FLUORESCENT LIGHT ACTIVATES THE IMMUNOMODULATOR CIS-UROCANIC ACID IN-VITRO - IMPLICATIONS FOR PATIENTS WITH SYSTEMIC LUPUS-ERYTHEMATOSUS

Objective-Erythemagenic (295-305 nm) ultraviolet-B (UVB) radiation is toxic to patients with systemic lupus erythematosus (SLE). Cool white fluorescent lamp emissions produce a similar toxicity even though the UVB radiation emitted is primarily at the relatively non-erythemagenic wavelength of 313 nm. The purpose of this study was to determine if f luorescent light, presumably acting predominantly along the 313 nm wav elength, exhibits photochemical activity sufficient to account for tox icity. Methods-The photochemical activity of fluorescent light was ass essed by testing its capacity to activate urocanic acid, a plentiful a nd potent epidermal immunological mediator normally activated by polyc hromatic UVB radiation but activated maximally at 313 nm. Irradiation- induced isomerisation of trans-urocanic to cis-urocanic acid was quant itated by UV spectroscopy after separation of the isomers by high perf ormance liquid chromatography. Results-Fluorescent light irradiation o f solutions containing the photoreceptor trans-urocanic acid produced a cumulative conversion of trans- to cis-urocanic acid. This photochem ical activity was compared with that of erythemagenic sun-lamps, high in polychromatic UVB emissions. When normalized for UVB irradiance, th e accumulation of cis-urocanic acid produced by both light sources was essentially equivalent. Conventional acrylic diffusers that absorb UV B emissions eliminated the fluorescent light-induced reaction. Conclus ion-The results indicate that radiation from fluorescent lamps possess es substantial photoimmunological capability, sufficient to activate a potent, potentially dangerous, disease-modifying, immunomodulatory pa thway and that poorly erythemagenic, primarily monochromatic UVB photo ns are responsible.