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

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.The serum KL-6 levels were determined using a specific ELISA in 91 patients with SSc, and in 38 healthy controls.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 (ISSc) (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).Serum KL-6 level may be a useful serum marker for evaluating pulmonary fibrosis in patients with SSc.