Early rearing conditions alter immune responses in the developing infant primate.

The influence of early rearing conditions on immunologic development was investigated in infant monkeys. Lymphocyte proliferation, natural killer cell activity, and antibody responses to tetanus vaccination were compared in 30 rhesus monkeys reared under five different conditions. Lymphocyte responses to two mitogens (concanavalin A and pokeweed) were significantly increased in infants from disturbed rearing conditions compared with control infants that had been reared in an undisturbed manner by their mothers. The largest increases occurred in nursery-reared monkeys that had been fed Similac infant formula. The nursery-reared monkeys also tended to show lower natural killer cell activity, but there were no significant differences in response to vaccination. These findings support other research indicating that psychologic and nutritional aspects of the early rearing environment may have long-lasting effects on some, but not all, immune responses in the developing infant.