Mononuclear phagocytes locally specify and adapt their phenotype in a multiple sclerosis model.

Mononuclear phagocytes are key regulators of both tissue damage and repair in neuroinflammatory conditions such as multiple sclerosis. To examine divergent phagocyte phenotypes in the inflamed CNS, we introduce an in vivo imaging approach that allows us to temporally and spatially resolve the evolution of phagocyte polarization in a murine model of multiple sclerosis. We show that the initial proinflammatory polarization of phagocytes is established after spinal cord entry and critically depends on the compartment they enter. Guided by signals from the CNS environment, individual phagocytes then switch their phenotype as lesions move from expansion to resolution. Our study thus provides a real-time analysis of the temporospatial determinants and regulatory principles of phagocyte specification in the inflamed CNS.

Cellular, subcellular and functional in vivo labeling of the spinal cord using vital dyes.

Here we provide a protocol for rapidly labeling different cell types, distinct subcellular compartments and key injury mediators in the spinal cord of living mice. This method is based on the application of synthetic vital dyes to the surgically exposed spinal cord. Suitable vital dyes applied in appropriate concentrations lead to reliable in vivo labeling, which can be combined with genetic tags and in many cases preserved for postfixation analysis. In combination with in vivo imaging, this approach allows the direct observation of central nervous system physiology and pathophysiology at the cellular, subcellular and functional level. Surgical exposure and preparation of the spinal cord can be achieved in less than 1 h, and then dyes need to be applied for 30-60 min before the labeled spinal cord can be imaged for several hours.

CX3CR1-deficiency is associated with increased severity of disease in experimental autoimmune uveitis.

The role of CX3CR1 in regulating the function of monocytes and microglia was examined in mice in which CX3CR1 had been replaced by green fluorescent protein (GFP). Induction of experimental autoimmune uveitis (EAU) in these mice resulted in increased disease severity at day 23 postimmunization with uveitogenic peptide when compared with CX3CR1-positive mice and increased apoptosis of neuronal cells in the inner nuclear layer. Resident microglia within the retina were activated equally as EAU developed in mice with or without CX3CR1, as determined by changes in morphology, suggesting that the microglial cell response did not account for the differences. Although the inflammatory infiltrate had increased in mice without CX3CR1 at day 23 postimmunization, the percentage of natural killer cells in the infiltrate was not changed in these mice. Similarly, increased disease severity at this stage was not associated with an overall increased percentage of macrophages in the retinal inflammatory infiltrate or in increased activation of these cells. The increased recruitment of monocytes to the retina in response to EAU induction in CX3CR1(GFP/GFP) mice compared with CX3CR1(GFP/+) mice was not reflected in increased migration away from vessels, leading to marked clustering of GFP(+) cells around veins and venules in these mice. It is possible that this monocyte/macrophage clustering leads to the increased severity of disease seen in the mice by focusing and so intensifying the inflammatory response.

Development of experimental autoimmune uveitis: efficient recruitment of monocytes is independent of CCR2.

PURPOSE: Macrophages are major contributors to the damage occurring in the retina in experimental autoimmune uveitis (EAU). CCR2 may be needed for efficient recruitment of monocytes to an inflammatory site, and the aim of this study was to determine whether this was the case in EAU. METHODS: EAU was induced and graded in C57BL/6J and CCR2(-/-) mice. Macrophage infiltration and CCR2 expression were assessed using immunohistochemistry. Retinas were examined for MCP-1 expression using RT-PCR. Rolling and infiltration of labeled bone marrow monocytes at the inflamed retinal vasculature were examined by scanning laser ophthalmoscopy and confocal microscopy, respectively. Effect of CCR2 deletion or blockade by antibody and antagonist was determined. RESULTS: Expression of mRNA for MCP-1 increased as EAU developed and was localized to the retina. CCR2 was associated with infiltrating macrophages. However, EAU induced in CCR2(-/-) mice was not reduced in severity, and neither was the percentage of macrophages in the retina. CCR2(-/-) monocytes, 48 hours after adoptive transfer to mice with EAU, showed no significant difference in percentage rolling or infiltration into the retina compared to WT. CCR2-independent rolling of monocytes was confirmed by CCR2 neutralizing antibody and antagonist treatment. CONCLUSIONS: CCR2 does not have a primary role in the recruitment of monocytes to the inflammatory site across the blood-retina barrier in well-developed EAU. Therapeutics targeting CCR2 are unlikely to be of value in treating human posterior uveitis.

Leukocyte extravasation: an immunoregulatory role for alpha-L-fucosidase?

Fucosylated oligosaccharides and glycoconjugates have been implicated in several biological events, including the cell-cell adhesion processes that mediate inflammation. Alpha-L-fucosidase (ALF) is an exoglycosidase that is involved in the hydrolytic degradation of alpha-L-fucose from glycoconjugates. In this study, we investigated the potential role of ALF in regulation of leukocyte migration. Measurement of transendothelial migration in response to CCL5 demonstrated that pretreatment of monocytic cells with ALF reduced migration (p = 0.0004) to a greater extent than treatment of the endothelial monolayer (p = 0.0374). Treatment with ALF significantly reduced the adhesion of monocytic cells to immobilized P-selectin.Fc. A murine model of experimental autoimmune uveitis was then used to show that treatment of splenic cells with ALF produced an 8.6-fold decrease in rolling and a 3.2-fold decrease in cell migration across the retinal vasculature. Further in vitro studies demonstrated that treatment of monocytes with the chemokines CCL3 or CCL5 increased the level of mRNA encoding ALF; this was accompanied by the detection of significant increases in both the 51- and 56-kDa components of ALF by Western blotting. Treatment of monocytic cells with ALF for 2 h significantly reduced the cell surface expression of CD31, with a further decrease in expression observed after 5 h (p = 0.002). Thus, CD31 and fucosylated ligands of P-selectin seem to be the candidates through which ALF mediates its effect in vitro. These data identify a previously unrecognized immunoregulatory role for ALF in late stages of inflammation.