Memory lymphocyte

a specific type of B or T lymphocyte (T or B cell) that can recognize foreign pathogens, such as bacteria or viruses, detected during a primary infection or vaccination

Description
Upon secondary infection (or a vaccination boost), memory lymphocytes can reproduce to mount a faster and stronger immune response. This behaviour is also utilized in lymphocyte proliferation assays, which can reveal exposure to specific antigens. Recognition of an antigen relies on interaction of a small exposed part of the antigen, the epitope, with its T-cell counterpart, the paratope. Upon proliferation during secondary encounter, high-level spontaneous mutation of the lymphocyte paratope (at a rate of 1:1600 as opposed to 1:106 for normal mitotic processes) leads to a further optimisation of epitope-paratope binding, with positive selection of optimised interactors. There are distinct sub-populations of T and B memory lymphocytes, with e.g. central memory T cells showing properties distinct from those of other memory T cell sub-populations, and with the possibility of memory-cell formation not from the naive state, but also by low-frequency conversion of effector cells.