To explore these immune factors contributing to the hyperinflammation in MIS-C, we set out to assess type I, II, and III interferons, serum BAFF, APRIL, and B cell phenotype and BAFFR expression in children with acute MIS-C and in healthy children after COVID-19. The gene discussed is TNFSF13B; the disease is COVID-19–associated multisystem inflammatory syndrome in children.