B cell activation When antigens enter tissues B cells are called
into the infected region. There the B cell interacts with the antigen. B cells specific
for the antigen will use their B cell receptors the BCR to bind to the antigen.
Once bound to the antigen the B cell internalizes the BCR with antigen and enzymes within the
B cell degrade the antigen down. The B cell then loads the piece of antigen onto an MHC
Class II molecule for presentation. Now the B cell is ready for full activation.
This requires the help of a helper T cell. The helper T cell will bind to the B Cell
if it recognizes both the MHC and piece of antigen.
AS you see here the T cell uses its CD4 marker to recognize the MHC on the B cell. The T cell
uses its TCR, the antigen receptor, to recognize the piece of antigen being presented.
Once the T cell binds to the B cell it will release interleukins which will activate the
B cell to proliferate. The B cell will then produce Memory Cells
and Plasma Cells.
Memory cells will go back to the secondary lymphoid tissue for future infections.
The Plasma cells will actively secrete antibody, These antibodies are used to help clear the
pathogen. Antibodies do this by binding to the antigen and tagging it for opsonization
by phagocytes, neutralizing it from binding to target tissue, and in some cases it will
cause the antigen to agglutinate and finally some antibodies will activate the classical
path of complement.