Antiglomerular basement membrane nephritis induced by IgA1 antibodies.

A 62-year-old man was admitted for acute renal failure due to crescentic rapidly progressive glomerulonephritis. Kidney biopsy showed intense staining for IgA, IgA1 and C3 in a linear pattern along the glomerular basement membrane (GBM). Serologic tests for detecting anti-GBM antibodies were positive for IgA class and IgA1 subclass and negative for IgG and IgA2. Serum IgA anti-GBM antibodies appeared essentially in the polymeric form, an observation in agreement with recent studies demonstrating polymeric IgA response after parenteral immunization. There was no sign of pulmonary involvement. This patient is the first to present with an isolated nephritis due to anti-GBM antibodies restricted to the IgA class (IgA1 subclass). Routine tests for circulating anti-GBM antibodies should also include the IgA class.