Beschreibung:
<jats:p>The studies on fractalkine and its unique receptor CX3CR1 in neurological disorders yielded contrasting results. We have explored the consequences of CX3CR1 deletion in ischemic (30′ MCAo) mice on: (1) brain infarct size; (2) microglia dynamism and morphology; (3) expression of markers of microglia/macrophages (M/M) activation and polarization. We observed smaller infarcts in <jats:italic>cx3cr1</jats:italic><jats:sup>−/−</jats:sup> (26.42 ± 7.41 mm<jats:sup>3</jats:sup>, mean ± sd) compared to wild type (36.29 ± 11.57) and <jats:italic>cx3cr1</jats:italic><jats:sup>−/+</jats:sup> (34.49 ± 8.91) mice. We longitudinally analyzed microglia by <jats:italic>in vivo</jats:italic> two‐photon microscopy before, 1 and 24 h after transient ischemia. Microglia were stationary in both <jats:italic>cx3cr1</jats:italic><jats:sup>−/−</jats:sup> and <jats:italic>cx3cr1</jats:italic><jats:sup>−/+</jats:sup> mice throughout the study. In <jats:italic>cx3cr1</jats:italic><jats:sup>−/−</jats:sup> mice, they displayed a significantly higher number of ramifications >10 μm at baseline and at 24 h after ischemia compared to <jats:italic>cx3cr1</jats:italic><jats:sup>−/+</jats:sup> mice, indicating that CX3CR1 deficiency impaired the development of microglia hypertrophic/amoeboid morphology. At 24 h after ischemia, we performed post mortem quantitative immunohistochemistry for different M/M markers. In <jats:italic>cx3cr1</jats:italic><jats:sup>−/−</jats:sup> immunoreactivity for CD11b (M/M activation) and for CD68 (associated with phagocytosis) were decreased, while that for CD45<jats:sup>high</jats:sup> (macrophage and leukocyte recruitment) was increased. In addition, immunoreactivity for Ym1 (M2 polarization) was enhanced, while that for iNOS (M1) was decreased. Our data show that in <jats:italic>cx3cr1</jats:italic><jats:sup>−/−</jats:sup> mice protection from ischemia at early time points after injury is associated with a protective inflammatory milieu, characterized by the promotion of M2 polarization markers.</jats:p>