On day 4 after infection there was a striking increase in two populations of IFN-activated myeloid cells in the BAL, one having monocyte-like features and the other more closely resembling alveolar macrophages, indicating that recruited monocytes and lung resident macrophages are key early responders to type I IFN after SARS-CoV-2 infection. This evidence concerns the gene IFNA1 and infection.