TMPRSS2 and infection: After initial infection, SARS-CoV-2 causes cells to overexpress ACE2 via 1) direct binding of its spike protein to the ACE2 receptor [203] or (as recently reported) 2) direct or indirect binding and activation of Toll-like receptor 4 (TLR4) [204], followed by fusion of the viral and host cell membranes, facilitated by TMPRSS2 and furin molecules [203,205,206], leading to replication, worsening of the infection, and ongoing inflammation [204].