Fig. 1

Nrg-1 treatment alters M1 and M2 macrophage populations after SCI. a, b Representative images of the gating strategy for flow cytometry are provided for infiltrated spinal cord macrophages at 42-day post-injury under each treatment group. c Flow cytometric analysis 3 days post-SCI showed a robust increase in the number of macrophages (CD45⁺CD68⁺) in the injured spinal cord. Nrg-1-treated animals demonstrated a significantly higher number of macrophages compared to the vehicle-treated group. Phenotypical analysis of macrophages at 3-day time-point showed no significant difference in the number of infiltrated M1 macrophages (CD45⁺CD68⁺CD86⁺) between vehicle- and Nrg-1-treated groups. However, Nrg-1-treated SCI animals had a significantly higher population of M2 macrophages (CD45⁺CD68⁺CD163⁺ and CD45⁺CD68⁺CD163⁺IL-10⁺) in the spinal cord. d, e At 7 and 14 days post-SCI, the total number of tissue macrophages and their M1 subpopulation was significantly higher in the injured animals compared to the uninjured group, while M2 macrophage population remained unaltered. There was also no significant difference in the total number of macrophages and their M1 or M2 phenotype between the vehicle- and Nrg-1-treated groups. f At 42 days post-SCI, the number of infiltrated macrophages was 30 times less than the acute 3-day time-point in SCI baseline condition but still significantly higher than uninjured animals. Compared to both vehicle and uninjured rats, Nrg-1-treated animals showed a significantly higher number of M1 macrophages. There was no significant difference in the number of M2 macrophages between the vehicle and Nrg-1 treatment groups at this time-point, although Nrg-1-treated rats had a significantly higher number of M2 macrophages as compared to uninjured animals. g Immunohistochemical analysis verified the presence of M1 (CD68⁺CD86⁺) and M2 (CD68⁺CD163⁺) macrophages in the perilesional area (N = 5/group/time-point, *p < 0.05, **p < 0.01, ***p < 0.001, one-way ANOVA followed by Holm-Sidak post hoc test)