Effect of neonatal milk-prolactin deprivation on the ontogeny of the immune system of the rat.

A growing body of evidence suggests that prolactin (PRL) is involved in regulation of the immune system in the adult. PRL provided to the neonate in mother's milk also has been shown to be important in development of the neonatal neuroendocrine regulation of PRL secretion. Therefore, in this study we asked if deprivation of the neonate of milk-PRL on days 2-5 postpartum affected the ontogeny of the immune system. Two aspects, DNA synthesis (3H-thymidine incorporation) of neonatal lymphocytes in response to polyclonal mitogens in vitro and expression of lymphoid cell surface antigens, were examined. Splenocytes and thymocytes from neonates ranging in age from 5 to 28 days were taken from mothers treated with bromocriptine or saline on days 2-5 of lactation. Splenocytes from pups of vehicle-treated mothers showed a gradual increase in surface antigen expression by day 5 to 28. Thymocyte patterns and percentages of these surface proteins were at adult levels at the earliest times tested. Thymocytes from day 5 and 10 neonates were more responsive to Con A than were splenocytes, but both thymocytes and splenocytes showed an increase in mitogenic responsiveness until day 18, a sharp decline at day 21, and an increase again at day 28. The fact that day 21 is the time of intestinal closure (cessation of absorption of macromolecules from the gut) suggested that milk-borne material plays a role in immune cell maturation.(ABSTRACT TRUNCATED AT 250 WORDS)