M1 macrophages were the dominant activated macrophage phenotype in the severely compressed spinal cord. (A, B) Fold change of the mRNAs for TNFα and CD86 (M1 macrophage markers), and for arginase1 and CD163 (M2 macrophage markers), determined by RT-PCR (n = 4 mice per group). **P <0.01, *P <0.05. (C) Representative magnified images of CD86/Iba-1 double-positive cells (arrowheads) in the S and M groups. Scale bar: 20 μm. (D) Quantitative analysis of the number of CD86/Iba-1 double-positive cells per field of view. **P <0.01. (E) Representative magnified image of arginase1 (Arg1)/Iba-1 double-positive cells in the S and M groups. Scale bar: 20 μm. (F) There was no significant difference in the Arg1/Iba-1 double-positive cells (arrowheads) between the S and M groups.