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Mediators of Inflammation
Volume 2013 (2013), Article ID 245804, 9 pages
http://dx.doi.org/10.1155/2013/245804
Research Article

IRF5 Is a Specific Marker of Inflammatory Macrophages In Vivo

1Kennedy Institute of Rheumatology, University of Oxford, Roosevelt Drive, Headington, Oxford OX3 7FY, UK
2Leukocyte Biology Section, National Heart and Lung Institute, Sir Alexander Fleming Building, Faculty of Medicine, Imperial College, South Kensington, London SW7 2AZ, UK

Received 31 August 2013; Revised 29 November 2013; Accepted 30 November 2013

Academic Editor: Salahuddin Ahmed

Copyright © 2013 Miriam Weiss et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Macrophages are an integral part of the innate immune system and key players in pathogen clearance and tissue remodelling. Both functions are accomplished by a pivotal network of different macrophage subtypes, including proinflammatory M1 and anti-inflammatory M2 macrophages. Previously, our laboratory identified the transcription factor interferon regulatory factor 5 (IRF5) as the master regulator of the M1 macrophage polarisation. IRF5 was found to be highly expressed in human M1 compared to M2 macrophages. Furthermore, IRF5 dictates the expression of proinflammatory genes such as IL12b and IL23a whilst repressing anti-inflammatory genes like IL10. Here we show that murine bone marrow derived macrophages differentiated in vitro with GM-CSF are also characterised by high levels of IRF5 mRNA and protein and express proinflammatory cytokines upon LPS stimulation. These macrophages display characteristic expression of M1-marker MHC II but lack the M2-marker CD206. Significantly, we develop intracellular staining of IRF5- expressing macrophages and utilise it to recapitulate the in vitro results in an in vivo model of antigen-induced arthritis, emphasising their physiological relevance. Thus, we establish the species-invariant role of IRF5 in controlling the inflammatory macrophage phenotype both in vitro and in in vivo.