Megakaryocyte and SARS-CoV-2 detection in tissue during COVID-19. (A) Representative immunofluorescence images of BM MK during SARS-CoV-2 infection. Femurs of mice inoculated with SARS-CoV-2 (3 DPI or 7 DPI) or Mock-infected were stained with anti-CD41 (green) and the nuclei counterstained with Hoechst (blue; scale bar, 20 μm). (B) Megakaryocyte number was quantified in femurs and expressed as mean (± SD) × mm^–2 of tissue. Statistics: 1-way ANOVA with Tukey's multiple comparisons, ^∗P < .05; n = 3-5 per group. (C) Frequency distribution of MK size (diameter in μm; left) and area (surface in μm² right panel) were analyzed, percentages of frequency are expressed as mean (± SD). Statistics, 2-way ANOVA, Mixed-effects analysis with Tukey's multiple comparisons test; n = 4-5 per group. (D) Representative immunofluorescence images of BM or lung during SARS-CoV-2 infection. SARS-CoV-2 was detected using anti–SARS-CoV-2 nucleocapsid (green), and nuclei were counterstained with Hoechst (blue) (scale bar, 25 μm). (E) Tissues from mice uninfected (Mock) or infected with SARS-CoV-2 for 3 days or 7 days were analyzed for the presence of SARS-CoV-2. Results are expressed as mean (± SD) of SARS-CoV-2 coverage (% of tissue; top; dotted line indicates the mean value obtained for mock tissues). Viral RNA levels were determined in BM by RT-ddPCR and compared with those in the lungs (bottom). SARS-CoV-2 E gene copies were normalized with Gapdh mRNA copies (n = 4-5 mice per condition). Results are expressed as mean (± SD). Statistics: 2-way ANOVA, mixed-effects analysis with uncorrected Fisher's LSD, ^∗P < .05; ^∗∗∗∗P < .0001; n = 3-5 per group. BM, bone marrow; DPI, day post-infection; LSD, least significant difference; MK, megakaryocytes; RT-ddPCR, reverse transcription digital droplet polymerase chain reaction.