In the cases of 2009 pandemic H1N1 influenza A virus (H1N1pdm) infection, serum IL-6 levels were significantly higher in hospitalized critical versus non-critical cases, and experimental infections of several different strains of mice with A/Mexico/4108/09 (H1N1) virus induced the expression of IL-6 mRNA in their lungs at 3 days after infection [13]. The gene discussed is IL6; the disease is infection.