During the effector phase of the CD8 T cell response, at day 9 following infection, LCMV GP33-specific CD8 T cells from all of the cohorts analyzed produced IFN-γ in response to a brief (5.5 hr) exposure to IL-12+IL-18 and IL-12+IL-18+IL-21 (Fig. 2). Here, IL18 is linked to infection.