Expression of PDPN in the lung in COVID-19 pneumonia. Tissue specimens from the lungs of patients with COVID-19 pneumonia and patients without COVID-19 obtained during autopsy were examined. (A) Hematoxylin and eosin (H&E) and (B) immunohistochemistry stain for PDPN of the non–COVID-19 lung. Immunofluorescence staining of non–COVID-19 lungs with (C) lower original magnification (×100) and (D) higher original magnification (×200) showing few platelets in the lung parenchyma inside blood vessels (white arrowheads). (E) H&E and (F) immunohistochemistry stain for PDPN of COVID-19 lungs. Immunofluorescence staining of COVID-19 lungs at (G) lower original magnification (×100) and (H′-H′′) higher original magnification (×200). Platelets inside blood vessels are indicated with white arrowheads, and those colocalized with PDPN with yellow arrowheads. (I) Expressions of PDPN in COVID-19 and non–COVID-19 lungs are compared as mean fluorescence intensity (MFI) of immunofluorescence-stained slides. The box and whisker graph shows minimum to maximum values in each group (non–COVID-19: 182.5 ± 24.8, COVID-19: 261.7 ± 7.42; n = 4 images per group; P = .02, unpaired t test).