Modulation of Mycobacterium avium growth in vivo by cytokines: involvement of tumour necrosis factor in resistance to atypical mycobacteria

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Abstract
SUMMARY: The protective mechanisms associated with resistance to atypical mycobacteria infections are not clear. In an effort to broaden our understanding of the mechanisms involved, susceptible mice were infected with a virulent strain of M. avium and various treatments were applied so as to modify the course of the disease. Treatment with an antiserum against tumour necrosis factor-alpha (TNF-α) significantly enhanced the experimental infection, as judged by enumeration of colony-forming units (CPU) in the spleens and livers of infected mice, suggesting a role for TNF-α in resistance to M. avium. In other sets of experiments, recombinant cytokines were directly infused into infected mice. Infusion of recombinant interferon-gamma (IFN-γ) did not modify the experimental infection significantly, and infusion of interleukin-2 was also without effect. Injection of TNF-α enhanced resistance in susceptible animals, as seen by a reduction in the viable bacilli recovered from the spleens and livers. In a final set of experiments, we demonstrate that combinations of cytokines may induce strong resistance against M. avium, namely injection of 1 μg of interleukin-lα and 1 μg of TNF-α at 5-day intervals which was seen to eradicate M. avium in both spleens and livers of susceptible BALB/c mice. Overall, our results suggest that induction of protection against M. avium by treatment with cytokines may be feasible, and that TNF-α may be a pivotal molecule in resistance to M. avium.