Expression of embryonic and MHC antigens in heterokaryons of murine embryonal carcinoma and human melanoma cells

Abstract

Mouse embryonal carcinoma cells were fused with human melanoma cells or with cytoplasts of these cells. The expression of embryonic and major histocompatibility complex (MHC) antigens was studied in single heterokaryons and cybrids in the population after fusion. Recognition of heterokaryons by differential staining of mouse and human nuclei was combined with indirect immunofluorescent staining of specific membrane antigens. Complete suppression of embryonic antigen expression was found in heterokaryons within 2 days after fusion. Cybrids, formed by fusion of embryonal carcinoma cells with melanoma cytoplasts, showed a transient decrease in the expression of embryonic antigens. The expression of human MHC antigens, both class I (HLA-A, B, C) and class II (HLA-DR), was only slightly influenced in heterokaryons. No activation of mouse MHC antigens was found. The results indicate that melanoma cells contain trans-acting factors exerting a negative control on the expression of embryonic antigens. In contrast the continued expression of human MHC antigens in heterokaryons suggests that embryonal carcinoma cells either are devoid of or contain only a very limited amount of trans-acting factors controlling the expression of MHC antigens.