CHI3L1 and asthma: YKL-40, a human chitinase-like protein encoded by the CHI3L1 gene, plays a significant role in the inflammatory response of asthma, especially in airway remodeling and tissue fibrosis.[10–13] Previous studies demonstrated that patients with asthma exhibit a significant elevation in serum YKL-40.[14] However, the relationship between circulating YKL-40 and asthma endotype remains inconsistent.