Microbiology (Chapter 17)

Which of these processes is in the proper sequence?

1. IgE is formed 2. IgE binds to mast cells and basophils 3. Antigen binds IgE 4. Histamine is released Reason: Antibodies of the IgE class are slightly larger than IgG molecules; they constitute only 0.002% of the total serum antibodies. IgE molecules bind tightly by their Fc (stem) regions to receptors on mast cells and basophils, specialized cells that participate in allergic reactions. When an antigen such as pollen links with the IgE antibodies attached to a mast cell or basophil, that cell releases histamine and other chemical mediators. These chemicals provoke a response—for example, an allergic reaction such as hay fever.

There are __________ classes of antibodies in the human immune system.

5

What is a plasma cell?

A cell that produces antibodies. Reason: A plasma cell is a cell that produces antibodies. The B cell proliferates into a large clone of cells. Some of these cells differentiate into antibody producing plasma cells. Other clones become long-lived memory cells that are responsible for the enhanced secondary response to an antigen. This process is called clonal selection.

Which of the following results in comparatively long-lasting immunity?

A person survives an infectious disease. Reason: A person surviving an infectious disease results in comparatively long-lasting immunity. Immunity resulting from infection is called naturally acquired active immunity. A baby receiving antibodies to chicken pox across the placenta and a baby receiving antibodies against many pathogens through breastfeeding are examples of naturally acquired passive immunity. An adult receiving gamma globulin is an example of artificially acquired active immunity. An adult receiving antiserum is an example of artificially acquired passive immunity.

A property of T cells, but not B cells, is their:

Ability to form cells that directly kill virus-infected host cells.

Which of the following statements abut T-dependent antigens is true?

Activation of a B cell by a T-dependent antigen requires cytokines secreted by a T H cell. Reason: B cells usually require the assistance of a T helper cell (TH); thus activation of a B cell by a T-dependent antigen requires cytokines secreted by a TH cell. 1) B cell receptors recognize and attach to antigen 2) Antigen is internalized into the B cell 3) Fragments of the antigen are presented on MHC proteins on the surface of the cell 4) A T helper cell that recognizes this antigen fragment is activated and releases cytokines, activating the B cell. 5) The activated B cell begins clonal expansion, producing an army of antibody producing plasma cells and memory cells.

The resistance to reinfection with measles virus following recovery from measles infection is called:

Adaptive immunity. Reason: Adaptive immunity is a range of microbial defenses that target specific pathogens. Unlike innate defenses, the adaptive immune system defenses are acquired through infection or vaccination and are highly specific.

Which of the following is a true statement about the major histocompatibility complex (MHC)?

All of the answers are correct: The MHC is a collection of genes that encode molecules of genetically diverse glycoproteins. Class I MHC are found on the plasma membranes of mammalian nucleated cells. Class II MHC molecules exist only on the surface of antigen-presenting molecules (APCs). Thymic selection will rid the body of T cells that will not recognize MHC molecules of the host.

Naturally Acquired Passive Adaptive Immunity

Antibodies pass from mother to fetus via placenta or to infant via the mother's milk.

An injection of pooled human gamma globulin may provide passive immunity to humans from hepatitis A because it contains:

Antibodies. Reason: An injection of pooled human gamma globulin may provide passive immunity to humans from hepatitis A because it contains antibodies. The name IgG is derived from the blood fraction gamma globulin. IgG accounts for about 80% of all antibodies in serum.

Which of these statements is NOT true of antibody molecules?

Antibody molecules can directly destroy antigens. TRUE: Cell-bound antibody molecules can bind cells that in turn release chemical compounds that damage parasitic worms. Cell-bound antibody molecules can initiate a process that results in cell lysis. Antibody molecules can enhance phagocytosis of the antigen. Cell-bound antibody molecules can bind complement, triggering the complement cascade. Reason: The following statement is NOT true of antibody molecules: Antibody molecules can directly destroy antigens. Antibodies are globulin proteins (immunoglobulins (Ig)). Globulin proteins are compact and relatively soluble. Antibodies are made in response to an antigen and can recognize and bind to the antigen. A bacterium or virus may have several epitopes that cause the production of different antibodies. Antibody molecules CANNOT directly destroy antigens.

Cyclosporine is a drug sometimes used to prevent transplant rejection after organ transplant surgery. This drug specifically disrupts cell-mediated immunity by cytotoxic T cells. Which of these events can be predicted based on this information?

Antibody production will NOT be disrupted in the recipient.

Foreign substances that cause the production of antibodies are called:

Antigen or Immunogens

Artifically Acquired Active Adaptive Immunity

Antigens are introduced in vaccines; body produces antibodies and specialized lymphocytes

Naturally Acquired Active Adaptive Immunity

Antigens enter the body naturally; body induces antibodies and specialized lymphocytes

While on safari in Serengeti National Park, Tanzania, your friend ventures away from camp and is bitten by a black widow spider. Fortunately, you are prepared and administer artificially acquired passive immunity. With what did you inject your friend?

Antivenin Reason: Artificially acquired passive immunity involves the injection of antibodies into the body. These antibodies come from an animal or a human who is already immune to the disease. You injected your friend with an antivenin in order to prevent a reaction to the toxin released by the black widow spider.

You are about to start a multi-year experiment in a laboratory that works with poliovirus. Although the chance of exposure is low, you are still required to get immunized. What type of immunity now protects you?

Artificially acquired active immunity Reason: The type of immunity that protects you is the artificially acquired active immunity. This is the result of vaccination. Vaccination, also called immunization, introduces vaccines into the body. These are antigens, such as killed or living microorganisms or inactivated bacterial toxins.

Which of the following would be a possible consequence of a disorder that selectively destroys the T regulatory cells in a patient?

Autoimmune diseases. Reason: A possible consequence of a disorder that selectively destroys the T regulatory cells in a patient are autoimmune diseases. T regulatory cells (Treg), formerly called T suppressor cells, make up about 5-10% of the T cell population. Their primary function is to combat autoimmunity by suppressing T cells that escape deletion in the thymus without the necessary "education" to avoid reacting against the body's self. A consequence of a disorder that selectively destroys the T regulatory cells in a patient would be the development of an autoimmune disease.

__________ are only involved in the humoral immune response.

B cells Reason: Only humoral immunity involves B lymphocytes, more commonly known as B cells, which remove viruses, bacteria, and toxins from body tissue fluids and blood by recognizing antigens and making antibodies against them. The recognition of different antigens depends on B cell receptors for antigens that coat the surface of the B cell. T helper cells are specialized T cells that often interact with an antigen before B cells interact with the antigen. Natural killer (NK) cells are lymphoid cells that destroy tumor cells and virus infected cells.

Which of these pathogens would most likely be attacked by antibody-dependent cell-mediated cytotoxicity?

Blood flukes (schistosomes) Reason: Blood flukes (schistosomes) would most likely be attacked by antibody-dependent cell-mediated cytotoxicity. If an organism, such as a parasitic worm, is too large for ingestion and destruction by phagocytosis, it can be attacked by immune system cells that remain external to it. The target cell is first coated with antibodies. Cells of the immune sytem bind the Fc region of the attached antibodies. The target cell is then lysed by substances secreted by the cells of the immune system.

B Cell: long lived memory cells

Can be stimulated to become antibody producing plasma cells at a later date.

A new chemical messenger has been discovered that enhances the chemotaxis of macrophages and neutrophils toward sites of infection. It would be specifically classified as a(n):

Chemokine Reason: A family of small cytokines that induces the migration of leukocytes into areas of infection or tissue damage is called chemokines, from chemotaxis. These are especially important for infections by HIV.

Cytokines that induce migration of leukocytes into areas of infection or tissue damage are known as:

Chemokines Reason: A family of small cytokines that induces the migration of leukocytes into areas of infection or tissue damage is called chemokines, from chemotaxis. These are especially important for infections by HIV. Interleukins are chemicals that cause T-cell proliferation. Interferons are a specific group of cytokines. Alpha- and beta-IFNs are antiviral proteins produced by certain animal cells in response to a viral infection. Gamma-IFN stimulates macrophage activity. Tumor necrosis factor (TNF) is a polypeptide released by phagocytes in response to bacterial endotoxins.

Antigenic stimulation of a particular B cell that results in the production of a large number of plasma and memory cells, all capable of responding to that specific antigen, is referred to as:

Clonal selection Reason: This is referred to as clonal selection. B cells can recognize an almost infinite number of antigens, but each particular cell recognizes only one type of antigen. An encounter with a particular antigen triggers the proliferation of a cell that is specific for that antigen into a clone of cells with the same specificity, hence the term clonal selection. Class switching refers to the ability of a B cell to produce a different class of antibody against one antigen. The strength of the bond between an antigen and an antibody is called affinity.

What type of molecule activates cytotoxic T lymphocytes?

Cytokines released from T helper cells. Reason: A virus-infected cell or a cancer cell produces abnormal endogenous antigens. The abnormal antigen is presented on the cell surface in association with MHC class I molecules. Binding of a T helper cell promotes secretion of cytokines. The cytokines released from T helper cells activate a precursor CTL, which produces a clone of CTLs. 1) A normal cell will not trigger a responce by a cytotoxic T lymphocyte (CTL), but a virus-infected cell or a cance cell produces abnormal endogenous antigens. 2) The abnormal antigen is presented on the cell surface in association with MHC class I molecules. Binding of a TH1 cell promotes secretion of cytokines. 3) The cytokines activate a precursor CTL which produces a clone of CTLs 4) The CTL induces destruction of the virus infected cell by apoptosis.

Which of these cells do not have a role in cell-mediated immunity?

Erythrocytes Reason: Erythrocytes are red blood cells that do not have a role in cell-mediated immunity. T cytotoxic cells, T helper cells, and antigen-presenting cells each have a role in cell-mediated immunity.

For a single antibody molecule, the two light chains have an identical amino acid sequence in the constant regions but different amino acid sequences in the variable regions. (T/F)

False

Haptens can bind to antibody molecules only if the haptens are attached to a carrier molecule. (T/F)

False

IgM circulating in a newborn's blood was produced by the mother and crossed the placenta to enter the fetal circulation before birth. (T/F)

False

Macrophages and dendritic cells are the only cells that can present antigen to T cells. (T/F)

False

The process of eliminated potentially self-reactive T cells in the thymus is called clonal selection. (T/F)

False

The most abundant Ig in the blood serum is:

G Reason: IgG accounts for about 80% of all antibodies in serum, the most abundant Ig. The name IgG is derived from the blood fraction gamma globulin.

Which of the following are NOT antigen-presenting cells?

Helper T Cells. ARE: Dendritic cells, B cells, and Macrophages Reason: Helper T cells are NOT antigen-presenting cells. TH cells can recognize an antigen presented on the surface of a macrophage and activate the macrophage, making it more effective in both phagocytosis and in antigen presentation.

Nonspecific lymphocytes capable of lysing host cells infected by viruses are _________ cells.

NK

Which of the following is a correct match?

IgA: found in secretions such as colostrum, tears, and mucus. Reason: IgA accounts for only about 13% of the antibodies in serum, but it is by far the most common form in mucous membranes and in body secretions such as mucus, saliva, tears, and colostrum (breast milk).

Which of the following is the least abundant Ig?

IgE Reason: Antibodies of the IgE class constitute only 0.002% of the total serum antibodies and are the least abundant Ig.

____________ antibodies are capable of crossing the placenta from mother to fetus.

IgG

Which answer is true of the anamnestic response?

IgG predominates. Reason: In the anamnestic response, IgG predominates. The antibody-mediated immune responses of the host intensify after a second exposure to an antigen. This secondary response is also called the memory (anamnestic) response. The intensity of the antibody-mediated humoral response can be reflected by the antibody titer, the relative amount of antibody in the serum. After the initial contact with an antigen, the exposed person's serum contains no detectable antibodies for 4 to 7 days. Then there is a slow rise in antibody titer: first, IgM class antibodies are produced, followed by IgG peaking in about 10 to 17 days, after which antibody titer gradually declines. This pattern is characteristic of a primary response to an antigen.

During the primary response to an antigen, the first class of anitbody produced is the _____________ class.

IgM

In humans, where do B cells mature?

In the bone marrow. Reason: T cells and B cells both develop from stem cells in the bone marrow. However, T cells owe their name to the fact that unlike B cells, they mature under the influence of the thymus.

Cell mediated immunity in part protects against:

Intracellular bacteria and viruses. Reason: Cell-mediated immunity in part protects against intracellular bacteria and viruses. The responses of cellular immunity center on attacking antigens that make their way inside cells, whereas humoral immunity responses are directed at antigens that are extracellular (such as in blood or other body fluids).

Antibody-dependent cell-mediated cytotoxicity:

Is particularly important for killing microbes that are too large to be destroyed by phagocytosis. Reason: Antibody-dependent cell-mediated cytotoxicity resembles opsonization in that the target organism becomes coated with antibodies; however, the target cell is destroyed by immune system cells that remain external to the target cell. It is particularly important for killing microbes that are too large be destroyed by phagocytosis.

Which of the following statements is NOT of the IgA antibody class?

It can trigger the complement cascade. IS of the IgA: It is the most abundant antibody class in body secretions. It prevents pathogens from attaching to mucosal surfaces. It can be found as a monomer in serum. It is a dimer in its most effective form. Reason: IgA accounts for only about 13% of the antibodies in serum, but it is by far the most common form in mucous membranes and in body secretions such as mucus, saliva, tears, and breast milk. It cannot trigger the complement cascade.

B Cell II

It encounters its specific antigen and proliferates.

Which of the following statements concerning adaptive immunity is FALSE?

It is always present and instantly protects against infection. TRUE: It can be stimulated by vaccination, it can form memory response, and it requires specific recognition of microbes and antigens. Reason: The adaptive immune system comes into play only when the innate defenses fail to stop a microbe. While the innate system responses are the same regardless of the foreign substance, the adaptive system tailors its fight to the specific microbial pathogen, toxin, or other substance at hand. The defenses of the adaptive system take several days or more to fully develop, whereas the effects of the innate system responses are more immediate.

Which of the following is NOT an effect an antibody might have on a target cell?

Lysis IS an effect: Neutralization, opsonization, and agglutination Reason: An antibody may NOT cause lysis of a target cell. Antibody binding to antigens may cause the following: agglutination, opsonization, neutralization, activation of complement, and antibody-dependent cell-mediated cytotoxicity.

______________ cells are important in facilitating immune responses against pathogens that enter the body via the digestive system.

M or Microfold Reason: M cells, or microfold cells, are located within Peyer's patches, which are located on the intestinal wall. Their function is to transport antigens encountered in the digestive tract to contact lymphocytes and antigen-presenting cells of the immune system. Humoral immunity involves B cells, which remove viruses, bacteria, and toxins from body tissue fluids and blood by recognizing antigens and making antibodies against them. T cells are the basis of cellular immunity. T they do not bind to antigens directly, but recognize antigenic peptides after they have been processed by phagocytic cells such as macrophages. M cells facilitate contact between antigens passing through the intestinal tract and cells of the body's immune system.

Immunity acquired by transplacental transfer is called:

Naturally acquired passive immunity. Reason: Immunity acquired by transplacental transfer is called naturally acquired passive immunity. It involves the natural transfer of antibodies from a mother to her infant. Antibodies in a pregnant woman cross the placenta to her fetus— transplacental transfer. If the mother is immune to diphtheria, rubella, or polio, for example, the newborn will be temporarily immune to these diseases as well.

You get the following antibody titers against West Nile virus in three patients. Which patient probably has a current infection? Patient A: 128 IgG, 0 IgM Patient B: 128 IgG, 256 IgM Patient C: 0 IgG, 0 IgM

Patient B The presence of a significant IgM titer indicates a recent infection. Reason: Patient B would probably have a current infection due to the high serum levels of IgG and IgM. IgM appears first in response to a primary infection and is relatively short-lived makes it uniquely valuable in diagnosing disease. If high concentrations of IgM against a pathogen are detected in a patient, it is likely that the disease observed is caused by that pathogen. The detection of IgG, which is relatively long-lived, may indicate only that immunity against a particular pathogen was acquired in the more distant past.

Which of these cell types is NOT involved in cell-mediated immunity?

Plasma cells. IS involved: T cytotoxic cells T regulatory cells T helper cells TH1 cells Reason: Plasma cells are NOT involved in cell-mediated immunity, they are produced by B cells. B cells, part of the humoral immune response, proliferate into B memory cells and plasma cells. Thus, plasma cells are NOT part of cell-mediated immunity. The other examples are all part of cell-mediated immunity. TH1 cells activates cells related to cell-mediated immunity. Cytotoxic T lymphocytes destroy target cells on contact. T regulatory cells regulate immune response and help maintain self-tolerance. Natural killer cells attack and destroy target cells and participate in antibody-dependent cell-mediated cytotoxicity.

Artifically Acquired Passive Adaptive Immunity

Preformed antibodies in immune serum are introduced by injection.

T cytotoxic cells:

Produce perforin Reason: T cytotoxic cells produce perforin. A T cytotoxic cell attaches to the target cell and releases a pore-forming protein, perforin. Pore formation contributes to the subsequent death of the cell.

Which of the following is a reaction of the adaptive immune response?

Production of antibodies. Reason: Adaptive immunity is considered a dual system, with humoral and cellular components. Humoral immunity describes immunity brought about by the production of antibodies.

B Cell: Antibody producing

Proliferating into antibody producing plasma cells.

What is a Stem cell?

Stem cells differentiate into mature B cells, each bearing surface immunoglobulins against a specific antigen.

Which of these lists is the correct order of differentiation?

Stem cells to B cells to Plasma cells Reason: Stem cells to B cells to plasma cells is the correct list order of differentiation. Stem cells differentiate into mature B cells, each bearing surface immunoglobulins against a specific antigen. A B cell encounters its specific antigen and proliferates. Some B cells proliferate into long-lived memory cells, which at a later date can be stimulated to become antibody producing plasma cells.

Which of the following CANNOT function as an antigen presenting cell?

T Cell CAN function: B cell, dendritic cell, and macrophage Reason: Antigen-presenting cells include B cells, dendritic cells, and macrophages; T cells CANNOT function as antigen-presenting cells.

_______________ are lymphocytes that mature in the thymus.

T cells or T lymphocytes

Which of the following T cell is a component of both the cellular and humoral immune response?

T helper cells. Reason: T helper cells are involved in both humoral and cellular immunity. In addition to T Helper cells, B cells are found in humoral immunity and other types of T cells are also found as part of the cellular immunity. Cytotoxic T lymphocytes destroy target cells on contact. T regulatory cells regulate immune response and help maintain self-tolerance. Natural killer cells attack and destroy target cells and participate in antibody-dependent cellmediated cytotoxicity.

What is the function of T cytotoxic cells?

They induce apoptosis of target cells. Reason: The function of T cytotoxic cells is to induce apoptosis of target cells. A cytotoxic T cell attaches to the target cell and releases a pore-forming protein, perforin. Pore formation contributes to the subsequent death of the cell and is similar to the action of the complement membrane attack complex Granzymes, proteases that induce apoptosis, are then able to enter through the pore.

How do NK cells recognize the target cells that they will destroy?

The target cells lack MHC I self antigens. Reason: NK cells recognize target cells because the target cells lack MHC I self-antigens. NK cells are not immunologically specific; they do not need to be stimulated by an antigen. NK cells first contact the target cell and determine whether it expresses MHC class I self-antigens. If it does not, they kill the target cell by mechanisms similar to that of a cytotoxic T lymphocyte.

Which of these answers is a potential concern of using T-independent antigens as vaccines?

These antigens will be ineffective in producing an immune response in infants. Reason: A potential concern of using T-independent antigens as vaccines is that these antigens will be ineffective in producing an immune response in infants. Antigens that stimulate B cells directly without the help of T cells are called T-independent antigens. Such antigens are characterized by repeating subunits such as are found in polysaccharides or lipopolysaccharides. The repeating subunits, can bind to multiple B cell receptors, which is probably why they do not require T cell assistance. T-independent antigens generally provoke a weaker immune response than do T-dependent antigens and the immune system of infants may not be stimulated by T-independent antigens until about age 2.

HIV selectively destroys CD4 cells and a result, a person with AIDS is susceptible to life-threatening viral infections. Knowing this, you can conclude that:

These viruses have T-dependent antigens. Reason: You can conclude that these viruses have T-dependent antigens. An antigen that requires a T-Helper (CD4) cell for antibody production is known as a T-dependent antigen. T-dependent antigens are mainly proteins, such as those found on viruses, bacteria, foreign red blood cells, and haptens with their carrier molecules.

Which of the following statements is NOT true for T helper cells?

They lyse target cells. TRUE: The recognize antigen presented by class II MHC molecules, they activate macrophages, they activate B cells, and they have CD4 molecules on the cell surface. Reason: T helper cells (TH) cooperate with B cells in the production of antibodies, mainly through cytokine signaling. Therefore, T helper cells are an important part of humoral immunity—and they are an even more essential element of cellular immunity. In their contributions to cellular immunity, T cells interact more directly with antigens. T helper cells do NOT lyse their target cells.

Which of the following statements is NOT true of antigens?

They often have a molecular weight of less than 10,000. ARE true: They can include nonmicrobial molecules, such as pollen, egg white, and blood cell surface molecules. They are typically nonself molecules. They are often surface molecules on microbes. They are often proteins or polysaccharides. Reason: Most antigens have a molecular weight of 10,000 or higher. A foreign substance that has a low molecular weight is often not antigenic unless it is attached to a carrier molecule. These low molecular-weight compounds are called haptens.

Helper T cells are involved in both the humoral and the cellular immune responses. (T/F)

True

T cells react to antigen on the surface of APCs only when those antigens are associated with proteins of the mahor histocompatibility complex. (T/F)

True

The Fc region of an antibody molecule can bind to host cells. (T/F)

True

The anamnestic response requires the presence of memory cells. (T/F)

True

The class I major histocompatibility molecules are found on most body cells. (T/F)

True

Each antibody has __________ antigen binding sites.

Two Reason: The two sections located at the ends of the Y arms are called variable (V) regions. These bind to the epitopes. The amino acid sequences and, therefore, the three-dimensional structure of these two variable regions are identical on any one antibody. Their structure makes the two antigen-binding sites found on each antibody monomer.

The number of regions on an antibody molecule can bind to an antigen is referred to as the ___________ of that antibody.

Valence Reason: Each antibody has at least two identical antigen-binding sites that bind to epitopes. The number of antigen-binding sites on an antibody is called the valence of that antibody. For example, most human antibodies have two binding sites; therefore, they are bivalent. Antibodies recognize and interact with specific regions on antigens called epitopes. A foreign substance that has a low molecular weight is often not antigenic unless it is attached to a carrier molecule. These lowmolecular-weight compounds are called haptens.

Programmed cell death is referred to as:

apoptosis Reason: Apoptosis is also called programmed cell death. The cell host has evolved mechanisms to detect the death of cells and to determine whether the death is natural, in which case no threat is involved and the remnants of the corpse are simply removed. In agglutination, antibodies cause antigens to clump together. Phagocytosis is the ingestion of particles by eukaryotic cells.

The secondary (anamnestic) immune response is due to:

long-lived memory cells. Reason: The secondary (anamnestic) immune response is due to long-lived memory cells. The antibody-mediated immune responses of the host intensify after a second exposure to an antigen. This secondary response is also called the memory (anamnestic) response. This response is comparatively more rapid, reaching a peak in only 2 to 7 days, lasts many days, and is considerably greater in magnitude. Some activated B cells do not become antibody-producing plasma cells but persist as long-lived but non-proliferating memory cells. Years, or even decades later, if these cells are stimulated by the same antigen, they very rapidly differentiate into antibody-producing plasma cells.