A mouse infected with the Δ27735 mutant released significantly higher levels of cytokines into the peripheral blood and induced the development of pathological lesions in the spleen and liver. The concentrations of TNF-α and IL-12p40 in the peripheral blood of mice infected with the WT strain and the Δ27735 mutant were determined at 2, 4, 6, 9, and 12 weeks pi (A). Histopathological analysis of the liver and spleen infected with the WT strain or the Δ27735 mutant at 12 weeks pi by hematoxylin–eosin staining (200×, B). Statistical significance was determined using two-way ANOVA followed by Holm-Sidak’s multiple test. ***p < 0.001.