B cell review Flashcards
What Ig’s are on the naive B cell?
IgM+, IgD+ , Igalpha and Igbeta
What happens when the naive B cell encounters an antigen?
it needs TWO antigen molecules/epitopes so that Ig membrane molecules can cross-link
ITAMs of IgAlpha and IgBeta are phosphorylated, recruit Syk tyrosine kinase, phosphorylate adaptor proteins, signaling cascade ensues
How does complement improve B cell activation?
B cells have a coreceptor, CR2, for C3d which is bound to the antigen
What is T independent B cell stimulation?
when B cell encounters polysaccharide and lipid antigen, it can just cross lin enough receptors that proliferation and differentiation is stimulated without T cell help
also works via complement system, TLR activation
What are hapten-carrier conjugates?
A hapten is a small chemical that is recognized by B cells, but stimulates strong antibody responses only if it is attached to a carrier protein.
The b cell binds the Hapten portion, ingests the conjugate, and displays peptides derived from the carrier to helper T cells.
What are conjugate vaccines, and why are they important?
Children under two can’t make good T-cell independent antibody responses, and vaccines might be using capsular polysaccharides as the way to induce immune response.
Instead, we conjugate bacterial polysaccharides to protein carriers, which do have peptides that antigen-specific T cells can respond to (making it a T cell dependent response).
Describe what is in the cortex, paracortex, and medulla
cortex: B cells, primary and secondary follicles
at the edge between the two: that’s where you see antigen activated helper T cells and B cells go., initially, where they produce low levels of antibodies with low affinity.
paracortex: T cells
medulla: B and T cells, macropahges
What does the activated helper T cell express that helps it find the B cells?
Activated helper T cells express CD40L, and secretes cytokines
B cells are activated by CD40 engagement, and they proliferate and differentiate
After B cells are activated and meet their helper T cells at the edge of lymphoid follicles, what happens?
low level of antibody production, low affinity (little isotype switch) – typically short-lived plasma cells, and few memory B cells.
some of the B and T cells migrate into follicles to form germinal centers, where B cells undergo proliferation, isotype switching, adn affinity maturation
nonfunctional ____, so Helper T cells can’t stimulate the progeny of IGm+, IgD+ B cells to produce antibodies of different heavy chain isotypes
then you have IgM errywhere
Disease name?
CD40L
What enzyme is required for heavy chain isotype switching, and how does it work? What is it induced by?
Activation-induced Deaminase (AID), induced by CD40 signals, converts cytosines in DNA to uracil, which then results into a double stranded DNA break
then you have recombination where VDJ exon is moved to a downstream, different C region, deletion of intervening genes.
What is affinity maturation? where does it happen? What cells/enzymes are necessary?
in germinal centers of lymphoid follicles
somatic hypermutation of Ig genes in dividing B cells, selection of high affinity B cells by antigen (which have undergone point mutations in the V regions, and particularly in the antigen-binding hypervariable regions)
Only in Helper T -cell dependent protein antigens
needs AID
When B cells proliferate, what can they differentiate in? Where do these go?
Some proliferating B cells differentiate into antibody-synthesizing plasmablasts, which have begun to secrete antibody but are still dividing adn can still interact with T cells (they still have B7 and MHC II)
Plasma cells (bone marrow, mucosal tissue) and memory cells (blood, mucosal tissue). Plasma cells secrete antibodies, memory cells do not.
What is antibody-mediated phagocytosis, and what does it defend the body against?
IgG opsonizes the microbe, and an array of IgG Fc regions projects outwardly.
the macrophage has an Fc receptor, called FcyRI (CD64), and will then bind this opsonized microbe
this activates the phagocyte, which phagocytoses the microbe.
What is antibody-dependent cellular cytotoxicity? What receptor is necessary, and what antibody?
NK cells and other luekocytes bind the antibody-coated cells and destroy them. they do so via their FcyRIII receptor, which also binds the IgG antibodies and then NK will kill the cell
