Furthermore, the expression levels of IL-1β, tumor necrosis factor-alpha (TNF-α), macrophage colony-stimulating factor (M-CSF), IL-4, and IL-12 (p40), which are inducible subunits of IL-12, IL-15, IL-17, and liposaccharide-induced CXC chemokine (LIX)/CXCL5, were higher in both young and aged BALB/c mice than in C57BL/6 J mice from the early to middle phases of infection (Fig. 4). Here, IL15 is linked to infection.