title: Lipoproteins, not lipopolysaccharide, are the key mediators of the proinflammatory response elicited by heat-killed Brucella abortus.
abstract: Inflammation is a hallmark of brucellosis. Although Brucella abortus, one of the disease's etiologic agents, possesses cytokine-stimulatory properties, the mechanism by which this bacterium triggers a proinflammatory response is not known. We examined the mechanism whereby heat-killed B. abortus (HKBA), as well as its LPS, induces production of inflammatory cytokines in monocytes/macrophages. Polymyxin B, a specific inhibitor of LPS activity, did not inhibit the production of TNF-alpha- and IL-6-induced HKBA in the human monocytic cell line THP-1. HKBA induced the production of these cytokines in peritoneal macrophages of both C3H/HeJ and C3H/HeN mice, whereas B. abortus LPS only stimulated cells from C3H/HeN mice. Anti-TLR2 Ab, but not anti-TLR4 Ab, blocked HKBA-mediated TNF-alpha and IL-6 production in THP-1 cells. Because bacterial lipoproteins, a TLR2 ligand, have potent inherent stimulatory properties, we investigated the capacity of two B. abortus lipoproteins, outer membrane protein 19 (Omp19) and Omp16, to elicit a proinflammatory response. Lipidated (L)-Omp16 and L-Omp19, but not their unlipidated forms, induced the secretion of TNF-alpha, IL-6, IL-10, and IL-12 in a time- and dose-dependent fashion. Preincubation of THP-1 cells with anti-TLR2 Ab blocked L-Omp19-mediated TNF-alpha and IL-6 production. Together, these results entail a mechanism whereby B. abortus can stimulate cells from the innate immune system and induce cytokine-mediated inflammation in brucellosis. We submit that LPS is not the cause of inflammation in brucellosis; rather, lipoproteins of this organism trigger the production of proinflammatory cytokines, and TLR2 is involved in this process.
authors.affiliation: Instituto de Estudios de la Inmunidad Humoral (Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina), Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Argentina. ggiambart@ffyb.uba.ar
authors.forename: Guillermo H
authors.initials: GH
authors.lastname: Giambartolomei
authors.forename: Astrid
authors.initials: A
authors.lastname: Zwerdling
authors.forename: Juliana
authors.initials: J
authors.lastname: Cassataro
authors.forename: Laura
authors.initials: L
authors.lastname: Bruno
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Fossati
authors.forename: Mario T
authors.initials: MT
authors.lastname: Philipp
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification; D002003:Brucella abortus / Q000235:genetics / Q000276:immunology*; D045744:Cell Line, Tumor; D016207:Cytokines / Q000096:biosynthesis / Q000502:physiology; D005260:Female; D006358:Hot Temperature; D007249:Inflammation / Q000276:immunology / Q000382:microbiology / Q000517:prevention & control; D018836:Inflammation Mediators / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008074:Lipoproteins / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000502:physiology; D051379:Mice; D008809:Mice, Inbred C3H; D011956:Receptors, Cell Surface / Q000502:physiology; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors
chemical_list: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D016207:Cytokines; D018836:Inflammation Mediators; D008070:Lipopolysaccharides; D008074:Lipoproteins; D008562:Membrane Glycoproteins; C097319:OMP19 protein, Brucella abortus; D011956:Receptors, Cell Surface; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors