TNFSF13B and systemic lupus erythematosus: Next, we measured the presence of autoantibodies and serum concentration of BAFF and APRIL, two cytokines supporting the development and survival of B cells, which are also implicated in other systemic autoimmune diseases reminiscent of MIS-C, such as SLE, systemic vasculitides, or Kawasaki disease [19–21].