Impact of acquired and innate immunity on spinal cord ischemia and reperfusion injury

Objective The aim of this study was to clarify the impact of acquired and innate immunity on spinal cord ischemia and reperfusion injury using a mouse model of spinal cord ischemia. Methods To define the ischemic duration that caused paraplegia, wild-type and severe combined immunodeficiency (SCID) mice were subjected to cross-clamping of the aorta for 7, 9, 9.5, or 10.5 min with ischemic preconditioning for intestinal protection. In wild-type and SCID mice with paraplegia, histological analyses were performed to investigate viable neurons, inflammatory cells, and reactive astrocytes at 12, 24, 48, and 72 h as well as 7 days after reperfusion. Results In both wild-type and SCID mice, immediate paraplegia was induced by occlusion for 10.5 min. In both wild-type and SCID mice, no infiltration of T or B lymphocytes was observed at any point after reperfusion, but reactive astrocytes were clearly visible at 7 days after reperfusion, and the number of activated microglia peaked at 12 and 48 h after reperfusion. Although there was no significant difference, wild-type mice had a tendency to have more activated microglia than SCID mice at 12 h after reperfusion, and to have less viable neurons than SCID mice at 12, 24, 48, and 72 h after reperfusion. There was a tendency that the frequency of immediate paraplegia in wild-type mice was more than SCID mice though no statistical difference was observed. Conclusions Innate immunity, rather than acquired immunity, may be involved in the developing immediate paraplegia in our mouse model.