Evidence for the release of a prolactin-like substance by mouse lymphocytes and macrophages

The influence of co-cultures of irradiated mouse thymocytes, splenocytes, and mesenteric lymph node cells on the proliferation of Nb2 cells in synthetic medium were studied. Irradiated thymocytes with or without the addition of ovine prolactin (oPRL) decreased the incorporation of 3H-thymidine into Nb2 cells. Irradiated splenocytes and lymph node cells when co-cultured with Nb2 cells and stimulated with concanavalin A (Con-A) induced Nb2 cell proliferation. Lipopolysaccharide stimulation of irradiated splenocytes and lymph node cells, however, did not alter Nb2 cell proliferation. Isolated thioglycolate-induced peritoneal macrophages stimulated Nb2 cells to incorporate 3H-thymidine while IFN-gamma-stimulated macrophages decreased PRL-induced Nb2 cell proliferation when isolated 48 but not 24 hr before co-culture. The addition of a mouse PRL antiserum to macrophage/Nb2 cell co-cultures did not alter the proliferative activity induced by macrophages. The preliminary data presented indicate that Con-A-stimulated, irradiated splenocytes and lymph node cells, and isolated peritoneal macrophages secrete a PRL-like activity. The PRL-like activity of macrophages, however, does not appear to be of mouse origin, and it is suggested that macrophages, which have surface PRL receptors, sequestered PRL from the fetal calf serum in the medium used to isolate them and release this PRL when co-cultured.