Mice deficient for Cyp1a1 and Cyp1b1, but heterozygous for Cyp1a2, whose expression and functional importance is largely restricted to the liver33, also displayed increased resistance to influenza-induced vascular leakage and lung damage (Extended Data Fig. 4a), indicating that the increased protection conferred by CYP1 deficiency is unrelated to altered CYP1A2-driven ligand metabolism in the liver. The gene discussed is CYP1A2; the disease is influenza.