Innate resistance against Listeria infection in B7-H4KO mice is independent of adaptive immunity. (A) Altered colony formation of Listeria in liver from B7-H4 × RAG-1 DKO mice. Mice were intraperitoneally injected with 3 × 106 CFUs Listeria. Forty-eight hours after infection, liver tissues at 0.2 mg from each mouse were homogenized in 10 mL PBS. Tissues (50 μL) were plated on agar plates of Listeria enrichment broth for colony counting. Data represent at least 3 independently performed experiments. DKO indicates B7-H4 × RAG-1 double KO; RKO, RAG-1 KO littermate. (B,C) Enumeration of Listeria colonies in livers (B) and spleens (C) on agar plates. Livers and spleens were prepared from RKO or DKO mice and cultivated as described in panel A to quantify Listeria colonies. Data represent 5 independently performed experiments. At day 3, differences of Listeria colonies in the organs from RKO and DKO are significant. *P < .05. (D) Resistance of DKO mice to Listeria infection. Five male RKO and 8 male DKO were intraperitoneally injected with 4 × 106 CFUs Listeria. Survival of mice was monitored daily for 15 days. Data represent 2 independently performed experiments. P < .05. (E,F) Gr-1+ cell depletion eliminated resistance to Listeria infection equally in both RKO and DKO mice. Three mice of RKO or DKO were intraperitoneally injected with 250 μg anti–Gr-1 mAb or isotype control rat IgG 24 hours before Listeria infection. Mice were then intravenously injected with 0.1 × 106 CFUs Listeria. Twenty-four hours after infection, mice were terminated and Listeria in liver was counted as described previously. The data are expressed as CFUs per gram of liver (E) and spleen (F). Data represent 2 independent experiments. * indicates significantly different from the control (Cont mAb; P < .05); **, significantly different from other control Ab group. No significant differences were found in anti–Gr-1 mAb-treated groups between RKO and DKO (P > .05). Error bars in panels B, C, E, and F indicate SD (n = 3 mice).
