The increased tissue damage in the lungs caused by CK4 infection, compared to ME49, may be related to the persistence of activated macrophages capable of producing pro-inflammatory cytokines (Park and Hunter, 2020), contributing to greater tissue damage (Montoya and Liesenfeld, 2004; Melchor and Ewald, 2019), and by disrupting anion channels in the airway epithelial cells and contributing to airway inflammation (Qiu et al., 2023). The gene discussed is KRT4; the disease is infection.