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

• Published in: PLoS pathogens 2008-06, Vol.4 (6), p.e1000081-e1000081
• Main Authors: Dao, Dee N, Sweeney, Kari, Hsu, Tsungda, Gurcha, Sudagar S, Nascimento, Ivan P, Roshevsky, Dan, Besra, Gurdyal S, Chan, John, Porcelli, Steven A, Jacobs, William R
• Format: Article
• Language: English
• Subjects: Acids; Animals; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacterial Proteins - physiology; Bone Marrow Cells; Cells, Cultured; Female; Genetics and Genomics/Gene Discovery; Immune system; Immunity; Immunology; Infectious Diseases; Interleukin-12 Subunit p40 - biosynthesis; Lipids; Macrophages - metabolism; Macrophages - virology; Methyltransferases - genetics; Methyltransferases - metabolism; Methyltransferases - physiology; Mice; Mice, Inbred BALB C; Microbiology; Mixed Function Oxygenases - genetics; Mixed Function Oxygenases - metabolism; Mixed Function Oxygenases - physiology; Mutation; Mycobacterium tuberculosis; Mycobacterium tuberculosis - enzymology; Mycobacterium tuberculosis - immunology; Mycobacterium tuberculosis - pathogenicity; Mycolic Acids - metabolism; Tuberculosis; Tumor Necrosis Factor-alpha - biosynthesis
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1000081

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.