BackgroundNeuroinflammation is an important secondary mechanism that is a key mediator of the long-term consequences of neuronal injury that occur in traumatic brain injury (TBI). Microglia are highly plastic cells with dual roles in neuronal injury and recovery. Recent studies suggest that the chemokine fractalkine (CX3CL1, FKN) mediates neural/microglial interactions via its sole receptor CX3CR1. CX3CL1/CX3CR1 signaling modulates microglia activation, and depending upon the type and time of injury, either protects or exacerbates neurological diseases.MethodsIn this study, mice deficient in CX3CR1 were subjected to mild controlled cortical impact injury (CCI), a model of TBI. We evaluated the effects of genetic deletion of CX3CR1 on histopathology, cell death/survival, microglia activation, and cognitive function for 30 days post-injury.ResultsDuring the acute post-injury period (24 h–15 days), motor deficits, cell death, and neuronal cell loss were more profound in injured wild-type than in CX3CR1−/− mice. In contrast, during the chronic period of 30 days post-TBI, injured CX3CR1−/− mice exhibited greater cognitive dysfunction and increased neuronal death than wild-type mice. The protective and deleterious effects of CX3CR1 were associated with changes in microglia phenotypes; during the acute phase CX3CR1−/− mice showed a predominant anti-inflammatory M2 microglial response, with increased expression of Ym1, CD206, and TGFβ. In contrast, increased M1 phenotypic microglia markers, Marco, and CD68 were predominant at 30 days post-TBI.ConclusionCollectively, these novel data demonstrate a time-dependent role for CX3CL1/CX3CR1 signaling after TBI and suggest that the acute and chronic responses to mild TBI are modulated in part by distinct microglia phenotypes.

Fractalkine, a chemokine anchored to neurons or peripheral endothelial cells, serves as an adhesion molecule or as a soluble chemoattractant. Fractalkine binds CX3CR1 on microglia and circulating monocytes, dendritic cells and NK cells. The aim of this study is to determine the role of CX3CR1 in the trafficking and function of myeloid cells to the central nervous system (CNS) during experimental autoimmune encephalomyelitis (EAE). Our results show that in models of active EAE Cx3cr1–/– mice exhibited more severe neurological deficiencies. Bone marrow chimeric mice confirmed that CX3CR1-deficiency in bone marrow enhanced EAE severity. Notably, CX3CR1 deficiency was associated with an increased accumulation of CD115+Ly6C–CD11c+ dendritic cells into EAE affected brains which correlated with enhanced demyelination and neuronal damage. Furthermore, higher IFN-γ and IL-17 levels were detected in cerebellar and spinal cord tissues of CX3CR1-deficient mice. Analyses of peripheral responses during disease initiation revealed a higher frequency of IFN-γ and IL-17 producing T cells in lymphoid tissues of CX3R1-deficient as well as enhanced T cell proliferation induced by CX3CR1-deficient DCs. In addition, adoptive transfer of MOG35-55 reactive wild type T cells induced substantially more severe EAE in CX3CR1-deficient recipients when compared to wild type recipients. Collectively, the data demonstrate that besides its role in chemoattraction, CX3CR1 is a key regulator of myeloid cell activation contributing to the establishment of adaptive immune responses.

Microglia are mononuclear phagocytes that make up about 10% of the central nervous system (CNS). They are known for their surveillant behavior which comprises continuously monitoring neural tissue by extending and retracting their processes. Microglial cells are derived from myeloid progenitor cells and play important roles in homeostasis, inflammatory and immune responses in the brain. This Unit describes several microglial cell isolation protocols (Basic Protocol 1, Alternate Protocol, and Basic Protocol 2) that can be easily adapted for projects requiring a rapid and efficient analysis of mouse microglial cells by flow cytometry (Support Protocol 1). Methods for visualizing microglial cells using in situ immunohistochemistry (Basic Protocol 3) and immunochemistry in free-floating sections (Basic Protocol 4) are also included.

Summary The action of chemokines (or ‘chemotactic cytokines’) is recognized as an integral part of inflammatory and regulatory processes. Leukocyte mobilization during physiological conditions, trafficking of various cell types during pathological conditions, cell activation and angiogenesis are among the target functions exerted by chemokines upon signaling via their specific receptors. Current research is focused in analyzing changes in chemokine/chemokine receptor patterns during various diseases with the aim to modulate pathological trafficking of cells, or to attract particular cell types to specific tissues. This review focuses on defining the role(s) of certain chemokine ligands and receptors in inflammatory neurological conditions such as multiple sclerosis. In addition, the role(s) of chemokines in neurodegenerative conditions such as Alzheimer’s disease and Parkinson’s disease are also described, as well as the contribution of chemokines to the pathogenesis of cancer, diabetes and cardiovascular disease.