Lifespans of naive, memory and effector lymphocytes.

Typical T and B lymphocytes in the secondary lymphoid organs are long-lived cells that are selected from a large pool of short-lived precursor cells in the primary lymphoid organs. The bulk of mature T and B cells are immunologically naive and remain in interphase for prolonged periods. Contact with specific antigen causes these naive cells to proliferate rapidly and differentiate into a mixture of short-lived effector cells and long-lived memory cells. Memory cells have a rapid turnover, and the survival of these cells appears to require persistent contact with antigen.