By analysing the bronchoalveolar lavage fluid (BALF) on day 6 post influenza virus infection, we found that Cyp1–/– mice were more resistant to infection-induced lung barrier leakage, with reduced total cells, red blood cells (RBCs), and immune cell infiltration within the lung airspace, relative to wild-type (WT) controls (Fig. 2b, c, Extended Data Fig. 1b, Extended Data Fig. 3a). The gene discussed is CYP1A1; the disease is infection.