Serum levels of KL-6 as a useful marker for evaluating pulmonary fibrosis in patients with systemic sclerosis

Objective. KL-6 is a mucin-like glycoprotein that is strongly expressed on type II pneumocytes in the lung. Circulating KL-6 has been shown to be a sensitive marker of the disease activity of interstitial lung diseases. We determined the serum levels of KL-6 in patients with systemic sclerosis (SSc) and investigated whether these levels would serve as a useful marker of pulmonary Fibrosis (PF) in patients with SSc. Methods. The serum KL-6 levels were determined using a specific ELISA in 91 patients with SSc, and in 38 healthy controls, Results. The serum levels of KL-6 were significantly higher in patients with SSc than in healthy controls (923 +/- 860 vs 382 +/- 55 U/ml; p < 0.0001). The serum KL-6 levels of the patients with diffuse cutaneous SSc (dSSc) tended to be higher than those with limited cutaneous SSc (lSSc) (1054 +/- 1000 vs 800 +/- 694 U/ml), but there was no significant difference between these 2 groups. The serum KL-6 levels in the patients with PF were significantly elevated compared to those without PF (1283 +/- 1056 vs 520 +/- 148 U/ml; p < 0.0001). Moreover, DLCO and VC were also significantly decreased in the patients with elevated KL-6 levels compared to those with normal levels (62 +/- 22% vs 72 +/- 17%, p < 0.05; 87 +/- 20% vs 100 +/- 18%, p < 0.01, respectively). Conclusion. Serum KL-6 level may be a useful serum marker for evaluating pulmonary fibrosis in patients with SSc.