Heterologous serum Ig(G+M) concentrations of mice immunized with IpaD or SipD.

Specific serum Ig (G+M) antibodies against SipD for mice immunized with IpaD (A) and against IpaD for mice immunized with SipD (B) were quantified by sandwich ELISA 2 weeks after the last immunization as described in experimental procedures. Data represent mean concentrations (ng/mL) and the standard errors (SEM) from 15 individual mice per group (control mice IN immunized with adjuvant + PBS). Asterisks and p values are indicated (**** p < 0.0001. Exact p value indicated in the figure. ns: non-significant) when comparing mice immunized by the IN or IG route versus control mice using a nonparametric Mann-Whitney test.°: indicates injected immunogen; *: indicates biotinylated recombinant protein used for the ELISA analyses.