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. (c) 2016 Wiley Periodicals, Inc.