The human materno-foetal relationship in malaria: I. Identification of pigment and parasites in the placenta

To facilitate investigations of the consequences of malarial infection during human pregnancy, several methods for the recognition of pigment and parasites in the placenta were evaluated. Pigment was visualized in infected blood smears and placental tissue using both white light and modified fluorescence microscopy. However, the characteristic pigment dots observed with fluorescent light were also apparent in unstained cryostat and deparaffinized placental sections, and following reaction with immunohistological reagents. Intact parasites were recognized immunohistologically in placental sections and blood smears using rabbit antisera to Plasmodium falciparum and P. berghei. Using these procedures, numerous erythrocytes containing parasites associated with small pigment dots were seen in intervillous spaces in heavily infected placentae. In these organs, larger irregular pigment aggregates were present within maternal cells which were shown to be monocytes by esterase staining. Pigment was also observed in the cytoplasm of the trophoblast and not infrequently in the mesenchymal stroma, but no intact parasites were observed within chorionic villi. These simple and sensitive methods thus confirm placental localization of parasites and pigment. Furthermore, the finding of pigment in all Gambian placentae examined, of which seven were thought initially to be uninfected, indicates that malaria may complicate pregnancy more frequently than hiterto anticipated.