Antibody Structure and Function Flashcards
** look at pictures on slides for important ways foreign bodies are ingested
1
Q
take home points from lecture
A
- IgG is most common immunoglobulin type and has the widest range of functions
- IgM is the most primitive immunoglobulin type, is the most potent at complement fixation but is unable to directly mediate many functions such as opsonization or ADCC
- IgA exists in two forms, one of which is secreted. the secreted form contains a secretory piece that inhibits degradation
- IgE is associated with immune response to parasites and is important in the allergic reaction
2
Q
B cells
A
- have Ig’s bound to them
- bacterium binds to antibody
- stimulated B cell gives rise to plasma cells that secrete more antiodies
3
Q
gamma globulin
A
-fraction contains most of the antibody
4
Q
Fab
A
- top part of the antibody
- contains light chain variable region, light chain constant region, heavy chain variable region and light chain variable region 1
- n terminal domain is variable
- each domain has a different function
5
Q
types of light chains
A
- kappa
- lambda
- can bind with any of the heavy chain “definers”
- kappa and labmda can bind with D, M, G, A and E
6
Q
why does IgM weigh so much more
A
- 970 kDa
- made from 5 single IgMs that float around
7
Q
IgG MW
A
- light chain is 25,000 x 2
- heavy chain is 50,000 x 2
- total is 150,000
- IgG is 75-90% of Ig in serum, and have the longest half life
8
Q
IgD
A
- regulatory for B cells
- 180 kDa
- located on surface of human immature B lymphocytes
- associated with some tumor cells
- 0.2% of serum Igs
- co-expressed with IgM on surface of B lymphocytes
- may function as an antigen receptor
9
Q
IgG
A
- MW 150 kDa
- predominant class in serum
- toxin neutralizing, agglutinating, opsonizing, bacteriolytic (with aid of complement system
- subclasses IgG1, IgG2, IgG3, IgG4
- intrachain disulfide bonds occur between the same residues
10
Q
IgM
A
- MW 900 kDa
- predominant class in primary immune response
- antigen receptor on B lymphocyte
- with the aid of complement it can be opsonizing and bacteriolytic
- without complement can’t aid in opsonization because cells do not have FcM receptors
- 5-10% of serum Igs
- 4 heavy chain domains, no hinge region
- J chain (15 kDa)
11
Q
Fc region
A
- constant region in the antibody
- cells have receptors for Fc regions
- Fab binds to the antigen and Fc binds to our immune cells
12
Q
IgA
A
- 160 kDa
- predominant class in secretions
- found as a monomer, dimer (secretion) and trimers
- 15% of serum Igs
- secretory piece (T- piece) resists acid hydrolysis
- J chain
- agglutinating, opsonizing
- flu
13
Q
IgE
A
- 200 kDa
- immediate hypersensitivty
- fixes to mast cells (now have IgE-antigen binds and releases histamine)
- 0.1% of serum Igs
- mediate changes in vascular permeability
- may be involved in host defense agains parasitic infection
- we have cleared most pathogens we would have IgE for out of our environment
14
Q
protelytic cleavage of IgG by papain
A
- digests the hinge region-interchain disulfide bonds
- yields 3 fragments
- one can by crystallized (Fc)-homogenous, most IgG specific antigenic determinants
- other two regions have ability to bind antigen and are not crystallized (more variable)-Fab
15
Q
pepsin degradation
A
- heavy chain beginning at coo terminal and ending at the region of interchain SS bonds
- divalent fraction with ability to bind and cross link antigen (not possible with Fab) but lacking the functions of the Fc portion
- called F(ab’)2
