B cell activation Flashcards
Primary immune responses occur
in secondary lymphoid tissues
B cell activation is initiated
in the outer areas of follicles in primary immune responses
antigen crosslinks
to mIG on b cell which upregulates BR3
antigen mIG complex is
endocytosed and undergoes peptide MHC class II expression on B cell surface
BR3 interaction with Blys is
critical for survival of the B cell because it escapes apoptosis
B cell receptors that interact with T cell
HLA class II/peptide, HLA class II, B7-1(CD80) B7-1 (CD86), LFA-3 ICAM-1,2, CD40 L
T cell receptors that interact with B cells
TCR, CD4, CD28 CD2, LFA-1, CD 154
Hyper IgM syndrome
patient only has IgM
Thp in interfollecular region leads to
Th1 and Th2 cells, Cd40 L is expressed and sytokines secreted
Cognate interaction is
the acrtivation of B cells by way of all the receptors.
after dissassociation of B cells and T cells
the B cells clonally expand
Some B cells turn into
plasma cells that secrete IgM for 4 days post immunization
Other B cells do
isotype switch 10-14 dyas post immunization
plasma cells secrete
higher affinity antibodies
some B cells become
long lived memory B cells that ciruclate in immunosurveillance
down regulation of B cells and Plasma cells happens when
IgG’s bind low affinity Fc-Gamma Rs on B cells and plasma cells and they eventually undergo apoptosis
BR3 is upregulated on B cells following
antigen crosslinking of B cells mIg
BLyS is produced by
activated monocytes, macrophates, and dendritic cells
BLyS release is triggered by
cytokine acting on the cells or by IgG-FcGamma R signallng
BLyS binds to BR3 and leads to
B cell survival
abnormal production of BLyS allows
survival of autoreactive b cells
high serum levels of BlyS have been reported in
patients with rheumatoid arthiritis, SLE and multiple sclerosis
Typically proteins, B cell activation requires
CD4+ T cell cytokines and cognate interaction
Haptens are
often chemical or degradation products less than 5kD
Haptens immunogenic when
coupled to large proteins and they become the epitope
Effecti=
carrier effect because large protein carrier of hapten
T independent antigens induce
naive B cell activation without T-B cell contact mainly saccharides
T-independent antigens lead to
mainly the production of IgM (LPS, Peuomococcal polysaccharide
Mitogens trigger
proliferation of many clones of lymphocytes
B cell mitogens
pokeweed mitogen (PWM) and HIgh Lipopolysaccharide(LPS)
T cell mitogens
concanavalin A (Con A) Phygohemagglutinin( PHA), PWM
Com A and PHA are
plant glycoproteins called Lectins that bind carb molecules
Superantigens
often bacterial products that activate subsets of T cells
Superantigens bind
specifically to regions of the T cell receptor called V beta
Activation of all T cell clones that express any V-beta lead to
excesive amount of cytokines being released
effect of excess cytokines is called
cytokine storm
IgG B cells can either
become a memory cell with sIgG or a plasmacell that secretes IgG
Memory cells usually express
high affinity immunoglobulin and isotypes other than IgM.
entry of memory cells into the lymphoid tissue happens at
the HEV High endothelial venules
