Naive T cells are maintained by thymic output in early ages but by proliferation without phenotypic change after age twenty

Abstract

Analysing T-cell receptor excision circle numbers in healthy individuals we find a marked change in the source of naive T cells before and after 20 years of age. The bulk of the naive T cell pool is sustained primarily from thymic output for individuals younger than 20 years of age whereas proliferation within the naive phenotype is dominant for older individuals. Over 90% of phenotypically naive T cells in middle age are not of direct thymic origin. Moreover, this change in source of naive T cells is accompanied either by an increased death rate of T cells from the thymus or reduced thymic export. Modelling of these processes shows that new naive T cells of a thymic origin have a half-life ..