Fig. 1.

Immunohistochemical and RNA-in situ stains.

(A, B) Immunostainings for SARS-CoV-2 spike (A) and nucleocapsid (B) proteins. Syncytiotrophoblast is positive for both proteins. Note the more extensive and stronger positivity for nucleocapsid expression, which also localizes to intervillous inflammatory cells (inset, arrowheads) and an Hofbauer cell (inset, arrow).

(C) Double stain for spike protein (brown) and CD14 (blue) indicates higher density of inflammatory infiltrate at sites where the viral protein is more intensely expressed.

(D) Double staining for CD14 (brown) and CD66b (blue) expression, respectively identifying monocyte-macrophages and neutrophils in the inflammatory infiltrate occupying the intervillous spaces. Note the CD14-positive Hofbauer cells in the villi.

(E) PD-L1 staining shows strong expression in the syncytiotrophoblast in areas displaying inflammation (left side). The inset shows an area infiltrated with inflammatory cells, which express PD-L1 (arrow), similarly to intravillous Hofbauer cells.

(F) SARS-CoV-2 RNA in situ hybridization using the S antisense probe (brown stain) combined with anti-CD14 immunostain (red stain). Strong expression of viral RNA is observed in the syncytiotrophoblast, and in scattered CD14⁺ intervillous mononuclear cells, identified as monocyte-macrophage (inset, arrowheads). (Bar corresponds to 100 μm for figs. A-B-B inset-C-F, 50 μm for fig. D and F inset, 200 μm for fig. E and 150 μm for E inset).