In Situ Characterization of Splenic Brucella melitensis Reservoir Cells during the Chronic Phase of Infection in Susceptible Mice

PLoS One. 2015 Sep 16;10(9):e0137835. doi: 10.1371/journal.pone.0137835. eCollection 2015.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brucella melitensis / pathogenicity*
  • Brucellosis / microbiology*
  • Brucellosis / pathology
  • Cells, Cultured
  • Chronic Disease
  • Female
  • Interleukin-12 / physiology*
  • Macrophages / microbiology*
  • Macrophages / pathology
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Mice, Knockout
  • Microscopy, Confocal
  • Microscopy, Fluorescence
  • RNA, Messenger / genetics
  • Real-Time Polymerase Chain Reaction
  • Reverse Transcriptase Polymerase Chain Reaction
  • STAT6 Transcription Factor / physiology*
  • Spleen / microbiology*
  • Spleen / pathology

Substances

  • RNA, Messenger
  • STAT6 Transcription Factor
  • Stat6 protein, mouse
  • Interleukin-12

Grants and funding

This work was supported by grants from the Fonds National de la Recherche Scientifique (FNRS) (convention FRSM FNRS 3.4.600.06.F, Belgium), Communauté Française de Belgique (Action de Recherches Concertées 08/13–015) and by the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office. E.M. is a Research Associate from the FRS-FNRS (Belgium). B.R. is supported by the “Agence Nationale pour la Recherche” (ANR 2007 MIME-103-02), “Fondation pour la Recherche Médicale” (FRM allergy DAL 2007 0822007), “Fonds Européen de Développement Régional” (FEDER Asthme 1575-32168) and Le Studium, Orléans (BR). D.H.M. holds PhD grants from the FRS-FNRS (Belgium). A.M. holds PhD grants from the FRIA (Belgium).