The proteome of the sera/plasma of patients with COVID-19 showed 21 common proteins (Figure 2A), which are ORM1, ITIH3, ALB, SAA2, PGLYRP2, APOA1, NID1, GSN, CPN2, LGALS3BP, AGT, LCP1, C2, CLEC3B, ITIH4, APOM, CRTAC1, APOA2, ORM2, AHSG, and GPLD1. The gene discussed is C2; the disease is COVID-19.