Monoclonal antibody mAY recognizes human YKL-40. YKL-40 is a human glycoprotein which is related to the chitinase protein family. However, without chitinase activity. YKL-40 is also called chitinase-3-like protein 1 or BRP-39. YKL-40 is expressed and secreted by inflammatory cells and some cancer cells.YKL-40 has no distinct function but is involved in processes related to inflammation, extracellular matrix (ECM) remodelling and proliferation of cancer cells. The cellular receptor is still unknown. Protein expression is predominantly found in macrophages, neutrophils and differentiated vascular smooth muscle cells, especially in tissues with inflammation vascular damage and ECM remodelling. Furthermore, YKL-40 stimulates the proliferation of connective tissue cells, like fibroblasts, in a dose dependent way. Studies report that YKL-40 signalling is associated with MAPK and PI3K pathways and possibly counteracts TNFα and Il1. YKL-40 is related to several pathogenic processes like infection, cardiovascular disease, fibrosis, diabetes, osteoarthritis and various cancers. Several studies demonstrate elevated levels in those diseases and the protein is investigated to function as a clinical biomarker. Serum YKL-40 is found to be a biomarker of prognosis already in 13 different types of cancer and associated with disease severity. In healthy individuals it is believed that there is no difference between gender and the serum concentration is quite constant.Antibody mAY is capable of binding native as well as recombinant YKL-40 and is capable to inhibit tube formation of microvascular endothelial cells in vitro. The antibody also blocks MAPK signalling via VEGFR2.