EMBRYONIC EXPRESSION OF MHC CLASS-I HEAVY AND LIGHT-CHAINS IN TRANSGENIC MICE

Class I membrane glycoproteins encoded by major histocompatibility com plex (MHC) genes are not expressed during early stages of development. This regulation is thought to play an important role in maternal tole rance of the fetal allograft. To elucidate the significance of develop mental regulation of MHC class I genes, we produced transgenic mice ex pressing transgenes encoding the class I L(d) heavy chain or the light chain, beta(2)-microglobulin, in the developing mouse embryo. These t ransgenes were driven by the chiken beta-actin promoter, which is very active in the developing mouse embryo. The heavy chain and light chai n transgenic mice were mated, and the resultant double transgenic offs pring expressed L(d) antigen in all the tissues examined by immunostai ning and Northern blot analysis. The L(d) antigen was also detected by immunostaining in the placenta of the double transgenic fetus. The do uble transgenic fetus was not rejected by the immunocompetent nontrans genic mother. These results suggest that expression of MHC class I ant igens in embryos is not sufficient to provoke a maternal immune respon se.