FIG. 5.

IFN-γ response to total listerial antigens. Mice were immunized as described in the legend to Fig. 4. After 6 days, splenocytes were recovered and stimulated in vitro with heat-killed L. monocytogenes; IFN-γ production was measured by an enzyme-linked immunosorbent assay. Data represent the mean and standard deviation for groups of six to eight mice. Splenocytes from mice infected with 10⁶ clpP mutant bacteria produced IFN-γ at levels comparable to those produced by splenocytes from mice infected with wild-type bacteria.