Immunogenicity of mouse trophoblast and embryonic sac

Abstract

ALTHOUGH it is generally accepted that the survival of the mammalian embryo as an intrauterine allograft can in part be attributed to the antigenic neutrality of the trophoblastic barrier of the placenta, the way in which this is achieved is unknown. It has been proposed that the trophoblast may either have an intrinsic deficit of transplantation antigens¹ or that these are present but masked in some way, possibly by a mucosubstance on the cell surface². Apparently convincing evidence for this latter hypothesis came from experiments by Currie et al.³ who reported that incubation with the enzyme neuraminidase rendered mouse trophoblast immunogenic on injection into recipient mice. As neuraminidase cleaves terminal ‘sialic’ (n-acetyl neuraminic) acid from underlying amino sugars⁴, it was suggested that antigens were masked by sialomucin on the trophoblast surface. These findings have, however, been disputed⁵ and the issue is unresolved. We now report the results of a collaborative study, using two different experimental approaches, which demonstrates that mouse trophoblast, at least at the early proliferative stage, does not possess any detectable quantity of immunogen masked by a neuraminidase-sensitive cell coat. In contrast, embryonic tissue from the same conceptus is highly immunogenic in similar test situations.