An update on the pathogenesis and treatment of IgA nephropathy

Over the past two decades significant progress has been made in unravelling the complex pathogenesis of immunoglobulin A nephropathy (IgAN). Excess amounts of poorly galactosylated immunoglobulin (Ig)A1 in the serum appear to be the trigger for generation of glycan-specific IgG and IgA autoantibodies, resulting in the formation of circulating IgA immune complexes, which are pivotal to the development of nephritis. It remains unclear why there is an increase in poorly galactosylated IgA1 molecules in the serum in IgAN. One intriguing possibility is that this IgA is derived from displaced mucosal B cells, which have mis-homed from their mucosal induction sites to systemic sites, where they secrete polymeric, poorly galactosylated IgA directly into the circulation rather than onto mucosal surfaces. Lack of a clear appreciation of the origins of poorly galactosylated IgA1 and an incomplete understanding of immune complex formation have hampered development of specific therapeutic strategies to prevent mesangial IgA deposition. Clinicians have therefore been left to manage patients with generic therapies, mainly by control of blood pressure and renin-angiotensin blockade. A paucity of high-quality clinical trials has meant that evaluation of additional therapies, particularly immunosuppressive regimens, has been difficult and there remains a great deal of confusion over the optimum treatment of patients at high risk of progressive chronic kidney disease.