SFTPB and COVID-19: SARS-CoV-2 was detected (using both our in-house G2 clone and a commercially available antibody from GeneTek) predominantly in AT2 cells, which were identified by TTF-1 and SP-B positivity, and in sparse inflammatory cells (alveolar and tissue macrophages) in all COVID-19 patients, ranging from <5 cells per 4 mm2 tissue to >50 cells per 4 mm2 tissue (figure 1a, supplementary table S1a).