CHI3L1 and chronic obstructive pulmonary disease: Recently, YKL-40 has attracted considerable attention due to its increased levels in individuals with asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis, rheumatoid arthritis, inflammatory bowel disease, alcoholic cirrhosis and different types of malignant tumors [26,27,28,29,30,31,32,33,34,35,36,37,38].