Figure 1. Monocyte-derived macrophages, spontaneously recruited to the injured spinal cord following the injury, promote functional recovery.

Wild-type mice were subjected to SCI and received passive transfer (injected intravenously) of monocytes (CD45.1⁺ or Cx₃cr1 ^GFP) during the first week of recovery. (A–C) Spinal cords were excised 7 d after the injury and analyzed for the presence of infiltrating monocyte-derived MΦ. Flow cytometric analysis of (A) lesion area (4 mm segment) of injured spinal cord from mice treated with and without (w/o) adoptive transfer of monocytes (CD45.1⁺/CD11b⁺), indicating the arrival of graft-derived MΦ to the lesion area. (B) Flow cytometric analysis of lesion and distal areas (4 mm segment each) from injured spinal cords of adoptively transferred mice indicating the accumulation of the graft-derived MΦ (CD45.1⁺/CD11b⁺) mainly at the lesion and not at the distal areas (2,259±431 engrafted cells per gram of tissue taken from lesion area [mean±SE]). (C) Immunohistochemical analysis showing the adoptively transferred cells (Cx₃cr1 ^GFP/+; green) restricted to the margins of the lesion site, delineated by GFAP expression (red, right frame) (scale bar = 100 µm). (D) Similarly treated animals were followed for locomotor activity assessed according to the BMS (repeated measures ANOVA; F[between groups]_1,18 = 16.7; p = 0.0007). y-Axis error bar represents SE. (E) Mean locomotor score (BMS) of individual mice on d28 after spinal cord injury (Student's t-test; t = −5.09; df = 15; p = 0.0001), suggesting that increasing the pool of naïve monocytes by IV injection of wt mice following SCI enhanced recovery beyond spontaneous levels. The assessment of the functional outcome presented here is from one experiment representative of three independent experiments performed.