High serum levels of YKL-40 in patients with systemic sclerosis are associated with pulmonary involvement.

OBJECTIVES: YKL-40, a growth factor of connective tissue cells, is elevated in sera from patients with diseases characterized by inflammation, tissue remodelling, or fibrosis. The aim of the study was to determine serum YKL-40 levels in patients with systemic sclerosis (SSc) and to explore any possible clinical and prognostic associations. METHODS: YKL-40 was measured in sera from 88 patients with SSc (26 with diffuse and 62 with limited skin involvement) and in sera from 88 matched healthy controls. Immunohistochemical staining for YKL-40 antigen was performed in a biopsy from a patient with pulmonary SSc. RESULTS: Serum YKL-40 levels of the SSc patients were significantly higher than those of the controls (p<0.00001). Patients with pulmonary fibrosis by chest X-ray, obstructive ventilatory pattern, reduced diffusing capacity (DLco), and digital joint deformity due to skin retraction had significantly higher serum YKL-40 compared with patients without these findings. Patients with elevated serum YKL-40 had shorter survival times than patients with normal serum YKL-40 (p = 0.0005), although this was not independent of age and pulmonary function. YKL-40 protein expression was found in inflammatory cells in fibrosing pulmonary tissue from a patient with SSc. CONCLUSIONS: Serum YKL-40 is elevated in patients with SSc with pulmonary involvement.