Immunological studies of aging. IX. Quantitative differences in T lymphocyte subsets in young and old individuals.

The enumeration and distribution of T-cell subsets in peripheral blood from young and old humans was studied. The percentage and absolute number of OKT3-reactive lymphocytes was comparable in healthy elderly individuals (65-84 years old) and young individuals (19-31 years old). The number of OKT4-reactive T lymphocytes from peripheral blood was significantly greater in the older group while the number of OKT8-reactive T lymphocytes was significantly lower. The OKT4/OKT8 ratio was significantly greater in old compared to young subjects. The change in the OKT4/OKT8 ratio did not correlate, in either young or old, with the proliferative response of lymphocytes induced by phytohemagglutinin (PHA) or concanavalin A (Con A). Although lymphocytes that form rosettes with autologous erythrocytes, a marker of early T lymphocyte lineage, are increased in old subjects, other markers of early T lineage were found to be absent (OKT6), showed no difference (OKT10), or were comparable in young and old subjects.