As a result of analyzing B cells that differentiated in the germinal center of patients with severe COVID-19, IgG2-producing B cells that were affected by type 1 IFN at the beginning of ICU hospitalization were dominant; however, the number of IgG1- and IgA1-producing B cells affected by IL-21 and TGF-β increased as the disease progressed, and eventually, the number of IgA2-producing B cells strongly affected by TGF-β increased [146]. The gene discussed is IL21; the disease is COVID-19.