B cell Flashcards
B cell negative selection occurs
bone marrow
B cell precursor rearranges its ig genes
in the bone marrow stromal cell
Immature B cell bound to self cell-surface is…
removed from the repertoire
Two ways to initiate B cell activation and humoral response
1) thymus depend
2) thymus indepedent tho not as efficent
which T cell activates the B cell
CD4 Helpter T cell
First signal
delivered by antigen via BCR
Second signal delivered by
1) thymus dependent > helper T cell
2) extensive crosslinking of surface igM
inefficent method of activation
thymus independent
T cells can only recognize small…presented in the MHC pocket of the antigen presenting cell
peptide
MHC II is loaded from material captured in the…
phaglysosome
The antigen recognized by BCR does NOT have to be the ……it presents to CD4 helper T cell
doesn’t have to be the same antigen recognized, can present something different
B cell captures molecular complexes/pathogen into its….via its…..
B cells use their BCR to capture antigen into their phagolysosome
What does B cell use to capture its antigen
BCR
BCR can recognize the external viral coat antigen but after digestion, the ……is presented to the T cell
internal viral antigen
hence forth the antigen recognized by B cell isn’t necessairly the same antigen it presents to CD4 t cell’
After B cell presents the antigen peptide to T helper cell, the T helper cell…..
releases cytokines to active the B cell, and the activated B cell PRODUCES AB against the viral coat protein
BCR can recognize……and…..unlike T cells which only recognize….
NON-peptides and peptides
Peptides for T cells only
epitope
the part of an antigen molecule to which an antibody attaches itself.
Read
Although the epitope recognized by the armed helper T cell must therefore be linked to that recognized by the B cell, the two cells need not recognize identical epitopes. Indeed, we saw in Chapter 5 that T cells can recognize internal peptides that are quite distinct from the surface epitopes on the same protein recognized by B cells. For more complex natural antigens, such as viruses, the T cell and the B cell might not even recognize the same protein. It is, however, crucial that the peptide recognized by the T cell be a physical part of the antigen recognized by the B cell, which can thus produce the appropriate peptide after internalization of the antigen bound to its B-cell receptors.
TCR and BCR do not have to……..
B cell and its helper T cell (which was activated early by apc cell) don’t have to recognize the same epitope
BCR captures a molecule by its polysacchride component but after digestion the…….component of the ingested is loaded onto the B cell’s ……and presented to CD4 T cell
PEPTIDE COMPONENT
MHC II
antigen binding portion of antibody
Fab
non antigen binding portion of antibody
Fc
Why is the BCR can also recognize non-peptides and that T cells recognize peptides, in that they need not recognize the exact thing?
For pathogens with non-protein coat
Basically to develop a WIDE VARIETY of pathogens and toxin
signal two invovles……
CD4 ligand on T helper cell, and CD4 ReCEPTOR on B cell
LFA-1 of T cell also helps with T / B cell interaction
True
T helper cells bound to b cells secrete
IL-4 into the space b/w the two cells
Somatic hypermutation
B cell activation leads to mutations in the antigen binding regios of ig
Rapidly proliferating cells are found in the….
germinal centers in secondary lymphoids
Only B cells able to present antigent T cell are …..
stimulated to survive
The ….the ab affinity the…..likelihood that B cell will outcompete other…..B cells for T cell help in surviving
HIGHER…..HIGHER….lower
Where does somatic hyper mutation takes place?
Lymph node, b cell follicle area
Where do immature B cells mature and and activate?
lymph node
B cell and T cell interact where in the lymph node
paracortex
Somatic hypermutation leads to changes in
BCR affinities
What is the advantage of somatic hypermutation?
increase antibody affinity due to selective survival of B cell expressing higher affinity
B cells ALL start out as ….. expressers but after actviation are stimulated to make…..,…..,or……
start out IgM
later activation
IgG or IgA or IgE
What’s the point in having isotope switching and somatic hypermutation?
1) somatic hypermutation is for variability in the ANTIGEN BINDING REGIONS of the immunoglobulin
the higher affinity of the antibody the higher likely hood the higher the chance that the B cell will outcompete other lower affinity B cells to T cell to survivie
2) isotope switching is in the constant region, and whatever region comes after the variable region, the immunoglobulin is named after that
by default without isotope switiching all antibodies will be IgM
All of this is the increase the DIVERSITY
may antigen needs G constant region and a subclass of G by hypermutatin the antigen binding regions of IgG
once the B cell has figured which isotype and subtype it will secrete more
