title: The Poly-γ-d-Glutamic Acid Capsule Surrogate of the Bacillus anthracis Capsule Is a Novel Toll-Like Receptor 2 Agonist.
abstract: Bacillus anthracis is a pathogenic Gram-positive bacterium that causes a highly lethal infectious disease, anthrax. The poly-γ-d-glutamic acid (PGA) capsule is one of the major virulence factors of B. anthracis, along with exotoxins. PGA enables B. anthracis to escape phagocytosis and immune surveillance. Our previous study showed that PGA activates the human macrophage cell line THP-1 and human dendritic cells, resulting in the production of the proinflammatory cytokine interleukin-1β (IL-1β) (M. H. Cho et al., Infect Immun 78:387-392, 2010, http://dx.doi.org/10.1128/IAI.00956-09). Here, we investigated PGA-induced cytokine responses and related signaling pathways in mouse bone marrow-derived macrophages (BMDMs) using Bacillus licheniformis PGA as a surrogate for B. anthracis PGA. Upon exposure to PGA, BMDMs produced proinflammatory mediators, including tumor necrosis factor alpha (TNF-α), IL-6, IL-12p40, and monocyte chemoattractant protein 1 (MCP-1), in a concentration-dependent manner. PGA stimulated Toll-like receptor 2 (TLR2) but not TLR4 in Chinese hamster ovary cells expressing either TLR2 or TLR4. The ability of PGA to induce TNF-α and IL-6 was retained in TLR4(-/-) but not TLR2(-/-) BMDMs. Blocking experiments with specific neutralizing antibodies for TLR1, TLR6, and CD14 showed that TLR6 and CD14 also were necessary for PGA-induced inflammatory responses. Furthermore, PGA enhanced activation of mitogen-activated protein (MAP) kinases and nuclear factor-kappa B (NF-κB), which are responsible for expression of proinflammatory cytokines. Additionally, PGA-induced TNF-α production was abrogated not only in MyD88(-/-) BMDMs but also in BMDMs pretreated with inhibitors of MAP kinases and NF-κB. These results suggest that immune responses induced by PGA occur via TLR2, TLR6, CD14, and MyD88 through activation of MAP kinase and NF-κB pathways.
authors.affiliation: Division of High-Risk Pathogen Research, Center for Infectious Diseases, National Institute of Health, Cheongju, Republic of Korea.
authors.forename: Jun Ho
authors.initials: JH
authors.lastname: Jeon
authors.affiliation: Division of High-Risk Pathogen Research, Center for Infectious Diseases, National Institute of Health, Cheongju, Republic of Korea.
authors.forename: Hae-Ri
authors.initials: HR
authors.lastname: Lee
authors.affiliation: Division of High-Risk Pathogen Research, Center for Infectious Diseases, National Institute of Health, Cheongju, Republic of Korea.
authors.forename: Min-Hee
authors.initials: MH
authors.lastname: Cho
authors.affiliation: Division of High-Risk Pathogen Research, Center for Infectious Diseases, National Institute of Health, Cheongju, Republic of Korea.
authors.forename: Ok-Kyu
authors.initials: OK
authors.lastname: Park
authors.affiliation: Department of Bioscience and Biotechnology, Hankuk University of Foreign Studies, Yongin, Republic of Korea Protein Research Center for Bioindustry, Hankuk University of Foreign Studies, Yongin, Republic of Korea.
authors.forename: Jungchan
authors.initials: J
authors.lastname: Park
authors.affiliation: Division of High-Risk Pathogen Research, Center for Infectious Diseases, National Institute of Health, Cheongju, Republic of Korea gerhie@nih.go.kr.
authors.forename: Gi-eun
authors.initials: GE
authors.lastname: Rhie
mesh_terms: D000818:Animals; D000881:Anthrax / Q000235:genetics / Q000276:immunology* / Q000382:microbiology; D001407:Bacillus / Q000276:immunology*; D001408:Bacillus anthracis / Q000235:genetics / Q000276:immunology*; D018932:Chemokine CCL2 / Q000235:genetics / Q000276:immunology; D006224:Cricetinae; D005260:Female; D006801:Humans; D057131:Immune Evasion; D015850:Interleukin-6 / Q000235:genetics / Q000276:immunology; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000276:immunology; D008264:Macrophages / Q000276:immunology / Q000382:microbiology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000276:immunology; D011099:Polyglutamic Acid / Q000276:immunology*; D051195:Toll-Like Receptor 2 / Q000819:agonists / Q000235:genetics / Q000276:immunology*; D051216:Toll-Like Receptor 6 / Q000235:genetics / Q000276:immunology; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000276:immunology
chemical_list: C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; D015850:Interleukin-6; D018950:Lipopolysaccharide Receptors; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; C495369:Tlr6 protein, mouse; D051195:Toll-Like Receptor 2; D051216:Toll-Like Receptor 6; D014409:Tumor Necrosis Factor-alpha; D011099:Polyglutamic Acid