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Infect. Immun. doi:10.1128/IAI.00290-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Mycolactone-mediated inhibition of TNF production by macrophages infected with Mycobacterium ulcerans has implications for the control of infection

Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Braga, Portugal, Department of Microbiology, University of Tennessee, M409 Walters Life Sciences, Knoxville, TN 37996-0845

^* To whom correspondence should be addressed. Email: jpedrosa{at}ecsaude.uminho.pt.

	Abstract

The pathogenicity of Mycobacterium ulcerans, the agent of Buruli ulcer, depends on the cytotoxic exotoxin mycolactone. Little is known on the immune response to this pathogen. Following the demonstration of an intracellular growth phase in the life cycle of M. ulcerans, we investigated the production of tumor necrosis factor (TNF) induced by intramacrophage bacilli of diverse toxigenesis/virulence, as well as the biological relevance of TNF during M. ulcerans experimental infections.

Our data show that murine bone-marrow derived macrophages infected with mycolactone-negative strains of M. ulcerans (non-virulent) produce high amounts of TNF, while macrophages infected with mycolactone-positive strains of intermediate or high virulence produce intermediate or low amounts of TNF, respectively. These results are in accordance with the finding that TNF-receptor P55 deficient (TNF-P55 KO) mice are not more susceptible than WT mice to the infection by the high virulent strains but are more susceptible to non-virulent and intermediate virulent strains, demonstrating that TNF is required to control the proliferation of these strains in animals experimentally infected by M. ulcerans. We also show that mycolactone produced by intramacrophage M. ulcerans bacilli inhibits, in a dose-dependent manner, but does not abrogate, the production of macrophage inflammatory protein 2 (MIP-2), which is consistent with the persistent inflammatory responses observed in experimentally infected mice.

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