Retrovirus p30‐related antigen in human syncytiotrophoblasts and IgG antibodies in cord‐blood sera

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Abstract
Sensitive immunological techniques were used to detect retrovirus markers in human pregnancy. A total of 1,540 human cord‐blood sera were tested for retrovirus‐reactive IgG antibodies using solid‐phase enzyme immunoassay and purified RD114 virus as antigen. Of these, 118 (7.7%) sera were positive. Blocking assays with specific animal anti‐p30 sera, use of control antigen, and electrophoretic protein experiments combined with immunological detection indicated that the human antibodies reacted specifically with the p30 protein. The occurrence of antibodies in cord‐blood serum had a highly significant correlation to complications during pregnancy and also correlated to the number of previous abortions and stillbirths. When goat anti‐RD114 p30 serum was used in the peroxidase‐anti‐peroxidase tissue staining procedure, p30‐related antigen was detected in sections of all placental specimens (early and term pregnancies, blighted ova, hydatidiform moles, destructive moles and choriocarcinomas). However, in each case only syncytiotrophoblastic cells were positive. These findings, supplemented with different types of blocking tests, lead us to conclude that retrovirus p30‐related antigen is selectively expressed in the highly differentiated syncytiotrophoblasts, which in the normal placenta are directly exposed to maternal blood. It is suggested that retrovirus‐reactive antibodies may represent an autoimmune‐like immune response to the p30‐related syncytiotrophoblast antigen escaping during cellular damage.