TNFSF13B and autoimmune disease: IgA, the most abundant immunoglobulin produced by the mucosal immune system, interacted with gut microbiota and contributed to autoimmune diseases.51 Studies reported that IgAN patients exhibited elevated levels of IgA, BAFF, and APRIL, suggesting a B cell homeostasis imbalance.52 Excessive IgA production in IgAN primarily occurs in B cells within the intestinal lamina propria.