title: Human toll-like receptors mediate cellular activation by Mycobacterium tuberculosis.
abstract: Recent studies have implicated a family of mammalian Toll-like receptors (TLR) in the activation of macrophages by Gram-negative and Gram-positive bacterial products. We have previously shown that different TLR proteins mediate cellular activation by the distinct CD14 ligands Gram-negative bacterial LPS and mycobacterial glycolipid lipoarabinomannan (LAM). Here we show that viable Mycobacterium tuberculosis bacilli activated both Chinese hamster ovary cells and murine macrophages that overexpressed either TLR2 or TLR4. This contrasted with Gram-positive bacteria and Mycobacterium avium, which activated cells via TLR2 but not TLR4. Both virulent and attenuated strains of M. tuberculosis could activate the cells in a TLR-dependent manner. Neither membrane-bound nor soluble CD14 was required for bacilli to activate cells in a TLR-dependent manner. We also assessed whether LAM was the mycobacterial cell wall component responsible for TLR-dependent cellular activation by M. tuberculosis. We found that TLR2, but not TLR4, could confer responsiveness to LAM isolated from rapidly growing mycobacteria. In contrast, LAM isolated from M. tuberculosis or Mycobacterium bovis bacillus Calmette-Guérin failed to induce TLR-dependent activation. Lastly, both soluble and cell wall-associated mycobacterial factors were capable of mediating activation via distinct TLR proteins. A soluble heat-stable and protease-resistant factor was found to mediate TLR2-dependent activation, whereas a heat-sensitive cell-associated mycobacterial factor mediated TLR4-dependent activation. Together, our data demonstrate that Toll-like receptors can mediate cellular activation by M. tuberculosis via CD14-independent ligands that are distinct from the mycobacterial cell wall glycolipid LAM.
authors.affiliation: Pulmonary Center, Boston University School of Medicine, Boston Medical Center, MA 02118, USA.
authors.forename: T K
authors.initials: TK
authors.lastname: Means
authors.forename: S
authors.initials: S
authors.lastname: Wang
authors.forename: E
authors.initials: E
authors.lastname: Lien
authors.forename: A
authors.initials: A
authors.lastname: Yoshimura
authors.forename: D T
authors.initials: DT
authors.lastname: Golenbock
authors.forename: M J
authors.initials: MJ
authors.lastname: Fenton
mesh_terms: D000209:Acute-Phase Proteins; D000818:Animals; D001426:Bacterial Proteins / Q000502:physiology; D016466:CHO Cells; D002352:Carrier Proteins / Q000502:physiology; D002460:Cell Line; D006224:Cricetinae; D029721:Drosophila Proteins; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology*; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000502:physiology; D008070:Lipopolysaccharides / Q000378:metabolism / Q000494:pharmacology; D008262:Macrophage Activation / Q000276:immunology; D008351:Mannans / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D009169:Mycobacterium tuberculosis / Q000254:growth & development / Q000276:immunology / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology*; D012995:Solubility; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D000099231:Lipopolysaccharide-Binding Protein
chemical_list: D000209:Acute-Phase Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029721:Drosophila Proteins; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D008351:Mannans; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D000099231:Lipopolysaccharide-Binding Protein; C495342:TLR2 protein, human; C495345:TLR4 protein, human; C050016:lipoarabinomannan; C012189:arabinomannan