Downmodulation of Vaccine-Induced Immunity and Protection against the Intracellular Bacterium Francisella tularensis by the Inhibitory Receptor FcγRIIB

Figure 3

iFt-immunized FcγRIIB KO mice exhibit increased protection against a lethal Ft-LVS challenge as compared to their WT counterparts. WT C57BL/6J and FcγRIIB KO mice were immunized i.n. with 20 μL of PBS (vehicle) or 2 × 10⁷ iFt-organisms in 20 μL of PBS on day 0 and boosted on day 21. On day 35 mice were challenged i.n. with approximately 4 × LD₅₀ (a) or 16 × LD₅₀ (b) of Ft-LVS. Survival was then monitored for 21 to 25 days. Panel (a) represents between 12 and 14 mice/group while panel (b) represents between 17 and 20 mice/group. Statistical analysis was determined by a contingency table analysis and two-tailed Fisher’s exact test on survival at day 21. . In addition, bacterial burden in the lungs of challenged mice was also determined. WT C57BL/6J and FcγRIIB KO mice were immunized i.n. with 20 μL of PBS (vehicle) or 2 × 10⁷ iFt-organisms in 20 μL of PBS on day 0 and boosted on day 21. On day 35 mice were given a sublethal challenge i.n. with approximately 0.4 × LD₅₀ of Ft-LVS. Five days after challenge lungs were collected, homogenized, and plated on chocolate agar to determine bacterial burden as described in Section 2. Each symbol represents a single mouse. Statistical analysis of the tissue bacterial burden was done via a nonparametric one-way ANOVA (Kruskal-Wallis test) coupled with a Dunn’s multiple comparison after test. While there appeared to be a substantial reduction in bacterial burden in the majority of iFt-immunized FcγRIIB KO versus WT mice, the difference was not significant based on this analysis.

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(b)

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