B Cell Immunity Flashcards
T-independent B cell activation
thymus-independent antigens on bacteria are typically polysaccharides in repeating subunits, which sends a strong signal to B cells to start secreting antibodies (without the need for T cell activation)
*the Lipid A on the bacteria is involved in TLR 4 signaling
why is T-independent B cell activation suboptimal
-doesn’t induce somatic hypermutation/affinity maturation of the B cell
-don’t get a lot of class switching
-don’t get a lot of memory B cells or plasma cells
thymus-dependent antigens
antigens with a PEPTIDE component can be presented to T cells
-can lead to class switching and immunologic memory
-primary way that B cells are activated
T-dependent B cell activation
- Th cells are activated
- B-cell receptor mediated endocytosis; foreign antigen presented on MHC II and recognized by TCR
- CD40 receptor on B-cell binds CD40L on Th cell
- Th cell secretes cytokines (diff cytokines for Th1 vs. Th2) that determine Ig class switching of V cells; B cells are activated, undergo class switching and affinity maturation, and begin producing antibodies
linked recognition
if the T cell - B cell interaction is to occur, BOTH cells must recognize EPITOPES on the SAME protein or protein conjugate or bacteria/virus
*used for conjugate vaccines
how does a conjugate vaccine work
conjugate an epitope of the desired antigen to the tetanus toxoid protein (which we already recognize because most people have already had the tetanus toxoid vaccine)
why does linked recognition protect against autoimmunity
low probability that self-reactive T AND B cells for the SAME antigen will survive development
what do B cells require to undergo somatic hypermutation and affinity maturation
require T cell interaction
what is affinity maturation
cells that make mutations that increase affinity for the antigen have a stronger T-cell interaction and have a stronger stimulus to develop further
where do B cells develop
develop in the bone marrow; migrate to the spleen and lymph nodes; once B cells encounter antigen, they form a germinal center
three fates of activated B cells
after undergoing maturation, the B cells can:
1) undergo apoptosis
2) become a plasma cell and start pumping out antibodies
3) become memory B cells
where do plasma cells reside once formed
may remain in the medullary cords
-may migrate to other sites such as bone marrow and spleen
where do memory B cells go once formed
found at several sites, but particularly the BONE MARROW
what is the immunoglobulin that can transport across the placenta
IgG
what do different Fc receptors do
different Fc receptors on OTHER CELLS allow ANTIBODIES to have different biological functions
