Adaptive Immunity: Specific Defenses of the Host CHAP 17

Humoral Immunity Response Process

(antibody-mediated) by a special group of lymphocytes called B cells - process starts when B cells are exposed to free, or extracellular, antigens.

IgM

(the M refers to macro, reflecting their large size) make up 6% -pentamer structure consisting of five monomers held together by a polypeptide called a joining (J) chain - generally remain in blood vessels without entering the surrounding tissues.,, too big -predominant type of antibody involved in the response to the ABO blood group antigens on the surface of red blood cells -more effective than IgG -in causing the clumping of cells and viruses-reactions involving the activation of complement -first in response to a primary infection and is relatively short-lived -Especially effective against microorganisms and agglutinating antigens; first antibodies produced in response to initial infection = M = many monomers= more affective than G =connects many cells = first of many to arrive at the damaged area=

Eosinophils

*What IgE-mediated cell secretes major basic protein and has elevated levels in the blood during asthma and parasitic infections? *What type of WBC is present in increased numbers during an allergic reaction?

eosinophils,

*What IgE-mediated cell secretes major basic protein and has elevated levels in the blood during asthma and parasitic infections? *What type of WBC is present in increased numbers during an allergic reaction?

haptens

-=antigens too small to provoke immune responses; attach to carrier molecules -These low-molecular-weight compounds -when the hapten is combined with a larger carrier molecule, usually a serum protein, the hapten and its carrier together form a conjugate that can stimulate an immune response. -antibody will react with the hapten independent of the carrier molecule.

Clonal Selection of Antibody-Producing Cells

-B cell carries immunoglobulins on its surface that are part of its makeup. The majority of the B cell's surface immunoglobulins are IgM and IgD -Ten percent or fewer of B cells carry other classes of immunoglobulins, but in certain locations their numbers may be high -activated when antibodies attach

immune serum globulin

-Concentrate of plasma globulins in aqueous solution -IgA-deficient persons should not receive this.

T Helper Cells (CD4+ T Cells)

-TCR on the TH cell recognize and bind to the antigen fragment and MHC class II on APC -APC or TH secrete a costimulatory molecule, activating the TH cell -TH cells can recognize an antigen presented on the surface of a macrophage and activate the macrophage -Dendritic cells are especially important in the activation of CD4+ T cells and in developing their effector functions -- -for a CD4+ T cell to become activated, its T cell receptor recognizes antigen fragments held in a complex with proteins of MHC class II on the surface of the APC. This is the initial signal for activation; a second signal, the costimulatory signal that comes from either the APC or T helper cell, is also required for activation. The activated TH cell begins to proliferate at the rate of two to three cell cycles a day and to secrete cytokines ---dfferentiate into populations of subsets such as TH1, TH2, and TH17. They also form a population of long-lived memory cells. The effector functions of these subsets are based on the cytokines produced by these TH cells,

Antibody Structure

-ends of the Y arms are called variable (V) regions -these two variable regions are identical on any one antibody. -The stem of the antibody monomer and the lower parts of the arms of the Y are called the constant (C) regions ---five major types of C regions, which account for the five major classes of immunoglobulins -The stem of the Y-shaped antibody monomer is called the Fc region,=These Fc regions are often important in immunological reactions.

Dendritic cells (DCs)

-engulf and degrade microbes and display them to T cells -found in the skin, genital tract, lymph nodes, spleen, thymus, and blood ---are characterized by long extensions called dendrites ---principal APCs to induce immune responses by T cells -act as sentinels in these tissues engulf invading microbes, degrade them, and transfer them to lymph nodes for display to T cells located there.

neutralization

IgG antibodies inactivate microbes by blocking their attachment to host cells, and they neutralize toxins in a similar manner.

secondary response

Later interactions with that same cell or substance -which will be faster and more effective as a result of a "memory"

Extracellular Killing by the Immune System

Natural killer (NK) cells lyse virus-infected cells, tumor cells, and parasites. They kill cells that do not express MHC class I antigens.

Types of Adaptive Immunity

Naturally acquired active immunity Naturally acquired passive immunity Artificially acquired active immunity Artificially acquired passive immunity

activation of the complement system

One aspect of inflammation is that it will often cause microbes in the inflamed area to become coated with certain proteins. This, in turn, leads to the attachment to the microbe of an antibody-complement complex. This complex lyses the microbe, which then attracts phagocytes and other defensive immune system cells to the area.

perforin

One of the proteins released by cytotoxic T cells on contact with their target cells. It forms pores in the target cell membrane that contribute to cell killing.

Immunity can be acquired actively

when a person is exposed to microorganisms or foreign substances and the immune system responds =can be obtained by natural or artificial means

Immunity is acquired passively

when antibodies are transferred from one person to another- lasts only as long as the antibodies are present—in most cases, a few weeks. =can be obtained by natural or artificial means ==However, although artificially acquired passive immunity is immediate, it is short-lived because antibodies are degraded by the recipient. The half-life of an injected antibody (the time required for half of the antibodies to disappear) is typically about 3 weeks.

tumor necrosis factor (TNF)

Secreted by macrophages and T cells to kill tumor cells and regulate immune responses and inflammation -tumor cells were observed to be one of its targets. These cytokines are a strong factor in inflammatory reactions of autoimmune diseases such as rheumatoid arthritis

T regulatory cells (Treg)

Subset of CD4+ cells; carry an additional CD25 molecule Suppress T cells against self; protect intestinal bacteria required for digestion; protect fetus -T suppressor cells, -make up about 5-10% of the T cell population. They are a subset of the CD4+ T helper cells and are distinguished by CD25 molecule -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.

antigens

Substances that cause the production of antibodies -from antibody generators. Most antigens are either proteins or large polysaccharides.

Cellular Immunity Response Process

T cells combat intracellular pathogens Mature in the thymus Thymic selection eliminates immature T cells Migrate from the thymus to lymphoid tissues Attach to antigens via T-cell receptors (TCRs) -. Some bacteria and parasites can also invade and live within cells. -not exposed to circulating antibodies. -T cells probably evolved in response to the need to combat intracellular pathogens. -T cell is specific for only a certain antigen - rather than antibodies - they have T cell receptors (TCRs.)

t cells

T cells migrate from the thymus by way of the blood and lymphatic system

Classes of T Cells

T helper cells (TH) T cytotoxic cells (TC) Cytotoxic T lymphocyte (CTL) T regulatory (Treg) cells

secondary response

The adaptive immune response provoked by a second exposure to an antigen. It differs from the primary response by starting sooner and building more quickly.

TH1 cells

The cytokines produce -IFN-γ, activate -cellular immunity, such as delayed hypersensitivity and are also responsible for activation of macrophages They also stimulate the production of antibodies that promote phagocytosis -especially effective in enhancing the activity of complement, such as opsonization and inflammation -cytotoxic T lymphocytes also requires action by a TH1 cell. - make signal to kill a infected cell

clonal deletion

The process of destroying B and T cells that react to self antigens -eliminates harmful B cells -These are usually eliminated at the immature lymphocyte stage by the process

serology

The study of reactions between antibodies and antigens

activated macrophages

Their phagocytic capabilities are greatly increased when they are stimulated -can be initiated by ingestion of antigenic material. Other stimuli, such as cytokines produced by an activated T helper cell, -more effective as phagocytes and as APCs\--larger and become ruffled.- - control of cancer cells, virus-infected cells, and ---APCs tend to migrate from their locations = where they present the antigen to T cells located there= Migration of APCs increases the opportunity for these particular T cells to encounter the antigen for which they are specific.

natural killer (NK) cells

These cells kill cancer cells and cells infected with viruses. They bind to their targets and deliver a lethal burst of chemicals to produce holes in the target cell's membrane leading to its destruction. --can also destroy certain virus-infected cells and tumor cells. These are large granular leukocytes (10-15% of circulating lymphocytes) -can also attack parasites, which are normally much larger than bacteria, ---not immunologically specific; that is, they do not need to be stimulated by an antigen. NK cells distinguish normal cells from transformed cells, or cells infected with intracellular pathogens. -first contact the target cell and determine whether it expresses MHC class I self-antigens-they kill the target cell by mechanisms similar to that of a CTL -With the help of antibodies

antigen-antibody complex

When an antibody encounters an antigen for which it is specific

B cells

When an inactive B cell meets an antigen that can bind to its particular surface receptor, it will engulf and process it, displaying antigen fragments bound to its MHC class II molecules. This, in turn, attracts T helper cells to the B cells. --T helper cell in contact with the antigenic fragment presented on the surface of the B cell begins producing cytokines that activate the B cell. 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. -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 (here, B cell "II") into a clone of cells with the same specificity, hence the term clonal selection. The initial antibodies produced are generally IgM, but later the same cell might produce different classes of antibody, such as IgG or IgE; this is called class switching. -Humoral antibodies are effective against pathogens such as viruses and bacteria that are circulating freely, where the antibodies can contact them

class switching

ability of a B cell to produce a different class of antibody against one antigen -l B cell is also capable of making different classes of antibody, such as IgG, IgE, or IgA, all with unchanged antigenic specificity =observed, especially, in the case of the primary and secondary immune response -when IgG begins to be produced in the secondary response, the production of IgM will decrease

TH2 cells

activate B cells to produce IgE; activate eosinophils =produce cytokines that are associated primarily with the production of antibodies, especially IgE, -important in allergic reactions - activation of the eosinophils that defend against infections by extracellular parasites, such as helminths

cytotoxic T lymphocyte (CTL)

adaptive immune cell that directly kills infected cells via perforin and granzymes, and releases cytokines to enhance the immune response -Destroys target cells on contact; generated from T cytotoxic (Tc) cell

Foreign organisms and toxins are rendered harmless by only a few mechanisms

agglutination, opsonization, neutralization, antibody-dependent cell-mediated cytotoxicity, and the activation of complement leading to opsonization, inflammation, and cell lysis

Peyer patches

aggregates of lymphoid tissue in the lining of the intestine -which are secondary lymphoid organs located on the intestinal wall

T-dependent antigen

an antigen that will stimulate the formation of antibodies only with the assistance of T helper cells -An antigen that requires a TH cell for antibody production

affinity

an attraction to -The strength of the bond between an antigen and an antibody -closer the physical = the more affinity -They can distinguish between minor differences in the amino acid sequence of a protein and even between two amino acid isomers --used to differentiate -tagging foreign cells and molecules for destruction by phagocytes and complement.

Antibody-dependent cell-mediated cytotoxicity

antibodies attached to target cell cause destruction by macrophages, eosinophils, and NK cells -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.

agglutination

antibodies cause antigens to clump together -are more easily ingested by phagocytes -IgM is more effective at cross-linking and aggregating particulate antigens

Immunological Memory

antibody-mediated immune responses of the host intensify after a second exposure

endogenous antigens

antigens produced by microbes that multiply inside the cells of the body -On their surface they carry fragments

immunogens

antigens that can elicit antibody production by themselves

Antibodies (immunoglobulins, Ig)

are globulin proteins -Globulin proteins are compact and relatively soluble. -recognize and bind to the antigen. -bacterium or virus may have several epitopes that cause the production of different antibodies

TH17

because of their production of large quantities of the cytokine IL-17 -Excessive amounts of TH17 cells probably contribute to the inflammation and injury to tissue found in certain autoimmune diseases -associated with the pathologic effects of diseases such as asthma and allergic dermatitis -helpfully, to combat microbial infections of the mucosa by the production of cytokines such as IL-22

Antigen-Presenting Cells (APCs)

cells that process protein antigens and present them on their surface in a form that can be recognized by lymphocytes (white blood cells) -cells such as B cells, macrophages, and dendritic cells that can present exogenous antigens to naive or memory T cells, activating them = B cells, in humoral - but in cellular immunity = These APCs are the dendritic cells and the activated macrophages

IgE

class are slightly larger than IgG molecules; they constitute only 0.002% -bind tightly by their Fc (stem) regions to receptors on mast cells and basophils, specialized cells that participate in allergic reactions -antigen such as pollen links with the IgE antibodies attached to a mast cell or basophil -Allergic reactions; possibly lysis of parasitic worms -, for it attracts complement and phagocytic cells = E = allergic reaction = eliminate parasites

Clusters of Differentiation (CD)

classification of T cells by the presence of certain glycoproteins on their surface -The CDs of greatest interest are CD4 and CD8; cells that carry these molecules are named CD41 and CD81 cells TH cells are classified as CD41, which bind to MHC class II molecules on B cells and APCs. CTL cells are classified as CD8+, which bind to MHC class I molecules.

opsonization

coating antigen with antibody enhances phagocytosis -the antigen, such as a bacterium, is coated with antibodies, or complement proteins, that enhance its ingestion and lysis by phagocytic cells

T helper cell (TH)

contacts the displayed antigen fragment and releases cytokines that activate B cells -For antibodies to be produced in response to a T-dependent antigen, it is necessary that both B and T cells be activated and interact.

T helper cells (TH)

cooperate with B cells in the production of antibodies, mainly through cytokine signaling. -essential element of cellular immunity

IgG

derived from the blood fraction -about 80% of all antibodies -monomers -cross the placenta and confer passive immunity to a fetus -circulating bacteria and viruses, neutralize bacterial toxins, trigger the complement system -enhance the effectiveness of phagocytic cells. -Enhances phagocytosis; neutralizes toxins and viruses; -which is relatively long-lived -Enhances phagocytosis; neutralizes toxins and viruses;protects fetus and newborn ===its a G so it neutralizes, protects babies in the uterus, enhances phagocytosis

thymic selection

destroys T cells that will not recognize MHC molecules of the host and T cells that will attack host cells -weeding-out process -Most immature T cells, an estimated 98%, are eliminated in the thymus, which is analogous to clonal deletion in B cells.

Naturally acquired active immunity

develops when a person is exposed to antigens through everyday life, becomes ill, and then recovers. Once acquired, immunity is lifelong for some diseases, such as measles. - some/ intestinal diseases/ only last 1 year

primary response

first time the adaptive immune system meets and combats a particular foreign substance

primary response

first time the immune system combats a particular foreign substance

hematopoietic cytokines

function in controlling the pathways by which stem cells develop into different red or white blood cells

The Diversity of Antibodies

human immune system is capable of recognizing —an estimated minimum of 1 quadrillion antigens -amount of antibody diversity is derived from a set of just hundreds of genes. -random rearrangements of the nucleotide sequence for the variable (V) region. These rearrangements occur even when no antigen is present during the early stages of the differentiation of a B cell. -only a relatively small amount of DNA is required to cope with the enormous number of different antigens

antiserum

human or animal serum containing antibodies -

cellular immunity

immune response that relies on T cells to destroy infected body cells

Cellular immunity (cell-mediated immunity)

immune response that relies on T cells to destroy infected body cells -T lymphocytes, or T cells, are the basis= T cells and B cells both develop from stem cells in the bone marrow = mature under the influence of the thymus.-- -recognize antigenic peptides after they have been processed by phagocytic cells such as macrophages.-- =center on attacking antigens that make their way inside cells/ cytoplasm =best at fighting viruses -as well as some fungal and parasitic infections, - respond by means of receptors on their surface—T cell receptors (TCRs).= some antigens Contact with an antigen can make T cells to proliferate and secrete cytokines rather than antibodies

Adaptive immunity

induced and specific to a particular microbial invader or foreign substance -consists of two parts = humoral immunity and cellular immunity. -includes a memory component -Both parts of adaptive immunity involve the recognition of specific antigens

interferons (IFNs)

interfere with viral infections of host cells -Another family of cytokines -INFγ stimulates the immune system.

Artificially acquired passive immunity

involves the injection of antibodies (rather than antigens) into the body. These antibodies come from an animal or a human who is already immune to the disease.

Naturally acquired passive immunity

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 -Certain antibodies are also passed from the mother to her nursing infant in breast milk, , called colostrum -lasts only as long as the transmitted antibodies persist

Adaptive immunity

is a range of microbial defenses that target specific pathogens -the adaptive immune system defenses are acquired through infection or vaccination and are highly specific -immunity to certain infectious diseases can be acquired during an individual's life -recovered almost always immune to that particular disease when exposed to it again. -the body had acquired a memory of the infection -defenses of the adaptive system take several days or more to fully develop, whereas the effects of the innate system responses are more immediate. --only when the innate defenses fail to stop a microbe -tailors its fight to the specific microbial pathogen, toxin, or other substance at hand. ----ability to differentiate between normal "self" cells and "nonself." This is essential, because without this ability the immune system might attack components of the body it is designed to protect.

Apoptosis

is also called programmed cell death. -if the cell's death is due to trauma or disease, the body's defense and repair mechanisms are mobilized. Therefore, if a cell cannot clear a pathogen in any other way, it clears it by dying -cut their genome into fragments, and the external membranes bulge outward in a manner called blebbing -. Signals are displayed on the cell's surface that attract circulating phagocytes to digest the remains before any significant leakage of contents occurs.

Dual Nature of the Adaptive Immune System

is considered a dual system, with humoral and cellular components. Next, we will briefly summarize both humoral and cellular immunity.

Artificially acquired active immunity

is the result of vaccination/immunization -These are antigens, such as killed or living microorganisms or inactivated bacterial toxins.

IgD

make up only about 0.02% -resembles that of IgG molecules. IgD antibodies are found in blood, lymph, and particularly on the surfaces of B cells -assists in the immune response. = THe D is on a B

cytokine storm

may stimulate cells to produce more cytokines. This feedback loop occasionally gets out of control, resulting in a harmful overproduction of cytokines -a factor in the pathology of certain diseases

immunization or vaccination

medicine developed over the centuries, methods were found to mimic the adaptive immunity to disease by deliberately exposing people to harmless versions of pathogens that caused certain diseases, thus rendering them immune

globulin

plasma protein; alpha, beta, and gamma (immune) globulins are examples

Pathogenic bacteria

possess a number of recognizable antigens called pathogen-associated molecular patterns (PAMPs)= serve as warning flags -receptors like Toll-like receptors (TLRs).

Granzymes

proteases that induce apoptosis, are then able to enter through the pore

B cells

remove viruses, bacteria, and toxins from body tissue fluids and blood by recognizing antigens and making antibodies against them -recognize by receptors on B cell - from red bone marrow. -T cells and B cells both develop from stem cells in the bone marrow--Both types of cells then migrate to lymphoid tissues, such as the lymph nodes or spleen.

gamma globulin

serum fraction containing antibodies -contains most of the antibodies, it is often used to transfer passive immunity.

IgA

13% of the antibodies -most common form in mucous membranes and in body secretions such as mucus, saliva, tears, and breast milk -most abundant immunoglobulin in the body -in serum, serum IgA, is usually in the form of a monomer. The most effective form of IgA, however, consists of two connected monomers that form a dimer called secretory IgA---produced by plasma cells in the mucous membranes -acquires a polypeptide called a secretory component that protects it from enzymatic degradation ===prevent the attachment of microbial pathogens to mucosal surfaces ---important in resistance to intestinal and respiratory pathogens. Because IgA immunity is relatively short-lived, the length of immunity to many respiratory infections is correspondingly short A = first thing you eat as a baby = 2 monomers = two breast = most common form in mucous membranes and in body secretions

chemokines

A family of small cytokines that induces the migration of leukocytes into areas of infection or tissue damage

nonself molecules.

A foreign antigen; a protein or other macromolecule that is not part of an organism's body.

complement system

A group of about 30 blood proteins that may amplify the inflammatory response, enhance phagocytosis, or directly lyse extracellular pathogens.

secondary response / memory (anamnestic) response

A rapid rise in antibody titer following exposure to an antigen after the primary response to that antigen -B cells do not become antibody-producing plasma cells but persist as long-lived but nonproliferating 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. -The second exposure to the same antigen stimulates the memory cells (formed at the time of initial exposure) to rapidly produce a large amount of antibody. The antibodies produced in response to this second exposure are mostly IgG.

Immunoglobulin Classes

simplest and most abundant immunoglobulins are monomers- -The five classes of Igs are designated IgG, IgM, IgA, IgD, and IgE -different role in the immune response

T Cytotoxic Cells (CD8+ T Cells)

Activated into cytotoxic T lymphocyte (CTL) with the help of TH cell and costimulatory signals CTLs recognize and kill self-cells altered by infection Self-cells carry endogenous antigens on a surface presented with MHC class I molecules CTL releases perforin and granzymes that induce apoptosis in the infected cell -requires sequential, and complex, activation of the precursor CTL by an antigen processed by a dendritic cell and interaction with a TH cell and costimulatory signals. The resulting CTL is an effector cell that has the ability to recognize and kill target cells that are considered nonself (see Figure 17.14). Primarily, these target cells are self-cells that have been altered by infection with a pathogen, especially viruses.

Humoral immunity

specific immunity produced by B cells that produce antibodies that circulate in body fluids -Effector cells in humoral immunity target antigens outside cells,

humoral immunity

specific immunity produced by B cells that produce antibodies that circulate in body fluids -immunity brought about by protective molecules called antibodies -Antibodies combat foreign molecules that we refer to as antigens. Humoral immunity involves B lymphocytes, more commonly known as B cells =are directed at antigens that are extracellular (such as in blood or other body fluids) --focus on bacteria and their toxins, as well as viruses before they penetrate -Humoral antibodies are effective against pathogens such as viruses and bacteria that are circulating freely, where the antibodies can contact them

antigenic determinants or epitopes

specific regions of the molecule that are recognized by antibodies -weight of 10,000 or higher

T-independent antigens

Antigens that stimulate B cells directly without the help of T cells -Such antigens are characterized by repeating subunits such as are found in polysaccharides or lipopolysaccharides -Bacterial capsules= ex= -can bind to multiple B cell receptors, which is probably why they do not require T cell assistance. -provoke a weaker immune response than do T-dependent antigens -primarily of IgM, and no memory cells are generated.

cytotoxicity

the capacity of certain T cells to kill a specific target cell

polysaccharides

Carbohydrates that are made up of more than two monosaccharides -Lipids and nucleic acids are usually antigenic only when combined with proteins and polysaccharides -often components of invading microbes, such as capsules, cell walls, flagella, fimbriae, and toxins of bacteria; the coats of viruses; or the surfaces of other types of microbes -Nonmicrobial antigens include pollen, egg white, blood cell surface molecules -provoke a highly specific immune response that, in humoral immunity, results in the production of antibodies that are capable of recognizing the antigen that gave rise to them

t cell

Cells created in the thymus that produce substances that attack infected cells in the body. -a lymphocyte that identifies pathogens and distinguishes one pathogen from another -skin and genital tract are still called Langerhans cells, or Langerhans DCs

microfold cells (M cells)

Cells in the gastrointestinal tract that take up and transfer antigens to lymphocytes in Peyer's patches -barrier in the gastrointestinal tract only by way of a scattered array of gateway cells -Most pathogens of the type that the cellular immune system is designed to combat first enter the gastrointestinal tract or lungs,-barrier of epithelial cells. -M cells are located over -take up antigens from the intestinal tract and allow their transfer to the lymphocytes and antigen-presenting cells of the immune system found throughout the intestinal tract, just under the epithelial-cell layer but especially in the Peyer's patches. It is also here that antibodies, mostly IgA essential for mucosal immunity, -/Their function is to transport antigens encountered in the digestive tract to contact lymphocytes and antigen-presenting cells

cytokines

Chemicals released by the immune system communicate with the brain. -immune response requires complex interactions between different cells. The communication required for this is mediated by chemical messengers -soluble proteins or glycoproteins that are produced by practically all cells of the immune system in response to a stimulus -more than 200 -may stimulate cells to produce more cytokines.

cytotoxicity

the quality of being toxic to cells

Clonal expansion (proliferation)

the rapid multiplication of B or T cell clones after activation by an antigen - when activated -B cells usually require the assistance of a T helper cell (TH)

antibody titer

the relative amount of antibody in the serum

passive immunity

the short-term immunity that results from the introduction of antibodies from another person or animal.

antibody-dependent cell-mediated cytotoxicity (ADCC).

the target cell is first coated with antibodies. A variety of cells of the immune system bind to the Fc regions of these antibodies and, thus, to the target cell. The attacking cells secrete substances that then lyse the target cell.

interleukins

Cytokines that serve as communicators between leukocytes

T Cytotoxic Cells (CTLp)

there is a class of T cells -T cells that kill target cells in an antigen-specific manner -A CTLp cell can differentiate into an effector cell called a cytotoxic T lymphocyte (CTL)

Macrophages

Found within the lymph nodes, they are phagocytes that destroy bacteria, cancer cells, and other foreign matter in the lymphatic stream. -(from the Greek for large eaters) -usually found in a resting state -ridding the body of worn-out blood cells (about 200 billion per day

major histocompatibility complex (MHC)

Group of genes that code for proteins found on the surfaces of cells that help the immune system recognize foreign substances. ---encode molecules of genetically diverse glycoproteins (that is, part carbohydrate and part protein). -II MHC molecules exist only on the surface of antigen-presenting molecules (APCs)—including B cells