BIO221 Chapter 17 Adaptive Immunity

Thymus

A mammalian organ responsible for maturation of the immune system

Which of the following will result in immunity that is comparatively long-lasting?

A person survives an infectious disease

Bivalent

Two antigen-binding sites; a human antibody

Colostrum

(first milk after birth), the fluid secreted by the breast during pregnancy and the first days after delivery before lactation begins. It consists of immunologically active substances (maternal antibodies) and white blood cells, water, protein, fat, minerals, vitamins, and carbohydrate in a thin, yellow serous fluid

Clusters of Differentiation

(or CD) Number assigned to an epitope on a single antigen, for example, CD4 protein, which is found on T helper cells. These are membrane molecules that are especially important for adhesion to receptors. The CDs of greatest interest are CD4 and CD8; cells that carry these molecules are named CD4+ and CD8+ cells, respectively. TH cells are classified as CD4+, which bind to MHC class II molecules on B cells and APCs. TC cells are classified as CD8+, which bind to MHC class I molecules

Microfold Cells

(or M cells) Cells that take up and transfer antigens to lymphocytes, on Peyer's patches

Antigens and Antibodies - Nature of Antibodies - Summary

1. An antibody, or immunoglobulin, is a protein produced by B cells in response to an antigen and is capable of combining specifically with that antigen. 2. Typical monomers consist of four polypeptide chains: two heavy chains and two light chains. 3. Within each chain is a variable (V) region that binds the epitope and a constant (C) region that distinguishes the different classes of antibodies. 4. An antibody monomer is Y-shaped or T-shaped: the V regions form the tips, the C regions form the base and FC(stem) region. 5. The FC region can attach to a host cell or to complement. 6. IgG antibodies are the most prevalent in serum; they provide naturally acquired passive immunity, neutralize bacterial toxins, participate in complement fixation, and enhance phagocytosis. 7. IgM antibodies consist of five monomers held by a joining chain; they are involved in agglutination and complement fixation. 8. Serum IgA antibodies are monomers; secretory IgA antibodies are dimers that protect mucosal surfaces from invasion by pathogens. 9. IgD antibodies are on B cells; they may delete B cells that produce antibodies against self. 10. IgE antibodies bind to mast cells and basophils and are involved in allergic reactions.

Antigens and Antibodies - Nature of Antigens - Summary

1. An antigen (or immunogen) is a chemical substance that causes the body to produce specific antibodies. 2. As a rule, antigens are proteins or large polysaccharides. Antibodies are formed against specific regions on antigens called epitopes, or antigenic determinants. 3. A hapten is a low-molecular-weight substance that cannot cause the formation of antibodies unless combined with a carrier molecule; haptens react with their antibodies independently of the carrier molecule.

Antigen-Antibody Binding and Its Results - Summary

1. An antigen-antibody complex forms when an antibody binds to its specific epitopes on an antigen. 2. Agglutination results when an antibody combines with epitopes on two different cells. 3. Opsonization enhances phagocytosis of the antigen. 4. Antibodies that attach to microbes or toxins cause neutralization. 5. Complement activation results in cell lysis.

Adaptive Immune System - Summary

1. An individual's genetically predetermined resistance to certain diseases is called innate immunity. 2. Adaptive immunity is the ability of the body to specifically react to a microbial infection.

Antibody-dependent cell-mediated cytotoxicity (ADCC)

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. (1) The target cell is first coated with antibodies. (2) Cells of the immune system, such as eosinophils, macrophages, and NK cells, bind to the Fc regions of the attached antibodies. (3) The target cell is then lysed by substances secreted by the cells of the immune system.

Which antibody is present in body secretions such as mucus, saliva, tears, and breast milk?

IgA

Immunoglobulin Classes

IgA The class of antibodies found in secretions. IgD The class of antibodies found on B cells. IgE The class of antibodies involved in hypersensitivities. IgG The most abundant class of antibodies in serum. IgM The first class of antibodies to appear after exposure to an antigen.

Which is in the proper sequence?

IgE is formed -- IgE binds to mast cells and basophils -- antigen binds IgE -- histamine is released

Which antibody can cross the placenta and confer passive immunity to a fetus?

IgG

Neutralization

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

Which is true of the anamnestic response?

IgG predominates

Which antibody shown is the first produced in response to an infection?

IgM

Which of the following has a J chain as part of its structure?

IgM

Primary and secondary immune responses to an antigen

IgM appears first in response to the initial exposure. IgG follows and provides longer-term immunity. 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

Humoral Immunity

Immunity produced by antibodies dissolved in body fluids, mediated by B cells; also called antibody-mediated immunity

Epitopes (antigenic determinants)

In this illustration the epitopes are components of the antigen—the bacterial cell wall. each antigen carries more than one epitope. each Y-shaped antibody molecule has two binding sites that can attach to a specific epitope on an antigen. an antibody can also bind to identical epitopes on two different cells at the same time, which can cause neighboring cells to aggregate.

Activation of B cells to produce antibodies

In this illustration, the B cell is producing antibodies against a t-dependent antigen

Separation of serum proteins by gel electrophoresis

In this procedure, serum is placed in a trough cut into a gel. In response to an electrical current, the negatively charged proteins of the serum migrate through the gel from the negatively charged end (cathode) to the positively charged end (anode)

Cell-mediated immunity in part protects against

Intracellular bacteria and viruses

Antibody-dependent cell-mediated cytotoxicity:

Is particularly important for killing microbes that are too large be destroyed by phagocytosis

All of the following are true of the IgG antibody class except

It is the most abundant antibody class in body secretions

Which is true for IgA?

It picks up the secretory component as it passes through mucosal cells

T regulatory (Treg) cells

Lymphocytes that appear to suppress other T cells. 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. They are also useful in protecting, from the immune system, the intestinal bacteria required for digestion and other useful functions. Similarly, in pregnancy they may play a role in protecting the fetus from rejection as nonself

Peyer's patches

Lymphoid organs on the intestinal wall

All of the following are true about helper T cells except

Lyse target cells

Antibodies can have all of the following effects on target cells except what?

Lysis

M cells

M 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

Macrophages

Macrophages are cells usually found in a resting state. They are important for innate immunity and for ridding the body of worn out blood cells and other debris, such as cellular remnants from apoptosis. Their phagocytic capabilities are greatly increased when they are stimulated to become activated macrophages. This activation can be initiated by ingestion of antigenic material. Other stimuli, such as cytokines produced by an activated T helper cell, can further enhance their capabilities. Once activated, macrophages are more effective as phagocytes and as APCs. Activated macrophages are important factors in the control of cancer cells and such intracellular pathogens as the tubercle bacillus and virus infected cells. Their appearance becomes recognizably different as well they are larger and become ruffled. After taking up an antigen, APCs tend to migrate from their locations in virtually all tissues to lymph nodes or other lymphoid centers on the mucosa, where they present the antigen to T cells located there. T cells carrying receptors that are capable of binding with any specific antigen are present in relatively limited numbers. Migration increases the opportunity for these particular T cells to encounter the antigen for which they are specific

T-cell receptors (TCRs)

Molecules on T cells that recognize antigens

Immunity following recovery from chickenpox is an example of

Naturally acquired active immunity

Naturally acquired active immunity

Naturally acquired active immunity develops when a person is exposed to antigens, becomes ill, and then recovers. Once acquired, immunity is lifelong for some diseases, such as measles. For certain other diseases, especially intestinal diseases, the immunity may last for only a few years. Subclinical infections or inapparent infections(those that produce no noticeable symptoms or signs of illness) can also confer immunity

Immunity acquired by transplacental transfer is called

Naturally acquired passive immunity

Which type of immunity involves the transfer of antibodies from a mother to her infant?

Naturally acquired passive immunity

Naturally acquired passive immunity

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, especially in the first secretions, called colostrum.In the infant, this passive immunity generally lasts only as long as the transmitted antibodies persist — usually a few weeks or months. These maternal antibodies are essential for providing immunity to the infant until its own immune system matures. Colostrum is even more important to some other mammals; calves, for example, do not have antibodies that cross the placenta and rely on colostrum ingested during the first day of life

Which process is depicted in the figure where antibodies are coating an antigen to enhance phagocytosis?

Opsonization

Cytokine Storm

Overproduction of cytokines; can cause damage to the human body

Passive Immunity

Passive immunity in the recipient lasts only as long as the antibodies are present — in most cases, a few weeks. Both actively acquired immunity and passively acquired immunity can be obtained by natural or artificial means

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

Which is not a cell type involved in cell-mediated immunity?

Plasma cells

The dendritic cell in the photo is capable of

Presenting an antigen to a T-cell

TH2 cells

Produce cytokines that are associated primarily with the production of antibodies, especially IgE, that are important in allergic reactions. They are also important in the activation of the eosinophils that defend against infections by extracellular parasites such as helminths

Cytotoxic T cells

Produce perforins

Colony Stimulating Factors (CSF)

Product that stimulates the differentiation of cells into macrophages, neutrophils, basophils to help those with low immune capabilities (cancer)

Apoptosis

Programmed cell death

Clonal Expansion

Proliferation. B cells usually require the assistance of a T helper cell (TH)

Granzyme

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

T suppressor cells

See T regulatory cells (Treg)

Which is in the correct order of differentiation?

Stem cells to B cells to plasma cells

Follicular helper T cells (TFH)

Stimulate B cells to produce plasma cells and are also involved in class switching

Endogenous Antigens

Surface antigens on human cells produced as a result of infection

T cells and Cellular Immunity - Classes of T Cells - Summary

T cells are classified according to their functions and cell-surface glycoproteins called CDs.

T cytotoxic cells (CD8+T cells)

T cytotoxic cells, despite their name, are not capable of attacking any target cell as they emerge from the thymus; rather, they are precursors to CTLs, which do have this capability. This differentiation requires sequential, and complex, activation of the precursor TC 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. Primarily, these target cells are self-cells that have been altered by infection with a pathogen, especially viruses. On their surface they carry fragments of endogenous antigens that are generally synthesized within the cell and are mostly of viral or parasitic origin. Other important target cells are tumor cells and transplanted foreign tissue. Rather than reacting with antigenic fragments presented by an APC in complex with MHC class II molecules, the CD8+T cell recognizes endogenous antigens on the target cell's surface that are in combination with an MHC class I molecule. MHC class I molecules are found on nucleated cells; therefore, a CTL can attack almost any cell of the host that has been altered

Classes of T Cells

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

T-independent antigens

T-independent antigens have repeating units (epitopes) that can cross-link several antigen receptors on the some B cell. These antigens stimulate the B cell to make antibodies without the aid of T helper cells. The polysaccharides of bacterial capsules are examples of this type of antigen

CD8+T

TC cells are classified as CD8+, which bind to MHC class I molecules

CD4+T

TH cells are classified as CD4+, which bind to MHC class II molecules on B cells and APCs. Dendritic cells are especially important in the activation of CD4+T cells and in developing their effector functions

TH17 cells

TH17 cells are situated in the skin and in the lining of the gastrointestinal tract, sites where they are well positioned to deal with potential invading microbes. When external pathogenic invaders are detected, the TH17 cells stimulate the innate immune system. For example, they activate cells that synthesize cytokines such as TNF-α that are responsible for inflammatory responses. TH17 cells also recruit neutrophils to help clear away extracellular pathogens

The top B-cell in the photo is undergoing apoptosis. What does this mean?

The B-cell is experiencing programmed cell death

CDs of greatest interest

The CDs of greatest interest are CD4 and CD8; cells that carry these molecules are named CD4+ and CD8+ cells, respectively. TH cells are classified as CD4+, which bind to MHC class II molecules on B cells and APCs. TC cells are classified as CD8+, which bind to MHC class I molecules

Antibody Structure

The Y-shaped molecule is composed of two light chains and two heavy chains linked by disulfide bridges (S—S). Most of the molecule is made up of constant regions (C), which are the same for all antibodies of the same class. The amino acid sequences of the variable regions (V), which form the two antigen-binding sites, differ from molecule to molecule

The structure of a typical antibody molecule

The Y-shaped molecule is composed of two light chains and two heavy chains linked by disulfide bridges (S—S). Most of the molecule is made up of constant regions (C), which are the same for all antibodies of the same class. The amino acid sequences of the variable regions (V), which form the two antigen-binding sites, differ from molecule to molecule

Adaptive Immunity

The ability, obtained during the life of the individual, to produce specific antibodies and T cells

Dual Nature of the Adaptive Immune System

The adaptive immune system is divided into two parts, each responsible for dealing with pathogens in different ways. These two systems function interdependently to keep the body free of pathogens. • Humoral immunity, also called antibody-mediated immunity, is directed at freely circulating pathogens and depends on B cells. • Cellular immunity, also called cell-mediated immunity, depends on T cells to eliminate intracellular pathogens, reject foreign tissue recognized as nonself, and destroy tumor cells

Antibody Titer

The amount of antibody in serum. It reflects the intensity of the antibody-mediated humoral response

Opsonization

The antigen, such as a bacterium, is coated with antibodies that enhance its ingestion and lysis by phagocytic cells. Antibody-dependent cell-mediated cytotoxicity resembles opsonization in that the target organism becomes coated with antibodies; however, destruction of the target cell is by immune system cells that remain external to the target cell

Results of antigen-antibody binding

The binding of antibodies to antigens to form antigen-antibody complexes tags foreign cells and molecules for destruction by phagocytes and complement

Serology

The branch of immunology that studies blood serum and antigen - antibody reactions in vitro

Clonal Selection

The central principle of adaptive immunity. It is the mechanism by which adaptive immune responses derive only from individual antigen-specific lymphocytes, which are stimulated by the antigen to proliferate and differentiate into antigen-specific effector cells

Globulin

The class of globular proteins that includes antibodies. See also immunoglobulin

Antigen-antibody Complex

The combination of an antigen with the antibody that is specific for it; the basis of immune protection and many diagnostic tests

TH1 cells

The cytokines produced by TH1 cells, especially IFN-γ, activate mostly those cells related to important elements of cellular immunity, such as delayed-type hypersensitivity, and are also responsible for activation of macrophages. They also stimulate the production of antibodies that promote phagocytosis and are especially effective in enhancing the activity of complement, such as opsonization and inflammation. The generation of cytotoxic T lymphocytes also requires action by a TH1 cell

Major Histocompatibility Complex (MHC)

The genes that code for histocompatibility antigens; also known as human leukocyte antigen (HLA) complex

Antibody Diversity

The human immune system is capable of recognizing a mind boggling number of different antigens — estimates are of a minimum of 10^15 antigens. The number of genes required for this amount of diversity would seem to require a major part of an individual's inherited DNA. The work of the Japanese immunologist Susumu Tonegawa, for which he received a Nobel prize in 1987, showed how this diversity could be obtained by a set of just hundreds, not billions, of genes. Simplistically, the mechanism is analogous to the generation of huge numbers of words from a limited alphabet. This "alphabet" is found in the genetic makeup of the variable (V) region amino acid sequence of the immunoglobulin molecule, which can be linked to various amino acid sequences in the antibody's constant (C) region. These combinations greatly reduce the amount of genetic information needed, so that a different gene is not needed to respond to each antigen

Cytokines

The immune response requires complex interactions between different cells. The communication required for this is mediated by chemical messengers called cytokines (A small protein released from human cells that regulates the immune response; directly or indirectly may induce fever, pain, or T cell proliferation). Cytokines that serve as communicators between leukocytes (white blood cells) are now known as interleukins (between leukocytes)

Antibody-dependent cell-mediated cytotoxicity

The killing of antibody-coated cells by natural killer cells and leukocytes

Immunoglobulin - IgA

The most common form in mucous membranes and in body secretions such as mucus, saliva, tears, and breast milk. If we take this into consideration, IgA is the most abundant immunoglobulin in the body (IgG is the most abundant in serum). The form of IgA that circulates 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. It is produced in this form by plasma cells in the mucous membranes — as much as 15 grams per day, mostly by intestinal epithelial cells. Each dimer then enters and passes through a mucosal cell, where it acquires a polypeptide called a secretory component that protects it from enzymatic degradation. The main function of secretory IgA is probably to prevent the attachment of microbial pathogens to mucosal surfaces. This is especially 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. IgA's presence in a mother's milk, especially the colostrum probably helps protect infants from gastrointestinal infections

Valence

The number of antigen-binding sites on an antibody. For example, most human antibodies have two binding sites; therefore, they are bivalent

Maturation

The process by which adaptive immune system cells learn to differentiate between nonself and self cells. T cells mature in the thymus, and B cells mature in red bone marrow

Vaccination

The process of conferring immunity by administering a vaccine; also called immunization

Immunization

The process of conferring immunity by administering a vaccine; also called vaccination

Gamma Globulin

The serum fraction containing immunoglobulins (antibodies); also called immune serum globulin

Antibody Structure - Fc Region

The stem of the Y-shaped antibody monomer is called the Fc region,so named because when antibody structure was first being identified, it was a fragment (F) that crystallized (c) in cold storage. These Fc regions are often important in immunological reactions. If left exposed after both antigen-binding sites attach to an antigen such as a bacterium, the Fc regions of adjacent antibodies can bind complement. This leads to the destruction of the bacterium. Conversely, the Fc region may bind to a cell, leaving the antigen binding sites of adjacent antibodies free to react with antigens

Antibody Structure - Constant (C) region

The stem of the antibody monomer and the lower parts of the arms of the Y. They are the same for a particular class of immunoglobulin

Affinity

The strength of the bond between an antigen and an antibody

Antibody Structure - Variable (V) region

The two sections located at the ends of the Y's arms of a given antibody. 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 reflects the nature of the antigen for which they are specific — they are specific to the two antigen-binding sites found on each antibody monomer

Immunoglobulin - IgD

Their structure resembles that of IgG molecules. IgD antibodies are found in blood, lymph, and particularly on the surfaces of B cells. Serum IgD has no well-defined function; on B cells it assists in immune response

Granulocyte-colony Stimulating Factors

Therapeutic cytokine; enhances neutrophil production in bone marrow in association with cancer therapies that cause neuropenia

Dendritic cell

These cells are named for their long extensions, or dendrites, because they resemble the dendrites of nerve cells. the dendritic cell here is interacting with lymphocytes that have been infected by a virus and are producing abnormal endogenous antigens

AIDS patients have a CD4 cell deficiency and they are susceptible to life-threatening viral infections. Knowing this, you can conclude that

These viruses have T-dependent antigens

What is the function of cytotoxic T cells?

They induce apoptosis

All of the following are true of antigens except

They often have a molecular weight of less than 10,000

Activation of CD4+T helper cells

To activate a CD4+T helper cell, at least two signals are required: the first signal is the binding of the TCr to the processed antigen, and the second signal requires a costimulating cytokine, such as IL-2 and others. Once activated, the TH cell secretes cytokines that affect the effector functions of multiple cell types of the immune system

For IgG, the antigen binding site is found on the

Variable region of a heavy and the variable region of a light chain

Activated macrophages

When activated, macrophages become larger and ruffled

T cells and cellular Immunity - Summary

1. Red bone marrow stem cells give rise to T cells, which mature in the thymus gland. Thymic selection removes T cells that don't recognize MHC-self molecules. 2. T-cell receptors on T cells recognize antigens. 3. T cells recognize antigens processed by antigen-presenting cells. 4. T cells recognize antigens in association with MHC on an APC.

Dual Nature of the Adaptive Immune System - Summary

1. Red bone marrow stem cells produce lymphocytes. Lymphocytes that mature in bone marrow become B cells. 2. Humoral immunity involves antibodies, which are found in serum and lymph and are produced by B cells. 3. Lymphocytes that migrate through the thymus become T cells. Cellular immunity involves T cells. 4. T cell receptors recognize antigens.

T cells and Cellular Immunity - T Helper Cells - Summary

1. TH1 cells activate cells involved in cellular immunity. 2. TH2 cells are associated with allergic reactions and parasitic infections. 3. TH17 cells activate innate immunity and responses to extracellular bacteria. 4. T helper cells, or CD4+T cells, are activated by MHC class II on APCs. After binding an APC, CD4+T cells secrete cytokines that activate other T cells and B cells.

Monomer

A bivalent antibody has the simplest molecular structure. A typical antibody monomer has four protein chains: two identical light chains and two identical heavy chains. ("Light" and "heavy" refer to the relative molecular weights.) The chains are joined by disulfide links and other bonds to form a Y-shaped molecule. The Y-shaped molecule is flexible and can assume a T shape

Antiserum

A blood-derived fluid containing antibodies

Plasma cells

A cell that an activated B cell differentiates into; plasma cells manufacture specific antibodies

Interleukins (IL)

A chemical that causes T-cell proliferation. See also cytokine

Chemokines

A cytokine that induces, by chemotaxis, the migration of leukocytes into infected areas

Haptens

A hapten is a molecule too small to stimulate antibody formation by itself. However, 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

Memory cells

A long-lived B or T cell responsible for the memory, or secondary, response

Natural Killer (NK) Cells

A lymphoid cell that destroys tumor cells and virus-infected cells

Antigen-presenting Cells (APCs)

A macrophage, dendritic cell, or B cell that engulfs an antigen and presents fragments to T cells

Tumor Necrosis Factor (TNF)

A polypeptide released by phagocytes in response to bacterial endotoxins. These cytokines are a strong factor in inflammatory reactions of autoimmune diseases such as rheumatoid arthritis. Monoclonal antibodies that block the action of TNF are an available therapy for some of these conditions

Perforin

A pore-forming protein, perforin. Pore formation contributes to the subsequent death of the cell

T Cytotoxic (TC) cells

A precursor to a cytotoxic T lymphocyte

Vaccine

A preparation of killed, inactivated, or attenuated microorganisms or toxoids to induce artificially acquired active immunity

Immunoglobulins (Ig)

A protein (antibody) formed in response to an antigen and can react with that antigen. See also Globulin

Antibodies

A protein produced by the body in response to an antigen, and capable of combining specifically with that antigen

Antibody

A protein produced by the body in response to an antigen, and capable of combining specifically with that antigen

Secondary Response

A rapid rise in antibody titer following exposure to an antigen after the primary response to that antigen; also called anamnestic response, secondary response or memory response

Memory (or anamnestic) Response

A rapid rise in antibody titer following exposure to an antigen after the primary response to that antigen; also called secondary response, secondary response or memory response

Antigen-binding Site

A site on an antibody that binds to an antigenic determinant

T helper cell (TH)

A specialized T cell that often interacts with an antigen before B cells interact with the antigen

Antitoxin

A specific antibody produced by the body in response to a bacterial exotoxin or its toxoid

Interferons (IFN)

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

Epitopes

A specific region on the surface of an antigen against which antibodies are formed; also called Antigenic Determinant

Antigenic Determinants

A specific region on the surface of an antigen against which antibodies are formed; also called epitope

Hapten

A substance of low molecular weight that does not cause the formation of antibodies by itself but does so when combined with a carrier molecule

T cell

A type of lymphocyte, which develops from a stem cell processed in the thymus gland, that is responsible for cell-mediated immunity. See also T cytotoxic cells, T helper cells, T regulatory cells

B cell

A type of lymphocyte; differentiates into antibody-secreting plasma cells and memory cells

Class Switching

Ability of a B cell to produce a different class of antibody against one antigen

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

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

Immunoglobulin - Igg

Accounts for about 80% of all antibodies in serum. In regions of inflammation these monomer antibodies readily cross the walls of blood vessels and enter tissue fluids. Maternal IgG antibodies, for example, can cross the placenta and confer passive immunity to a fetus. IgG antibodies protect against circulating bacteria and viruses, neutralize bacterial toxins, trigger the complement system, and, when bound to antigens, enhance the effectiveness of phagocytic cells

The resistance to re-infection with measles virus following recovery from measles infection is called

Adaptive immunity

T-dependent Antigen

An antigen that will stimulate the formation of antibodies only with the assistance of T helper cells. See also T-independent antigen.

T-independent Antigens

An antigen that will stimulate the formation of antibodies without the assistance of T helper cells. See also T-dependent antigen

Cellular Immunity

An immune response that involves T cells binding to antigens presented on antigen-presenting cells; T cells then differentiate into several types of effector T cells

Bursa of Fabricius

An organ in chickens responsible for maturation of the immune system

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

Antibodies

Humoral immunity is a term describing the immunity conferred by

Antibodies

While on safari in Serengeti National Park, Tanzania, your friend ventures away from camp and is bitten by a boomslang snake. The venom will cause hemorrhaging and death within hours. Fortunately, you are prepared and administer artificially acquired passive immunity. With what did you inject your friend?

Antibodies

Specificity

Antibodies can be used to differentiate between the viruses of chickenpox and measles and between bacteria of different species

Agglutination

Antibodies cause antigens to clump together. For example, the two antigen binding sites of an IgG antibody can combine with epitopes on two different foreign cells, aggregating the cells into clumps that are more easily ingested by phagocytes. Because of its more numerous binding sites, IgM is more effective at cross-linking and aggregating particulate antigens. IgG requires 100 to 1000 times as many molecules for the same results.

Immunoglobulin - IgE

Antibodies of the IgE class are slightly larger than IgG molecules. 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 cross-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. However, the response can be protective as well, for it attracts complement and phagocytic cells. This is especially useful when the antibodies bind to parasitic worms. The concentration of IgE is greatly increased during some allergic reactions and parasitic infections, which is often diagnostically useful

Immunoglobulin - IgM

Antibodies of the IgM (from macro, reflecting their large size). IgM has a pentamer structure consisting of five monomers held together by a polypeptide called a J (joining) chain. The large size of the molecule prevents IgM from moving about freely, so IgM antibodies generally remain in blood vessels without entering the surrounding tissues. IgM is the predominant type of antibody involved in the response to the ABO blood group antigens on the surface of red blood cells. It is much more effective than IgG in causing the clumping of cells and viruses and in reactions involving the activation of complement.The fact that IgM appears first in response to a primary infection and is relatively short-lived makes it uniquely valuable in the diagnosis of 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 the following is not true of antibody molecules?

Antibody molecules can directly destroy antigen

Primary Response

Antibody production in response to the first contact with an antigen. See also memory response

Toxin

Any poisonous substance produced by a microorganism

Antigens

Any substance that causes antibody formation; also called immunogen

Antigen

Any substance that causes antibody formation; also called immunogen. Most antigens are either proteins or large polysaccharides. Lipids and nucleic acids are usually antigenic only when combined with proteins and polysaccharides. Antigenic compounds are 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. Non microbial antigens include pollen, egg white, blood cell surface molecules, serum proteins from other individuals or species, and surface molecules of transplanted tissues and organs

T-dependent antigens

Are antigens that require helper T cells to stimulate antibody production

Immunity due to an injection of diphtheria toxoid is an example of

Artificially acquired active immunity

What type of immunity might you be required to have before starting a new job where you may handle animals with rabies?

Artificially acquired active immunity

Artificially acquired active immunity

Artificially acquired active immunity 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

Immunity due to an injection of anti-tetanus toxin is an example of

Artificially acquired passive immunity

Artificially acquired passive immunity

Artificially acquired passive immunity involves the injection of antibodies (rather than antigens) into the body. These antibodies come from an animal or person who is already immune to the disease

A patient with Bruton's agammaglobulinemia has decreased immunoglobulin. This means the disease affects

B cells

Clonal selection and differentiation of b cells

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. 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

Clonal deletion

B cells that recognize self are deleted / terminated

Differentiation of T cells and B cells

Both B cells and t cells originate from stem cells in adult red bone marrow or in the fetal liver. (red blood cells, macrophages, neutrophils, and other white blood cells also originate from these same stem cells.) Some cells pass through the thymus and emerge as mature t cells. Other cells probably remain in the red bone marrow and become B cells. Both types of cells then migrate to lymphoid tissues, such as the lymph nodes or spleen

Blebbing

Cells that die from apoptosis first cut their genome into fragments, and the external membranes bulge outward in a manner

B cells and Humoral Immunity - Summary

Clonal Selection of Antibody-Producing cells 1. Red bone marrow stem cells give rise to B cells with IgM and IgD on their surfaces, which recognize specific epitopes. 2. For T-independent antigens: B cells are selected by free antigens. 3. For T-dependent antigens: the B cell's immunoglobulins combine with an antigen, and the antigen fragments combined with MHC class II activate TH cells. The TH cells activate a B cell. 4. Activated B cells differentiate into plasma cells and memory cells. 5. B cells that recognize self are eliminated by clonal deletion. The diversity of Antibodies 6. During development, the genes in embryonic B cells recombine so that mature B cells each have different genes for the V region of their antibodies.

Hematopoietic Cytokines

Cytokines that control development of hematopoietic (blood) stem cells

Antigen-Presenting Cells (APCs) Types

Dendritic Cells Macrophages B Cells

Dendritic cells (DCs)

Dendritic cells (DCs) are characterized by long extensions called dendrites because they resemble the dendrites of nerve cells. (Vaccines injected between skin layers, where there are more such dendritic cells, are often more effective than injections into muscle.) This represents only one of at least four populations of DCs named for their derivation or location. Other populations are found in the lymph nodes, spleen, thymus, blood, and various tissues, except the brain. Dendritic cells that act as sentinels in these tissues engulf invading microbes, degrade them, and transfer them to lymph nodes for display to T cells located there. Dendritic cells are the principal APCs to induce immune responses by T cells. Macrophages, although more efficient for phagocytosis, are less efficient in antigen presentation for T cells in cellular immunity, but they play a key role in the later stages of the adaptive response

A person with purine phosphorylase deficiency lacks T cells. You would expect this person to

Develop chronic viral infections

Activation of the complement system

Either IgG or IgM antibodies may trigger activation of the complement system. For example, inflammation is caused by infection or tissue injury. 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

Thymic selection

Elimination of T cells that don't recognize self antigens (major histocompatibility complex); similar to colonal deletion

CD4+T Activation

For a CD4+T cell to become activated, its TCR recognizes an antigen that has been processed and is presented as 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, which is present on the APC and the TH cell, is also required. Activation should be directed against harmful pathogens; therefore, antigenic fragments displayed with Toll-like receptors signal a dangerous microbe. The activated TH cell begins to proliferate at the rate of two to three cell cycles a day and to secrete cytokines, which are essential for its effector functions. The proliferating TH cells differentiate 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, which act on different cells of the body's defensive systems

When serum is separated into its various components, the fraction that contains most of the antibodies is the

Gamma fraction

When serum is subjected to electrophoresis, antibodies are found in which fraction?

Gamma globulin fraction

Which one of the following events stimulates a B cell?

Helper T cell secretes interleukin-2

Cytotoxic T lymphocytes are activated by

Helper T cells' cytokines

Innate Immunity

Host defenses that afford protection against any kind of pathogen