ABUNDANCE OF AN ENDOGENOUS RETROVIRAL ENVELOPE PROTEIN IN PLACENTAL TROPHOBLASTS SUGGESTS A BIOLOGICAL FUNCTION

To investigate the hypothesis that the human endogenous sequence ERV-3 has a function, we have cloned and expressed the transmembrane region of its envelope gene and raised specific antibodies to the fusion pro tein and to a synthetic peptide. These antibodies reacted with a 65-kD a polypeptide which constituted approximately 0.1% of the cellular pro tein in syncytiotrophoblasts in placenta. The evolutionary conserv,ati on and abundant expression of this endogenous retroviral protein in a specific cell type support the concept of a biological function. The s imilarity of a domain of ERV-3 env to putative immunosuppressive p15E sequences suggests that ERV-3 might form part of the placental immunos uppressive barrier between mother and foetus. (C) 1995 Academic Press, Inc.