title: Early Secreted Antigenic Target of 6-kDa of Mycobacterium tuberculosis Stimulates IL-6 Production by Macrophages through Activation of STAT3.
abstract: As early secreted antigenic target of 6 kDa (ESAT-6) of Mycobacterium tuberculosis (Mtb) is an essential virulence factor and macrophages are critical for tuberculosis infection and immunity, we studied ESAT-6 stimulated IL-6 production by macrophages. ESAT-6 stimulated significantly higher IL-6 secretion by murine bone marrow derived macrophages (BMDM) compared to culture filtrate protein 10 kDa (CFP10) and antigen 85A. Polymyxin B, an LPS blocker, did not affect ESAT-6 stimulated macrophage IL-6 production. ESAT-6 but not Pam3CSK4 induced IL-6 by TLR2 knockout BMDM. ESAT-6 induced phosphorylation and DNA binding of STAT3 and this was blocked by STAT3 inhibitors but not by rapamycin. STAT3 inhibitors suppressed ESAT-6-induced IL-6 transcription and secretion without affecting cell viability. This was confirmed by silencing STAT3 in macrophages. Blocking neither IL-6Rα/IL-6 nor IL-10 affected ESAT-6-induced STAT3 activation and IL-6 production. Infection of BMDM and human macrophages with Mtb with esat-6 deletion induced diminished STAT3 activation and reduced IL-6 production compared to wild type and esat-6 complemented Mtb strains. Administration of ESAT-6 but not CFP10 induced STAT3 phosphorylation and IL-6 expression in the mouse lungs, consistent with expression of ESAT-6, IL-6 and phosphorylated-STAT3 in Mtb-infected mouse lungs. We conclude that ESAT-6 stimulates macrophage IL-6 production through STAT3 activation.
authors.affiliation: Department of Pulmonary Immunology, University of Texas Health Science Center at Tyler, Texas 75708, USA.
authors.forename: Bock-Gie
authors.initials: BG
authors.lastname: Jung
authors.affiliation: Department of Pulmonary Immunology, University of Texas Health Science Center at Tyler, Texas 75708, USA.
authors.forename: Xisheng
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Pulmonary Immunology, University of Texas Health Science Center at Tyler, Texas 75708, USA.
authors.forename: Na
authors.initials: N
authors.lastname: Yi
authors.affiliation: Department of Pulmonary Immunology, University of Texas Health Science Center at Tyler, Texas 75708, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Ma
authors.affiliation: Department of Microbial Infection and Immunity and Center for Microbial Interface Biology, the Ohio State University, Columbus, OH 43210, USA.
authors.forename: Joanne
authors.initials: J
authors.lastname: Turner
authors.affiliation: Department of Pulmonary Immunology, University of Texas Health Science Center at Tyler, Texas 75708, USA.
authors.forename: Buka
authors.initials: B
authors.lastname: Samten
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology*; D001426:Bacterial Proteins / Q000276:immunology* / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology*; D051379:Mice; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D010766:Phosphorylation; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D050796:STAT3 Transcription Factor / Q000378:metabolism*
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C093276:ESAT-6 protein, Mycobacterium tuberculosis; D015850:Interleukin-6; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; C577686:interleukin-6, mouse