The expression of forms of prolactin receptors in splenocytes and thymocytes of neonatal rats: the effect of milk ingestion.

Because prolactin (PRL) plays a role in neonatal immune development, we examined the expression of prolactin receptors (PRL-R) in neonatal lymphoid tissues. We had shown previously that deprivation of milk-borne PRL, days 2-5 in the neonatal rat, leads to enhanced in vitro mitogenesis of thymocytes and splenocytes as well as a change in lymphoid-specific, cell surface antigens (GROVE et al. 1991). In this present study, we asked if neonatal lymphocytes express PRL-R; which forms of PRL-R are expressed (long vs. short form); when these forms are expressed during development; and if milk ingestion plays a role in receptor expression. Two approaches were taken using neonatal rat thymocytes and splenocytes: RNA was analyzed by polymerase chain reaction (PCR) and cells were stained with antibody to PRL-R and analyzed by flow cytometry. In regard to cell surface expression, the percentage of PRL-R positive splenocytes was greater than thymocytes at all ages tested. In the spleen, the percentage of PRL-R positive cells gradually increased to adult levels by day 10; in the thymus the percentage fell to adult levels by the first day after birth. Finally, milk ingestion in the first 7 h decreased the percentage of cells expressing cell surface PRL-R. Tissues from animals deprived of milk during this time expressed PRL-R at the same level as the newborn.