An analysis of T lymphocyte subpopulations in patients with Alzheimer's disease.

The relative proportions of regulatory T lymphocyte subpopulations and T lymphocyte proliferative responses to the mitogen phytohemagglutinin (PHA) were studied in 30 patients with clinically apparent Alzheimer's disease (mean age = 71.5). Comparisons were made with 30 age-matched, nondemented healthy controls (mean age = 68.8) and with 20 younger, normal adult controls (mean age = 27.5). The relative percentages of total peripheral T lymphocytes, T helper/inducer lymphocytes (Th), and T suppressor/cytotoxic lymphocytes (Ts) were similar between the Alzheimer patient group and the age-matched controls. However, when the two older groups were compared with the young adult controls, a significant decrease was seen in the percentage of Ts cells, with a concomitant increase in the ratio of Th:Ts. Lymphocyte proliferative responses to PHA were similar in the Alzheimer patients and their age-matched controls; however, when compared with the young adult controls, a significant decrease in responsiveness for both older groups was observed. These results confirm decreases in certain immune indices with aging, but suggest that there are no changes in T lymphocyte subsets or in lymphocyte proliferation, which are unique to Alzheimer's disease.