Mycolic acid modification by the mmaA4 gene of M. tuberculosis modulates IL-12 production.
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.
Howard Hughes Medical Institute, Albert Einstein College of Medicine, Bronx, New York, United States of America.
Dee N
DN
Dao
Kari
K
Sweeney
Tsungda
T
Hsu
Sudagar S
SS
Gurcha
Ivan P
IP
Nascimento
Dan
D
Roshevsky
Gurdyal S
GS
Besra
John
J
Chan
Steven A
SA
Porcelli
William R
WR
Jacobs
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D001854:Bone Marrow Cells; D002478:Cells, Cultured; D005260:Female; D007109:Immunity; D053762:Interleukin-12 Subunit p40 / Q000096:biosynthesis*; D008264:Macrophages / Q000378:metabolism / Q000821:virology*; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000201:enzymology / Q000276:immunology / Q000472:pathogenicity*; D009171:Mycolic Acids / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*
D001426:Bacterial Proteins; D053762:Interleukin-12 Subunit p40; D009171:Mycolic Acids; D014409:Tumor Necrosis Factor-alpha; D006899:Mixed Function Oxygenases; C102349:mma4 protein, Mycobacterium tuberculossis; D008780:Methyltransferases