FCN1 and COVID-19: In the bronchoalveolar lavage fluid collected from COVID-19 patients, a large number of SARS-CoV-2 viruses are detected (Lu et al., 2020; Zhou et al., 2020a), and highly inflammatory monocyte-derived FCN1+ macrophages are present and responsible for producing enormous cytokines (Liao et al., 2020), indicating inflammatory microenvironment in the alveolar fluid.