Psychosocial factors and immune senescence in the aged primate.

With increasing age, old animals and humans show decreases in a number of immune responses indicative of the process of immune senescence. Our studies investigated whether social companionship, as a potentially positive psychological intervention, would increase lymphocyte proliferation and natural killer cell activity in the aged nonhuman primate. Contrary to our initial hypothesis, social stimulation resulted in decreased immune responses in old monkeys. With specific modifications of the housing conditions it was possible to prevent these decreases in immune responses from occurring, but social companionship still failed to enhance immune responses in the aged monkey.