Mitogenic effect of naturally occurring elevated plasma prolactin on ring dove lymphocytes

3H-thymidine incorporation into isolated ring dove lymphocytes in vitro was used as a measure of lymphocyte proliferation. Lymphocytes taken from doves with increased plasma concentrations of prolactin demonstrated significantly increased 3H-thymidine incorporation. In vitro incubation with mitogens significantly increased incorporation of 3H-thymidine into lymphocytes from non-breeding doves. However, similar treatment of lymphocytes taken from doves which had elevated levels of plasma prolactin failed to induce any further increase in the stimulation index. Antigen caused a significant increase in 3H-thymidine incorporation in non-breeding doves. Antigen administration also led to the production of specific antibodies. The titre of specific anti-human red blood cell (HRBC) agglutinins was greatest in those birds which also had elevated levels of plasma prolactin, reaching significance in the group of incubating doves with naturally occurring increased concentrations of plasma prolactin. The results presented here may be relevant to our understanding of the role of hormones such as prolactin on lymphocyte activation.