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, effect or and memory cells, The recirculating pool of mature T cells is forme d during young life through gradual release of naive T cells from the thymus, In adults, the pool of mature T cells is relatively self-suffi cient, 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 yea rs in humans), Examination of the phenotype of dividing versus nondivi ding 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 ver y infrequently and eventually return to a resting state, The factors c ontrolling the generation and maintenance of memory T cells are discus sed.