CD40LG and influenza: 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).