Figure 4. Nitrite and hydrogen peroxide production in the organs of mice following R. equi infection.

BALB/c mice were orally immunized on days 0 and 14 with S. enterica Typhimurium χ3987-pYA3137vapA (closed triangles/dashed line), or inoculated with either S. enterica Typhimurium χ3987-pYA3137 (closed squares) or PBS (open circles). All mice were intravenously challenged with 4×10⁶ CFU of R. equi ATCC33701 14 days after the last immunization. On days 2, 4, 8, and 10 after infection, the lung, liver, and spleen were harvested and homogenized for NO (A, C, and E) and H₂O₂ (B, D, and F) detection. The endogenous H₂O₂ release was measured by the horseradish peroxidase-dependent phenol red oxidation methods, whereas the nitrite levels were measured by Griess reaction. Data are expressed as means of five mice per group ± SD and are representative of three separate experiments. *p<0.05, **p<0.01, and ***p<0.001 compared to the two control groups.