title: The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages.
abstract: Previously, we reported that mutants ofLegionella pneumophilalacking a type II secretion (T2S) system elicit higher levels of cytokines (e.g., interleukin-6 [IL-6]) following infection of U937 cells, a human macrophage-like cell line. We now show that this effect of T2S is also manifest upon infection of human THP-1 macrophages and peripheral blood monocytes but does not occur during infection of murine macrophages. Supporting the hypothesis that T2S acts to dampen the triggering of an innate immune response, we observed that the mitogen-activated protein kinase (MAPK) and nuclear transcription factor kappa B (NF-κB) pathways are more highly stimulated upon infection with the T2S mutant than upon infection with the wild type. By using short hairpin RNA to deplete proteins involved in specific pathogen-associated molecular pattern (PAMP) recognition pathways, we determined that the dampening effect of the T2S system was not dependent on nucleotide binding oligomerization domain (NOD)-like receptors (NLRs), retinoic acid-inducible protein I (RIG-I)-like receptors (RLRs), double-stranded RNA (dsRNA)-dependent protein kinase receptor (PKR), or TIR domain-containing adaptor inducing interferon beta (TRIF) signaling or an apoptosis-associated speck-like protein containing a CARD (ASC)- or caspase-4-dependent inflammasome. However, the dampening effect of T2S on IL-6 production was significantly reduced upon gene knockdown of myeloid differentiation primary response 88 (MyD88), TANK binding kinase 1 (TBK1), or Toll-like receptor 2 (TLR2). These data indicate that theL. pneumophilaT2S system dampens the signaling of the TLR2 pathway in infected human macrophages. We also document the importance of PKR, TRIF, and TBK1 in cytokine secretion duringL. pneumophilainfection of macrophages.
authors.affiliation: Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois, USA.
authors.forename: Celeste A
authors.initials: CA
authors.lastname: Mallama
authors.affiliation: Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois, USA.
authors.forename: Kessler
authors.initials: K
authors.lastname: McCoy-Simandle
authors.affiliation: Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois, USA n-cianciotto@northwestern.edu.
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Cianciotto
mesh_terms: D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D006801:Humans; D058847:Inflammasomes / Q000276:immunology / Q000378:metabolism; D016952:Legionella pneumophila / Q000502:physiology*; D008264:Macrophages / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D015398:Signal Transduction; D051195:Toll-Like Receptor 2 / Q000378:metabolism*; D000069178:Type II Secretion Systems; D019892:eIF-2 Kinase / Q000378:metabolism
chemical_list: D016207:Cytokines; D058847:Inflammasomes; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D051195:Toll-Like Receptor 2; D000069178:Type II Secretion Systems; C000602769:EIF2AK2 protein, human; D019892:eIF-2 Kinase; D020928:Mitogen-Activated Protein Kinases
keywords: Legionella pneumophila; TLR2; cytokine; innate immunity; macrophage; type II secretion