B cells Flashcards
Where does B cell maturation occur?
in the bone marrow in the ABSCENCE of antigen
When does clonal selection occur?
when an antigen binds to a mature B cell whose membrane-bound Ig molecules are specific for that antigen
What are the steps in B cell development?
- B-cell precursor rearranges its Ig genes
- negative selection in the bone marrow of B cells that recognise self antigen
- migration of B cells to peripheral lymphoid organs and activation
- Ab secretion and memory cells in bone marrow & lymphoid tissue
How are Abs formed in the cell?
Abs are synthesized on the rough ER, then move to the Golgi where they are glycosylated, then are either anchored to the membrane or secreted through vesicles
What part of the Ab do pre-B cells make?
ONLY cytoplasmic M heavy chain
What part of the Ab do immature and mature B cells make?
produce kappa or lambda light chains that protect the M heavy chain from degradation & allow membrane IgM
Can B cells switch from IgM isotype?
Yes. They can switch to have the same variable region but be a different isotype. They can also undergo somatic cell mutations to change their heavy and light variable regions to give higher affinities
How do Igs differentiate?
during development, the cell undergoes somatic DNA recombination to make different variations of the genes for Igs
What does the C region of the Ig confer?
functional specialization and isotype
Why does IgG have a long half-life?
cells randomly uptake serum proteins through endocytosis and send them to the lysosome for degradation. However, endosomes with FcRn molecules bind to the Fc receptor on IgG, which causes the IgG to be recycled instead of degraded
Define affinity maturation
a process that yields Abs that bind tightly to their Ag.
it involves subtle changes through somatic cell mutations in mature B cells to change the variable region
What are the steps to a primary response?
lag phase, primary response, plateau, & decline
Define isotypic epitope
isotypic determinants are constant-region determinants that distinguish each Ig class & subclass within a species
Define allotypic epitope
allotypic determinants are subtle amino acid differences encoded by different alleles of isotype genes
Define idiotypic epitope
idiotypic determinants are generated by the conformation of the amino acid sequences of the heavy & light chain variable regions specific for each antigen.
Each individual determinant is called an idiotope and the sum of the idiotopes is the iodotype
