When the B cells in the germinal center of patients with acute COVID-19 were analyzed, IgG2-producing B cells responsive to type 1 IFN were dominant at the beginning of ICU hospitalization; however, as the disease progressed, the number of IgG1- and IgA1-producing B cells responsive to IL-21 and TGF-β increased, and ultimately the number of IgA2-producing B cells responsive to TGF-β increased. The gene discussed is IL21; the disease is COVID-19.