Objective　To observe the effect of Complement 5a receptor antagonist (C5aRA) in the early inflammatory reaction and outcome of hindlimb function after spinal cord injury (SCI) in mice

and to investigate the role of complement C5a after spinal cord injury. 　Methods　Totally 173 female C57BL/6J mice were randomly divided into sham operation

C5aRA group

methylprednisolone (MP) group

and normal saline group. Another 9 mice with no any treatment served as normal control. The mice of C5aRA group received an intraperitoneal injection of C5aRA peptides (1.0 mg/kg) in 45 min before

and 24 h after SCI establishment. MP (30 mg/kg) was given i.p. to the mice of this group followed by another 4 injections in every 6 h. Normal saline group received an injection of normal saline. Tumor necrosis factor alpha (TNF-α) and interleukin 1β(IL-1β) in injured spinal cord were measured by ELISA and RT-PCR. Microglia was examined by flow cytometry

and hindlimb locomotion was observed the by Mouse Scale for Locomotion (BMS). 　Results　TNF-α and IL-1β were increased greatly at 1 h following SCI

with the peak at 1 h and 12 h respectively

and nearly returned to the normal level at 72 h. The percentage of activated microglial cells was raised at 1 d after SCI

with obvious increase at 3 d and the peak at 7. At 14 d it was decreased but still higher than the normal level. The level of TNF-α

IL-1β and microglia percentage of the C5aRA group was obviously lower than that of the NS group (P0. 05)

although significantly higher than the MP group (P0.05). 　Conclusion　C5aRA suppresses early inflammatory reaction and improves BMS score after SCI in mice. C5a may participate in the secondary damage process through up-regulating the early inflammation reaction after SCI.