Serum and BAL YKL-40 levels in different inflammatory lung diseases: an update

YKL-40 (also called chitinase 3-like-1 or human cartilage glycoprotein 39) is a chitinase-like protein belonging to the family 18 of glycosyl hydrolase (GH18). This protein is involved in the inflammatory process acting as pro-inflammatory cytokine secreted by neutrophils, activated human macrophages, vascular smooth muscle cells and cancer cells. It has been shown that YKL-40 has a role in pathological tissue remodeling and development of fibrosis of several diseases. To date, the biological and pathophysiological function of YKL-40 protein in pulmonary diseases is still unclear. This review focuses on the role of YKL-40 in diagnosis and monitoring of different lung diseases in order to assess whether this protein could be used as biomarker of specific conditions featured by inflammation and fibrosis. A comprehensive review of the literature using PubMed database, with appropriate terms, was undertaken for articles in English published since 1997. The literature search was undertaken in October 2014