CHIT1 and pulmonary fibrosis: In addition, further mechanistic understanding on the putative receptors and interacting partners of CHIT1 and CHI3L1 in profibrotic macrophage activation and invasive fibroblast differentiation and their heterocellular interactions will be crucial for the development of effective therapeutics targeting CHIT1 and CHI3L1 for the patients with progressive pulmonary fibrosis.