title: Haemophilus ducreyi infection induces activation of the NLRP3 inflammasome in nonpolarized but not in polarized human macrophages.
abstract: Recognition of microbial infection by certain intracellular pattern recognition receptors leads to the formation of a multiprotein complex termed the inflammasome. Inflammasome assembly activates caspase-1 and leads to cleavage and secretion of the proinflammatory cytokines interleukin-1 beta (IL-1β) and IL-18, which help control many bacterial pathogens. However, excessive inflammation mediated by inflammasome activation can also contribute to immunopathology. Here, we investigated whether Haemophilus ducreyi, a Gram-negative bacterium that causes the genital ulcer disease chancroid, activates inflammasomes in experimentally infected human skin and in monocyte-derived macrophages (MDM). Although H. ducreyi is predominantly extracellular during human infection, several inflammasome-related components were transcriptionally upregulated in H. ducreyi-infected skin. Infection of MDM with live, but not heat-killed, H. ducreyi induced caspase-1- and caspase-5-dependent processing and secretion of IL-1β. Blockage of H. ducreyi uptake by cytochalasin D significantly reduced the amount of secreted IL-1β. Knocking down the expression of the inflammasome components NLRP3 and ASC abolished IL-1β production. Consistent with NLRP3-dependent inflammasome activation, blocking ATP signaling, K(+) efflux, cathepsin B activity, and lysosomal acidification all inhibited IL-1β secretion. However, inhibition of the production and function of reactive oxygen species did not decrease IL-1β production. Polarization of macrophages to classically activated M1 or alternatively activated M2 cells abrogated IL-1β secretion elicited by H. ducreyi. Our study data indicate that H. ducreyi induces NLRP3 inflammasome activation via multiple mechanisms and suggest that the heterogeneity of macrophages within human lesions may modulate inflammasome activation during human infection.
authors.affiliation: Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana, USA. wl1@iupui.edu
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Barry P
authors.initials: BP
authors.lastname: Katz
authors.forename: Margaret E
authors.initials: ME
authors.lastname: Bauer
authors.forename: Stanley M
authors.initials: SM
authors.lastname: Spinola
mesh_terms: D015153:Blotting, Western; D002352:Carrier Proteins / Q000276:immunology*; D002602:Chancroid / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D055785:Gene Knockdown Techniques; D006191:Haemophilus ducreyi / Q000276:immunology; D006801:Humans; D058847:Inflammasomes / Q000276:immunology*; D008262:Macrophage Activation / Q000276:immunology*; D008264:Macrophages / Q000276:immunology* / Q000382:microbiology; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D015398:Signal Transduction / Q000276:immunology
chemical_list: D002352:Carrier Proteins; D058847:Inflammasomes; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C453881:NLRP3 protein, human