Interstitial cystitis is associated with intraurothelial Tamm-Horsfall protein

A defective barrier between the urine and urothelium has been suggested as an etiology for interstitial cystitis. With immunohistochemical techniques we assayed the bladder biopsies of 14 interstitial cystitis patients and 10 normal controls for intraurothelial Tamm-Horsfall protein to assess indirectly the in vivo permeability of the urothelium. Eight pathological controls, including bladder biopsies from 3 patients with inflammation owing to infection or catheterization and biopsies of 5 transitional cell carcinomas of the bladder, also were assayed. Superficial intraurothelial Tamm-Horsfall protein was identified in the biopsies from 10 of 14 interstitial cystitis patients (71 per cent) but only 1 of 10 controls (10 per cent) (p less than 0.01). Tamm-Horsfall protein was not identified in biopsies from the pathological controls. In 6 of 7 cases when more than 1 biopsy was available for analysis the findings were identical in each specimen. There was a direct correlation between the density of detrusor mast cells and the demonstration of intraurothelial Tamm-Horsfall protein. Seven of the 9 evaluable interstitial cystitis patients with intraurothelial Tamm-Horsfall protein but only 1 of 4 without intraurothelial Tamm-Horsfall protein experienced a favorable response to intravesicle oxychlorosene sodium (p greater than 0.05). These data suggest that abnormal permeability of the urothelium is associated with and a possible cause of interstitial cystitis and that the demonstration of intraurothelial Tamm-Horsfall protein in bladder biopsy specimens may prove to be useful as a diagnostic test for interstitial cystitis.