Age-related changes in human T cells throughout a person's lifespan have been observed only in analyses of blood; however, such studies capture only a tiny proportion of the overall T cell population and repertoire. In Science Immunology, Farber and colleagues study T cells in primary and secondary lymphoid tissue from organ donors of a wide age range. Thymopoiesis does not diminish gradually, as expected; instead, it seems to be generally stable until around 40 years of age, at which time it undergoes a precipitous decrease. Naive T cells (which are essential for responses to antigens not previously encountered) are most numerous in the young yet still persist even in the elderly and maintain naive functionality, as assessed by production of interleukin 2. Naive T cells occupy lymphoid tissues at varying frequencies and with largely distinct non-overlapping repertoires of T cell antigen receptors. Collectively, these findings indicate that throughout life, secondary lymphoid organs serve as important reservoirs of functional naive T cells.

Sci. Immunol. (2 December 2016) http://dx.doi.org/10.1126/sciimmunol.aah6506