IFN-γR and IL-6 are not necessarily required for the control of Ye Δ yopH infection. IFN-γR-/- (A) or IL-6-/- (B) mice as well as C57BL/6 mice were infected intravenously with 5 × 104 pYV+ (black bars) or 5 × 104 ΔyopH (white bars). The bacterial number was assessed in spleens 24 and 72 hours after infection. Values represent the average log10 CFU per spleen with the standard errors of the means indicated by error bars (5–10 mice per group). Asterisks indicate significant differences (p < 0.05, Wilcoxon Rank test) between the compared groups. Two further independent experiments showed comparable results.