In this study, A549 cells expressing human ACE2 and TMPRSS2 (A549-hACE2+TMPRSS2 cells) along with SARS-CoV-2 lentiviral pseudoparticles were used to assess if C1q and C4BP interfered with SARS-CoV-2 infection at the cellular level. The gene discussed is TMPRSS2; the disease is COVID-19.