Identification of α3, α4, and α5 chains of type IV collagen as alloantigens for Alport posttransplant anti-glomerular basement membrane antibodies

Background. Alport syndrome is a hereditary disorder of basement membranes especially affecting the kidneys, ears, and eyes. Some patients who undergo renal transplantation lose their kidneys as a result of posttransplant anti-glomerular basement membrane (anti-GEM) disease. Methods. In the present study, we analyzed serum from 21 unselected Alport patients who underwent renal transplantation. Eleven samples were from patients without posttransplant anti-GEM nephritis, and 10 were from patients with this disease. Results. Thirteen serum samples [10 alport posttransplant nephritis serum (APTN) and three alport posttransplant serum (APT)] revealed linear binding to the GEM by indirect immunofluorescence, By using direct ELISA and immunoblotting with GEM constituents and type IV collagen NC1 domains from bovine, human, and recombinant sources, we detected anti-GBM antibodies in all Alport patients in varying titers, Five samples showed specific reactivity to the alpha 3 chain, four to the alpha 5 chain, six to both alpha 3 and alpha 5 chains, one to the alpha 3 and alpha 4 chains, and two to the alpha 3, alpha 4, and alpha 5 chains of type IV collagen. The varied spectrum of reactivities was present equally in nephritic and non-nephritic sera, Ten control samples from non-Alport transplant patients did not exhibit specific binding to the GEM. Conclusions. These results suggest that the absence of alpha 3, alpha 4, and alpha 5 chains of type TV collagen in the Alport kidney leads to alloantibodies in all Alport patients who receive transplants, irrespective of whether they develop nephritis or not, Although all Alport transplant patients develop this humoral response, only a select few develop anti-GEM disease, We suggest that this difference could be attributable to a genotypic effect on the ability of some individuals to launch a cell-mediated immune response.