Free radicals in antigen formation: reduction of contact allergic response to hydroperoxides by epidermal treatment with antioxidants

SummaryBackground For patients with allergic contact dermatitis, the main therapy is anti-inflammatory steroids, a non-specific and symptomatic treatment. In contact allergy, the antigen formation is considered to be the binding of a chemical (hapten) to a biological macromolecule, e.g. a protein. Limonene-2-hydroperoxide (Lim-OOH) is a hapten with a known allergenic effect. It is likely to bind to proteins in the skin via a radical mechanism. It might be possible to inhibit the allergic reaction by epidermal application of substances that can trap free radicals, e.g. antioxidants such as ascorbic acid or α-tocopherol, prior to the application of the hapten. Objectives To study the influence of antioxidants on the allergenic effect of Lim-OOH in sensitization experiments on guinea pigs. Methods Pretreatment with the antioxidants was performed before induction to study the effect on sensitization as well as before challenge testing to study the effect on elicitation. Results A reduction in the response rate was found both at sensitization and at elicitation. The antioxidants had no effect on cobalt allergy or on the allergenic effect of haptens that form antigens via nucleophilic–electrophilic reactions. No reduction of the effect was seen for irritants. Conclusions The protective effect of antioxidants in elicitation could be of practical therapeutic value, as it indicates a possibility for the treatment of patients who have become sensitized to haptens that form full antigens via a radical mechanism.