Immunohistologic detection of antigen related to primate type C retrovirus p30 in normal human placentas

This study reports the immunohistologic detection of SSAV/GaLV type C retrovirus p30-related antigen in unfixed cryostat sections of normal human term placentas by the indirect immunofluorescence method. Goat anti-SSAV p28 serum reacted specifically with 10 of 10 anatomic specimens of human placenta. Goat anti-GaLV p29 serum reacted similarly with 8 of 10 specimens. Goat anti-BaEV p28, anti-RD-114 p28, anti-FeLV p27, anti-R-MuLV p30, and anti-MPMV p27 gave no specific reaction with placenta. The anti-SSAV p28 and anti-GaLV p29 reactive antigen was located in the placenta mainly at the basal aspect of syncytiotrophoblast near the underlying trophoblastic basement membrane where type C retroviruslike particles have been found electronmicroscopically. The specific antibody activity of anti-SSAV p28 serum against placenta was removed by critical absorption with disrupted SSAV or GaLV but not RD-114 or MuLV. These results suggest the presence in human placenta of a putative type C retroviral protein which cross-reacts with the p30 protein of the SSAV/GaLV type C retrovirus group.