C5AR1 and COVID-19: Similar to what we observed in the lung tissue of COVID-19 patients, immunofluorescence analyses of the lung tissue of SARS-CoV-2-infected Tgfl/fl mice revealed that C5aR1 was mainly expressed in cells positive for NE (neutrophils, 41.2% ± 16.07%) and Iba-1 (macrophages, 48.62% ± 15.07%) (Figure 3, E and F).