Human chorionic gonadotropin. Its inhibitory effect on cell-mediated immunity in vivo and in vitro

An inhibitory effect of human chorionic gonadotropin (HCG) on delayed hypersensitivity skin test responses in guinea-pigs given 4000 i.u. of HCG intraperitoneally, 1--7 days prior to skin testing, is presented. The effect of HCG on skin test responses lasted for at least 3 weeks. Inhibition of lymphocyte response to PHA or PPD in the HCG-treated guinea-pigs was also observed. Guinea-pig peripheral blood lymphocyte response to mitogen or antigen is unequivocally inhibited by HCG in vitro. The effect of this hormone is not due to direct cytotoxicity, and its inhibitory effect seems to be dose related. These observations support the hypothesis that the HCG and possibly other placental hormones might play an important role in protecting the foetus against maternal rejection.