Human oocytes express murine retroviral equivalents.

Unfertilized human oocytes expressed a gp70-related epitope as observed when staining section immunocytochemically with a panel of monoclonal antibodies against gp70 of murine leukemia virus. Some oocytes also expressed virus-like particles at the cell membrane. Follicular fluids, corresponding to these oocytes, contained p30- and gp70-related antigens, reverse transcriptase, and an increased titer of interferon. The three- to four-cell human cleavage stages did not contain the gp70-related epitope. It is concluded that human oocytes, but not early cleavage stages, express products that suggest the presence of an active endogenous retrovirus genome.