Limited fluctuations in T lymphocyte parameters in the human as a marker of aging

Analysis of T lymphocytes was performed on SENIEUR protocol selected young and old individuals. Parameters examined were phenotype and reactivity to phytohemmagglutinin (PHA) measured under standard and limiting dilution conditions. Blood samples were drawn twice, at an interval of one month, to establish the stability of values measured. The results showed no statistically significant difference as in proportion of CD4⁺ and CD8⁺ cells between the young and old peripheral blood samples. Standard proliferative responses to PHA were reduced in the old. Limiting dilution analyses revealed a reproducible, pronounced decrease in the frequency of precursors of PHA-reactive T lymphocytes in the old. Twice repeated determinations showed fluctuations in the above parameters in the young, whereas in the old the values were lower and less fluctuating. This observation was not associated with any change in the clinical status of the elderly subjects during the one-year follow up period.