In vitro effects of low-level laser irradiation at 660 nm on peripheral blood lymphocytes

Background and Objective: The effects of low-level laser light irradiation are still highly contested, and the mechanisms of its action still unclear. This study was conducted to test the effects of low-level laser irradiatio n at 660 nm on human lymphocytes and to investigate the possible mechanisms by which these effects are produced. Study Design/Materials and Methods: Whole blood obtained by phlebotomy was irradiated at 660 nm by using energy fluences between 0 and 5.0 J/cm(2). Th e lymphocytes were isolated after irradiation of the whole blood. For the c ontrol experiment, the lymphocytes were first isolated and then irradiated at the same wavelength and energy fluence for comparison. The proliferation of lymphocytes and the formation of free radicals and lipid peroxides were monitored. Hemoglobin was also irradiated in a cell-free environment to te st for the production of lipid peroxides. Results: Lymphocyte proliferation was significantly higher (P < 0.05) as ex pressed by a Stimulation Index in samples irradiated in the presence of who le blood compared with lymphocytes irradiated after isolation from whole bl ood. Free radical and lipid peroxide production also increased significantl y when samples were irradiated in the presence of red blood cells. Conclusion: The present study supports the hypothesis that one mechanism fo r the photobiostimulation effect after irradiation at 660 nm is the reactio n of light with hemoglobin, resulting in oxygen radical production. Lasers Surg. Med. 27:255-261, 2000 (C) 2000 Wiley-Liss, Inc.