Ig Structure Flashcards
List the classes of Ig and their conc. in serum
IgM, IgG, IgE, IgA, IgD
IgG (12mg/ml) > IgA (2.5mg/ml) > IgM (1.5mg/ml) > IgD (.03mg/ml) > IgE (5x10(-5)mg/ml)
Describe the major biological characteristics of IgM
Predominant Ab induced in primary response (elicited by T-independent polysaccharide)
pentameric in secreted form, appears as a monomer on B cells (part of B cell receptor (BCR)) - IF A CELL HAS IG ON THE SURFACE, PARTICULARLY IGM, IT IS A B CELL
J chain joins subunits
Activates complement
Describe the major biological characteristics of IgG
Predominant Ab induced in secondary response (T dependent)
Three classes, IgG1, IgG2, IgG3, IgG4, with slightly different characteristics, monomeric in membrane bound and secreted form
All are good at neutralization and are particularly good at diffusion into extravascular sites
1 and 3 are especially good at opsonization, sensitization for killing by NK cells, crossing the placenta, and activating compement
Describe the major biological characteristics of IgE
Involvement in allergic hypersensitivities
Sensitization of Mast Cells (IgE fixes to mast cells and basophils via an Fc receptor on the cells)
secreted as a monomer, low serum concentrations
Describe the major biological characteristics of IgA
Two subclasses, IgA1, IgA2
Predominant Ab in external secretions, occurs as a dimer joined by a J chain (it appears in serum as a monomer)
can fix complement via alternative pathways (non-classical)
key role in mucosal immunity
Transport across epithelium (dimer), neutralization, diffusion into extravascular sites (monomer)
Describe the major biological characteristics of IgD
Found predominantly on some B cells (membrane bound, generally not found in blood)
Functions as a B cell Ag receptor along with IgM
Describe three mechanisms by which Ab protects the host from microorganisms
Neutralization: Ab prevents bacterial adherence
Opsonization: Ab promotes phagocytosis
Activation of complement: Ab activates complement, which enhances opsonization and lyses some bacteria
What is a polyclonal Ab?
Ab from multiple clones of B cells are polyclonal
What is a monoclonal Ab?
Ab from a clone of B cells are monoclonal
What is the difference between monoclonal and polyclonal Ab?
Individual B cells make Ab against a single epitope. If that B cell proliferates and produces Ab, it will all be against that one epitope on the Ag - monoclonal. If multiple B cells encounter the same Ag, they will all produce Ab against various epitopes on the Ag - polyclonal. They are all specific for the Ag, but for different Epitopes.
What are some examples of monoclonal and polyclonal Ab used clinically?
polyclonal - IVIG against many different diseases
monoclonal - tumor-specific monoclonal Ab
State the approximate half-life of antibody titers after tetanus vaccination and after infection-caused measles
Tetanus (ppl immunized for tetanus): 11yrs even though recommendation is 5-10 yrs
Measles (people who got measles): 3014yrs
What part of the heavy an light chains are considered the variable domain? The constant domain?
For both, the N terminus is considered the variable domains. The remainder is considered the constant domain
What are some functions of the Constant domain?
ability to cross placenta
sites of attachment for Fc receptors of macrophages, monocytes, and mast cells
binding of complement
What is the function of the variable domain, and why are complementarity-determining regions (CDR) important?
The variable domain is the site of antigen binding, and is responsible for the specificity of Ag binding. Each heavy and light chain has three CDRs, which are sites of greatest AA variability. The 6 CDRs (3 from heavy, 3 from light) are projecting loops that are in close proximity, and form the Ag binding groove.
