C3 and infection: After 72 h of infection, the tissue models were fixed and stained for immunofluorescence analysis using antibodies against SARS-CoV-2 spike 1 (S1) and nucleocapsid (N) proteins to detect virus, Hoechst stain for nuclei, complement component C3 as a marker for innate immune activation and Phalloidin for detecting the F-actin within the cytoskeleton.