Antibodies, Antigens & Interactions Flashcards
describe basic immunoglobulin structure
2 heavy chains (mu, delta, gamma, epsilon, or alpha) and 2 light chains (kappa or lambda)
chains held together by disulfide bonds
constant region: Fc
antigen binding region: Fab
3 major mechanisms for generation of antibody diversity
primary: multiple germ-line genes and junctional diversity (addition of nucelotides [P/templated or N/non-templated] during process of D-J or V-D/J joining; catalyzed by TdT [terminal deoxyribonucleotidyl transferase])
secondary: somatic hypermutation (point mutations occurring in fully assembled V-J or V-D-J regions during an immune response)
define allelic exclusion; why is this a good thing?
rearranged heavy chain or light chain genes come from only one chromosome (maternal or paternal)
“Bobby dress-up”
expression of both alleles would render the B cell multispecific -> not as useful
describe receptor editing
non-productive light chain gene rearrangement can be rescued by further gene rearrangement
ex. 5’ Vk gene segment can recombine with an unused 3’ Jk gene segment and replace nonproductive Jk gene segment
can happen up to 5 times (?) for kappa light chain
T-B-NK+ SCID - cause, effects
null mutations in RAG1 and/or RAG2
autosomal recessive
account for 3-4% of SCID cases
decreased IgG, WBCs, and B cells
neither lymphocyte pool matures into effector cells (no receptors, no fxn!)
typically severe, life-threatening opportunistic infxns in early infancy
X-linked agammaglobulinemia - cause, effects
also Bruton’s agammaglobulinemia
Bruton tyrosine kinase (Btk) normally delivers signal from pre-BCR for survival of cell -> mutation destroys this fxn
recurrent infxns - haemophilus influenzae, streptococcus pneumoniae, staphylococcus aureus, enteroviruses, giardia, etc.
define isotype
determined by C region of H chain, defines class and subclass each isotype has its own gene differ in size, charge, aa sequence and carb content
define allotype
allelic differences in H chains
define idiotype
antigenic determinants on the V regions
we all may see an antigen, but we respond with slightly different V region determinants
IgM - structure, fxn
pentamer; 10 Ag-binding sites
first antibody produced in primary Ag response
efficient binding of multiple repeating epitopes and C’
J piece: Fc linked polypeptide disulfide-bonded to 2 of the 10 mu chains; binds to secretory cells -> mucosa
5-10% of total serum Igs
IgG - structure, fxn
singular “Y” Ab
predominant Ab of secondary immune response
4 subclasses: IgG1, IgG2, IgG3, and IgG4
IgG3 - efficient activator of C’
IgG1/3 bind w/ high affinity to Fc receptors on phagocytic cells (opsonization)
FcR CD markers are all multiples of 16! (CD16, CD32, CD64)
80% of total serum Igs
IgA - structure, fxn
secretory (dimer) or serum (80% monomeric)
constituent of secondary immune response
polypeptide produced by epithelial cells of mucous membranes binds to Fc domain of IgA dimer -> allows secretion
IgA plasma cells concentrated along mucous membrane surfaces
IgE - structure, fxn
singular “Y” antibody
binds to basophils and mast cells by Fc receptor with very high affinity
primarily fight helminths (worms)
IgD - structure, fxn
singular “Y” antibody
no known fxn in serum
monomeric form present as Ag-specific receptor on mature B cells
only monofxnal Ab
describe heavy chain formation
1) D+J -> (Rag-1/Rag-2) -> D/J
2) LV +D/J -> (Rag-1/Rag-2) -> LVDJ
3) VDJ + Cm/Cd (make IgM and IgD, respectively)
RSSs (recombination signal sequences) flanking V, D, and J segments aid process
