Lec6 Antigen recognition Flashcards
Features of antibodies
- recognize: macromolecules, small chemicals, conformational and linear epitopes - diversity: each clone has unique specificity - antigen recognition mediated by: V regions of heavy and light chains [CDRs] - signal function mediated by: proteins [Iga and IgB] associated with membrane Ig - effector function mediated by constant C region of secreted Ig - get changes in constant region in secretion and in class-switching - fast on-rate, variable off-rate - higher affinity for antigen than TCR
Features of T cell receptors
- recognize: linear epitopes, peptides displayed by MHC molecule on APCs - diversity: each clone has unique specificity [more diverse than Ig] - antigen recognition mediated by: variable regions [CDRs] of a and B chains - signal function mediated by: proteins [CD3] associated with TCR - no effector function - no changes in constant region - no change in affinity for antigen in immune response - slow on-rate, slow off-rate
B cell receptor structure
- B cell receptor = membrane bound Ig - 2 heavy chains, 2 light chains attached into monomer with 2 binding sites - 2 types of light chains exist but never mixed on same antibody - can bind antibody molec in their native conformation
Complementary determining region [CDR] [function, where is it location]
- 3 In each of light and heavy V domains of antibody and in each of Va and Vb in TCR - hypervariable domains - function like fingers to interact with antigens
T cell receptor structure
- one variable domain, one constant domain - one B and one a chain - binds linear protein epitope presented on MHC
T and B cell maturation
- common lymphoid progenitor - pre B or T cell expresses one chain of antigen receptor - immature cell expresses complete antigen receptor - then undergoes positive selection for receptors with weak antigen recognition [negative for those with high affinity] to get mature cell
Somatic recombination
- responsible for generation diversity in both B and T cells - V-D-J joining - Heavy and light [or alpha and Beta in T cells] BOTH rearrange to get diversity
Junctional diversity
- often gene segments to not align properly - gaps filled by terminal deoxyribonucleotidyl transferase [TDT] - nucleotides also may be gained or lost in other ways - occurs in by B and T receptors
Sequence of rearrangement for Ig?
- D-J in heavy chain rearranged, then V - if successful: light chain rearranges - if both succesful: other chromosome rerrangement prevented
Processes for diversity generation
- combinatorial diversity [somatic recombination[ - junctional diversity - any heavy chain can associated with any light chain
IgA [function]
mucosal immunity
IgD function
on naive b cells no effector function
IgE function
- mast cell activation [immediate hypersensitivity] 2. defense against helminthic parasites
IgG Function
- opsonization 2. complement activation 3. antibody-dependent cell mediated cytotoxicity 4. neonatal immunity 5. feedback inhibition of B cells
IgM function
- naive b cell antigen receptor 2. complement activation
Are there more types of b cells or t cells?
T cells
Does pre-B/T cell express antigen receptor?
yes - one chain of antigen receptor
Does immature B/T cells express antigen receptor?
yes - complete receptor
Does immunoglobulin or TCR get change in constant region?
- Ig does: get heavy chain class switching from membrane to secretory Ig - TCR does not
Does Ig or TCR have higher affinity
Ig higher affinity Ig affinity increases during immune rxn TCR has no change
Which MHC does CD4 recognize?
class II MHC
Which T cell recognizes MHC 1?
CD8
What is order of recombination [in V,D,J]
- D-J in heavy chain rearranges first - Then V in heavy chain rearranges - Then light chain rearranges
Heavy chain has which things ?
VDJ Part of variable region of Ig
