Figure 7. IgG against Murein Lipoprotein Confers Protection against Salmonella Infection.

(A–C) GF mice were i.p. administered PBS or 10⁷ WT or ΔMLP E. coli. 2 weeks later, the concentrations of serum IgG, IgA, and IgM against fecal bacteria were determined by ELISA (A), and the presence of anti-MLP IgG in the sera of these mice were also confirmed by immunoprecipitation of MLP from WT E. coli lysates and immunoblotted using sera from these mice or monoclonal anti-MLP (B). 2–3 weeks after administration of PBS or 10⁷ CFU of WT and or ΔMLP E. coli, GF mice were i.p. infected with 10⁴ CFU of Salmonella M525P and the levels in spleens and livers were determined at 72 hr (C).

(D and E) Salmonella were incubated with anti-MLP IgG or isotype for 30 min, and then assessed for surface IgG coating (D) and killing by neutrophils in vitro (E). 6- to 8-week-old WT mice were i.p. administered 1 mg of anti-MLP IgG or isotype for 24 hr before i.p. infection with 4 × 10⁴ ST M525P. CFU of ST M525P in spleens and livers were determined at 72 hr.

Data represent two to three independent experiments. Error bars indicate SD. *p < 0.05, **p < 0.01,

***p < 0.001. See also Figure S6.