To determine whether IL-13 is a critical factor promoting radiation-induced pulmonary fibrosis we compared the survival duration of wild type and IL-13 deficient mice (IL-13−/−, c57BL/6NTac-[KO]IL13) exposed to thoracic irradiation (n = 15 per group, Fig. 3a). The gene discussed is IL13; the disease is pulmonary fibrosis.