Expression of H-2K major histocompatibility antigens on preimplantation mouse embryos

Genes in the major histocompatibility complex (MHC) have been shown to play a role in development and reproduction. In the mouse, class I MHC proteins are expressed on oocytes and preimplantation embryos. Each mouse strain contains multiple class I genes located in the classical regions, K and D, and the nonclassical regions, Q and TL, of the mouse MHC, the H-2 complex. This study was undertaken to evaluate the expression of the classical class I MHC antigen, H-2K, on preimplantation mouse embryos. Through use of appropriate monoclonal antibodies (mAb) and an ELISA procedure, it was shown that H-2K antigens are detectable on oocytes and blastocyst-stage embryos, but not on 2-cell or 8-cell embryos. This pattern of expression is different from that reported in previous studies showing expression of total class I antigens and the nonclassical MHC antigen, Qa-2, on all stages of preimplantation embryos, including 2-cell- and 8-cell-stage embryos. To analyze the nature of the H-2K protein on blastocysts, H-2K antigens were isolated from an H-2K overproducing cell line (RDM-4) and used in blocking experiments. It was found that the purified antigen blocked binding to tissue culture cells by 54% and to embryos by 68%. Therefore, H-2K antigens on tissue culture cells and embryos appear to be very similar, but perhaps not identical. Thus escape of embryos from surveillance by the maternal immune system may not be effected by the expression of a different or embryonic form of MHC antigens.