Migration of radiolabeled, adoptively transferred T-lymphocytes into the mammary gland and milk of lactating rats

The maternal component in the transfer of cellular immunity from the mother to the neonate during lactation was investigated by analyzing the migration of adoptively transferred T-lymphocytes to the mammary gland and into the milk of lactating rats. A T-enriched cell population, containing less than 2.5% of contaminating B-cells, was obtained from mesenteric and peripheral lymph node cells of donor rats by removing B-cells with a panning technique. The T-enriched cells, radiolabeled with [³H]uridine, were injected intravenously into syngeneic lactating females, between 1 and 4 days post-partum. Samples of mesenteric and cervical lymph nodes, spleen, Peyer's patches, small intestine, and mammary gland taken at 48 h and milk obtained at 24 and 48 h were processed for scintillation counting and autoradiography. A large portion of the injected T-cells migrated to T-dependent lymphoid areas (the paracortical and medullary regions of the mesenteric and cervical lymph nodes and the Peyer's patches) and a substantial number also migrated into the small intestine and mammary gland, although the frequency of cells per high-power field was lower than in the lymph nodes. However, total counts of activity recovered were significantly higher in the small intestine and mammary gland than in either the mesenteric or cervical groups of lymph nodes. The distribution of the T-cells within the mammary gland showed a relative predominance of labeled cells in the connective tissue adjacent to the alveolar secretory cells, with a small percentage of cells present within the mammary epithelium. The direct transfer of T-cells through the alveolar epithelium was demonstrated by the presence of labeled cells in milk. These results substantiate that a significant number of T-lymphocytes migrate not only to the mammary gland during lactation but also into milk. These cells may play a passive regulatory or inductive role within the mammary gland or an active role in the maternal-to-neonatal transfer of immunity.