CD40 interaction with CD40L, is important to fully activate APCs [46,47] and the role of CD40 in stimulating the production of IL-12 is well documented (reviewed in [43,48]) The concentration of IL-12p70, the active form of IL-12, was not only significantly higher in the lungs of adult mice, but also spiked earlier compared to aged mice following influenza infection (Fig. 7A). This evidence concerns the gene CD40 and influenza.