Relative mRNA transcript expression of MDM from purebred animals of a resistant or susceptible genotype. MDM were infected with MAP for 24 h before expression of the genes iNOS, IL-1α, TNF-α, IL-23p19, IL-12p35 and IL-10 was measured by Q-PCR. Fold changes (mean ± SEM) are defined as expression upon infection compared to the uninfected control, n = 20 (10 resistant, 3 intermediate and 7 susceptible). Three animals of susceptible genotype were removed from the susceptible group into an “intermediate” category on observing that their macrophage gene expression profiles resembled a resistant-type animal for the iNOS, IL-1α, TNF-α and IL-23p19 molecules. Statistical significance has been calculated using the Mann–Whitney test where ** denotes p < 0.01 and *** denotes p < 0.001.