Comparative potency of broad-band and narrow-band phototherapy sources to induce edema, sunburn cells and urocanic acid photoisomerization in hairless mouse skin.

The Philips TL01 narrow-band (311-313 nm) fluorescent lamp provides effective phototherapy for psoriasis and atopic eczema while emitting less erythemogenic radiation than conventional broad-band (e.g. Philips TL12; 270-350 nm) sources. We studied the potency of TL01 and TL12 radiation to induce edema and sunburn cells (SBC) and to photoisomerize naturally occurring trans-urocanic acid (UCA) to cis-UCA in hairless mouse skin. Cis-UCA has immunosuppressive properties and is a putative mediator of UV-induced suppression of immune responses. For each source, there was UV dose dependence for all three responses. Within the dose ranges used, the potency ratio of TL12:TL01 radiation to induce equivalent edema and SBC was about 6:1. However, the potency ratio to induce cis-UCA was less than 2.3:1. Therefore, at a given level of edema or SBC induction, TL01 was more efficient than TL12 at UCA photoisomerization. The TL01 induction of immunomodulating cis-UCA, while causing minimal skin injury, may relate to the therapeutic efficacy of this source in skin conditions with an immunological component.