Immunohistological identification of macrophages in murine placentae, yolk-sac membranes and pregnant uteri.

Several studies have indicated the presence of mononuclear phagocytes in placentae and in extra-placental membranous structures from various mammalian species, but little is known of the cells' precise location or of their possible functions. Because localization of macrophages in mice is facilitated by the existence of specific antisera, indirect immunofluorescence was used in the present study to identify and approximate the numbers of macrophages associated with murine placentae, yolk-sac membranes and pregnant uteri. Substantial numbers of cells which were reactive with the specific antiserum were observed in uterine tissue, in the uterine cavity and in the mesodermal layer of the yolk sac. There was no readily apparent quantitative relationship between macrophages in either location and antigenic disparity between mother and fetus. Furthermore, the macrophages contained substantial amounts of immunoglobulin, apparently in the form of antigen-antibody complexes, an observation which suggested that those Fc receptor-positive cells may function to remove complexes of soluble fetal antigen and anti-fetal antibody during passage of immunoglobulin from mother to fetus.