After extensive exposure to Mycobacterium tuberculosis (Mtb), most individuals acquire latent Mtb infection (LTBI) defined by a positive tuberculin skin test (TST) or interferon-γ release assay (IGRA). To identify mechanisms of resistance to Mtb infection, we compared transcriptional profiles from highly-exposed contacts who resist TST/IGRA conversion (resisters, RSTRs) and controls with LTBI using RNAseq. Gene sets related to carbon metabolism and free fatty acid (FFA) transcriptional responses enriched across two independent cohorts suggesting RSTR and LTBI monocytes have distinct activation states. We compared intracellular Mtb replication in macrophages treated with FFAs and found that palmitic acid (PA), but not oleic acid (OA), enhanced Mtb intracellular growth. This PA activity correlated with its inhibition of pro-inflammatory cytokines in Mtb-infected cells. Mtb growth restriction in PA-treated macrophages was restored by activation of AMP kinase (AMPK), a central host metabolic regulator known to be inhibited by PA. Finally, we genotyped AMPK variants and found seven SNPs in PRKAG2, which encodes the AMPKγ subunit, that strongly associated with RSTR status. Taken together, RSTR and LTBI phenotypes are distinguished by FFA transcriptional programs and by genetic variation in a central metabolic regulator, which suggests immunometabolic pathways regulate TST/IGRA conversion.
Jason D. Simmons, Phu T. Van, Catherine M. Stein, Violet Chihota, Thobani Ntshiqa, Pholo Maenetje, Glenna J. Peterson, Anthony Reynolds, Penelope Benchek, Kavindhran Velen, Katherine L. Fielding, Alison D. Grant, Andrew D. Graustein, Felicia K. Nguyen, Chetan Seshadri, Raphael Gottardo, Harriet Mayanja-Kizza, Robert S. Wallis, Gavin Churchyard, W. Henry Boom, Thomas R. Hawn
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