Tenascin, a large oligomeric
glycoprotein, is a recent addition to a list of increasing
extracellular matrix proteins. Previous studies have documented the strong expression of
tenascin in embryonic kidney and in both normal and abnormal mature glomeruli implicating an important role of this
extracellular matrix protein in nephrogenesis and glomerular
scarring. Whether
tenascin plays any role in interstitial
fibrosis, a common final pathway of
tubulointerstitial nephritis, is no known; on the other hand, a detailed knowledge of the structural components of interstitial
fibrosis is essential for further studies on other fundamental aspects of this biologically and clinically important process. In this study, the expression of
tenascin in the renal interstitium was immunohistochemically evaluated in 208 renal specimens during normal kidney (23 cases), acute tubular
necrosis (8),
acute tubulointerstitial nephritis (8), chronic primary
tubulointerstitial nephritis (30),
tubulointerstitial nephritis secondary to glomerular diseases of mild (46) and severe (55) degree, ischemic damage (24), and rejection (14). It was found that in normal kidney
tenascin expression was limited to the medullary interstitium. In kidney with
tubulointerstitial nephritis,
tenascin was ubiquitously and constantly expressed in any areas with tubulointerstitial damage regardless of diagnosis, etiology, the cortical vs. medullary location of the lesions, stage of the fibrogenetic process, density of fibroblasts, or severity of interstitial
inflammation in the affected areas. Indeed, strong
tenascin expression was seen in areas where there was only interstitial
edema or
inflammation as judged by routine light microscopic preparations. In summary, this study systematically documents
tenascin as a novel
extracellular matrix protein selectively expressed in the medullary interstitium in normal kidney, and ubiquitously present in areas with interstitial
fibrosis.