Objective

To investigate the relationship between Krebs von den Lungen 6 (KL-6) and CCL18 levels and the severity and progression of systemic sclerosis (SSc)-related interstitial lung disease (ILD).

Methods

Patients enrolled in the Scleroderma Lung Study II (cyclophosphamide [CYC] versus mycophenolate mofetil [MMF]) were included. Baseline and 12-month plasma samples were analyzed by enzyme-linked immunosorbent assay to assess CCL18 and KL-6 levels. The forced vital capacity (FVC) and the diffusing capacity for carbon monoxide (DLco) were measured every 3 months. Joint models were created to investigate the relationship between baseline CCL18 and KL-6 levels and the course of the FVC and DLco over 1 year according to treatment arm.

Results

Baseline KL-6 and CCL18 levels each correlated with the extent of radiographic fibrosis. Levels of both CCL18 and KL-6 declined significantly at 1 year. In both treatment arms (n = 71 for CYC, n = 62 for MMF), a higher baseline KL-6 level predicted progression of ILD based on the course of FVC (P = 0.024 for CYC; P = 0.005 for MMF) and DLco (P < 0.001 for CYC; P = 0.004 for MMF) over 1 year. A higher baseline CCL18 level predicted progression of ILD based on the course of the FVC (P < 0.001 for CYC; P = 0.007 for MMF) and DLco (P = 0.001 for CYC; P < 0.001 for MMF) over 1 year, as well as mortality (P = 0.0008 for CYC arm only).

Conclusion

In a rigorously conducted clinical trial for SSc-related ILD, KL-6 and CCL18 levels correlated with ILD severity and declined with immunosuppression. Patients with higher baseline KL-6 and CCL18 levels were more likely to experience disease progression despite treatment. KL-6 and CCL18 levels could be used to identify patients with a progressive ILD phenotype who may benefit from a more aggressive initial treatment approach.