LIFE-SPAN OF NAIVE AND MEMORY T-CELLS

The life span of mature T cells is reviewed. Peripheral T lymphocytes are a heterogeneous population and comprise a mixture of naive, effector and memory cells, The recirculating pool of mature T cells is formed during young life through gradual release of naive T cells from the thymus, In adults, the pool of mature T cells is relatively self-sufficient, and input of new T cells from the thymus declines to low levels, Studies on T cell turnover indicate that most peripheral T cells can remain in a resting state for long periods (months in rodents and years in humans), Examination of the phenotype of dividing versus nondividing cells suggests that typical naive T cells are long-lived resting cells whereas the majority of effector and memory T cells have a much more rapid turnover, However, some memory T cells appear to divide very infrequently and eventually return to a resting state, The factors controlling the generation and maintenance of memory T cells are discussed.