Chapter 21 The Immune System: Innate and Adaptive Body Defenses

Which of the following T cells would survive education in the thymus? (a) one that recognizes neither MHC nor self-antigen, (b) one that recognizes both MHC and selfantigen, (c) one that recognizes MHC but not self-antigen, (d) one that recognizes self-antigen but not MHC.

The T cell that would survive is (c), one that recognizes MHC but not self-antigen.

congenital immunodeficiency

The inability, due to an individual's genotype, to produce specific antibodies or T cells.

What distinguishes the innate defense system from the adaptive defense system?

The innate defense system is always ready to respond immediately, whereas it takes considerable time to mount the adaptive defense system. The innate defenses consist of surface barriers and internal defenses, whereas the adaptive defenses consist of humoral and cellular immunity, which rely on B and T lymphocytes.

How do vaccines protect against common childhood illnesses such as chicken pox, measles, and mumps?

Vaccinations protect by providing the initial encounter to an antigen—the primary response to that antigen. As a result, when the pathogen for that illness is encountered again, the pathogen elicits the much faster, more powerful secondary response, which is generally effective enough to prevent clinical illness.

provirus

Viral DNA that inserts into a host genome.

dendritic cells

capture antigens and deliver them to lymph nodes

________________ is also resistant to most weak acids and bases and to bacterial enzymes and toxins.

keratin

involves lectins, water-soluble protein molecules that the innate immune system produces to recognize foreign invaders. When lectins bind specific sugars on the surface of microorganisms, they can then bind and activate complement.

lectin pathway

an increase in the amount of white blood cells (leukocytes); usually the result of a pathogen attack on the body

leukocytosis

phagocyte mobilization

leukocytosis (neutrophils enter blood from bone marrow), margination (neutrophils cling to capillary wall), diapedesis (neutrophils flatten and squeeze out of capillaries), chemotaxis (neutrophils follow chemical trail)

_________derive from white blood cells called monocytes that leave the bloodstream, enter the tissues, and develop into _______________

macrophages

the most voracious phagocytes are ____________ ("big eaters").

macrophages

TH2 cell

mainly defend against parasitic worms. They mobilize eosinophils and activate immune responses that depend on B cells and antibody formation. They are also the cells that promote allergies.

molecules on the outer surface of the plasma membrane of all cells, help the immune system distinguish self from nonself. T cells recognize antigens only when combine with these

major histocompatibility complex (MHC)

are abundant in connective tissues of the skin and beneath the mucosa of respiratory passages and the gastrointestinal tract, and these areas are common sites of local allergic reactions.

mast cells

immune cells that function to detect foreign substances in the tissue spaces and initiate local inflammatory responses against them; typically found clustered deep to an epithelium or along blood vessels

mast cells

________ afflicted with SCID have little or no protection against disease-causing organisms.

children

Hodgkin's lymphoma

chronic malignant disease of the lymph nodes (a cancer of B cells)

involves antibodies, water-soluble protein molecules that the adaptive immune system produces to fight off foreign invaders. When antibodies bind to pathogens, they can also bind complement components. This double binding is the first step in this complement activation pathway.

classical pathway of complement activation

process during which a B or T cell becomes activated by binding with an antigen

clonal section

If pathogens provoked the inflammation, a group of plasma proteins known as________ is activated to form potent inflammatory chemicals.

complement

a group of blood borne proteins, which, when activated, enhance inflammatory and immune responses may lead to cell lysis

complement

complement activation by any of these pathways involves a cascade in which proteins are activated in an orderly sequence—

converge at C3, which is split into C3a and C3b. Splitting C3 initiates a common terminal pathway that enhances inflammation, promotes phagocytosis, and can cause cell lysis.

The chemical messengers involved in cellular immunity belong to a group of molecules called _____________, a general term for mediators that influence cell development, differentiation, and responses in the immune system.

cytokines

activated CD8 cells) are T cells that can directly attack and kill other cells.

cytotoxic T (Tc) cells

Mucous membranes and skin secrete small amounts of broad-spectrum antimicrobial peptides called _____________. output increases dramatically in response to inflammation when surface barriers are breached. Using various mechanisms, such as disruption of microbial membranes, ________ help to control bacterial and fungal colonization in the exposed areas.

defensins

are found at the body's frontiers (skin, for example) where they act as mobile sentinels. With their long, wispy extensions, dendritic cells are very efficient antigen catchers

dendritic cells

Passage of white blood cells through intact vessel walls into tissue.

diapedesis

self-tolerance

each lymphocyte must be relatively unresponsive to self-antigens so that it does not attack the body's own cells

the cells that actually do the work of fighting infection.

effector cells

fragments of proteins synthesized inside the cell

endogenous antigens

found in saliva, respiratory mucus, and lacrimal fluid of the eye—destroys bacteria. Protein-digesting____________ in the stomach kill many different microorganisms.

enzymes - lysozyme

antigens from outside the cell that have been engulfed by the cell that displays them.

exogenous antigens

fluid containing clotting factors and antibodies

exudate

2. T/F: B cells mature in the thymus

false, B cells mature in bone marrow

T/F: C3a molecules act as opsonins

false, C3b

what type of macrophages such as stellate macrophages in the liver, are permanent residents of particular organs?

fixed macrophages

mast cells

found in the connective tissue of the dermis; respond to injury, infection, or allergy by producing and releasing substances, including heparin and histamine

each antibody consists of ______________

four looping polypeptide chains linked together by disulfide (sulfur-to-sulfur) bonds.

what type of macrophages wander throughout the tissue spaces in search of cellular debris or "foreign invaders."?

free macrophages

isolates the injured area and prevents bacteria and other harmful agents from spreading.

gel like fibrin mesh

an incomplete antigen, has reactivity but not immunogenicity

hapten

three major groups of effector T cells

helper, cytotoxic, and regulatory T cells.

a chemical messenger (neurotransmitter or paracrine); causes vasodilation and increased capillary permeability; in stomach causes acidic secretion

histamine

causes blood vessels to dilate and become leaky, and is largely to blame for the best-recognized symptoms of allergy: runny nose, itching reddened skin (hives), and watery eyes.

histamine

also called antibody-mediated immunity, is provided by antibodies present in the body's "humors," or fluids (blood, lymph, etc.).

humoral immunity

Vasodilation of local arterioles causes local __________-

hyperemia

result when the immune system damages tissue as it fights off a perceived threat (such as pollen or animal dander) that would otherwise be harmless to the body. People rarely die of _________ . They just make you miserable.

hypersensitivities

a functional system whose components attack foreign substances or prevent their entry into the body

immune system

ability of the body immune cells to recognize (by binding) specific antigens; reflects the presence of plasma membrane- bound receptors

immunocompetence

is a congenital or acquired condition that impairs the production or function of immune cells or certain molecules, such as complement or antibodies.

immunodeficiency

stellate macrophages

in the walls of the sinusoids; destroy bacteria and other foreign particles in blood

An innate ( non-specific) defensive response of the body to tissue injury; includes dilation of arterioles and an increase in capillary permeability; cardinal signs are redness, heat, swelling, and pain

inflammation

surface barriers: skin and mucous membranes. internal defense: phagocytes, natural killer cells, inflammation, antimicrobial proteins, fever.

innate defense

most important antimicrobial proteins are

interferon and complement proteins

proteins released from virus infected (and other) cells that protect uninfected cells from viral takeover. also inhibit some cancers.

interferons (IFNs)

how does Every autoimmune disease represents a failure of self-tolerance?

maturing lymphocytes undergo an extensive education (negative selection) that weeds out self-reactive cells. This weeding is thorough, but not too thorough, since there are pathogens that look somewhat like self. Weakly self-reactive lymphocytes that can detect these pathogens are allowed to survive negative selection and so they may cause autoimmune disease if they become activated.

Clone cells that do not become plasma cells become long-lived

memory cells

members of T and B cell clones that provide immunological memory

memory cells

re pure antibody preparations specific for a single antigenic determinant. They are produced by descendants of a single cell

monoclonal antibodies

are fairly poor phagocytes, but within 12 hours of leaving the blood and entering the tissues, they swell and develop large numbers of lysosomes, becoming macrophages with insatiable appetites. These late-arriving macrophages replace the neutrophils on the battlefield.

monocytes

dissolved in water forms thick, sticky mucus that lines the digestive and respiratory passageways. This mucus traps many microorganisms. Likewise, the ____________ in watery saliva traps microorganisms and washes them out of the mouth into the stomach where they are digested.

mucin

Immunocompetent B and T cells that have not yet been exposed to antigen are called

naive

"police" the body in blood and lymph, are a unique group of defensive cells that can kill cancer cells and virus-infected body cells before the adaptive immune system is activated.

natural killer cells (NK)

the second test, ensures that T cells do not recognize self-antigens displayed on self-MHC. If they do, they are eliminated by apoptosis. Negative selection is the basis for immunological self-tolerance, making sure that T cells don't attack the body's own cells, which would cause autoimmune disorders. Because the self-reactive lymphocyte and all of its potential progeny are eliminated, this is called clonal deletion.

negative selection

the simplest defensive mechanism, occurs when antibodies block specific sites on viruses or bacterial exotoxins (toxic chemicals secreted by bacteria). As a result, the virus or exotoxin cannot bind to receptors on tissue cells. Phagocytes eventually destroy the antigen-antibody complexes.

neutralization

____________ the most abundant type of white blood cell, become phagocytic on encountering infectious material in the tissues.

neutrophils

_________ and ___________ generally kill ingested prey by acidifying the phagolysosome and digesting its contents with lysosomal enzymes.

neutrophils and macrophages

mucin

protein element of mucus

strongest antigen?

proteins

a mixture of dead or dying neutrophils, broken-down tissue cells, and living and dead pathogens

pus

anaphylactic shock

severe allergic reaction that causes respiratory distress due to swelling of the upper airways (bee sting, spider bite, or injection of a foreign substance (such as penicillin or other drugs that act as haptens).

result from various genetic defects that produce a marked deficit of B and T cells.

severe combined immunodeficiency syndromes (SCID)

What is the body's first line of defense?

skin and mucous membranes

why do the symptoms of asthma appear?

smooth muscle in the walls of bronchioles (small airways) contracts, constricting those small passages and restricting air flow.

are caused by antibodies (IgG and IgM rather than IgE). However, their onset is slower (1-3 hours after antigen exposure) and the reaction lasts longer (10-15 hours).

subacute hypersensitivities

pyrogens

substances that cause fever

cell lysis

swelling of cell b/c excess turgor pressure

The different types of hypersensitivity reactions are distinguished by ______________

(1) their time course, and (2) whether they involve antibodies or T cells.

Toll-like receptors (TLRs)

-A type of PRR (pattern recognition receptor) -Recognize PAMPs (pathogen associated molecular pattern) -Set in motion a cascade of events inside the cell that amplifies and orchestrates a defense response to the pathogen

What is the difference between a complete antigen and a hapten?

A complete antigen has both immunogenicity and reactivity, whereas a hapten has reactivity but not immunogenicity.

keratin

A fiber protein that is the principal component of hair, skin, and nails

Julian has a mutation in the gene that codes for interferon. What type of pathogen is Julian particularly susceptible to?

A mutation in the gene that codes for interferon would make Julian particularly susceptible to viruses.

light (L) chains

A smaller polypeptide in an antibody.

How do these endogenous antigens end up attached to class I MHCs on the outside of our cells?

As proteases (protein-digesting enzymes) degrade cytoplasmic proteins as part of their natural recycling, a random sample of the resulting protein fragments is transported into the endoplasmic reticulum. Inside the ER, these peptides bind to newly synthesized class I MHC proteins. Transport vesicles then export the "loaded" class I MHC proteins to the cell surface.

are restricted to binding antigens only on class II MHC proteins, which are typically displayed on antigen-presenting cell (APC) surfaces.

CD4 cells (which usually become helper T cells)

become cytotoxic T (TC) cells that destroy cells in the body that harbor anything foreign.

CD8 cells

are activated by antigen fragments on class I MHC proteins, also found on the surface of APCs. Once activated, cytotoxic T cells look for this same antigen presented on class I MHC proteins located on any cell in the body.

CD8 cells (which become cytotoxic T cells)

Phagocytosis

Cell eating

immunocompetent cells

Cells that are able to recognize and respond to antigens

cytokines

Chemicals released by the immune system communicate with the brain. (inflammation chemical)

are found on the surface of virtually all body cells except red blood cells.

Class I MHC proteins

are typically found only on the surfaces of cells that present antigens to CD4 cells: dendritic cells, macrophages, and B cells.

Class II MHC proteins

Class II MHC proteins display what kind of antigens? What class of T cell recognizes antigens bound to class II MHC? What types of cells display these proteins?

Class II MHC proteins display exogenous antigens. Class II MHC proteins are recognized by CD4 T cells. APCs display class II MHC proteins.

occur when antibodies bind to antigens on specific body cells and stimulate phagocytosis and complement-mediated lysis of the cellular antigens. ____________ hypersensitivity may occur after a patient has received a transfusion of mismatched blood and complement lyses the foreign red blood cells.

Cytotoxic (type II) reactions

are caused by T cells and take longer to appear (1-3 days) than antibody-mediated hypersensitivity reactions. Inflammation and tissue damage result from the action of cytokine-activated macrophages, and sometimes cytotoxic T cells.

Delayed (type IV) hypersensitivity reactions

How do APCs obtain endogenous antigens from another cell and display them on class I MHCs to activate CD8 cells?

Dendritic cells have the special ability to do this. They obtain other cells' endogenous antigens either by engulfing dying virus-infected or tumor cells, or by importing antigens through temporary gap junctions with infected cells. Dendritic cells then display these antigens on bothclass I and class II MHCs.

Name three different APCs. Which is most important for T lymphocyte activation?

Dendritic cells, macrophages, and B cells can all act as APCs. Dendritic cells are most important for T cell activation.

What event (or observation) signals that a B or T cell has achieved immunocompetence?

Development of immunocompetence of a B or T cell is signaled by the appearance on its surface of specific and unique receptors for an antigen. In the case of a B cell, this receptor is a membranebound antibody. (In T cells, it is simply called the T cell receptor.)

T/F: Unlike lymphocytes of the adaptive immune system, which only recognize and react against specific infected or tumor cells, NK cells even pickier.

False, NK cells are far less picky

what triggers self- reactive lymphocytes to slip out?

Foreign antigens resemble self-antigens. New self-antigens appear.

Name four key characteristics of adaptive immunity.

Four key characteristics of adaptive immunity are that it involves B and T lymphocytes, it is specific, it is systemic, and it has memory.

which damages the kidney's filtration membrane and severely impairs renal function

Glomerulonephritis

which prompts the thyroid gland to produce excessive amounts of thyroxine

Graves' disease

What makes HIV particularly hard for the immune system to defeat?

HIV is particularly hard for the immune system to defeat because (1) it destroys helper T cells, which are key players in adaptive immunity and (2) it has a high mutation rate and so it can avoid detection by the immune system by changing its surface antigens.

play a central role in adaptive immunity, mobilizing both its humoral and cellular arms

Helper T (Th) cells

Which type of T cell is the most important in both cellular and humoral immunity? Why?

Helper T cells are central to both humoral and cellular immunity because they are required for activation of both cytotoxic T cells and most B cells.

a key growth factor. Acting on the cells that release it (as well as other T cells), it sets up a positive feedback cycle that encourages activated T cells to divide even more rapidly.

IL-2

occurs in both monomer and dimer (two linked monomers) forms

IgA

the dimer, referred to as secretory IgA, is found in body secretions such as saliva, sweat, intestinal juice, and milk. secretory IgA helps stop pathogens from attaching to epithelial cell surfaces (including mucous membranes and the epidermis).

IgA

found on the B cell surface. functions as B cell antigen receptor

IgD

monomers and have the same basic Y-shaped structure.

IgD, IgG, and IgE

stem end binds to mast cells or basophils. antigens binding to its receptor end triggers these cells to release histamine and other chemicals that mediate inflammation and allergic reaction

IgE (monomer)

the most abundant antibody in plasma, accounting for 75-85% of circulating antibodies. the main antibody of both secondary and late primary responses. readily activates complement

IgG (monomer)

in plasma is huge compared to the other antibodies. It is constructed from five Y-shaped units, or monomers, linked together to form a pentamer (penta = five).

IgM

the first immunoglobulin class secreted by plasma cells during the primary response. readily activates complement.

IgM (pentamer)

Activation of CD8 T cells

Like B cells, CD8 cells usually require help from TH cells to activate into destructive cytotoxic T cells. As shown in Figure 21.18b, TH cells cause dendritic cells to express on their surfaces the co-stimulatory molecules required to activate CD8 cells.

What marks a cell as "self" as opposed to "nonself"?

Self-antigens, particularly MHC proteins, mark a cell as self.

Treatment of autoimmune diseases

Suppress entire immune system- Anti-inflammatory drugs, such as corticosteroids Blocking the actions of various cytokines using antibodies against them or their receptors Blocking the co-stimulatory molecules required to activate effector cells

What is the first line of defense against disease?

Surface barriers (the skin and mucous membranes) constitute the first line of defense.

a systemic disease that particularly affects the kidneys, heart, lungs, and skin

Systemic lupus erythematosus (SLE),

cells can recognize and respond only to processed fragments of protein antigens displayed on surfaces of body cells (APCs and others).

T

________ cause delayed hypersensitivities.

T cells

are best suited for cell to cell interaction

T cells

are non-antibody-producing lymphocytes that constitute the cellular arm of adaptive immunity.

T lymphocytes (T cells)

application of innate defenses

TH cells also amplify the responses of the innate immune system.The cytokines released by TH cells not only mobilize lymphocytes and macrophages but also attract other types of white blood cells into the area.

stimulate inflammation, activate macrophages, and promote differentiation of cytotoxic T cells. They mediate most aspects of cellular immunity.

TH1 cells

link together adaptive and innate immunity by releasing IL-17, which promotes inflammatory responses against extracellular microbes and may underlie most autoimmune diseases.

TH17 cells

mucous membranes line all body cavities that open to the exterior:

the digestive, respiratory, urinary, and reproductive tracts.

constant region

these are the effector regions of the antibody that dictate (1) the cells and chemicals of the body the antibody can bind to, and (2) how the antibody class functions to eliminate antigens.

1. T/F: both B and T lymphocyte precursors originate in red bone marrow

true

2. T/F: during maturation lymphocytes develop immunocompetence and self tolerance

true

2. T/F: lymphocyte precursors destined to become T cells migrate (in blood) to the thymus and mature there

true

3. T/F: (sending secondary lymphoid organs and circulation) immunocompetent but still naive lymphocytes leave the thymus and bone marrow

true

3. T/F: B and T cells "seed" the secondary lymphoid organs and circulate through blood and lymph

true

4. T/F: when a lymphocytes antigen receptors bind its antigen, that lymphocyte can be activated

true

5.T/F: activated lymphocytes proliferate (multiply) and then differentiate into effector cells and memory cells memory cells and effector T cells circulate continuously in the blood and lymph and throughout the secondary lymphoid organs

true

Although macrophages, like dendritic cells, can activate naive T cells, macrophages often present antigens to T cells for other reasons—to maintain T cell activation or to be activated themselves.

true

An immunocompetent but naive B lymphocyte is activated when matching antigens bind to its surface receptors and cross-link adjacent receptors together.

true

Another interferon, IFN gamma (γ), or immune interferon, is secreted by lymphocytes and has widespread immune mobilizing effects, such as activating macrophages.

true

Fever causes the liver and spleen to sequester iron and zinc, which may make them less available to support bacterial growth. Additionally, fever increases the metabolic rate of tissue cells, and may speed up repair processes.

true

IFN alpha (α) and beta (β) have the antiviral effects that we've just described and also activate NK cells.

true

In the skin, some lipids in sebum and dermcidin in eccrine sweat are toxic to bacteria.

true

Our genes, not antigens we encounter, determine which specific foreign substances our immune system will be able to recognize and resist

true

T cell antigen receptors (TCRs) bind to an antigen-MHC complex on the surface of an APC.

true

T/F: Unless attached to protein carriers, haptens have reactivity but not immunogenicity

true

T/F: phagocytic attempts are not always successful because in order for a phagocyte to ingest a pathogen, the phagocyte must first adhere to that pathogen, a feat made possible by recognizing the pathogen's carbohydrate "signature." Many bacteria have external capsules that conceal their carbohydrate signatures, allowing them to elude capture because phagocytes cannot bind to them.

true

only about 2% of T cells survive it and continue to become successful immunocompetent, self-tolerant T cells.

true

only immunocompetent B cells are allowed to mature.

true

some pathogens such as the _____________________________________ are resistant to lysosomal enzymes and can even multiply within the phagolysosome

tuberculosis bacillus and certain parasites

heavy (H) chains

two chains that are identical, are polypeptide chains, consists of about 450 amino acids. short carbohydrate chains are attached to each heavy polypeptide chain

The adaptive immune system involves three crucial types of cells

two distinct populations of lymphocytes, plus antigen-presenting cells (APCs).

Conventional Vaccines

usually contain inactivated disease-causing organisms or proteins made by the pathogen (antigens), which work by mimicking the infectious agent

How does HIV enter the body ?

via blood-contaminated needles, or during sexual intercourse.

when does cell lysis begin?

when C3b binds to the target cell's surface and triggers the insertion of a group of complement proteins called MAC (membrane attack complex) into the cell's membrane.

vasodilation

widening of blood vessels

which destroys pancreatic beta cells, resulting in a deficit of insulin and inability to use carbohydrates

Type 1 (insulin-dependent) diabetes mellitus

Two major populations of T cells

1. CD 4: Helper T cell and Regulatory T cell. 2. CD 8: Cytotoxic T cell - Both groups come from memory T cells.

What causes AIDS?

AIDS cripples the immune system by interfering with the activity of helper T cells. AIDS is caused by the human immunodeficiency virus (HIV), a virus transmitted in body secretions—especially blood, semen, and vaginal secretions.

do not respond to specific antigens as lymphocytes do. Instead, they play essential auxiliary roles. As we will see, T cells cannot recognize their antigens without ________

APCs

Immunogenicity

Ability of pathogens to induce an immune response

what inhibits bacterial growth?

Acid. The acidity of skin, vaginal, and stomach secretions—the acid mantle

Proliferation and differentiation of T cells

Activated, sensitized T cells divide and differentiate to produce clones (Once activated by antigen binding and co-stimulation, a T cell enlarges and proliferates.)

approaches still being developed for reestablishing self tolerance for autoimmune diseases

Activating regulatory T cells Inducing self-tolerance using vaccines Destroying self-reactive immune cells by directing antibodies against them

Activation of B cells

Activation by antigen is aided by cytokine (secreted by helper T) Stimulated by antigen and cytokines, B Cells proliferate into memory and effector/plasma cells (secrete antibodies)

cellular immunity

Also called cell-mediated immunity. This process results in the production of T cells and natural killer, NK, cells that directly attach to foreign cells. This immune response fights invasion by viruses, bacteria, fungi, and cancer.

Lyzozyme

An enzyme that breaks down pathogens on the skin's surface

List four ways in which antibodies can bring about destruction of a pathogen.

Antibodies can bring about destruction of pathogen via "PLAN"—phagocytosis, lysis (via complement), agglutination, or neutralization.

_______________ reactions cause immediate and subacute hypersensitivities.

Antibody-associated

oversee humoral immunity

B lymphocyte (B cells)

Unlike dendritic cells and macrophages, B cells do not activate naive T cells. Instead, they present antigens to a certain kind of T cell (a helper T cell) in order to obtain "help" in their own activation.

B lymphocytes

What event triggers the release of histamine from mast cells in an allergic response?

Binding of an allergen onto specific IgE antibodies attached to mast cells triggers the mast cells to release histamine.

Kinins in inflammation

Blood proteins that help inflammation, blood pressure control, coagulation, and pain

HIV targets _________ cells via their ____________ surface proteins

CD4

usually become helper T (TH) cells that help activate B cells, other T cells, and macrophages, and direct the adaptive immune response.

CD4 cells

The five major immunoglobulin classes are designated _____________________

IgM, IgA, IgD, IgG, and IgE, on the basis of the C regions in their heavy chains. (Remember the name MADGE to recall the five Ig types.)

also called acute or type I hypersensitivities, are simply what most of us would call allergies

Immediate hypersensitivities

Two killing mechanisms that we have seen in this chapter create pores in their target. Name the proteins that form this structure if they are (a) secreted by an immune cell that binds to the target cell or (b) derived from plasma proteins. Describe how these pores kill.

Immune cells that secrete proteins that form a pore are cytotoxic T cells and NK cells. In this case, perforins are the proteins that form the pore. (b) Complement proteins are plasma proteins that can form a pore [which is called a membrane attack complex (MAC)]. Specifically, in complement-mediated cell lysis, MAC complexes cause a target cell (usually a bacterium) to become leaky. This allows water to enter and cytoplasmic contents to exit the cell, killing the cell. In contrast, cytotoxic T cells and NK cells kill their targets (usually virus-infected cells) by releasing perforins and granzymes onto the identified target cell. Perforins form a pore in the target cell membrane, and granzymes enter through this pore, activating enzymes that trigger apoptosis (cell suicide).

result when antigens are widely distributed through the body or blood and the huge number of insoluble antigen-antibody complexes formed cannot be cleared from a particular area.

Immune-complex (type III) hypersensitivities

Complete antigens have two important functional properties:

Immunogenicity, which is the ability to stimulate specific lymphocytes to proliferate (multiply). Reactivity, which is the ability to react with the activated lymphocytes and the antibodies released by immunogenic reactions.

In clonal selection, "who" does the selecting? What is being selected?

In clonal selection, the antigen does the selecting. What is being selected is a particular clone of B or T cells that has antigen receptors corresponding to that antigen.

What happens if a T cell binds to antigen without receiving the co-stimulatory signal?

In this case, the T cell becomes tolerant to that antigen and is unable to respond. This state of unresponsiveness to antigen is called anergy.

the adaptive immune response has four key characteristics that set it appart from the innate defenses:

It involves lymphocytes called B and T lymphocytes. These lymphocytes are not involved in innate immunity. It is specific. It recognizes and targets identified pathogens or foreign substances that initiate the immune response. It is systemic. Adaptive immunity is not restricted to the initial infection site. It has "memory." After an initial exposure, it recognizes and mounts even stronger attacks on previously encountered pathogens.

active immunity is acquired in two ways :

It is (1) naturally acquired when you get a bacterial or viral infection, during which time you may develop symptoms of the disease and suffer a little (or a lot), and (2) artificially acquired when you receive a vaccine. I

what are the inflammation beneficial effects?

It prevents the spread of damaging agents to nearby tissues. It disposes of cell debris and pathogens. It alerts the adaptive immune system. It sets the stage for repair.

The respiratory burst promotes killing of pathogens by:

Liberating a deluge of highly destructive free radicals (p. 86) Producing oxidizing chemicals (hydrogen peroxide and a substance identical to household bleach) Increasing the phagolysosome's pH and osmolarity, which activates other protein-digesting enzymes that digest the invader

What does MAC do?

MAC forms and stabilizes a hole in the membrane that allows a massive influx of water, lysing the target cell.

. Naive T cells can only be activated by antigens that are presented to them on ____________

MHC proteins by APCs.

which destroys the myelin of the white matter of the brain and spinal cord

Multiple sclerosis

which impairs communication between nerves and skeletal muscles (autoimmune disease)

Myasthenia gravis

Are NK cells phagocytic?

NO. NK cells play a major role in the host-rejection of both tumours and virally infected cells. NK cells are cytotoxic. they release small granules to attract phagocytic cells to destroy target cells.

Helper T cells

One type of T lymphocyte that activates B cells and other T lymphocytes

What is opsonization and how does it help phagocytes? Give an example of a molecule that acts as an opsonin.

Opsonization is the process of making pathogens more susceptible to phagocytosis by decorating their surface with molecules that phagocytes can bind. Antibodies and complement proteins are examples of molecules that act as opsonins.

Under what circumstances might NK cells kill our own cells?

Our own cells are killed by NK cells when they have been infected by viruses or when they have become cancerous.

What is the function of the abundant endoplasmic reticulum in plasma cells? What other organelle(s) (described in Chapter 3) would be especially abundant in plasma cells? Why?

Plasma cells make large amounts of antibodies—proteins that are exported from the cell. Rough endoplasmic reticulum is the site where proteins that are exported are synthesized. Ribosomes, the Golgi apparatus, and secretory vesicles are also required for protein synthesis and export, and so would also be abundant in these cells.

What are the cardinal signs of inflammation and what causes them?

Redness, heat, swelling, and pain are the cardinal signs of inflammation. Redness and local heat are both caused by vasodilation of arterioles, which increases the flow of blood (warmed by the body core) to the affected area. The swelling (edema) is due to the release of histamine and other chemical mediators of inflammation, which increase capillary permeability. This increased permeability allows proteins to leak into the interstitial fluid (IF), increasing the IF osmotic pressure and drawing more fluid out of blood vessels and into the tissues, thereby causing swelling. The pain is due to two things: (1) the actions of certain chemical mediators (kinins and prostaglandins) on nerve endings, and (2) the swelling, which can compress free nerve endings.

which systematically destroys joints (autoimmune disease)

Rheumatoid arthritis

acquired immunodeficiency syndrome (AIDS)

The most advanced, and fatal, stage of an HIV infection.

phagolysosome formation

The phagosome then fuses with lysosomes and granules forming the phagolysosome Lysosomes and granules contain antimicrobial chemicals

Why is the secondary response to an antigen so much faster than the primary response?

The secondary response to an antigen is faster than the primary response because the immune system has already been "primed" and has memory cells that are specific for that particular antigen.

Vaccines provide two benefits

Their weakened antigens provide functional antigenic determinants that are both immunogenic and reactive. They spare us most of the symptoms and discomfort of the disease that would otherwise occur during the primary response.

Once cytotoxic T cells recognize their targets, how do they deliver a lethal hit?

There are two major mechanisms. One involves perforins and granzymes (Figure 21.19). The other involves binding to a specific membrane receptor on the target cell that stimulates the target cell to undergo apoptosis.

cells are important in preventing autoimmune reactions because they suppress self-reactive lymphocytes in the periphery—that is, outside the lymphoid organs. TReg cells and their subpopulations are currently hot research topics.

Treg

are true "killers"—insatiable phagocytes that also trigger powerful inflammatory responses and recruit additional defenses.

activated macrophages

When your B cells encounter antigens and produce antibodies against them, you are exhibiting _______________

active humoral immunity

immunity produced by an encounter with an antigen; provides immunological memory

active immunity

Humoral immunity (B cells), cellular immunity (T cells)

adaptive defense

The clumping of foreign cells that occurs when cross-linking of antigen-antibody complexes occur

agglutination

is an antigen that causes an allergic reaction.

allergen

which follow skin contact with poison ivy, some metals (nickel in jewelry), and certain cosmetic and deodorant chemicals. These agents diffuse through the skin and attach to self-proteins as haptens.

allergic contact dermatitis

a type of hypersensitivity that involves IgE antibodies and histamine release

allergies

how are the engulfed exogenous antigens broken down?

by proteases inside a phagolysosome

is triggered when spontaneously activated C3 and other complement factors interact on the surface of microorganisms. These microorganisms lack the complement activation inhibitors our own cells have.

alternative pathway

Corticosteroids

anti-inflammatory agents that treat skin inflammation

are proteins secreted in response to an antigen by effector B cells called plasma cells, and the antibodies bind specifically with that antigen.

antibodies

a specialized cell (dendritic cell, macrophage, or B cell) that captures, processes, and presents antigens on its surface to t lymphocytes

antigen- presenting cell (APC)

Defensive mechanisms used by antibodies include neutralization, agglutination, precipitation, and complement activation, with the first two most important.

antigen-antibody (or immune) complexes.

are substances that can mobilize the adaptive defenses.

antigens

enhance our innate defenses by attacking microorganisms directly or by hindering their ability to reproduc

antimicrobial proteins

subacute hypersensitivities

are caused by antibodies (IgG and IgM) and can be transferred via blood plasma or serum. However, their onset is slower and the duration of the reaction is longer

where are class II MHC proteins synthesized?

at the ER and bind to peptide fragments.

production of antibodies or effector T cells that attack a persons own tissue

autoimmunity

lymphocytes become immunocompetent______________ meeting the antigens they may later attack.

before

variable region of antibody

binds to antigen

how does our immune system get around the phagocytic problem?

by coating pathogens with opsonins

monoclonal antibodies are used to

o diagnose pregnancy, certain sexually transmitted infections, some cancers, hepatitis, and rabies. These monoclonal antibody tests are more specific, sensitive, and rapid than other tests. Monoclonal antibodies are also used to treat leukemia and lymphomas, cancers that are present in the circulation and so are easily accessible to injected antibodies. They also serve as "guided missiles" to deliver anticancer drugs only to cancerous tissue, and to treat certain autoimmune diseases (as we will discuss later).

something to know: The increased tissue fluid causes the local swelling (edema) that presses on adjacent nerve endings, contributing to a sensation of pain. Pain also results from the release of bacterial toxins, and the sensitizing effects of released prostaglandins and kinins. (Aspirin and some other anti-inflammatory drugs reduce pain by inhibiting prostaglandin synthesis.)

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are complement proteins or antibodies. Both provide "handles" to which phagocyte receptors can bind. Any pathogen can be coated with ____________ a process called opsonization ("to make tasty"), which greatly accelerates phagocytosis of that pathogen.

opsonins

what happens when tuberculosis bacillus and certain parasites are resistant to lysosomal enzymes?

other immune cells called helper T cells release chemicals that stimulate the macrophage. This activates additional enzymes that produce a lethal respiratory burst.

antigenic determinants

parts of antigen that antibodies or lymphocyte receptors bind to

short lived immunity resulting from the introduction of "borrowed antibodies" obtained from an immune animal or human donor; immunological memory is not established

passive immunity

harmful or disease-causing microorganisms

pathogens

macrophages, mast cells, white blood cells and etc identify potentially harmful substances by recognizing (binding to) molecules with specific shapes that are part of infectious organisms (bacteria, viruses, fungi, and various parasites) but not normal human cells. The receptors that do this are called_________________

pattern recognition receptors.

Macrophages

phagocytize foreign substances and help activate T cells

Vesicle formed as a result of phagocytosis

phagosome

the antibody-secreting effector cells of the humoral response

plasma cells

chemicals that act on haptens are found in:

poison ivy, animal dander, detergents, cosmetics, and a number of common household and industrial products.

is the first of two tests a developing T lymphocyte must pass. It ensures that only T cells with receptors that are able to recognize self-MHC proteins survive. Remember that T cells cannot bind antigens unless the antigens are presented on self-MHC proteins. T cells that are unable to recognize self-MHC are eliminated by apoptosis.

positive selection

soluble molecules (instead of cells) are cross-linked into large complexes that settle out of solution. Like agglutinated bacteria, precipitated antigen molecules are much easier for phagocytes to capture and engulf than are freely moving antigens.

precipitation

Apoptosis

programmed cell death

a lipid based chemical messenger synthesized by most tissue cells; acts locally as a paracrine

prostaglandin (inflammation chemical )

Activation and differentiation of T cells

• T cells can be activated only when antigen is presented to them • Activation is a two-step process 1. Antigen binding 2. Co-stimulation • Both occur on surface of same APC • Both are required for clonal selection of T cell