TMPRSS2 and viral infectious disease: In addition, nafamostat has attracted attention as an inhibitor for the activity of transmembrane protease serine 2 (TMPRSS2), a host cell serine protease that mediates viral cell incursion for influenza virus and coronavirus, thereby inhibiting viral infection and replication (Yamamoto et al., 2016 ▸, 2020 ▸; Hoffmann et al., 2020 ▸).