Fig. 1: c-FLIP and pSTAT3 expression in SARS-CoV-2-infected hosts.

A Representative H&E-stained microscopy images of lung tissue of non-respiratory disease (NRD), bacterial pneumonia (BP), and COVID-19 patients (upper panel). Scale bar, 200 μm. Representative immunofluorescence (IF) staining of alveolar macrophages (second, third, and fourth lines) and histiocytic cells (fifth and sixth lines). Cells were stained for CD68 (green), c-FLIP (red), pSTAT3 (white), and DAPI (blue). Scale bar, 20 μm. B Quantification and representative IF staining of c-FLIP in circulating monocytes (CD14⁺ cells) purified from healthy donors (HD, n = 4) or COVID-19 patients (n = 5). Cells were stained for DAPI (blue) and c-FLIP (red). Scale bar, 10 μm. C Correlation between percentage of suppression and percentage of circulating c-FLIP-expressing monocytes isolated from COVID-19 patients (n = 16). D Correlation between pSTAT3 and c-FLIP normalized expression in circulating monocytes (CD14⁺ cells) isolated from COVID-19 patients (n = 10). E Correlation between the release of IL-6 or TNF-α cytokines and pSTAT3 expression in monocytes (CD14⁺ cells) from HD (red, n = 4) and COVID-19 patients (black, n = 13). F Representative hematoxylin and eosin (H&E)-stained microscopy images of lung tissue of HFH4-hACE2 transgenic mice SARS-CoV-2-infected or mock-infected mice. Scale bar, 200 μm. pSTAT3, c-FLIP, and CD11b expression levels were detected by indirect immunofluorescence (IFA) staining. Scale bar, 100 μm. Correlation analysis was performed by Spearman’s rank correlation (C–E).