Aging and immunity in non-human primates. II. Lymphocyte response in thymosin treated middle-aged monkeys.

Thymic hormone production declines with age, and recent strategies for enhancing immune function in elderly people include the administration of various thymic preparations. In an effort to develop an animal model for such therapeutic intervention, the current study was undertaken. Fourteen female rhesus monkeys (Macaca mulatta), aged 18-25 years, received a 7-day course of either Thymosin Alpha One (TA1) or placebo, and in vitro and in vivo immunologic analyses were performed. The relative percentage of T-cells and T-cell subsets declined during treatment in both TA1 and placebo groups. Nevertheless, mitogen-induced proliferation and NK-cell function were increased in most monkeys that received TA1, a trend that was apparent but not statistically significant. The antibody response to tetanus toxoid vaccine was not greater in the TA1 treatment group when compared to the placebo group. These findings suggest that TA1 can be safely administered to old monkeys and that such treatment, if undertaken in a larger or more sustained trial, may be associated with demonstrable biologic activity. Further studies are warranted to determine the potential for this or similar agents to reduce the consequences of age-associated immune deficiency.