Age-related changes in the absolute number of CD95 positive cells in T cell subsets in the blood

Comparison of the absolute number of cells in distinct T cells subsets expressing CD95 (Fas) was carried out in two populations of healthy female volunteers. In one population, the average age was 30 +/- 5 years, and in the second population the average age was 73 +/- 13 years, No significant difference was noted in the total number of lymphocytes, CD3(+), CD4(+). or CD8(+) cells per mu L of blood between the two age groups, but major differences were noted in the number of cells expressing CD95. A significant reduction was seen in the number of cells per mu L of blood in both the CD4(+) CD45RA(+) CD95(+) and CD8+ CD45RA(+) CD95(+) populations in the older group compared with the younger group. Within the memory pool significantly fewer CD8(+) CD45RO(+) CD95(+) cells were found in the older population compared with the younger group. No such difference were found in the number of CD4(+) CD45RO(+) CD95(+) cells between groups. Such a significant decline in the number of CD95(+) cells, whose expression is known to be linked with activation, may be implicated as a mechanism by which cells that have reached a stage of replicative senescence remain in the peripheral T cell pool. Anti-CD3-mediated activation of cells from both groups revealed much lower proliferative responses from the older group, supporting the idea that there is an age-associated increase in the number of cells that have reached their replicative limit. These cells may not be lost from the peripheral pool because they fail to express CD95. (C) 1998 Elsevier Science Inc.