To characterize the immune response of the host to the studied M. avium strains, expression of the anti-mycobacterial defense cytokine genes was quantified in the lungs of the infected mice by real-time RT-PCR ( e first 5 d after infection, both strains had increased expression of IFN-γ, IL-4 and IL-17 in WT mice this was accompanied by macrophage activation and enhanced expression of the pro-inflammatory mediators IL-12, TNF-α and iNOS. Here, TNF is linked to infection.