CHI3L1 is produced by a multitude of cells including macrophages, neutrophils, stem cells, bone cells, synoviocytes, chondrocytes, fibroblast-like cells, endothelial cells, vascular smooth muscle cells, hepatic stellate cells, mammary epithelial cells, and cancer cells.42,45–48 Overexpression of CHI3L1 has been observed in a number of inflammatory conditions including asthma, sepsis, diabetes, cirrhosis, preeclampsia, rheumatoid arthritis, and coronary artery disease.33,38,49–54. Here, CHI3L1 is linked to asthma.