Adaptive Immune System: Antibodies

immunoglobulin

a molecule that is synthesized by both B-cells and plasma cells and is secreted by plasma cells

antibody

an immunoglobulin with a specificity to a specific epitope

humoral response

immunity mediated by antibodies

immunoglobulin structure

4 polypeptides

2 light chains

2 heavy chains

light chains

kappa and lambda

light chain components

1 variable domain

1 constant domain

heavy chains

delta, gamma, alpha, mu, epsilon

heavy chain components

1 variable domain

3-4 constant domains

antigen binding region

the portion of the antibody that is made of the light and heavy variable domains

Fab

epitope binding region

Fc

constant fragment bound by Fc receptors

F(ab’)2

both Fab fragments together

IgD

surface antibody

unclear role

may be in homeostasis and immune surveillance

IgG

surface and secreted antibody

4 subclasses

highest concentration of Ig in circulation

activates complement

opsonization, neutralization, cytotoxicity

crosses blood vessels and placenta easily

IgE

smallest concentration in circulation

binds to mast cells and basophils

crosslinks to cause degranulation

immediate hypersensitivity - allergic response

IgM

secreted in pentameric form with J chain

expressed on surface of unstimulated B cells

immobilizes antigen and activates classical complement pathway

IgA

secreted in monomeric or dimeric form with J chain

in mucus, saliva, tears, breast milk, and GI secretions

most synthesized Ig

secretory component

needed for transport of IgA to mucosal surfaces

IgG and IgM

the immunoglobulins that activate the classical complement cascade

qrs

binding in the classical complement pathway

light chain variability

rearrangement of V and J genes on the DNA level at random

uniting regions

the splicing of the VJ segment to mRNA that is translated into a single polypeptide

heavy chain variability

rearrangement of V, D, and J genes at random

VDJ recombinase

the protein that facilitates the recombination of the variable regions of an antibody

isotype switch

the stimulation of an antibody that causes a change in isotype, but not in specificity

isotype-mediated functions

activation of complement

secretion into mucus membranes

binding to cell surface

memory B cells

the fate of B cells that don’t become plasma cells; undergo further rearrangement with C region genes

somatic hypermutation

small point mutations that provide additional variation to B cells and occur during rapid proliferation

affinity maturation

the increase in effectiveness of binding to an antigen

human leukocyte antigen

another name for major histocompatibility complex

transplant rejection

occurs when the transplanted organ does not match in MHC

MHC I

expressed with Beta 2

found on surface of all nucleated cells

binds to an 8-9 aa peptide

MHC II

expressed on DCs, macrophages, and B-cells

binds to 18-20 aa peptide

CD8+

cells that interact with MHC-I or intracellular antigens

CD4+

cells that interact with MHC-II or extracellular antigens