Lecture 43+44+DLA Flashcards
role of the thymus dependent antigens
protein antigens processed in APCs and recognized by
helper T cells
help with B cell activation
heavy chain isotope switching
affinity maturation
thymus independent antigens
non-protein antigens
little isotope switching
little affinity maturation
B cell activation (dependent vs independent)
thymus dependent:
B cells need direct contact with Th cells (follicular B cells; B2)
thymus independent:
marginal zone B cells in spleen and B1 cells are major responders
activate by pattern recognition receptors
type 1: LPS
type 2: highly repetitious molecules (flagella)
what are the B cell co-receptors
CD19: cytoplasmic tail for signal transduction
CR2: receptor for C3d (from complement)
TAPA-1: transmembrane molecule
what is the inhibitory co receptor for B cells
CD22: cytoplasmic tail for signal transduction
Contains ITIM (Immunoreceptor tyrosine-based inhibitory motif)
ITIM (Immunoreceptor tyrosine-based inhibitory motif)
associated with CD22
Functions to deactivate B cells – negative regulation
Important in preventing autoimmunity
outcomes of B cell activation
B cell proliferation
IgM secretion
B cell interaction with Th cells
Role of the innate immune system in B cell
activation
Microbes become coated with C3d
(product of Factor I on C3b)
B cells have a C3d receptor CR2 or CD21
enhances antigen-dependent activation of B cells
B cells also express Toll-like receptors that can
recognize microbial products directly
what is produced by FDC and Tfh and why is it important
TNF beta
Promote expression of activation-induced cytidine deaminase (AID):
Important in somatic hypermutation (SHM) and Class Switching (CSR)
Tfh cells
T cell express CXCR5: draw cells to follicles
Generation and function of follicular helper T cells (Tfh)
depend on costimulatory ICOS
They secrete IL-21: antibody production and proliferation
in the germinal center is where class switching and affinity maturation occurs
ICOS
activation
follicular helper T cells in antibody response
what is needed for class switching
AID
interaction between CD40 on the B cell and CD40L on the T cell
X-linked hyper-M syndrome
TH cells don’t express CD40L
patients only produce IgM
No memory cell populations
no germinal center
affinity maturation process
in response to a protein antigen increases with prolonged or repeated exposure
the result of somatic hypermutation of ig genes (point mutation)
Enzyme activation-induced cytidine deaminase (AID) is required: creates mutations in DNA by deamination of cytosine base
FcgRIIB receptors
▪ Inhibition of receptor-mediated B cell activation
