Chapter 15 - Adaptive Immunity

adaptive immunity

product of B and T lymphocytes dual system

immunocompetence

ability of the body to interact with a wide spectrum of foreign substances

antigens

molecules that stimulate response by T and B cells

specificity

antibodies produced, function only against the antigen that they were produced in response to

memory

lymphocytes are programmed to “recall” their first encounter with an antigen and respond rapidly to subsequent encounters

perceive/attach to non-self

promote recognition of self

receive/transmit chemical messages among other cells of system

aid in cellular development

major functions of receptors

major histocompatibility complex (MHC)

set of cell surface proteins (receptors) essential for the acquired immune system in the recognition of self and in rejection of foreign molecules; found on all cells except erythrocyte

class I MHC

genes code for markers that display unique characteristics of self and allow recognition of self molecules and regulation of immune reactions; required for T lymphocytes to interact with pathogens

class II MHC

genes code for immune regulatory receptors found on antigen-presenting cells (APCs): macrophages, dendritic cells, and B cells; involved in presenting antigen to T-cells

b-cell receptors

bind free antigens

t-cell receptors

bind processed antigens together with the MHC molecules on the cells that present antigens to them

microorganisms and chemical compounds in the environment

sources of antigens

variety

lymphocytes use 500 genes to produce a tremendous _____ of specific receptors

clonal selection theory

undifferentiated lymphocyte in embryo and fetus undergo a continous serires of divisions and genetic changes that generate millions of different cell types, each with a particular/unique receptor specificity

lymphocytic stem cells

these differentiate into either T or B cells in bone marrow

B cells

stay in teh bone marrow for maturation

T cells

migrate to thymus for maturation

B; T

secondary lymphoid tissues will constantly be resupplied with __ and __ cells

clone

each genetically different type of lymphocyte expresses a single specificity

antigen

first introduction of each type of _____ into the immune system “selects” a genetically distinct lymphocyte (clone)

expand

contact after first introduction causes the clone to _____, through mitotic divisions, into a larger population of lymphocytes that can react to that antigen (same single specificity)

immunoglobulins (Ig)

large glycoproteins that serve as specific receptors of B cells and as antibodies; composed of 4 polypeptide chains in a y-shaped arrangement

variable regions

wide range of variable antigen binding sites at the end of immunoglobulin forks formed by these chains is due to

undifferentiated lymphocyte

has 150 genes that code for variable regions of light chains

has 250 genes for variable and diversity regions of heavy chains

only has a small number of genes that code for the consstant and joining regions that link segments of the final molecule

specificity

after development, only the selected V and D gene segments are active in the mature cell and all other V and D genes have been deleted - this maintains the lymphocyte’s _______

receptor

once synthesized, immunoglobulin is transported to cell membrane and inserted there to act as a _______

V, D, J, C

heavy-chain genes are composed of four separate segments:

transcribed; translated

heavy-chain genes are _____ and ______ to form the heavy polypeptide chains

spliced

the light-chain genes are put together like heavy ones except that the final gene is ______ from three gene groups (V, J, C), making smaller polypeptides

immunoglobulin

during final assembly, first the heavy and light chains are bound, and then the heavy-light combinations are connected to form the ________ molecule

not secreted

unlike B-cell receptors, T-cell receptors are small, ___ ______

CD4

cluster of differentiation of T helper cells

CD8

cluster of differentiation on T cytotoxic cell

lymph nodes; spleen; GALT

millions of distinct B cells develop and “hone” to specific sites in the _____, _____, and ____

immunoglobulin

mature B-cells have ______ as surface receptors for antigens

T-cells receptor, CD molecules, MHC I receptors

immune surface markers on T-cells

immunoglobulin, MHC I and II receptors

immune surface markers on B-cells

high

high or low number of T-cells in blood?

low

high or low number of B-cells in blood?

T-cell receptor

receptors for antigen on T-cells

immunoglobulin D and M

receptors for antigen on B cells

yes

do T cells require antigen presented with MHC?

no

do B cells require antigen presented with MHC?

antigen (Ag)

substance that elicits immune response in specific lymphocytes

antigenicity

property of behaving as an antigen

epitopes (antigenic determinants)

small molecular group recognized by lymphocytes

good

complex molecules with several epitopes make good/bad immunogens

haptens

small foreign molecules that consist of only a determinant group and too small by themselves to elicity an immune response

antigen-presenting cells (APC)

T-cell dependent antigens must by processed by phagocytes called ______ before their contact with T cells

macrophages, dendritic cells (most common), B cells

cells that can serve as antigen-presenting cells

T helper

antigen presentation involves a direct collaboration among an APC and a ______ cell

interleukin-1

cytokine secreted by APC to activate T helper cells

interleukin-2

cytokine produce by T helper cells to active B and other T cells

cell-mediated immunity (CMI)

requires the direct involvement of T lymphocytes in the immune response

T helper cells (CD4)

express CD4 receptors; most prevalent type of T cell in blood and lymphoid organs

cytoxic T cells (CD8)

express CD8 receptors; destroy foreign or abnormal cells by secreting perforins and granzymes

natural killer cells

lack specificity; circulate through the spleen, blood, and lungs

Th1

primary receptor - CD4; responsible for delayed hypersensitivity

Th2

primary receptor - CD4; drives B-cell proliferation

Treg

primary receptors - CD4, CD25; immune tolerance, autoimmunity

Tc

primary receptor - CD8; important in destruction of cancer cells, virus-infected cells

perforins

released from natural killer cells; polymerize and form a hole in the foreign cell membrane

granzyme

released from natural killer cells - enter newly made hole in the cell membrane and degrade foreign cell proteins

apoptosis

foreign cells die by ______ because of natural killer cells

superantigens

found primarily in bacteria and viruses; form of virulence factor; provoke overwhelming immune responses by large numbers of T cells regardless of specificity

release cytokines; blood vessel damage; toxic shock; multiorgan failure

what superantigens do

mitosis; clonal expansion

once B cells process the antigen, interact with T helper cells, and are stimulated by growth and differentiation factors, they enter the cell cycle in preparation for ____ and ______ _______

plasma; memory

divisions of B cells give rise to _____ cells that secrete antibodies and _____ cells that can react to the same antigen later

clonal selection and binding of antigen

induction by chemical mediators

B cell/Th cell cooperation/recognition

B cell activation

clonal expansion

antibody production/secretion

main events involved in B cell responses:

immunoglobulins

molecule with 4 polypeptide chains connected by disulfide bonds

antigen binding fragments (Fabs)

part of antibody; “arms” with their amino-terminal end (variable regions of the heavy and light chains) as antigen-binding sites

crystallizable fragment (Fc)

part of antibody; binds to various cells and molecules of the immune system

hypervariable

the Fab antigen-binding site is composed of _______ regions with an extremely variable amino acid content

unite with, immobilize, call attention to, or neutralize the antigen for which it was formed

principle activity of antibodies:

opsonization

process of coating microorganisms or other particles with specific antibodies so they are more readily recognized by phagocytes

neutralization

antibodies fill the surface receptors on a virus or the active site on a microbial enzyme to prevent it from attaching

cell membrane

Fc fragments bind to ____ ______

IgG

isotope of immunoglobulin; monomer, produced by plasma cells (primary response) and memory cells (secondary response; most prevalent

IgA

isotope of immunoglobulin; monomer circulates in blood, dimer in mucous and serous secretions

IgM

isotope of immunoglobulin; five monomers, first class synthesized following antigen encounter

IgD

isotope of immunoglobulin; monomer, servies as a receptor for antigen on B cells

IgE

isotope of immunoglobulin; involved in allergic responses and parasitic worm infections

Fc

differences in isoptopes of immunoglobulin are primarily due to variations in the ___

80; 13; 6; 0.001; 0.002

percentage of total antibody in serum (in order): IgG, IgA, IgM, IgD, IgE

primary response

latent period with no measurable antibody, occurs early on; first antibody to appear is IgM, followed later by IgG arising from activation of the first memory cells; within weeks, the titer tapers back to low levels

secondary response

latent period is lacking because other memory lymphocytes from the earlier response are immediately ready to react; rapid rise in antibody titer, mainly of IgG, is sustained for several weeks; smaller amount of IgM is also produced by naive B cells

monoclonal antibody (MAB)

originate from a single clone and have a single specificity for an antigen; used in diagnosis of disease, identification of microbes, and therapy

active immunity

results when a person is challenged with antigen that stimulates production of antibodies; creates memory, takes time, and is lasting

passive immunity

pre-formed antibodies are donated to an individual; does not create memory, acts immediately, and is short-term

natural immunity

acquried as part of normal life experiences

artificial immunity

acquired through a medical procedure such as a vaccine

natural active immunity

getting and infection; after recovering from infectious disease, a person may be actively resistant to reinfection (period varies according to the disease)

natural passie immunity

mother to child; IgG antibodies bodies from the maternal bloodstream can pass or be actively transported across the placenta to the fetus; IgA antibodies from mother’s milk react against microbes entering the intestine

artificial active immunization

“vaccination”; microbial (antigenic) stimulus, which triggers the immune system to produce antibodies and memory cells; not pathogenic, but is antigenic

artifical passive immunization

“immunotherapy”; a patient at risk for acquiring a particular infection is administered a preparation that contains specific antibodies against that infectious agent

killed whole cells/inactivated viruses

live, attentuated cells/viruses

antigenic molecules derived from bacterial cells/viruses

genetically engineered microbes/microbial agents

most vaccines are prepared from:

organisms can multiply/produce infection (but not disease) like the natural organism

confer long-lasting protection

usually require fewer doses/boosters

advantages of live (attenuated) preparations:

require special storage, can be transmitted, can conceivably mutate back to virulent strain

disadvantage of live (attenuated) preparations:

pneumococcus, meningococcus

capsules in vaccines:

anthrax, hepatitis B

surface proteins in vaccines: