TARGETS OF ALLOANTIBODIES IN ALPORT ANTIGLOMERULAR BASEMENT-MEMBRANE DISEASE AFTER RENAL-TRANSPLANTATION

A minority of patients with Alport syndrome develop anti-GBM disease i n their allografts after renal transplantation. Clinically, the renal disease appears indistinguishable from Goodpasture's disease of native kidneys, in which the target of autoantibodies has been identified as the NC1 domain of the alpha 3 chain of type IV collagen, alpha 3(IV)N C1. However, in the majority of cases, Alport syndrome is due to mutat ions in the gene encoding the alpha 5 chain of type IV collagen, locat ed on the X chromosome. Neither chain is detectable in the glomerular basement membrane (GBM) of most patients with Alport syndrome. We inve stigated the targets of the alloantibodies of 12 Alport patients who d eveloped post-transplant anti-GBM disease by Western blotting onto rec ombinant NC1 domains made in insect cells. Binding to these antigens, for both typical Goodpasture and Alport anti-GBM antibodies, was stron g and conformation-sensitive. Nine antibodies showed selective binding to alpha 5(IV)NC1. This specificity was confirmed by the demonstratio n of binding to a 26 kDa band of collagenase-solubilized human GBM, an d/or binding to normal epidermal as well as renal basement membranes b y indirect immunofluorescence. One antibody showed binding to alpha 5 and alpha 3(IV)NC1, while two showed predominant binding to alpha 3(IV )NC1. All seven patients whose pedigree or mutation analysis showed X- linked inheritance had predominant anti-alpha 5 reactivity. One with p redominant anti-alpha 3 reactivity had a COL4A3 mutation. These findin gs show that human anti-GBM disease can be associated with antibodies directed towards different molecular targets. alpha 5(N)NC1 is the pri mary target in most patients with X-linked Alport syndrome who develop post-transplant anti-GBM disease.