FIG. 3.
IFN-γ production by splenocytes from naive or B. pertussis- or B. parapertussis-immune hosts. C57BL/6 mice were inoculated with 5 × 105 CFU of B. pertussis (Bp) or B. parapertussis (Bpp). Immunized and naive mice were sacrificed 28 days postinoculation, spleens were excised, and splenocytes were exposed to media alone (hatched bars), heat-killed B. pertussis (black bars), or heat-killed B. parapertussis (white bars) for 3 days. The supernatant was collected, and cytokine ELISAs were performed to quantify the levels of IFN-γ produced by splenocytes. Values are expressed as the means ± standard deviations. *, P < 0.05; **, P < 0.01.