Sunlight is the most important and universal source of non-ionising radiation essential for life on Earth. Despite the fact that infra-red (IR) is known to be a beneficial therapeutic agent, for example, in the treatment of musculo-skeletal disorders and healing indolent wounds, there is at present no knowledge of any photo biological effects induced by solar IR radiation in nature. This is curious when cells might have been expected to adapt through evolutionary processes to this energy source and particularly to those wavelengths transmitted through the two optical windows within the near infrared spectrum. Non-thermal quantities of IR light (700nm-2000nm) has been shown to induce a strong cellular defence against solar UV toxicity in normal human fibroblasts (Menezes et al., 1998). Furthermore, one single 5-minute application of 1072nm narrow waveband light was effective in the treatment of cold sores (herpes labialis). 1072nm light was chosen as it represents a peak in the transmission spectrum of the water molecule. Cold sores can be activated by UV exposure, which is also known to suppress the immune defence system. Inhibition of apoptosis by NO has been shown in a variety of cells, including B- lymphocytes, splenocytes and endothelial cells. The aims of this study were to investigate the wavelength dependence and possible mechanism of IR-mediated preconditioning in human lymphocytes. Phytohemagglutinin (PHA)-induced lymphocytes isolated using standard methods (Lecoeur et al., 1998) were exposed to 4 x 3 min infrared light source, IR1072 or IR880, on day 3 and 1 x 3 min on day 4 prior to UV exposure. The cells were then assayed on day 5 using the Annexin V Apoptosis Detection Kit (Autogen Bioclear, UK) for % cell viability. The cells were exposed daily to 1 x 3min infra red source, IR1072 or IR880 and assayed for iNOS protein expression using quantitative immunoblotting with a selective anti-iNOS antibody (Autogen Bioclear, UK) (standardized with β-actin). Data were compared by compared by unpaired students t-test with a level of significance set at p <0.01.

Following irradiation with IR1072, % cell viability was significantly higher (73 ± 3%), compared to respective control data (63 ± 3%) (n= 6 separate dishes). In contrast, % cell viability significantly decreased after treatment with IR880 (53 ± 5%), compared to cells treated with IR1072. After pre-treatment with IR1072, and subsequent exposure to UVA, % cell viability was significantly higher (46 ± 4%) compared to cells treated with UVA on ly (38 ± 5%). Following preconditioning with IR1072, a significan t increase of 4.9 ± 2.1-fold in i NOS immunoreactivity was detected compared to controls. In contrast, no significant increase in iNOS was observed with IR880 (2.1 ± 2.2-fold), performed in para llel studies. In conclusion, we report new evidence for IR wavelength-selective preconditioning of human lymphocytes, and the possible involvement of iNOS.

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This study was funded in part by Virulite Ltd. (UK).