Based on our findings that Hps1−/− mice had a significantly greater ILC2 population in the lung compared with the control group and that CRTH2 is widely expressed on ILC2s, we hypothesized that CRTH2 played a role in ILC2 accumulation in the bleomycin-induced pulmonary fibrosis. Here, PTGDR2 is linked to pulmonary fibrosis.