Our analyses of mixed bone marrow chimeras show that although both IL-18Rα+/+ and IL-18Rα-/- CD8 T cells do initially participate in the response to LCMV cl13 infection, the virus-specific IL-18Rα-/- CD8 T cells are outcompeted by their IL-18Rα+/+ counterparts following the peak of the effector phase of the response. Here, CD8A is linked to infection.