IgA nephropathy is the commonest form of glomerulonephritis worldwide, and is one of the major causes of terminal renal failure in most industrialised countries. It is defined by the dominance of IgA mesangial deposits in immunofluorescence studies. Corticosteroid-sensitive nephrosis lipoides (minimal change disease) with IgA deposits and superimposed crescentic glomerulonephritis are to be differentiated from primary IgA nephropathy (Berger's disease). In the latter, clinical manifestations are dominated by synpharyngitic macroscopic haematuria and permanent proteinuria. Terminal renal failure occurs in about 25% of patients after 10 years or more. Heavy proteinuria, hypertension, altered renal function and severe histological lesions at diagnosis are markers of poor prognosis. Primary IgA nephropathy is thought to be related to mesangial deposition of polymeric IgA1-containing immune complexes, owing to altered B cell responses to exogenous and endogenous antigens, together with hyperactivity of T helper type 1 and type 2 cells, both favoured by a genetic background. The 2 compartments of the IgA system (medullary and mucosal) may participate in the pathogenesis of the disease. Modulation of gut-associated lymphoid tissue and immune tonsillectomy are current lines of research. Although impressive results were obtained with an oligoantigenic diet, it is somewhat impractical. Pharmacological modulation of the mucosal immune response seems more promising. There is no proof that phenytoin, a drug which reduces bone marrow IgA synthesis, is beneficial. Emerging data suggest the potential of immune intervention in severely proteinuric patients before sclerotic lesions have occurred, using azathioprine and intravenous immunoglobulins. The benefit of early corticosteroid therapy is still unknown in both adults and children, and the efficiency of alkylating agents is unproven. The search for bacterial foci in primary IgA nephropathy is mandatory, as appropriate treatment may have a protective effect on renal function and help to improve or stabilise some patients. Slowing the progression of renal failure by a combination of ACE inhibitors, fish oil and, possibly, antiplatelet drugs is a promising therapeutic approach.
