CD163 Expression in Chronic Intervillositis of Unknown Etiology and SARS-CoV-2 Placentitis.

Chronic intervillositis of unknown etiology (CIUE) is an aberrant maternal inflammatory infiltrate comprised primarily of macrophages that collect in the intervillus space and is associated with poor outcomes including recurrent pregnancy loss. An abnormal maternal Th1-type response to pregnancy may be the basis for pathogenesis of CIUE but macrophage in the maternal infiltrate of CIUE have been reported to have an anti-inflammatory M2 phenotype characterized by increased expression of CD163. This study assesses expression of CD163 in CIUE and SARS-CoV-2 placentitis, which has a similar histopathological presentation, using an automated approach to minimize observer-related variability. The data show that the maternal inflammatory infiltrate of CIUE contains a blended population of high and low CD163 expressing macrophage with a prominent bias towards an anti-inflammatory M2 phenotype when compared to normal control tissue. A similar pattern is seen in SARS-CoV-2 placentitis, suggesting pathophysiologic similarity with CIUE, although SARS-CoV-2 also appears to promote decreased CD163 expression in Hofbauer cells, which is not seen in CIUE.