CHI3L1 and pulmonary fibrosis: The fact that CHI3L1 mediates its profibrotic effects through CRTH2, and that CRTH2-positive ILC2s are indicated in pulmonary fibrosis development in both humans and mice, allows us to speculate that CRTH2, via its expression on ILC2s, mediates the cellular and tissue effects of CHI3L1 that lead to fibroproliferation (41–43).