Abstract
Pressure ulcers represent a crucial clinical problem, especially in hospitalized patients. Ischemia-reperfusion (I-R) is an important cause of these lesions. Natural killer (NK), invariant NK T (iNKT), and dendritic epidermal T-cells, which express the natural killer group 2, member D (NKG2D) receptor, have been reported to have physiological roles in skin tissue repair and wound healing. However, a role for NKG2D-NKG2D ligand interactions in I-R-induced skin injury has not been determined. Using a murine pressure ulcer model, we demonstrated that I-R-induced ulcers in NKG2D-deficient mice were larger than those in wild-type or T-cell receptor δ knockout mice. Histopathological evaluation revealed that accumulation of macrophages and neutrophils at the peripheral deep dermis and subcutaneous tissue of the ulcers was enhanced in NKG2D-deficient mice. Rae-1 mRNA, which encodes an NKG2D ligand, was induced, and RAE-1 protein was detected immunohistochemically in fibroblasts and inflammatory cells in the dermis after reperfusion. RAE-1 expression was also increased in primary mouse fibroblasts treated with sodium arsenite. These results suggested that NKG2D ligand expression was induced by oxidative stress after I-R injury and support a putative role for this ligand in wound repair. Furthermore, the influx of NKG2D-positive cells at I-R sites may mitigate pressure ulcers via NKG2D-NKG2D ligand interactions.