After their maturation, lymphocytes migrate from the primary lymphoid organs to the secondary lymphoid organs and tissues. Once in the secondary tissues the lymphocytes do not simply remain there; many move from one lymphoid organ to another via the blood and lymph. This process allows a large number of antigen-specific lymphocytes to come in contact with their appropriate antigen in the microenvironment of the peripheral lymphoid organs and this is important since lymphocytes are monospecific and only a limited number of cells are able to recognize and interact with a particular antigen. When B cells are activated by antigen, with the help from the T cells, they mature either into AFCs (Antibody-Forming Cells), or they develop into memory cells. The germinal centers in various lymphoid tissues represent the sites of the immune response development and memory B cells generation. At these sites, the B cells undergo active hypermutation of the variable genes, a process that can lead to death by apoptosis for some cells.