Antibodies 2/3 Flashcards
Carbohydrate region of Fc Fragment
"- Btwn CH2 domains Functions : - Increase solubility of AB - Protection against degradation - enhance functional activity of Fc domain "
Hinge Region importance and function
“Segment of H chain btwn CH1 and CH2 regions (alpha/delta/gamma chains)
High content of proline and hydrophobic residues -> flexibility “
What is class switching and how is it influenced by cytokines?
"Cytokines acting on B cells determine the class of AB that will be expressed -> mostly IgG [IFN-y + IgM -> IgG switch] [ IL-4 + IgM -> IgE switch] [Others + IgM -> IgA] "
Importance of Class switching to B cell activation
Resting B cells express IgM and IgD, but when they get signals from a Tcell they can switch
Cytodine deaminase
“AKA AID
- deaminates the dc residues with switch regions
?enzyme?”
Antibody synthesis : Primary antibody response
“IgM AB response has 4 phases (Lag, log, plateau, decline)
Lag - no AB detected
Log - AB titier increases logarithmically
Plateau - AB titer stabilizes
Decline - AB is catabolized “
Antibody synthesis : Secondary response
“Similar to primary (4 phases)
Differences : time, AB type, AB titer
Time - shorter lag, longer plateau, and more gradual decline
AB type - IgM (primary), IgG (secondary)
AB titer - higer level; plateau is 10x higher “
Monomer vs dimer structure functions of Ig (esp IgA)
“Monomer (AKA serum IgA) : ~15% of circulatory Ig
Dimer (AKA secretory IgA) : predominant in tears, saliva, milk, sweat “
Describe the IgA allotypes and their differences
“IgA1 & IgA2
IgA2 - more resistant to bacterial proteases (missing hinge region), predominant IgA in secretions at mucosal surface
IgA1 - found in serum
*22 amino acid, 13 at hinge region (deleted in IgA2) “
Function of Secretory IgA
“Transverses epithelial cells using secretory component (sc)
(sc - precursor found on surface of epithelial cells and serves as IgA receptor)
- patrols mucosal surfaces and act as a first line of defense
- neutralizes microbial toxins
- helps to prevent microbial attachment to mucosal surfaces “
Immune Exclusion
Complexes of IgA and microbial antigen become trapped in mucous and eliminated by ciliated epithelial cells of respiratory and intestinal tract
How does IgA fix complement?
“Alternative pathway; lack of complement activation may assist in the clearing of the AG w/out triggering inflammation (minimize the damage)
- Neutrophils, monocytes, Macs have IgA receptors
- binding triggers cell activation “
IgD function and characteristics
“Monomer - serum = <1% of circulating Ig
- typically bound to surface of unstimulated B cells (+IgM); susceptible to proteolytic enzymes
- bound IgD play a role in B maturation/differentiation “
IgE function and characteristics
“Monomer - serum = <1% of circulating Ig
- After synthesis, attaches to mast cells by high affinity TcERI receptor
- May serve a protective role by triggering an acute inflammatory response that recruits neutrophils and eosinophils
*parasitic infections
IgE + Antigen + Mast cell -> cellular cascade -> mast cell degranulation -> histamine -> allergic rxn “
IgG function and characteristics
“Monomer - serum = ~75%; 4 subtypes/Allotypes (IgG1-4)
- Newborn immunity (IgG1,3,4) - transplacental
- Complement fixation (IgG3)
- Opsonisation (IgG1,3) (coat antigen -> phagocytosis (Macs, Monos, Neutros have IgG receptors))
- Neutralization of toxins and viruses
- Agglutination and precipitation rxns “
