrates, but so far have not been found in invertebrates. initiate a protein kinase cascade, which induces histamine secretion in neighboring cells. leave blood vessels to bind to pathogenic bacteria, which in turn attracts phagocytes. are found in the cell membrane of certain cells, where they recognize and bind to nonself molecules associated with pathogens. if blocked would enhance overly strong inflammatory responses.

The correct answer is: are found in the cell membrane of certain cells, where they recognize and bind to nonself molecules associated with pathogens.

T cell receptors Please choose the correct answer from the following choices, and then select the submit answer button. are carbohydrates. are the primary receptors for the humoral immune system. cannot function unless the animal has previously encountered the antigen. are produced by plasma cells. are important in combating viral infections.

The correct answer is: are important in combating viral infections.

Interferons Please choose the correct answer from the following choices, and then select the submit answer button. are released by healthy cells. target cancerous cells. are released by virus-infected cells. are released by antigen-presenting cells. target mast cells.

The correct answer is: are released by virus-infected cells.

Multiple sclerosis is a degenerative disease that is caused by the immune response attacking the myelin sheath that surrounds the nerves of the central nervous system. An immunologist would describe this as a(n) Please choose the correct answer from the following choices, and then select the submit answer button. immediate hypersensitivity. acquired immunodeficiency. autoimmune disease. genetic immunodeficiency. opportunistic infection.

The correct answer is: autoimmune disease.

When compared with B cell receptors, T cell receptors Please choose the correct answer from the following choices, and then select the submit answer button. are larger. have more polypeptide chains. bind only to an antigen displayed by an MHC protein on an antigen-presenting cell or target cell. lack a variable amino acid sequence. differ in having a constant region that fixes the receptor in the plasma membrane.

The correct answer is: bind only to an antigen displayed by an MHC protein on an antigen-presenting cell or target cell.

Cytotoxic T cells Please choose the correct answer from the following choices, and then select the submit answer button. can kill cancer cells and virus-infected cells. activate B lymphocytes. have receptors that bind to specific antibodies. coordinate humoral and cellular immune responses. function primarily in the humoral immune response.

The correct answer is: can kill cancer cells and virus-infected cells.

The process by which immature B or T cells with the potential to respond strongly to self antigens and undergo apoptosis is called Please choose the correct answer from the following choices, and then select the submit answer button. clonal selection. the secondary immune response. the primary immune response. immunological memory. clonal deletion.

The correct answer is: clonal deletion.

If a new vaccine against HIV is developed, it will be important to test its effectiveness by determining if it stimulates both the production of antibodies in a humoral response against HIV and the proliferation of a clone of _______ that can destroy HIV-infected cells. Please type the correct answer in the following input field, and then select the submit answer button or press the enter key when finished. Your answer:

The correct answer is: cytotoxic T cells

An adaptive immune defense Please choose the correct answer from the following choices, and then select the submit answer button. responds to a large number of antigens. does not distinguish self from nonself. has immunological memory. is nonspecific. is found in all organisms.

The correct answer is: has immunological memory.

Clonal deletion removes Please choose the correct answer from the following choices, and then select the submit answer button. immature lymphocytes showing the potential to mount an immune response against self antigens. antibodies produced by one person and received by another. B and T cells that have proliferated by clonal selection. aging memory cells. mature effector cells.

The correct answer is: immature lymphocytes showing the potential to mount an immune response against self antigens.

An allergen Please choose the correct answer from the following choices, and then select the submit answer button. stimulates production of IgE by T cells. is an antigen capable of stimulating immediate hypersensitivity. stimulates production of IgA by intestinal cells. stimulates release of histamine by natural killer cells. results in delayed hypersensitivity when there is no immediate immune response.

The correct answer is: is an antigen capable of stimulating immediate hypersensitivity.

There are two major kinds of white blood cells: _______ engulf pathogens, while _______ are involved in adaptive immunity. Please choose the correct answer from the following choices, and then select the submit answer button. lymphocytes; phagocytes monocytes; macrophages mast cells; neutrophils phagocytes; lymphocytes natural killer cells; dendritic cells

The correct answer is: phagocytes; lymphocytes

The major histocompatibility complex Please choose the correct answer from the following choices, and then select the submit answer button. plays no role in T cell immunity. plays no role in antibody responses. represents gene-encoding proteins found on the surfaces of cells. plays no role in skin graft rejection. is encoded by a single locus with multiple alleles.

The correct answer is: represents gene-encoding proteins found on the surfaces of cells.

What type of feedback is exemplified by the secretion of interferon-gamma by NK cells?

This is an example of positive feedback, because the stimulus (interferon-gamma) results in an activated cell that produces more of the stimulus.

Briefly describe the Interferon system

To protect against viruses, cells that have been infected with viruses produce interferons, proteins that prevent viral replication and dispersion. Interferons cause nearby cells to decrease production of both viral and cellular proteins. They also decrease the permeability of these cells, making it harder for a virus to infect jhem. In addition, interferons upregulate MHC class I and class II molecules, resulting in increased antigen presentation and better detection of the infected cells by the immune system, as described in the next section. Interferons are responsible for many "flu-like" symptoms that occur during viral infection, including malaise, tiredness, muscle soreness, and fever.

1. Phagocytes kill harmful bacteria by a. endocytosis. b. producing antibodies. c. complement proteins. d. T cell stimulation. e. inflammation.

21. Which of the following conditions is not considered a disease or malfunction of the immune system? a. MHC-induced transplant rejection b. SCID (severe combined immunodeficiency) c. lupus, multiple sclerosis, and type I diabetes d. allergic anaphylactic shock

Describe each of the following mechanisms by which antibodies mediate the disposal of antigens: a. neutralization b. opsonization c. complement activation and formation of membrane attack complex

a. neutralization-neutralizes the ability of a virus to infect a host cell by blocking binding sites; binds to and neutralizes toxins in body fluids b. opsonization is the binding of multiple antibodies to bacterium makes it more recognizable to macrophages or neutrophils; the cross-linking of bacteria, virus particles, or antigens into aggregates facilitates phagocytosis c. Complement activation and formation of membrane attack complex-antigen-antibody complexes on microbes activate the complement system. Complement proteins form a membrane attack complex, which produces a pore in the membrane of a foreign cell and causes it to lyse.

12. The clonal selection theory says that a. an antigen selects certain B cells and suppresses them. b. an antigen stimulates the multiplication of B cells that produce antibodies against it. c. T cells select those B cells that should produce antibodies, regardless of the antigens present. d. T cells suppress all B cells except the ones that should multiply and divide. e. Both b and c are correct.

22. From which of the following conditions would an AIDS patient be least likely to suffer? a. Kaposi's sarcoma or other cancers b. rheumatoid arthritis c. pneumonia d. yeast infections of mucous membranes

20. In which of the following circumstances would a B cell display antigens to a T cell? a. A B cell takes in a few antigen molecules and displays them in class II MHC molecules to activated helper T cells. b. A B cell engulfs bacteria and displays bacterial peptide antigens in class II MHC molecules to a helper T cell. c. After being infected by a virus, a B cell displays viral peptides it has synthesized in its class I MHC molecules to a cytotoxic T cell. d. Both a and c are possible ways that a B cell could display antigens to a T cell.

Which cells are professional antigen-presenting cells?

2. Professional antigen-presenting cells include macrophages, dendritic cells in the skin, some B-cells, and certain activated epithelial cells.

360. Which of the following pairs are most closely related? (A) Monocyte-lymphocyte (B) Erythrocyte-leukocyte (C) Macrophage-monocyte (D) Eosinophil-basophil (E) Thrombocyte-granulocyte

15. Which of the following cell types is NOT a granulocyte? A. Natural killer cell B. Mast cell C. Eosinophil D. Basophil

A Granulocytes are cells with granules in their cytoplasm. These granules are released in immune responses to attack a pathogen. Granulocytes include neutrophils, basophils, eosinophils, and mast cells. Natural killer cells are agranulocytes, which include lymphocytes (B-, T-, and NK cells) and monocytes/macrophages.

13. Which cell type is a phagocyte that attacks bacterial pathogens in the bloodstream? A. Neutrophils B. Eosinophils C. Basophils D. Dendritic cells

A The only phagocytes that attack bacteria on this list are neutrophils and dendritic cells. Dendritic cells are able to sample and present any type of material, and reside in the skin. Neutrophils, on the other hand, are present in the blood-stream and can attack bacteria present there or in tissues. Eosinophils and basophils are involved in the formation of allergies; eosinophils also defend against parasites.

7. Which of the following is true regarding passive and active immunity? A. Active immunity requires weeks to build, whereas passive immunity is acquired immediately. B. Active immunity is short-lived, whereas passive immunity is long-lived. C. Active immunity may be acquired during pregnancy through the placenta. D. Passive immunity may be acquired through vaccination.

A Active immunity refers to the production of antibodies during an immune response. Active immunity may be conferred by vaccination, such as when an individual is injected with a weakened, inactive, or modified form of a particular antigen that stimulates the immune system to produce antibodies. Active immunity may require weeks to build. Passive immunity, on the other hand, involves the transfer of antibodies either passively or by injection. An example would be during pregnancy, when some maternal antibodies cross the placenta and enter fetal circulation, conferring passive immunity to the fetus. Although passive immunity is acquired immediately, it is very short-lived, lasting only as long as the antibodies circulate in blood.

4. Which of the following are involved in antibody production? A. Plasma cells B. Memory cells C. Helper T-cells D. Cytotoxic cells

A Antibodies are produced by plasma cells derived from B-Iymphocytes. The other cells are all types of T-lymphocytes, although memory B-cells can also exist. Still, memory B-cells do not produce antibodies; plasma cells do.

10. Which of the following correctly indicates the response of CD8+ T-cells when activated? A. Secretion of cytotoxic chemicals B. Causing isotype switching C. Presentation of antigens D. Activation of B-cells

A CD8+ T-cells are largely responsible for the cytotoxic immune response. By releasing toxic chemicals into virally infected cells, CD8+ T-cells are able to kill these cells in an effort to contain viral infections. Isotype switching refers to changes in the isotype of antibody produced, which is not caused by CD8+ cells, eliminating choice (B). Antigens are presented by macrophages, dendritic cells, certain epithelial cells, and some B-cells, eliminating choice (C). B-cells are not activated by cytotoxic T-Iymphocytes, eliminating choice (D).

1. In DiGeorge syndrome, the thymus can be completely absent. The absence of the thymus would leave an individual unable to mount specific defenses against which of the following types of pathogens? A. Viruses B. Bacteria c. Parasites D. Fungi

A T-lymphocytes, which mature in the thymus, are the only specific defense against intracellular pathogens. While some bac- teria, fungi, and parasites can live intracellularly, viruses-by definition-must replicate within cells. The absence of T-cells would leave an individual unable to fight viral infections with specific defenses.

What is the difference between active and passive immunity? • Active immunity: • Passive immunity:

Active immunity refers to the stimulation of the immune system to produce antibodies against a pathogen. Passive immunity refers to the transfer of antibodies to prevent infection, without stimulation of the plasma cells that produce these antibodies.

4. If the Fc portion of a person's antibodies is abnormal, what effects could this have on antibody-mediated responses?

Antibodies would bind normally to antigen but may not be able to activate complement, act as opsonins, or recruit NK cells in ADCC. The reason for these defects is that the sites to which complement C1, phagocytes, and NK cells bind are all located in the Fc portion of antibodies.

What prevents B cells and T cells from reacting against the body's own molecules?

As lymphocytes mature in the thymus or bone marrow, they are tested for self-reactivity, and those that react against self-components are inactivated or destroyed.

2. Which of the following are NOT involved in cell- mediated immunity? A. Memory cells B. Plasma cells c. Cytotoxic cells D. Suppressor cells

B The lymphocytes involved in cell-mediated immunity are the T-Iymphocytes, or T-cells. There are four types of T-cells, each playing a different role in cell-mediated immunity: cytotoxic T-cells, helper T-cells, memory T-cells, and suppressor T-cells. Thus, from the answer choices, the only cells not involved in cell-mediated immunity are the plasma cells, which are differentiated immunoglobulin-secreting B-lymphocytes involved in humoral immunity.

3. The lymphatic system: A. transports hormones throughout the body. B. transports chylomicrons to the circulatory system. C. causes extravasation of fluid into tissues. D. is the site of mast cell activation.

B The main function of the lymphatic system is to collect excess interstitial fluid and return it to the circulatory system, main- taining the balance of body fluids. However, this is not one of the answer choices. In addition, the lymphatic system accepts chylomicrons from the small intestine and delivers them to the cardiovascular circulation. Transport of hormones is a function of the cardiovascular system, eliminating choice (A). The lymphatic system absorbs fluid that has been pushed into tissues, but does not cause the extravasation of the fluid, eliminating choice (C). Mast cells reside in (and are activated in) the skin and mucous membranes, eliminating choice (D).

14. What type of immunity is likely to be affected by removal of the spleen? A. Cytotoxic immunity B. Humoral immunity C. Innate immunity D. Passive immunity

B The spleen is a location where B-cells mature and proliferate. Therefore, removal of the spleen is likely to result in a reduction of humoral immunity. In fact, many people receive vaccinations prior to removal of the spleen in order to bolster their immunity.

7. The organ that contains red pulp, which filters the blood, and white pulp, where lymphocytes respond to antigens in the blood, is the a. bone marrow. c. spleen. b. lymph node. d. thymus.

14. Plasma cells are committed to large-scale production of antibodies for export. You would expect these cells to contain a. many mitochondria. b. an extensive network of rough endoplasmic reticulum. c. an extensive network of smooth endoplasmic reticulum. d. multiple nucleoli.

10. How does the vertebrate immune system come to produce so many different antibodies? a. Vertebrates inherit millions of different antibody genes. b. The genes for the polypeptide chains in an antibody are generated by recombination among many gene sequences. c. Meiotic recombination and independent assortment lead to new antibody variations. d. The immune system creates new B cells each time it is exposed to a new antigen.

11. Major histocompatibility complex molecules a. are involved in the ability to distinguish self from nonself. b. may trigger T cell responses after transplant operations. c. are a collection of cell surface proteins that present antigen fragments on infected cells. d. are or do all of the above.

5. Would you predict that patients with AIDS would develop fever in response to an infection? Explain. Hint: Which cells are affected in AIDS, and which cells secrete substances that cause fever?

They do develop fever, although often not to the same degree as normal. They can do so because IL-1 and other cytokines secreted by macrophages cause fever, whereas the defect in AIDS is failure of helper T-cell function.

2. What abnormalities would a person with a neutrophil deficiency display? A person with a monocyte deficiency?

Neutrophil deficiency would impair nonspecific (innate) inflammatory responses to bacteria. Monocyte deficiency, by causing macrophage deficiency, would impair both innate inflammation and adaptive immune responses.

For questions 14-17, note the antibody class described (lgA, IgE, IgG, or IgM). 14. The major class of antibody found in the blood 15. The first class of antibodies produced 16. The major class secreted in milk, tears, and saliva 17. The class that is mostly bound to eosinophils and mast cells

14. IgG 15. IgM 16. IgA 17. IgE

T or F ? 5. Antibiotics are useful for treating illnesses caused by viruses. 6. Chronic inflammatory diseases may occur even in the absence of any infection. 7. All T cells are lymphocytes, but not all lymphocytes are T cells. 8. Edema (swelling), which occurs during inflammation, has important adaptive value in helping defend against infection or injury. 9. Bone marrow and the thymus are examples of secondary lymphoid organs. 10. Toll-like receptors are the major defense against specific pathogens and therefore have an important function in adaptive immunity.

5. F Antibiotics are bactericidal. They are sometimes given in viral diseases to eliminate or prevent secondary infections caused by bacteria, however. 6. T For example, rheumatoid arthritis and inflammatory bowel disease are not associated with infection. 7. T Some lymphocytes are B cells. 8. F Edema is a consequence of inflammation and has no known adaptive value. 9. F These are the primary lymphoid organs. An example of a secondary organ is a lymph node. 10. F Toll-like receptors are an important part of the innate immune system and recognize conserved molecular features on pathogens.

6. Vaccination increases the number of (A) different receptors that recognize a pathogen. (B) lymphocytes with receptors that can bind to the pathogen. (C) epitopes that the immune system can recognize. (D) MHC molecules that can present an antigen.

Describe the differences between the antigens that B cell antigen receptors recognize and the antigens that T cell antigen receptors recognize.

B cell antigen receptors recognize epitopes of intact antigens that are either molecules on the surfaces of infectious agents or molecules free in the body. T cell antigen receptors recognize pieces of antigens that have com- plexed with an MHC molecule inside a cell and are then presented on the cell surface.

If an individual failed to develop a thymus because of a genetic defect, what would happen to the immune responses mediated by antibodies and those mediated by cytotoxic T cells? Hint: Think how helper T cells and B cells are functionally related.

Both would be impaired because T cells would not differentiate. The absence of cytotoxic T cells would eliminate responses mediated by these cells. The absence of helper T cells would impair antibody-mediated responses because most B cells require cytokines from helper T cells to become activated.

2. An epitope associates with which part of an antigen receptor or antibody? (A) the tail (B) the heavy-chain constant regions only (C) variable regions of a heavy chain and light chain combined (D) the light-chain constant regions only

3. Which statement best describes the difference between responses of effector B cells (plasma cells) and those of cytotoxic T cells? (A) B cells confer active immunity; cytotoxic T cells confer passive immunity. (B) B cells respond the first time a pathogen is present; cytotoxic T cells respond subsequent times. (C) B cells secrete antibodies against a pathogen; cytotoxic T cells kill pathogen-infected host cells. (D) B cells carry out the cell-mediated response; cytotoxic T cells carry out the humoral response.

7. Which of the following would not help a virus avoid triggering an adaptive immune response? (A) having frequent mutations in genes for surface proteins (B) infecting cells that produce very few MHC molecules (C) producing proteins very similar to those of other viruses (D) infecting and killing helper T cells

What does an activated helper T cell release, and what do these substances do?

Cytokines released from helper T cells stimulate cytotoxic T cells, B cells, and themselves.

What does a cytotoxic T cell attached to an infected body cell release, and what do these substances do?

Cytotoxic T cells release perforin molecules that form pores in the target cell and granzymes that initiate apoptosis of the target cell.

How is the great diversity of B and T cells produced?

During development of B cells and T cells, the V and J gene segments of one light chain allele and one heavy-chain allele are randomly recombined. The joining of these diverse light and heavy chains produces a huge number of different antigen-binding specificities among Band T cells.

Go to Animated Tutorial Cellular Immune Response www.Life11e.com/a41.4

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Immunoglobulin structure www.Life11e.com/ac41.4

What is immunological memory?

Immunological memory is an enhanced response to a previously encountered foreign molecule that arises from the presence of memory Band T cells, which rapidly form clones of effector cells upon reexposure to that specific antigen.

7. Describe the antiviral function of type I interferon.

Interferons stimulate the production of intracellular proteins that nonspecifically inhibit viral replication. Interferons are cytokines and are grouped into two families called type I and type II interferons. The type I interferons include several proteins that nonspecifically inhibit viral replication inside host cells. In response to infection by a virus, most cell types produce these interferons and secrete them into the extracellular fluid. The type I interferons then bind to plasma membrane receptors on the secreting cell and on other cells, whether they are infected or not (Figure 18.8). This binding triggers the synthesis of dozens of different antiviral proteins by the cell. If the cell is already infected or eventually becomes infected, these proteins interfere with the ability of the viruses to replicate. Type I interferons also function in the killing of tumor cells and in generating fever during an infection.

20. How do NK cells recognize which cells to attack in ADCC?

NK cells have the same targets as cytotoxic T cells, but they are not antigen-specific; most of their mechanisms of target identification are not understood. NK cells bind directly and nonspecifically to virus-infected cells and cancer cells and kill them. They function as killer cells in antibody-dependent cellular cytotoxicity (ADCC)

What is the advantage of having some B cells differentiate into memory cells ?

The body may encounter many common pathogens multiple times over the course of a lifetime. By establishing a population of memory cells, each subsequent infection can be defended against more efficiently and quickly.

3. An experimental animal is given a drug that blocks phagocytosis. Will this drug prevent the animal's immune system from killing foreign cells via the complement system?

The drug may reduce but would not eliminate the action of complement, because this system destroys cells directly (via the membrane attack complex) as well as by facilitating phagocytosis.

How does the HIV virus work ?

The infectious agent responsible for acquired immunodeficiency syndrome (AIDS) is the human immunodeficiency virus (HIV). HIV infects helper T cells (by binding with surface CD4 accessory protein), macrophages, and brain cells. HIV RNA is reverse-transcribed into DNA, which is integrated into the host cell genome, from which it directs production of new viral particles. HIV escapes the immune system through both antigenic variation (when it mu- tates rapidly during replication) and latency (when it integrates into host cell DNA). As HIV infection kills helper T cells, both humoral and cell-mediated immune responses are impaired. Individuals with AIDS are highly susceptible to opportunistic infections and cancers that take advantage of a suppressed immune system. HIV is transmitted by the transfer of body fluids, such as blood, semen, and breast milk, containing viral particles or infected cells. Although new drug combinations are unable to cure HIV infection, they are slowing the progression to AIDS.

1. Receptors for pathogen-associated molecular patterns, or PAMPS, are found in all but which type of organism? a. amoebas b. fruit flies c. humans d. plants

12. In opsonization, a. antibodies coat microorganisms and help phagocytes bind to and engulf the foreign cell. b. a set of complement proteins lyses a hole in a foreign cell's membrane. c. antibodies coat binding sites of viruses. d. a flood of histamines is released and may result in anaphylactic shock.

2. Which is/are important in innate immune responses? a. interferons b. clonal inactivation c. lymphocyteactivation d. secretion of antibodies from plasma cells e. class 1 MHC proteins

6. The major histocompatibility complex a. codes for specific proteins found on the surfaces of cells. b. plays no role in T cell immunity. c. plays no role in antibody responses. d. plays no role in skin graft rejection. e. is encoded by a single locus with multiple alleles

6. Which of the following destroys a target cell by phagocytosis? a. a neutrophil b. a cytotoxic T cell c. a natural killer cell d. complement proteins

11. How do the functions of B cells and T cells differ?

a. B cells, upon activation, differentiate into plasma cells, which secrete antibodies. Antibody-mediated responses constitute the major defense against bacteria, viruses, and toxins in the extracellular fluid. b. Cytotoxic T cells directly attack and kill virus-infected cells and cancer cells, without the participation of antibodies. c. Helper T cells stimulate B cells and cytotoxic T cells via the cytokines they secrete. With few exceptions, this help is essential for activation of the B cells and cytotoxic T cel

10. Natural killer cells a. are known for attacking large parasites, such as tapeworms. b. engulf pathogens and present antigens to T cells. c. recognize the absence of MHC-I molecules on a cell surface. d. produce antibodies.

a. Why is AIDS such a deadly disease? b. Why has AIDS proved so difficult to prevent and cure?

a. HIV destroys helper T cells, thereby crippling the humoral and cell-mediated immune systems and leaving the body unable to fight opportunistic diseases such as Kaposi's sarcoma and Pneumocystis pneumonia. b. HIV is readily passed through unpro- tected sex and needle sharing. The frequent mutational changes during replication generate drug-resistant strains of HIV. And frequent mutational changes in surface antigens have made development of an effective vaccine difficult.

17. Which of the lists in choices a-d places the following steps in the helper T cell activation of cell-mediated and humoral immunity in the correct order? 1. Macrophage and helper T cell secrete cytokines. 2. Macrophage engulfs pathogen and presents antigen in class II MHC. 3. Plasma cells secrete antibodies, and cytotoxic T cells attack cells with class I MHC molecule-antigen complex. 4. Helper T cell receptor recognizes class II MHC molecule-antigen complex. 5. Activated B cells produce plasma cells and memory cells, and activated T cells produce cytotoxic T cells and memory cells. a. 1,3,5,2,4 b. 2,4, 1,5,3 c. 5,2,4, I, 3 d. 2, 1,4,5,3

18. What is the key advantage to the use of monoclonal antibodies as medicines? a. Because we already have antibodies in our blood these molecules are not recognized as foreign. b. They are specific for a single antigen, or even for a specific epitope on an antigen. c. Because they are produced by living cells, they are more natural and healthful than artificially synthesized drugs. d. They are inexpensive to produce, so they can be widely distributed.

21. Immediate hypersensitivity occurs after an allergen combines with a. IgG antibodies. b. IgE antibodies. c. IgM antibodies. d. IgA antibodies.

4. Like veins, lymphatic vessels a. have thick walls of smooth muscle. b. contain valves for a one-way flow of fluids. c. empty directly into the heart. d. receive fluids directly from capillaries.

4. The process of clonal selection accounts for a. the ability of natural killer cells to detect and eliminate cancerous cells. b. the production of large numbers of lymphocytes with identical antigenic specificity. c. the ability of the cellular innate defenses to attack foreign cells. d. the antigenic specificity of lymphocytes.

8. Neutrophils are recruited to a site of inflammation by a. histamine released from mast cells. b. cytokines released from macrophages. c. antibodies produced by plama cells. d. interferon produced by infected body cells.

9. Which cell is not a phagocyte? a. neutrophil b. lymphocyte c. dendritic cell d. macrophage

3. A second exposure to a given foreign antigen elicits a rapid and pronounced immune response because a. passive immunity occurs after the first exposure. b. some B cells differentiate into memory B cells after the first exposure. c. a greater number of antigen-presenting cells are available due to the earlier exposure. d. the array of class II MHC proteins expressed by antigen-presenting cells is permanently altered by the first exposure. e. Both a and b are correct.

b This is known as active immunity

13. A transfusion of type A blood into a person who has type AB blood would result in a. the recipient's anti-A antibodies reacting with the donated red blood cells. b. enzymes in the recipient's blood cleaving the A carbohydrates from the donated red blood cells. c. probably no reaction in that the recipient has neither anti-A nor anti-B antibodies. d. the introduced blood cells being destroyed by innate defense mechanisms.

15. Which of the following best describes the relationship between antibodies and complement? a. They are both coded for by genes that have hundreds of alleles. b. They are both involved in innate defenses. c. Antibodies bound to antigens on a pathogen's membrane may activate comple ment proteins to form a membrane attack complex. d. Complement proteins tag foreign cells; antibodies disable these marked cells by neutralization.

22. A positive skin test for tuberculosis is mediated mainly by a. histamine. b. IgE antibodies. c. memory T cells. d. neutrophils.

3. True adaptive immunity, involving the production of a large number of diverse antigen receptors, first evolved in a. amphibians. c. jawed vertebrates. b. invertebrates. d. mammals.

3. Which of the following cells would release interferon? a. a macrophage that has become an antigen-presenting cell b. an injured endothelial cell of a blood vessel c. a cell infected by a virus d. a mast cell that has bound an antigen

4. According to the clonal selection theory, a. an antibody changes its shape to match the antigen it meets. b. an individual animal contains only one type of B cell. c. an individual animal contains many types of B cells, each producing one kind of antibody. d. each B cell produces many types of antibodies. e. many clones of antiself lymphocytes appear in the bloodstream.

5. Which of these is a primary lymphoid organ? a. lymph nodes b. spleen c. thymus

7. Antibodies are proteins a. or polysaccharides usually found on the surface of invading bacteria. b. embedded in T cell membranes. c. circulating in the blood that may tag foreign cells for phagocytosis or destruction by complement. d. that are predominantly found in lymph nodes and other organs of the lymphatic system.

9. A secondary immune response is more rapid and effective than a primary immune response because a. the second response is an active immunity, whereas the primary one was a passive immunity. b. helper T cells are available to activate B cells and T cells. c. memory cells respond to the pathogen and rapidly proliferate into effector cells. d. chemical signals cause the more rapid accumulation of phagocytic cells.

4. Which statement is incorrect? a. The most abundant immunoglobulins in serum are IgG and IgM antibodies. b. IgG antibodies are involved in adaptive immune responses against bacteria and viruses in the extracellular fluid. c. IgM antibodies are primarily involved in immune defense mechanisms found in the surface or lining of the gastrointestinal, respiratory, and genitourinary tracts. d. All antibodies of a given class have an Fc portion that is identical in amino acid sequence. e. Antibodies can exist at the surface of a B cell or be circulating freely in the blood.

c IgA antibodies act in this way also.

16. In an adaptive immune response, a dendritic cell a. binds to an accessory protein on cytotoxic T cells to activate their production of perform. b. destroys antibody-labeled cells by phagocytosis. c. activates humoral and cell-mediated immunity by releasing interferons after engulfing a virus. d. presents peptide antigens of an engulfed pathogen in its class II MHC molecules to helper T cells, and releases cytokines.

19. Active immunity can be produced by a. having a disease. b. receiving a vaccine. c. receiving gamma globulin injections. d. Both a and b are correct. e. Both band c are correct.

19. Which of the following statements about cell-mediated immunity is incorrect? a. It may be induced by vaccination as a form of active immunity. b. It protects against pathogens that have invaded body cells as well as against cancer cells. c. It is mounted by lymphocytes that have matured in the thymus. d. It requires recognition of class II MHC molecule-antigen complexes on infected body cells.

2. Which of the following defense mechanisms is incorrectly paired with its function? a. fever-may stimulate phagocytosis b. histamine-causes blood vessels to dilate c. cytokines-attract phagocytes in the inflammatory response d. lysozyme-attacks the cell wall of viruses

2. Which of these are examples of pathogen-associated molecular patterns? a. bacterial cell wall components b. double-stranded viral RNA c. fungal cell wall components d. All of these are correct.

23. Which condition is not an autoimmune disease? a. multiple sclerosis b. rheumatoid arthritis c. systemic lupus erythematosis d. transplant rejection

5. The extraordinary diversity of antibodies results in part from a. the action of monoclonal antibodies. b. the splicing of protein molecules. c. the action of cytotoxic T cells. d. the rearrangement of genes. e. their remarkable nonspecificity.

5. Which of the following statements correctly describes the main difference between innate immunity and adaptive immunity? a. Innate immunity responds only to free pathogens in a localized area; adaptive immunity responds only to pathogens that have entered body cells. b. Innate immunity involves only leukocytes, whereas adaptive immunity involves only lymphocytes. c. Innate immunity relies on phagocytes to destroy pathogens, whereas adaptive immunity does not involve phagocytes. d. Innate immunity recognizes molecules common to a set of pathogens, whereas adaptive immunity reacts to specific microbes on the basis of their unique antigens.

6. B cells mature within a. the lymph nodes. b. the spleen. d. tonsils c. the thymus. d. the bone marrow.

11. Complement a. is an innate defense mechanism. b. is involved in the inflammatory response. c. is a series of proteins present in the plasma. d. plays a role in destroying bacteria. e. All of these are correct.

18. Which of these statements pertain(s) to T cells? a. They have specific receptors. b. They recognize antigen presented by MHC proteins. c. They are responsible for cell-mediated immunity. d. They stimulate antibody production by B cells. e. All of these are correct.

2. Which statement about an antigenic determinant is not true? a. It is a specific chemical grouping. b. It may be part of many different molecules. c. It is the part of an antigen to which an antibody binds. d. It may be part of a cell. e. A single protein has only one on its surface.

3. T cell receptors a. are the primary receptors for the humoral immune system. b. are carbohydrates. c. cannot function unless the animal has previously encountered the antigen. d. are produced by plasma cells. e. are important in combating viral infections.

8. Which of the following is an innate defense against pathogens? a. skin b. gastric juice c. complement d. interferons e. All of these are correct.

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