Fig. 3: Clinical M. bovis frd mutant exhibits enhanced pathogenicity.

a–f C57BL/6 mice were infected with ~5000 CFU of two different clinical isolates intranasally for 12 and 22 days. a Body weight gain rate curves of C57BL/6 mice uninfected or infected with two different clinical isolates. b, c The ratio of lung or spleen weight to the total body weight at 12 and 22 dpi. d, e Bacterial loads (CFU) in lung or spleen. f The percentage of lung’s area occupied by inflammatory lesions. g Hematoxylin and eosin (H&E)-stained lung sections at 12 and 22 dpi. Arrows indicate lymphocytes, and arrowheads indicate neutrophils. h, i Number of cells and activated CD4⁺ T cells in draining lymph nodes of mice at 12 dpi. j, k Percentage of CD4⁺CD69⁺ T cells expressing IFN-γ or IL-17A in the draining lymph nodes of mice as in (h). Data are presented as mean values  ± SD. Sample size of n  =  5 mice was included in each group. P values depicted on the graphs were assessed using one-way ANOVA with Tukey’s multiple comparisons test (a–c) and two-tailed unpaired Student’s t-test (d–f, h–k). Scale bars, 1 mm (top) and 20 μm (bottom). Source data are provided as a Source Data file.