Antigen expression on early mouse trophoblast

Abstract

THE mammalian foetus inherits paternal as well as maternal genes and can be considered to constitute a naturally occurring and highly successful allograft¹. It has been suggested that an important factor in the survival of the foetus in an immunocompetent histoincompatible mother might be the presence of an antigenically deficient barrier of foetal trophoblast cells^2–4. Cell surface antigens determined by minor (non-H–2) histocompatibility loci have been demonstrated on cleavage stage mouse embryos⁵, and subsequently major (H–2) as well as non-H–2 determinants have been detected on the trophectoderm of pre-implantation mouse blastocysts^6,7. The expression of these antigens, however, is considerably reduced, below detectable levels in the case of H–2, on blastocytes which have been activated for implantation from a state of experimentally induced delay^6,7. In addition, immunofluorescence⁸, immunoperoxidase⁷ and mixed haemadsorption (MHA)⁹ studies have failed to demonstrate histocompatibility antigens on the trophoblast component of blastocysts cultured as outgrowths in vitro. In contrast to all these findings, however, a recent report has claimed to demonstrate both maternally and paternally inherited antigens on blastocyst outgrowths by means of an MHA technique¹⁰. We have now confirmed this report and reconciled the apparently contradictory results by investigation of the identity of the antigens expressed by the trophoblast at this early stage of its differentiation in four mouse inbred strains.