Purification and localization of Tubulointerstitial Nephritis antigen (TIN-ag) in kidney and small intestine K. KOUZI-KOLIAKOS, M. KANELLAKI-KYPARISSI, A. CHARONIS, A. MICHAEL, E. CHRISTOFORIDIS, G. KOLIAKOS Abstract Tubulointerstitial Nephritis antigen (TIN-ag) is a novel recently described basement membrane component. It is the target of tubular basement membrane autoantibodies, which have been developed in patients with Tubular Interstitial Nephritis. In our study, TIN-ag was extracted and purified from rabbit kidney cortex basement membranes, by collagenase digestion and detected by Western blotting. The indirect avidin-biotin method and the immunogold and silver enhancement method were performed on thin and semi-thin sections from rabbit and human kidney cortices and small intestines, using the monoclonal antibody A8 and the polyclonal antibody Ab95.. TIN-ag was detected on the tubular basement membrane (especially in proximal tubules), the parietal layer of Bowman’s capsule (especially at the urinary pole) and on the basement membrane of the villi of the duodenum, jejunum and ileum and the crypts of Lieberkuhn as well. It was not detected on the glomerular basement membrane. Because of the localization of TIN-ag on the basement membranes under epithelial cells which are involved in active and extensive transport of many metabolites, it is tempting to speculate that TIN-ag has a specific role in the homeostasis of the body. Further molecular analysis will reveal the antigenic epitope, which is responsible for the development of the circulated autoantobodies in the blood of patients with tubulointerstitial nephritis.   < back .