Fig. 4

Primary injury after SCI causes cell membrane disruption and rupture of blood vessels leading to secondary injury with extensive upregulation of cytokines/chemokines and infiltration of immune cells. Microglia, the resident macrophages, are early responders and become indistinguishable in terms of morphology from peripherally derived macrophages. In rats, neutrophils peak early in the injury at around 24 h and gradually decrease over the next 7–10 days, while lymphocytes peak at lower levels and at a much later time. Pericytes also infiltrate later and interact with microglia around the edges of the injury and this entire injury site is encased by activated astrocytes