WT and Hps1−/− mice were subjected to intraperitoneal (i.p.)bleomycin administration to induce lung fibrosis (Figure 2A), mouse lungs were perfused with PBS to remove circulating cells, and frequency of Lineage–Thy1.2+ICOS+T1/ST2+ ILC2s was quantitated at baseline and after bleomycin challenge using flow cytometry (Figure 2B and Supplemental Figure 2). Here, ICOS is linked to pulmonary fibrosis.