Figure 6.

FcμR^−/− mice are impaired in response to LPS and highly susceptible to Citrobacter rodentium infection. (A) Antibody production to a TI antigen, NP-LPS. Eight pairs of WT and FcμR^−/− mice were immunized i.v. with 10 µg of NP-LPS and analyzed for the production of NP-specific IgM (left) and IgG₃ (right) antibodies in the serum at 1–4 weeks after immunization. The mean values of WT and FcμR^−/− mice at the indicated time points are shown. (B,C) Marginal zone B cells (MZB) in FcμR^−/− mice responded poorly to LPS administration. WT and FcμR^−/− mice were injected i.v. with 20 µg LPS or PBS as a control, and the cell size (FSC) of MZB and follicular B (FOB) was analyzed 24 h later. (B) FSC of MZB and FOB in WT (blue lines) and FcμR^−/− (red lines) mice injected with LPS. Shaded areas, FSC of MZB and FOB in mice injected with PBS. (C) Summary of three mice per group. *p < 0.05; **p < 0.01 (unpaired t-test). (D) FcμR^−/− mice are highly susceptible to acute bacterial infection. Eight pairs of WT and FcμR^−/− mice were injected i.v. with C. rodentium (6 × 10⁸ CFU) or PBS as a control and monitored for their survival. Kaplan–Meier survival plot for WT (solid line) and FcμR^−/− (dotted line) mice are shown. ***p < 0.005 (log-rank test).