IL6 and infection: Consistent with gene expression studies, we similarly detected an elevated level proinflammatory cytokine, IL-6, in the lung of aged mice compared to young mice at day 2 and day 4 post-infection (2dpi: 87.3 vs. 66.8 pg/mL, 4dpi: 73.0 vs. 49.0 pg/mL).