Lecture 6: B & T Cell Receptors Flashcards
How is B and T cell diversity achieved?
Through VDJ recombination: the random assembly of key genes that together make up the B or T cell receptor
Why do B cells produce antibodies?
- neutralise toxins and pathogens
- promote phagocytosis
- activate compliment
- mediate immunity through Fc receptors
Why is tight control of B and T cells important?
To prevent self-reactivity
What is the B cell process leading to MHC II expression?
- BCR recognises specific peptide sequence in an antigen
- BCR/antigen complex induces a signalling cascade resulting in B cell activation
- B cell endocytoses the antigen and processes it into many peptide fragments to be presented on MHC II
How are T cells recruited for B cell help?
Help for the B cell can come from any T cell that is specific for any of the presented peptides, where the T cell epitope is physically linked to the B cell epitope
What sort of cells are B cells?
Professional APCs
What are CDRs?
Complementary determining regions: 3 short segments in the V region with hyper variable amino acid sequences
What are FRs?
Framework regions: 4 regions which alternate with CDRs to provide antibody with structure, and are less variable than CDRs
What determines B cell receptor specificity?
VDJ genomic rearrangement, where large numbers of VDJ genes allows for massive diversity
How many variable regions are generated per cell, and how does this impact Ig specificity?
Only 1 variable region is generated per B cell, so all Igs from a single b cell will have same specificity
What are the large set of variable regions determined by?
Junctional diversity and somatic mutations
What is the impact of affinity maturation?
Can increase the binding strength of antibodies via somatic mutations in the hyper variable regions, so improved affinity mean better antibodies
Why is class switching used by B cells?
Allows them to alter the effector function of antibodies they produce
In mice, what are the 2 light chains?
kappa and lambda
In what order are the mice light chains used?
Kappa chains are used first as the gene is more complex, so can give rise to higher diversity
Where is the joint between V and J located?
CDR3