Interestingly, TMPRSS2 and TMPRSS4 had been previously ascribed diverse roles in mucosal pathobiology, including that of the lung, such as the activation of influenza and SARS-CoV viruses [39,40,41], promotion of lung fibrosis [42], as well as the induction of lung cancer stem-cell-like properties [43], growth, metastasis, and resistance to chemotherapy [44]. The gene discussed is TMPRSS4; the disease is influenza.