Blue light irradiation suppresses dendritic cells activation in vitro

Blue light is a UV ‐free irradiation suitable for treating chronic skin inflammation, for example, atopic dermatitis, psoriasis, and hand‐ and foot eczema. However, a better understanding of the mode of action is still missing. For this reason, we investigated whether dendritic cells ( DC ) are directly affected by blue light irradiation in vitro . Here, we report that irradiation neither induced apoptosis nor maturation of monocyte‐derived and myeloid DC . However, subsequent DC maturation upon LPS / IFN γ stimulation was impaired in a dose‐dependent manner as assessed by maturation markers and cytokine release. Moreover, the potential of this DC to induce cytokine secretion from allogeneic CD 4 T cells was reduced. In conclusion, unlike UV irradiation, blue light irradiation at high and low doses only resulted in impaired DC maturation upon activation and a reduced subsequent stimulatory capacity in allogeneic MLR s with strongest effects at higher doses.