Highly prevalent Beijing strains exhibit enhanced virulence compared to low-prevalence variants, with distinct immunomodulatory profiles: high-virulence strains induce strong but transient TNF-α expression during early infection, followed by elevated IL-4 production in later stages; low-virulence strains demonstrate progressive IFN-γ and TNF-α expression throughout infection [204]. This evidence concerns the gene IFNG and infection.