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Open Access Highly Accessed Review

Inflammatory monocytes and the pathogenesis of viral encephalitis

Rachael L Terry124, Daniel R Getts4, Celine Deffrasnes12, Caryn van Vreden12, Iain L Campbell23 and Nicholas JC King12*

Author Affiliations

1 Department of Pathology, School of Medical Sciences, Blackburn Circuit, The University of Sydney, Sydney, 2006, Australia

2 Bosch Institute, The University of Sydney, Sydney, 2006, Australia

3 School of Molecular and Microbial Biosciences, Butlin Avenue, The University of Sydney, Sydney, 2006, Australia

4 Department of Microbiology-Immunology, Feinberg School of Medicine, Chicago Avenue, Northwestern University, Chicago, 60611, USA

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Journal of Neuroinflammation 2012, 9:270  doi:10.1186/1742-2094-9-270

Published: 17 December 2012

Abstract

Monocytes are a heterogeneous population of bone marrow-derived cells that are recruited to sites of infection and inflammation in many models of human diseases, including those of the central nervous system (CNS). Ly6Chi/CCR2hi inflammatory monocytes have been identified as the circulating precursors of brain macrophages, dendritic cells and arguably microglia in experimental autoimmune encephalomyelitis; Alzheimer’s disease; stroke; and more recently in CNS infection caused by Herpes simplex virus, murine hepatitis virus, Theiler’s murine encephalomyelitis virus, Japanese encephalitis virus and West Nile virus. The precise differentiation pathways and functions of inflammatory monocyte-derived populations in the inflamed CNS remains a contentious issue, especially in regard to the existence of monocyte-derived microglia. Furthermore, the contributions of monocyte-derived subsets to viral clearance and immunopathology are not well-defined. Thus, understanding the pathways through which inflammatory monocytes migrate to the brain and their functional capacity within the CNS is critical to inform future therapeutic strategies. This review discusses some of the key aspects of inflammatory monocyte trafficking to the brain and addresses the role of these cells in viral encephalitis.

Keywords:
Ly6Chi inflammatory monocytes; Viral encephalitis; Neurotrophic virus; CCL2; CCR2; VLA-4; LFA-1; Integrins