Temporal kinetics of CD8+ CD28+ and CD8+ CD28- T lymphocytes in the injured rat spinal cord.

This study aims to explore the temporal changes of cytotoxic CD8+ CD28+ and regulatory CD8+ CD28- T-cell subsets in the lesion microenvironment after spinal cord injury (SCI) in rats, by combination of immunohistochemistry (IHC) and flow cytometry (FCM). In the sham-opened spinal cord, few CD8+ T cells were found. After SCI, the CD8+ T cells were detected at one day post-injury (dpi), then markedly increased and were significantly higher at 3, 7, and 14 dpi compared with one dpi (p < 0.01), the highest being seven dpi. In CD8+ T cells, more than 90% were CD28+ , and there were only small part of CD28- ( < 10%). After 14 days, the infiltrated CD8+ T cells were significantly decreased, and few could be found in good condition at 21 and 28 dpi. Annexin V and propidium iodide (PI) staining showed that the percentages of apoptotic/necrotic CD8+ cells at 14 dpi and 21 dpi were significantly higher than those of the other early time-points (p < 0.01). These results indicate that CD8+ T cells could rapidly infiltrate into the injured spinal cords and survive two weeks, however, cytotoxic CD8+ T cells were dominant. Therefore, two weeks after injury might be the "time window" for treating SCI by prolonging survival times and increasing the fraction of CD8+ regulatory T-cells.