Figure 1. Gut Microbiota Induces Antigen-Specific IgG in the Steady State.

(A) ELISA of serum IgG, IgA, and IgM against fecal bacteria (FB) in naive SPF J_H^−/− and WT mice and GF WT mice. 6–10 mice were used for each genotype.

(B) ELISA of serum IgG1, IgG2c, IgG2b, and IgG3 against fecal bacteria in 6- to 8-week-old naive SPF WT mice. Six WT mice were used.

(C) ELISA of serum IgG, IgA, and IgM against fecal bacteria in 6- to 8-week-old WT and Tcrb^−/− naive mice. 6–10 mice were used for each genotype.

(D) ELISA of serum IgG against fecal bacteria of 4-, 6-, 10-, and 40-week-old mice.

(E) Peritoneal B1 and B2 cells and splenic marginal zone (MZ) and follicular (FO) B cells were stimulated ex vivo with LPS, heat-killed fecal bacteria, or E. coli for 3 days, and cells producing IgG that recognized fecal bacteria were detected by ELISpot.

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

***p < 0.001. See also Figure S1.