Lymphocyte traffic in pregnant or oestrogen stimulated rats

Lymphocyte migration was studied at three stages of rat pregnancy by the tracer sample principle of injecting syngeneic thoracic duct lymphocytes labelled with chromium-51 (for organ counting) or [3H]leucine (for autoradiography). Except for one abnormal embryo no entry of lymphocytes into the foetus was detected. There was a small localization of lymphocytes in the placenta which did not differ significantly between allogeneic or syngeneic mating. Pregnancy produced little or no alteration of lymphocyte traffic into the spleen or lymph nodes, including those draining the uterus. The administration of oestrogens to virgin rats increased the height of the specialized endothelium lining the post-capillary venules in the mesenteric lymph nodes but had no effect on lymphocyte traffic.