Mycolic acid modification by the mmaA4 gene of M. tuberculosis modulates IL-12 production

PLoS Pathog. 2008 Jun 6;4(6):e1000081. doi: 10.1371/journal.ppat.1000081.

Abstract

Mycobacterium tuberculosis has evolved many strategies to evade elimination by the host immune system, including the selective repression of macrophage IL-12p40 production. To identify the M. tuberculosis genes responsible for this aspect of immune evasion, we used a macrophage cell line expressing a reporter for IL-12p40 transcription to screen a transposon library of M. tuberculosis for mutants that lacked this function. This approach led to the identification of the mmaA4 gene, which encodes a methyl transferase required for introducing the distal oxygen-containing modifications of mycolic acids, as a key locus involved in the repression of IL-12p40. Mutants in which mmaA4 (hma) was inactivated stimulated macrophages to produce significantly more IL-12p40 and TNF-alpha than wild-type M. tuberculosis and were attenuated for virulence. This attenuation was not seen in IL-12p40-deficient mice, consistent with a direct linkage between enhanced stimulation of IL-12p40 by the mutant and its reduced virulence. Treatment of macrophages with trehalose dimycolate (TDM) purified from the DeltammaA4 mutant stimulated increased IL-12p40, similar to the increase observed from DeltammaA4 mutant-infected macrophages. In contrast, purified TDM isolated from wild-type M. tuberculosis inhibited production of IL-12p40 by macrophages. These findings strongly suggest that M. tuberculosis has evolved mmaA4-derived mycolic acids, including those incorporated into TDM to manipulate IL-12-mediated immunity and virulence.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Bacterial Proteins / physiology
  • Bone Marrow Cells
  • Cells, Cultured
  • Female
  • Immunity*
  • Interleukin-12 Subunit p40 / biosynthesis*
  • Macrophages / metabolism
  • Macrophages / virology*
  • Methyltransferases / genetics
  • Methyltransferases / metabolism*
  • Methyltransferases / physiology
  • Mice
  • Mice, Inbred BALB C
  • Mixed Function Oxygenases / genetics
  • Mixed Function Oxygenases / metabolism*
  • Mixed Function Oxygenases / physiology
  • Mutation
  • Mycobacterium tuberculosis / enzymology
  • Mycobacterium tuberculosis / immunology
  • Mycobacterium tuberculosis / pathogenicity*
  • Mycolic Acids / metabolism*
  • Tumor Necrosis Factor-alpha / biosynthesis*

Substances

  • Bacterial Proteins
  • Interleukin-12 Subunit p40
  • Mycolic Acids
  • Tumor Necrosis Factor-alpha
  • Mixed Function Oxygenases
  • mma4 protein, Mycobacterium tuberculossis
  • Methyltransferases