The Effect of Visible Light on the Immune System Cells

Introduction: Blue light is used extensively in restorative dentistry. Several studies have reported that blue light disrupts cellular processes such as mitosis, mitochondrial function or DNA integrity, mediated by light-induced formation of reactive oxygen species (ROS). However, the effects of blue light sources on inflammatory response regulation at the cellular and cytokine levels have not been established. Objective: 1. To investigate the effects of blue light sources at wavelengths of 400-500 nm on splenocytes proliferation, and the release of IL-10, and TNF-á by stimulated splenocytes in vitro. 2. To identify the role of light-induced ROS on these effects. Materials and Methods: Splenocytes from mouse spleens were isolated, seeded on 96- well micro-plates containing RPMI media and stimulated with heat-killed Porphyromonas gingivalis for periopathogenic challenge. Prior to the challenge, the cells were exposed to a plasma arc curing (PAC) light with power density of 1W/cm2 for 2, 10, 30, 60 and 120 sec, equivalent to fluences of 2, 10, 30, 60 and 120 J/cm2 respectively. The plates were incubated for 48h. Cell proliferation was assessed by XTT assay and the levels of IL-10, and TNF-á were determined by ELISA. The role of ROS was tested by adding a mixture of ROS scavengers to cell medium. Results: Blue light exposure arrested splenocytes growth (60 and 120 sec). Blue light induced secretion of IL-10 to a maximum after short exposure (2 and10 sec). Adding scavengers did not affect the splenocytes number. However, the scavengers inhibited the secretion of IL-10. TNF-á secretion was affected neither by light exposure nor by the scavengers. Conclusions: Blue light sources, which are used in dental practice, induce the release of IL-10 mediated by ROS. This phenomenon suggests that such light may exert biological effects, such as down regulation of the inflammatory responses.