Human chorionic gonadotropin: effects of crude and purified preparations on lymphocyte responses to phytohemagglutinin and allogenenic stimulation.

The factors that prevent maternal immunologic rejection of the histoincompatible fetus are not understood. High levels of human chorionic gonadotropin (HCG) are present in the placenta, and several reports have noted suppresion of mitogen-induced lymphocyte transformation when cultures were supplemented with crude preparations of HCG. Purified HCG and multiple lots of crude HCG obtained from different suppliers were examined for their ability to suppress lymphocyte transformation produced by phytohemallutinin (PHA) or allogeneic stimulation. Crude preparations of HCG produced suppression of the lymphocyte stimulation induced by low doses of PHA, but the suppression could be overcome completely by increasing the PHA dose. The purified preparations of HCG produced no suppression of lymphocyte responses, even at the lower PHA dose. Purified HCG did not give a dose-related suppression of allogeneic lymphocyte responses, and crude lots of HCG gave highly variable results. One lot of crude HCG produced spontaneous stimulation of lymphocytes. Isoelectric focusing of HCG preparations demonstrated multiple bands, and lymphocyte suppression may be secondary to these additional unidentified proteins. The failure of pruified HCG to suppress lymphocyte responses makes it unlikely that the absence of maternal rejection of the fetus is due to high placental levels of HCG.