In IgA nephropathy (IgAN), elevated levels of the circulating autoantigen galactose-deficient IgA1 are critical to disease pathogenesis. Abnormal B-cell glycosylation pathways produce the autoantigen that, on recognition by autoantibodies, forms immune complexes. Genetic as well as in vitro, in vivo, and human immunologic studies have identified APRIL (a proliferation-inducing ligand) and BAFF (B-cell activating factor) as key cytokines controlling B-cell development and the differentiation of antibody-secreting cells.