Detection of photoreactivity demonstrated in a modified local lymph node assay in mice.

Photoallergic and phototoxic reactions are an increasing problem in dermatologic practice. Currently available test models are heterogeneous and do not allow differentiation between photoallergic and phototoxic reactions. We have modified the local lymph node assay to screen for photoreactive compounds. We found an ultraviolet A (UVA) irradiation-dependent increase in the weights and cell counts of the auricular lymph nodes after application of 8-methoxypsoralen, tribromosalicylanilide, trichlorosalicylanilide, chlorpromazine and promethazine. In contrast to these photoreactive compounds, contact sensitizers did not produce any reaction to UVA irradiation in the local lymph node assay. This assay system has the advantage of being less expensive and less time-consuming and might even be able to differentiate between phototoxic, photoallergic and contact allergic reactions.