Antibodies - Diebel Flashcards
Basic structure of an antibody
- Fab region (basic unit) = 2 heavy chains and 2 light chains
- Fc region = 2 heavy chains
H chain
5 kinds: gamma, alpha, mu, epsilon, delta
-defines the class of antibody to which the molecule belongs
L chain
2 varieties: kappa or lambda
What chain changes in class switching?
Heavy chain!
Secreted IgA structure?
Dimer of the basic unit (2 H’s and 2 L chains)
Basic units held together by J chain
IgM structure?
Pentamer
Basic units held together by J chain
Constant Region
Made up of 1 to 4 compact, structurally-similar domains call C domains
Variable Domains
Different in sequence between antibodies of different specificities.
-At N-terminal
Hyper variable regions make it more different
Valence=
of antigenic determinates (epitopes) an antibody molecule can theoretically bind.
Valence of IgG
2 (1 antibody with 2 Fab parts)
Valence of secreted IgA
4
Valence of IgM
10 in theory but 5 in practice b/c of puckering
Valence of Fab?
1
Valence of F(ab’)2:
2
Valence of isolated VL or VH?
0 –takes a combo of VL and VH to make antibody binding sites
Isotypes:
- Constant domains change but variable domains stay the same
- slight differences in the AA sequence of their H chain C regions
10 isotypes
IgG 1-4 IgA 1-2 IgM 1-2 IgD IgE
Allotypes
- minor ALLELIC differences in sequence of Igs between individuals
- depends on if you are using your mom or dad’s genes to produce chain
Ex: two IgG1 molecules that are the same but the AA sequence is slightly different
Idiotypes
=unique combining region, made up of the CDR (complementarity- determining regions) amino acids of its L and H chains
- Antigen determinate part of Ab
- *Antibody’s unique combining site considered as an antigen.
CDR (complementarity-determining regions)
AA sequence variablity is not distributed uniformly along V domain
- These 3 areas are called CDR or hypervariable regions
- CDR comprise the actual antigen-binding site
Anti-idiotype
Antibodies made that recognize the unique sequence of that combining site and no other.
IgG (1000 mg/dL)
- main antibody in blood and fluids
- Neutralizes toxins and blood-borne viruses,
- activates complement to destroy bacteria
-main antibody! - memory
IgA (200 mg/dL)
Does same as IgG in blood
- Real work is SECRETIONS
- Forms a DIMER and secretory components protects it from proteolysis
IgM (100 mg/dL)
- same as IgG
- FIRST antibody to appear in serum after immuniztion
- very efficient at activating complement
IgD (5 mg/dL)
role uncertain
- functions mainly as receptor on naive B cells
- always surface bound
IgE (0.02 mg/dL)
Causes Type 1 immunopathology (immediate hypersensitivity)
- ALLERGIES
- BUT true importance is in resistance to WORMS/PARASITES
2 things initiated after antibody binds an antigen?
IgG or IgM binds to antigen and conformational change happens so 2 things are initiated:
- Binding to phagocytic cells - have receptors FcR for the altered Fc of IgG
- C1q (1st part of the complement system) now binds to 2 adjacent Fcs and is ACTIVATED
IgG activation of Complement
Secreted as a monomer but forms a HEXAMER to activate complement
IgG1 structure
Disulfide bonds hold chains together
3 constant heavy domains
IgG3 structure
Monomer
-larger hinge region so it is better at binding complement than IgG1
IgM structure
Secreted form:
- 5 antibodies linked by J chain = PENTAMER
- 4 constant heavy domains
IgA structure
Dimer (linked by J chain)
Secretory component that helps it go through epithelial cell layers
IgD structure
ONLY membrane bound
- only on naive B cells
- monomer
IgE structure
- 4 constant heavy domains
- always secreted as a monomer
