Elevation of Serum Krebs von den Lunge-6 Levels in Patients With Tubulointerstitial Nephritis and Uveitis Syndrome

Background: Tubulointerstitial nephritis and uveitis (TINU) syndrome is characterized by a combination of idiopathic acute tubulointerstitial nephritis and uveitis. Krebs von den Lunge-6 (KL-6) is a human glycoprotein secreted by type II alveolar cells in the lung, and its serum levels increase in patients with pneumonia of various causes, as well as ocular sarcoidosis. The aim of the present study is to quantify serum KL-6 levels in patients with TINU syndrome, which has no pulmonary and sarcoid lesions, and elucidate the usefulness of KL-6 for the diagnosis and follow-up of this syndrome. Methods: Serum and urinary samples were obtained from 17 patients with TINU syndrome and 36 age-matched patients with uveitis from other causes. Sarcoidosis was eliminated because serum KL-6 levels increased during their lung lesion. Serum KL-6 level was determined by using a human KL-6 electrochemiluminescence immunoassay. Formalin-fixed paraffin-embedded renal tissue sections were incubated with anti-KL-6 monoclonal antibody, then examined immunohistochemically. Results: Mean serum KL-6 levels for patients with TINU syndrome and those with uveitis from other causes were 363.35 ± 51.06 and 213.19 ± 10.28 U/mL, respectively (P < 0.001). Urinary β2-microglobulin levels of patients with TINU syndrome and uveitis from other causes were 4.06 ± 1.31 and 0.16 ± 0.20 mg/L, respectively (P < 0.001). All patients with TINU syndrome showed a simultaneous decrease in serum KL-6 and urinary β2-microglobulin levels after the beginning of treatment. Strong immunoreactivity for KL-6 was observed in renal distal tubules in biopsy tissue of patients with TINU syndrome. Conclusion: We show a significant increase in serum KL-6 levels in patients with TINU syndrome, whereas levels were normal in patients with other causes of uveitis without nephritis. Renal distal tubules stained strongly with anti-KL-6 antibody, suggesting that high KL-6 levels may reflect the renal lesion of TINU syndrome. Serum KL-6 may be a potential laboratory parameter for the diagnosis and follow-up of patients with TINU syndrome that could complement urinary β2-microglobulin measurements.