B cell selection, activation and functions | Cellular Components| Immunology|First Aid Lectures|Lec9
Channel: Dr. Jamil Lectures
Date: 2022-03-27

In this lecture we will discuss about Colonal selection of B cells, their activation via t cell dependent activation and t cell independent activation,and major functionds of B cells,Humoral immunity.Positive and Negative selection of b cells.


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Colonal Selection of B cells
There are two steps by which B cells are selected in bone marrow;
1-Positive selection 
Pre B cells lack surface BCR, if pre B Cells rearrangre its gene and generate functional BCR these are allowed to survive and selected otherwise undergo apoptosis
2-Negative Sel;ection
At this stage IgM BCR of B cells are encountered to self antigen,if B cells strongly bind to self antigen then before apoptosis they are been given one chance to escape this problem via receptor editing.but still autoreactive  B cells undergo apoptosis or become anergic B cells.And B cells that dont show reaction against self antigren they are  been succesfully negatively selected
B cell activation
Bells are activated by 2 process;
1-T cell dependent activation
MHC 2 from B cells binds with TCR on Th2 and Th2 secretes CD4 for confiormation 0f antigen processing.
then as a second signal CD40L from Th2 and CD40R from B cells interact and activated Th2 secretes IL4 and IL5 that activates the B cells and cuases its class switching from IgM to other types of Ig.
2 -T cell Inependent activation
1st signal multivalent antigen cross links with IgM BCR on B cells.
then as a second signal B cells recognize PAMPS via TLRs,b cells have complement receptors CR2 that recognize opsonization by C3b binding with antigen,Vaccine adjuvant also acts as second signal
Major functions of B cells
Humoral Immunity
B cells recognize antigen and undergo hypermutation to optimize the antigen specificity and produce antibodies by plasma cells.these immunologlobulins kills the pathogen.some B cells remain as memory B cells as well to accelerate future response to antigen

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