Our previous studies showed that CRTH2 plays an important role in the augmented fibrotic responses in the bleomycin-induced pulmonary fibrosis in Hps1−/− mice, as collagen accumulation was significantly upregulated when CHI3L1 was overexpressed and was reduced in the mice treated with a CRTH2 inhibitor (16, 17). This evidence concerns the gene PTGDR2 and pulmonary fibrosis.