Figure 3. Gut Microbiota-Induced IgG Confers Protection against DSS-Induced Bacteremia.

(A) ELISA of fecal IgG, IgA, and IgM against fecal bacteria in feces of naive (mock) or day 7 DSS-treated mice (mock = 5 mice; day 7 DSS = 7 mice).

(B) Flow cytometry for IgG on fecal bacteria from naive (mock) or day 7 DSS-treated mice.

(C) WT and J_H^−/− mice were treated with DSS for 7 days and CFU of aerobes and anaerobes in the blood were determined. Each dot represents one mouse.

(D) Survival of WT and J_H^−/− mice, treated with or without antibiotics, after administration of 2.5% DSS in drinking water for 7 days.

(E) Percentages of bacterial isolates from spleens, livers, and blood of day 7 DSS-treated J_H^−/− mice.

(F) WT and J_H^−/− mice were i.p. injected with 5 × 10⁷ CFU of ECM6L4 (an isolate from a DSS-treated J_H^−/− mouse), and E. coli was recovered from the peritoneum 6 hr after infection and analyzed for IgG or IgA coating by FACS.

(G) Survival of WT, J_H^−/−, and Fcer1g^−/− mice after i.p. injection with 10⁷ CFU of M6L4 (WT n = 9; J_H^−/− n = 8; Fcer1g^−/− n = 8).

(H) Survival of untreated J_H^−/− mice or J_H^−/− mice that were administered 400 mg of purified serum IgG from WT or QM mice 24 hr prior to i.p. infection with 10⁷ CFU of ECM6L4 (J_H^−/− n= 6; J_H^−/− +WT IgG n = 7; J_H^−/− +QM IgG n = 6).

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

***p < 0.001. See also Figure S2.