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 μL 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 μL of blood in both the CD4⁺ CD45RA⁺ CD95⁺ and CD95⁺ 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.