Intrinsic and environmental influences on immune senescence in the aged monkey

Several factors associated with the age-related decline in immunity were ex amined in three studies on aged rhesus monkeys. Natural killer (NK) cell ac tivity was found to be low in many monkeys after 20 years of age, but excep tionally long-lived animals, older than 25 years, often had vigorous cytoly tic responses. When NK activity was decreased in an aged monkey, it was pre dictive of fewer years of survival and a younger age at death, This predict ion of mortality was associated with one nonimmune biomarker of aging in th e monkey: nail growth rate. Monkeys with very slow nail growth and low NK a ctivity were likely to die sooner. Although these: findings might suggest a n immutable course for the aging process, the housing conditions of old mon keys also had a pronounced effect on their NK activity. The highest NK resp onses were: Found in old monkeys housed with just one other old animal when compared to living alone or with just a young, juvenile monkey. It remains to be determined whether this type of psychosocial influence could have a sustained effect on immunity and ultimately change the pace of aging and ti me to mortality. (C) 2001 Elsevier Science Inc. All rights reserved.