Homozygous genetic deletion, or knockout (KO), of either IL-33 (IL33KO), ST2 (ST2KO), or both (IL33KOST2KO, or double-knockout [DKO]) attenuates the magnitude of bleomycin-induced pulmonary fibrosis [8,9,13]. The gene discussed is IL1RL1; the disease is pulmonary fibrosis.