antibodies and B lymphocytes Flashcards
B lymphocyte activation: explain the process of activation of B lymphocytes to divide and differentiate into antibody-secreting and memory cells, and the differences in antibody production in primary and secondary immune responses
what causes B cell activation
interaction between foreign antigen and BCR on naïve cell
upon BCR-antigen binding, what do B cells interact with before entering lymph nodes
T cells
3 pathways for activated B cells
affinity maturation: antibody response improves; memory cell: stored for later exposure; plasma cell: produce antibodies - specifically make antibodies so many ER and ribosomes present
describe T cell activation in B cell context
naïve B-Cells cannot be activated by antigen alone, also need accessory signal from Th cells or from microbial constituents, leading to different types of antigens
what are the 2 types of antigen
thymus independent and thymus dependent
2 features of T-dependent activation
all Ig classes and memory
2 features of T-independent activation
only IgM and no memory
T-independent activation: structure
often bacterial polysaccharides with repetitive structure
T-independent activation: what provides second signal
microbial constituent
T-independent activation: process
polysaccharide recognised by many BCRs, pulling them closer together to same space, activating B-Cell and secondary signal from PAMPs
T-dependent activation: what is specifically involved
MHC Class II on cell surface (must also occur on dendritic cell)
T-dependent activation: process
T-Cell recognises antigen on MHC Class II with TCR on dendritic cell, activating it; divides and travels to lymph node, allowing it to provide second signal to B-Cell with same presented antigen
principle of affinity maturation by somatic hypermutation
VDJ section of antigen recognition slightly mutates, inducing point mutations; cytosine changed to uracil in G-C pairings, so next generation has UT pairing - slight changes may increase affinity of antibodies to antigens (or may not and B-Cells die)
differences in antibody production in primary and secondary immune responses
due to immunological memory, there is a more rapid and heightened immune reaction to eliminate pathogens fast; antibody quality also improves over time (affinity maturation) so better secondary response
what CDs are B cells associated with
CD19, CD20
