Ovarian hormones, antiestrogen and pregnancy effects on the expression of class II histocompatibility antigens by N-nitroso-N-methylurea-induced rat mammary carcinomas.

Hormonal modulation of Class II histocompatibility antigen expression was studied in female Sprague-Dawley rats with N-nitroso-N-methylurea-induced mammary tumors. The effects of ovarian hormones, pregnancy and lactation were examined when cancers appeared. At this time, rats with tumors were divided into several groups. Different groups received respectively 17 beta-estradiol alone, 17 beta-estradiol in association with progesterone, and tamoxifen alone. Other groups were selected to undergo pregnancy. The control group received carcinogenic treatment only. For all removed tumors, Class II histocompatibility antigens were radiolabeled, specifically immunoprecipitated with monoclonal antibody and quantified by chromatofocusing. The amount of Class II histocompatibility antigens measured in NMU-induced rat mammary tumors without any hormonal treatment decreased significantly after treatment with estrogen alone or in association with antiestrogen and during the pregnancy. Nevertheless, Class II histocompatibility antigen expression was not changed in mammary carcinoma from rats receiving progesterone, but increased significantly during the lactation. These results demonstrated clearly that ovarian hormones change the Class II histocompatibility antigen expression of NMU-induced mammary tumors in female Sprague-Dawley rats.