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 f emale volunteers. In one population, the average age was 30 +/- 5 year s, and in the second population the average age was 73 +/- 13 years, N o 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 expre ssing CD95. A significant reduction was seen in the number of cells pe r mu L of blood in both the CD4(+) CD45RA(+) CD95(+) and CD8+ CD45RA() CD95(+) populations in the older group compared with the younger gro up. Within the memory pool significantly fewer CD8(+) CD45RO(+) CD95() cells were found in the older population compared with the younger g roup. 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 activat ion, may be implicated as a mechanism by which cells that have reached a stage of replicative senescence remain in the peripheral T cell poo l. Anti-CD3-mediated activation of cells from both groups revealed muc h lower proliferative responses from the older group, supporting the i dea that there is an age-associated increase in the number of cells th at have reached their replicative limit. These cells may not be lost f rom the peripheral pool because they fail to express CD95. (C) 1998 El sevier Science Inc.