Effect of 710-nm visible light irradiation on neuroprotection and immune function after stroke

The phototherapeutic effects of low level infrared laser irradiation (808 nm) on brain neuronal cell protection after stroke have been presented recently. We previously reported that 710-nm wavelength visible light (VIS) increases total lymphocyte counts in vivo, especially CD4(+) T lymphocytes. In this study, we investigated the effects of 710-nm VIS irradiation on neuronal protection and recovery correlating with cellular immunity in stroke rats.

Rats were subjected to 90-min middle cerebral artery occlusion (MCAO) followed by reperfusion and were divided into two groups: irradiation and no irradiation. The irradiation group had been exposed to 710-nm VIS for 3 weeks after MCAO establishment or sham operation. The helper T cell (CD4(+)) count in the whole blood and infarct volume were measured. Messenger RNA expression levels of IL-4 and IL-10 in peripheral blood mononuclear cells were measured, a histologic study including microglia activation and regulatory T (Treg) cell markers, neurological severity scoring and a parallel bar walking test were all performed.

CD4(+) cell count was reduced after MCAO but was significantly increased by 710-nm VIS irradiation. The infarct sizes were decreased in the MCAO + irradiation group compared with the MCAO control group. IL-10 mRNA expression and the immunoreactivity of Treg cells were increased in the MCAO + irradiation group compared with the MCAO control group. Increased microglia activation after MCAO was reduced by 710-nm VIS irradiation. The irradiation group also showed improved neurological severity score levels and step fault scores after MCAO.

Our data suggest that 710-nm VIS irradiation may activate cellular immunity, reduce brain infarction and ultimately induce functional recovery in a stroke animal model.