TLR1 is important for inducing IL-17–mediated immunity during oral infection. (A and B) TLR1^−/−, TLR6^−/−, and littermates were infected orally (A) or i.v. (B) with 10⁵ CFU Y. enterocolitica. 6 d after infection, MLNs (oral) or SPLs (i.v.) were harvested. Intracellular cytokine production was analyzed by flow cytometry; plots are representative of one out of six infected mice. Total cell counts were determined for naive (open circles) or infected (closed circles) mice. *, P < 0.05; **, P < 0.01 (unpaired Student’s t test). (C and D) Levels of anti-Yersinia IgA, IgG1, and IgG2a from TLR1^−/− or TLR1^+/− mice infected orally (C) or i.v. (D) with 10⁵ CFU Y. enterocolitica. Fresh fecal pellets or serum were collected on days 0, 10, and 14, and antibody titers were detected by ELISA. Data are represented as the mean ± SEM and are pooled from two experiments (n = 6). (E) The ratio of anti-Yersinia IgA, IgG1, and IgG2a from infected TLR1^+/− and TLR1^−/− mice at day 14. (F) Survival curve of C57BL/6 mice infected orally (squares) or i.v. (circles) with 10⁵ CFU Y. enterocolitica and injected i.p. with 100 µg monoclonal anti–IL-17 (open symbols) or isotype control (rat Ig; closed symbols) every other day for 8 d. Data are pooled from two individual experiments (n = 10). Statistical significance was determined by Wilcoxon Log-rank test (P = 0.0125, oral; P = 0.8972, i.v.). (G) Fecal antibody levels of IgG1, IgG2a, and IgA in anti–IL-17– or isotype control–treated mice. Data are the mean ± SEM (n = 6) from two independent experiments. *, P < 0.01 (paired Student’s t test). (H) Bacterial burden of orally (squares) or i.v. (circles) infected mice treated with isotype control (closed symbols) or anti–IL-17 (open symbols). MLNs and SPLs were harvested at days 3 and 7, respectively, for oral infections, and both organs were harvested at 7 d for i.v. infection. Data are from two pooled experiments (n = 6). *, P < 0.01 (paired Student’s t test). BD, below detection. (A, B, and H) Horizontal bars represent the mean.