Individual changes in T lymphocyte parameters of old human subjects

Parameters of peripheral blood T lymphocytes were determined repeatedly (twice, 2-4 weeks apart), in ten old (78 + 5) and compared to nine young (31 + 5) human subjects. Assays included percentage of total, helper, and suppressor, T lymphocytes, and the reaction to PHA stimulation for 24, 48, 72, and 96 h, as assessed by levels of proliferation and IL-2 production. A lower response to PHA was observed in the old as compared to the young, with no significant changes in T cell subsets. A marked variability was noted between the results of the first and second determinations of the response to PHA in each individual. The lack of correlation between the two determinations was more prominent in the old. Unresponsiveness to PHA throughout the incubation period, was noted in two old subjects, but, in only one of the two determinations. This transient unresponsiveness was not accompanied by any changes in their clinical state. Thus, establishments of the immune status of the aged should be based on at least two repeated determinations.