title: Brucella abortus Induces the Premature Death of Human Neutrophils through the Action of Its Lipopolysaccharide.
abstract: Most bacterial infections induce the activation of polymorphonuclear neutrophils (PMNs), enhance their microbicidal function, and promote the survival of these leukocytes for protracted periods of time. Brucella abortus is a stealthy pathogen that evades innate immunity, barely activates PMNs, and resists the killing mechanisms of these phagocytes. Intriguing clinical signs observed during brucellosis are the low numbers of Brucella infected PMNs in the target organs and neutropenia in a proportion of the patients; features that deserve further attention. Here we demonstrate that B. abortus prematurely kills human PMNs in a dose-dependent and cell-specific manner. Death of PMNs is concomitant with the intracellular Brucella lipopolysaccharide (Br-LPS) release within vacuoles. This molecule and its lipid A reproduce the premature cell death of PMNs, a phenomenon associated to the low production of proinflammatory cytokines. Blocking of CD14 but not TLR4 prevents the Br-LPS-induced cell death. The PMNs cell death departs from necrosis, NETosis and classical apoptosis. The mechanism of PMN cell death is linked to the activation of NADPH-oxidase and a modest but steadily increase of ROS mediators. These effectors generate DNA damage, recruitments of check point kinase 1, caspases 5 and to minor extent of caspase 4, RIP1 and Ca++ release. The production of IL-1β by PMNs was barely stimulated by B. abortus infection or Br-LPS treatment. Likewise, inhibition of caspase 1 did not hamper the Br-LPS induced PMN cell death, suggesting that the inflammasome pathway was not involved. Although activation of caspases 8 and 9 was observed, they did not seem to participate in the initial triggering mechanisms, since inhibition of these caspases scarcely blocked PMN cell death. These findings suggest a mechanism for neutropenia in chronic brucellosis and reveal a novel Brucella-host cross-talk through which B. abortus is able to hinder the innate function of PMN.
authors.affiliation: Programa de Investigación en Enfermedades Tropicales, Escuela de Medicina Veterinaria, Universidad Nacional, Heredia, Costa Rica; Centro de Investigación en Enfermedades Tropicales, Universidad de Costa Rica, San José, Costa Rica.
authors.forename: Elías
authors.initials: E
authors.lastname: Barquero-Calvo
authors.affiliation: Programa de Investigación en Enfermedades Tropicales, Escuela de Medicina Veterinaria, Universidad Nacional, Heredia, Costa Rica.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Mora-Cartín
authors.affiliation: Centre d'Immunologie de Marseille-Luminy (CIML), Aix-Marseille University, UM2, Marseille, France; Institut National de la Santé et de la Recherche Médicale (INSERM), U1104, Marseille, France; Centre National de la Recherche Scientifique (CNRS), UMR7280, Marseille, France.
authors.forename: Vilma
authors.initials: V
authors.lastname: Arce-Gorvel
authors.affiliation: Department of Cell Microbiology, Max Planck Institute for Infection Biology, Berlin, Germany.
authors.forename: Juana L
authors.initials: JL
authors.lastname: de Diego
authors.affiliation: Centro de Investigación en Enfermedades Tropicales, Universidad de Costa Rica, San José, Costa Rica.
authors.forename: Carlos
authors.initials: C
authors.lastname: Chacón-Díaz
authors.affiliation: Programa de Investigación en Enfermedades Tropicales, Escuela de Medicina Veterinaria, Universidad Nacional, Heredia, Costa Rica; Centro de Investigación en Enfermedades Tropicales, Universidad de Costa Rica, San José, Costa Rica.
authors.forename: Esteban
authors.initials: E
authors.lastname: Chaves-Olarte
authors.affiliation: Programa de Investigación en Enfermedades Tropicales, Escuela de Medicina Veterinaria, Universidad Nacional, Heredia, Costa Rica; Centro de Investigación en Enfermedades Tropicales, Universidad de Costa Rica, San José, Costa Rica.
authors.forename: Caterina
authors.initials: C
authors.lastname: Guzmán-Verri
authors.affiliation: Biological Sciences, Inflammation Research Network, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Andre G
authors.initials: AG
authors.lastname: Buret
authors.affiliation: Centre d'Immunologie de Marseille-Luminy (CIML), Aix-Marseille University, UM2, Marseille, France; Institut National de la Santé et de la Recherche Médicale (INSERM), U1104, Marseille, France; Centre National de la Recherche Scientifique (CNRS), UMR7280, Marseille, France.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Gorvel
authors.affiliation: Programa de Investigación en Enfermedades Tropicales, Escuela de Medicina Veterinaria, Universidad Nacional, Heredia, Costa Rica; Instituto Clodomiro Picado, Facultad de Microbiología, Universidad de Costa Rica, San José, Costa Rica.
authors.forename: Edgardo
authors.initials: E
authors.lastname: Moreno
mesh_terms: D002003:Brucella abortus / Q000276:immunology* / Q000302:isolation & purification; D002006:Brucellosis / Q000276:immunology*; D016923:Cell Death; D016207:Cytokines / Q000378:metabolism; D006801:Humans; D007113:Immunity, Innate / Q000276:immunology; D007962:Leukocytes / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology*; D061213:Mortality, Premature; D009504:Neutrophils / Q000166:cytology*
chemical_list: D016207:Cytokines; D008070:Lipopolysaccharides