Differential expression of human leukocyte antigen-A, -B, and -C locus specific genes in trophoblast and embryonic cells.

Research on the escape mechanism of the fetoplacental unit has focused on the placental trophoblast, which is though to play an important role in the survival of the fetus. There are two major findings in the present study: (a) The expression of human leukocyte antigen (HLA)-A, -B, and -C locus specific genes is greatly reduced in trophoblast cells compared to embryonic cells by Northern blot analysis using locus specific oligonucleotide probes. This is true even though the transcripts detected by a complementary DNA probe, which contains a very conserved sequence present in all members of the HLA gene family, are equally abundant in trophoblast and embryonic cells. (b) When trophoblast cells or embryonic cells are cocultured with peripheral blood lymphocytes from the corresponding female in the presence of recombinant interleukin 2, allogeneic cytotoxic T lymphocytes are generated only in cultures with embryonic cells, and trophoblast cells express the resistance to lysis by the allogeneic cytotoxic T lymphocytes. These results strongly suggest that the reduction in expression of transplantation antigens (HLA-A, -B, and -C) might address the question why maternal tissue does not reject trophoblast cells.