The expression of major histocompatibility complex antigens by trophoblast in ectopic tubal pregnancy.

The reactivity of the various trophoblast populations found in ectopic fallopian tube pregnancy with established trophoblast-reactive markers and monoclonal antibodies to MHC antigens has been studied. In ectopic tubal pregnancy fetal trophoblast shows an identical reaction pattern with these antibodies to that seen in intrauterine pregnancy, suggesting that ectopic implantation is not related to an inherent immunological abnormality of fetal trophoblast. However, from this and other studies, it appears that extravillous trophoblast displays an unusual class I MHC antigenic structure. This observation may explain the ability of class I MHC--bearing fetal trophoblast--to survive both in the uterus and at an abnormal implantation site.