title: In Situ Characterization of Splenic Brucella melitensis Reservoir Cells during the Chronic Phase of Infection in Susceptible Mice.
abstract: Brucella are facultative intracellular Gram-negative coccobacilli that chronically infect humans as well as domestic and wild-type mammals, and cause brucellosis. Alternatively activated macrophages (M2a) induced by IL-4/IL-13 via STAT6 signaling pathways have been frequently described as a favorable niche for long-term persistence of intracellular pathogens. Based on the observation that M2a-like macrophages are induced in the spleen during the chronic phase of B. abortus infection in mice and are strongly infected in vitro, it has been suggested that M2a macrophages could be a potential in vivo niche for Brucella. In order to test this hypothesis, we used a model in which infected cells can be observed directly in situ and where the differentiation of M2a macrophages is favored by the absence of an IL-12-dependent Th1 response. We performed an in situ analysis by fluorescent microscopy of the phenotype of B. melitensis infected spleen cells from intranasally infected IL-12p40-/- BALB/c mice and the impact of STAT6 deficiency on this phenotype. Most of the infected spleen cells contained high levels of lipids and expressed CD11c and CD205 dendritic cell markers and Arginase1, but were negative for the M2a markers Fizz1 or CD301. Furthermore, STAT6 deficiency had no effect on bacterial growth or the reservoir cell phenotype in vivo, leading us to conclude that, in our model, the infected cells were not Th2-induced M2a macrophages. This characterization of B. melitensis reservoir cells could provide a better understanding of Brucella persistence in the host and lead to the design of more efficient therapeutic strategies.
authors.affiliation: Unité de Recherche en Biologie des Microorganismes, Laboratoire d'Immunologie et de Microbiologie, Université de Namur, Namur, Belgium.
authors.forename: Delphine
authors.initials: D
authors.lastname: Hanot Mambres
authors.affiliation: Unité de Recherche en Biologie des Microorganismes, Laboratoire d'Immunologie et de Microbiologie, Université de Namur, Namur, Belgium.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Machelart
authors.affiliation: Laboratory of Neurophysiology, Université Libre de Bruxelles, Campus Erasme, Brussels, Belgium.
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Vanderwinden
authors.affiliation: Department of Molecular and Cellular Interactions, Vlaams Interuniversitair Instituut voor Biotechnologie, Vrije Universiteit Brussel, Gebouw E, Verdieping 8, Pleinlaan 2, 1050, Brussels, Belgium.
authors.forename: Carl
authors.initials: C
authors.lastname: De Trez
authors.affiliation: CNRS, UMR7355, Orleans, France; Experimental and Molecular Immunology and Neurogenetics, University of Orléans, Orléans, France; Institute of Infectious Disease and Molecular Medicine, IDM, Cape Town, South Africa.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Ryffel
authors.affiliation: Unité de Recherche en Biologie des Microorganismes, Laboratoire d'Immunologie et de Microbiologie, Université de Namur, Namur, Belgium.
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Letesson
authors.affiliation: Unité de Recherche en Biologie des Microorganismes, Laboratoire d'Immunologie et de Microbiologie, Université de Namur, Namur, Belgium; Laboratoire de Parasitologie, Université Libre de Bruxelles, Campus Erasme, Bruxelles, Belgique.
authors.forename: Eric
authors.initials: E
authors.lastname: Muraille
mesh_terms: D000818:Animals; D017347:Brucella melitensis / Q000472:pathogenicity*; D002006:Brucellosis / Q000382:microbiology* / Q000473:pathology; D002478:Cells, Cultured; D002908:Chronic Disease; D005260:Female; D018664:Interleukin-12 / Q000502:physiology*; D008264:Macrophages / Q000382:microbiology* / Q000473:pathology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050800:STAT6 Transcription Factor / Q000502:physiology*; D013154:Spleen / Q000382:microbiology* / Q000473:pathology
chemical_list: D012333:RNA, Messenger; D050800:STAT6 Transcription Factor; C494100:Stat6 protein, mouse; D018664:Interleukin-12