CD4⁺ CD8⁺ T cells in young and elderly humans. Comment on Macchia I, Gauduin MC, Kaur A, Johnson RP. Expression of CD8α identifies a distinct subset of effector memory CD4⁺ T lymphocytes. Immunology 2006; 119:232–42

Peripheral CD4+ CD8+ T cells have been described in animals as well as in humans. Two distinct populations can be distinguished, namely CD4lo CD8hi and CD4hi CD8lo T cells. We demonstrate here that the increase in the number of peripheral CD4+ CD8+ T cells in the elderly is the result of an increase of the CD4lo CD8hi T-cell population. While the phenotype of CD4lo CD8hi and CD4hi CD8lo T cells was very similar in young persons, CD4hi CD8lo, T cells from elderly subjects expressed a more differentiated phenotype and produced less interleukin-2 compared to CD4lo CD8hi T cells. In conclusion, our results suggest that aging leads to a phenotypic and functional difference between CD4+ CD8+ T-cell subsets. It may therefore be of relevance to distinguish between these subsets before assessing their functional significance in elderly humans. [ABSTRACT FROM AUTHOR]