IRF4 promotes the production of plasma cells and regulates Ig class-switch recombination, XBP1 maintains protein production in plasma cells, and PRDM1 determines the secretory arm in B cell differentiation and increases Ig production.29 In addition, CD2AP expression in CD4+ T cells from COVID-19 patients was significantly elevated compared with healthy donors (Fig. 5e). This evidence concerns the gene XBP1 and COVID-19.