Humoral Immunity Flashcards
complement system
set of interacting proteins released into the blood after production in the liver.
has two pathways of activation, enhances inflammation, enhances phagocytosis by opsonization, causes lysis of particles by membrane pore formation, removes extracellular pathogens
both pathways produce anaphylatoxins (C3a, C4a C5a). C5a is also chemotactic.
alternative pathway of complement activation
completely innate, does not require antibody to initiate, C3 spontaneously lysis in serum and C3b finds surface of bacteria, forms membrane attack complex, major opsonin
classical pathway of complement activation
activated by antigen-antibody complexes (ex. IgM or IgG)
cleavage of C3 results in recruitment of inflammatory cells, opsonization of pathogens, and perforation of pathogen cell membranes
Inappropriate activation of the complement cascade is controlled at the level of
C1, C3, and C5
Contact between B and T helper cells involves
MHC class 2/peptide presentation, costimulatory molecules (B7/CD28), CD40/CD40L binding, and cytokine production (IL-2, IL-4, IL-5, IL-6)
cytokines induce differentiation, memory cell, class switching
costimulatory molecules (B7:CD28)
needed for T-cell activation
CD40/CD40 Ligand binding
needed for B cell class switching and memory response
Papain cleavage
results in 2 Fab and 1 Fc, cannot agglutinate, each part can only bind to single antigen
Pepsin cleavage
results in one divalent molecule, can bind 2 antigen, can still agglutinate
avidity
increases with number of binding sites. IgM has greater avidity than IgG because it is secreted as a pentamer
idiotype
defines antigen specificity, determined by variable region
isotype
dictates effector functions, constant region
IgM
first antibody made, secreted as pentamer that is joined together by J chains, can bind 10 antigens, traps free antigen, activates complement, low affinity (weaker binding strength) to antigen compared to IgG, cannot act as opsonin
class switching (what it requires, when it occurs, where it occurs)
requires: T-cell, CD40 Ligand, Cytokines, occurs only during immune response, happens in germinal center in secondary lymphoid tissues
result of recombination within constant region. antigen specificity unchanged. dependent on AID (activation induced cytidine deaminase).
somatic hypermutation
random mutations in the coding of the variable domain region, creates single point mutations in the antibody idiotype which can increase affinity
occurs after b cell is activated by antigen, does not affect constant region, dependent on AID (activation induced cytidine deaminase) enzyme
TH2 cell release of cytokine
induces the differentiation of B cells into fully differentiated, antibody-secreting cells and memory cells and induce class switching
thymus-independent antigens
antigens contain no peptides, stimulates secretion of IgM antibodies only and does not result in immunologic memory
germinal centers
clones of proliferating antigen specific B cells, where somatic hypermutation occurs, follicles of the lymph nodes and spleen
clonal selection
results in affinity maturation, predominance of clones capable of producing antibodies with increasing affinity for the antigen
isotype switching
changing the heavy chain constant domains to classes of antibodies with new and different effector functions. rearranges the DNA encoding the constant region of the heavy chain. one way reaction.
IgG
activates complement, opsonizes, mediates ADCC, can be transported across placenta which protects fetus during gestation
has a gamma heavy chain,
IgA
exists as dimer, protective defense of the mucosal surfaces of the body, not opsonin
neutralization, crosses epithelium, present in urinary and gut, predominate class in secretions
B cell activation requires
needs to enter lymphoid follicles and be stimulated by antigen with T cell help to become activated
thymus independent 1 (TI-1) antigen
such as LPS can activate a B cell by replacing T-cell signals with TLR4 (toll receptor). This results in antibodies specific for LPS.
no immunologic response, no memory B cells, no IgG, only IgM response, responses are short lived
