Blocking infiltration of macrophages to the injured spinal cord increases chronic microglial activation and impairs functional recovery after SCI.

Spinal cord contusion injury was performed in CCR2 KO mice and WT controls. (a) FACS analysis of CD45low/CD11b+ve/Ly6G−ve/Ly6C−ve microglia shows significant increase in CD11b mean fluorescent intensity (MFI) in CCR2 KO mice seven days after SCI. (b) Schematic of spinal cord shows area imaged and quantified in panels c and d, 28 days after injury—600 μm caudal to T11 lesion and boxed regions in left and right lateral white and gray matter. (c) Representative images in WT and CCR2 KO of CD11b immunoreactivity 28 days after SCI. Graphs show CD11b average area (μm−2) and fluorescent intensity (Integrated Density a.u) are significantly increased in CCR2 KO mice (which lack macrophage infiltration) versus WT controls. (d) CD86 expression (magenta) colocalized with Iba1 (cyan) is also significantly increased in CCR2 KO 28 days after SCI. (e, f) Luxol Fast Blue staining revealed that CCR2 KO mice showed greater myelin loss, a marker for secondary tissue damage, caudal to the lesion 28 days after SCI compared with control (g). Locomotor recovery assessed by the BMS shows CCR2 KO mice have impaired functional recovery compared to WT, beginning seven days after SCI. Statistical analysis for (a, c, d, e) Student t tests; a, n = 4; c and d, n = 12; e, n = 6 per group. (g) Two-way repeated measures ANOVA with post hoc Tukey analysis. n = 12 per group, mean ± SEM. *p p c and f = 100 μm; d = 50 μm. Corresponding raw data (S1 Data). BMS, Basso Mouse Scale; CCR2, C–C chemokine receptor type 2; FACS, fluorescently activated cell sorting; KO, knock-out; MFI, mean fluorescent intensity; SCI, spinal cord injury; WT, wild-type.