FIG 4.

CD4⁺ T cells are important for antibody isotype switching. WT, CD4 KO, and MHC-II KO mice were vaccinated and challenged as previously described. Mice receiving Alhydrogel adjuvant alone served as unvaccinated controls. C. burnetii NMI-specific serum IgM and IgG were evaluated weekly until 28 dpv (A) and 14 dpi (B). Each experimental group includes five mice, with error bars representing the standard deviations from the mean. *, P < 0.05; **, P < 0.01; ****, P < 0.0001 (as determined by two-way ANOVA with Tukey’s multiple-comparison test [A] or one-way ANOVA with Tukey’s multiple-comparison test [B]).