Context
YKL-40, also known as human cartilage glycoprotein-39 (HCgp-39), is a mammalian member of the family 18 glycosyl hydrolases. Its function is unknown but it is a heparin- and chitin-binding lectin which is secreted in large quantities by articular cartilage and synoviocytes in patients with rheumatoid arthritis (RA). It is recognized by T cells in over 50% of patients with RA, although the pathological significance of this is unclear. YKL-40 is also secreted by differentiating vascular smooth muscle, some cancer cells, neutrophils and human macrophages at a late stage of differentiation. The pattern of secretion of YKL-40 in humans, and of its homologues in other mammals, has led to the proposal that it is involved in tissue remodelling. GCA and polymyalgia rheumatica (PMR) are related (overlapping) vasculitic diseases, characterised by an inflammatory infiltrate of T cells, macrophages and multinucleated giant cells. However, the expression of YKL-40 in inflammatory lesions in these patients has not previously been explored. To assess whether YKL-40 levels are elevated in patients with GCA or PMR and whether YKL-40 can be detected in macrophages and giant cells in the inflammatory lesions.