Class I major histocompatibility complex antigen expression on early murine trophoblast and its induction by lymphokines in vitro. II. The role of gamma interferon in the responses of primary and secondary giant cells.

The induction of paternal Class I and II MHC antigens by crude lymphokine preparations or purified recombinant gamma interferon was investigated on (C57BL/6J X CBA/H)F1 primary and secondary trophoblast giant cell outgrowths from 3.5-day post-coital (pc) blastocyst and 7.5-day pc ectoplacental cone preparations, respectively, using sensitive immunogold labelling techniques and electron microscopy. Class I MHC (but not Class II) antigens could readily be induced on secondary trophoblast giant cells, by incubation in vitro with gamma interferon for 40 h. However, repeated attempts to induce detectable MHC antigens on primary trophoblast giant cells failed. Mock-treated (C57BL/6J X CBA/H)F1 secondary trophoblast giant cell control preparations failed to express detectable MHC antigens. These findings suggest that, at the time of implantation, there is a time window during which MHC antigens are neither expressed constitutively nor are inducible by soluble factors which normally modulate cell surface MHC antigen concentration.