Experimental Photoallergic Contact Dermatitis: A Mouse Model

We have induced photoallergic contact dermatitis in mice to 3,3',4',5 tetrachlorosalicylanilide (TCSA), chlorpromazine and 6-methylcoumarin. These compounds are known to produce photoallergic contact dermatitis in humans. The photoallergic contact dermatitis reaction in the mouse is immunologically specific viz. mice photosensitized to TCSA react, by photochallenge, to that compound and not to chlorpromazine, and conversely. The reaction requires UVA at both sensitization and challenge. It appears to be T-cell medicated in that it can be passively transferred to syngeneic mice by lymph node cells from actively sensitized mice, histology of the reactions resembles that of classic allergic contact dermatitis in mice, challenge reactions are seen at 24 but not at 4hr, and photoallergic contact dermatitis can be induced in B-cell deficient mice. The availability of a mouse model for the study of photo-ACD will facilitate the identification of pertinent control mechanisms and may aid in the management of the disease. It is likely that a bioassay for photoallergens of humans can be based on this mouse model

The Influence of UVA and Visible Radiation on Acute Damage by Short-Wave UVR (λ < 320 nm)

The influence of UVA and visible radiation on the acute damage by short-wave ultraviolet radiation (UVR) (λ < 320 nm) was investigated in human volunteers, using delayed erythema and sunburn cell production as markers of injury. It was found that subsequent exposure to UVA + visible radiation produced a significant reduction of the threshold erythema dose by short-wave UVR, in a dose-dependent manner. Subsequent exposures to varying doses of UVA + visible radiation, as well as to visible light alone failed to influence sunburn cell production. It is concluded that there is a positive interaction between short-wave UVR and UVA in the induction of delayed erythema, but this may not apply to epidermal cell injury. Photorecovery was not observed

Identification of Systemic Phototoxic Drugs by Human Intradermal Assay

An improved method is presented for the detection of systemically administered photosensitizing drugs in humans. Test agents were injected intradermally in physiologic saline and then exposed to broad spectrum radiation from a Xenon solar simulator. Several clinically recognized photosensitizers were identified by this technique. The activating spectrum depended on the test drug. Sulfonamides and vinblastin were activated by sunburning erythemic radiation (UV-B), while tetracyclines, nalidixic acid and phenothiazines by near UV (UV-A), and chlorothiazide by both. It is suggested that intradermal phototesting offers a means of verifying the phototoxic potential of agents suspected clinically of provoking a photosensitivity eruption