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

Objective: 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.

Methods: 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.

Results: 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.

Conclusions: 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.