Proliferating cell nuclear antigen in human placenta and trophoblastic disease.

Expression of proliferating cell nuclear antigen (PCNA), an auxiliary factor for the DNA polymerase delta, is closely related to cell proliferation. Using the monoclonal anti-PCNA antibody 19F4, we examined the distribution of PCNA in formalin-fixed, paraffin-embedded sections of mature and first-trimester placentas, 8 hydatidiform moles, and 7 choriocarcinomas. In normal placentas there was strong expression of PCNA in cytotrophoblastic nuclei, while the syncytium and the amnionic epithelium were PCNA unreactive. Staining of stromal cells was variable. These results are in complete agreement with the autoradiographic localization of [3H]thymidine incorporation and demonstrate that immunoreactivity for PCNA accurately defines areas of proliferative activity in routinely processed placental tissues. In choriocarcinomas and hydatidiform moles PCNA was predominantly expressed in the cytotrophoblast and intermediate trophoblast. Again, the syncytium was largely unreactive for PCNA. These findings indicate that even after neoplastic transformation the syncytium has comparatively little proliferative activity whereas the mononuclear trophoblastic cells divide actively.