Immunohistochemical localization of retroviral-related antigens expressed in normal baboon placental villous tissue

Endogenous retroviral particles (ERVs) have been detected in the genome of all eukaryotes. They are generally non-pathogenic except in mice where they have been found to induce tumors and immunological disorders. The ERVs hav e morphological features consistent with type-C retroviral particles and ar e commonly expressed in normal placental villous tissues. ERVs may have a r ole in the regulation of placental gene expression, syncytiotrophoblast for mation, or pregnancy-related immunosuppression. In this study, well-charact erized antibodies (monoclonal and polyclonal antibodies) raised against ret roviral proteins (anti-HIV and anti-HIV) and endogenous retroviral (ERV) pa rticles were assessed for their cross-reactivity (by using immunohistochemi stry) with normal baboon placental and other adult tissues. The monoclonal antibodies to exogenous retroviral proteins (anti-HIV-2 gp120, anti-HIV-1 g p41, anti-SIVmac p27, anti-HIV-1 RT, and anti-HIV-2 core protein) showed sp ecific immunohistochemical reactivity with the syncytiotrophoblast. Antibod ies to endogenous retroviral gene products (anti-ERV3 env, anti-HERV-K RT, and anti-HERV-K env) also reacted in a similar manner and did not crossreac t with other adult tissues. These studies have shown that retroviral-cross- reactive proteins are expressed in baboon placental syncytiotrophoblast and may have a role to play at the fete-maternal interface.