ID: 199: Expression of IL-20-related cytokines in PPD-induced allergic contact dermatitis and their role in a mouse model

Para-Phenylenediamine (PPD) is an aromatic amine used in hair dyes and in temporary black henna tattoos, which is a frequent cause of allergic contact dermatitis (ACD). ACD is a skin inflammatory disease characterized by modifications such as spongiosis, exocytosis and acanthosis. The aim of this study is to characterize the expression and the role of IL-20-related cytokines, including IL-19, IL-20, IL-22 and IL-24, in ACD. In 11 patients with a history of positive patch-test reaction to PPD, patch tests with PPD 1% in petrolatum were applied and skin biopsies were performed after 8, 24 and 48 h. The mRNA level of IL-20-related cytokines is increased in affected vs uninvolved skin from PPD allergic patients (positive patch test to PPD). In order to assess the role of these cytokines, we set up a mouse model of PPD-induced allergic contact dermatitis and we showed that IL-22R−/− or IL-20R2−/− mice are partially protected against development of PPD-induced contact hypersensitivity. These mice presented a lower ear thickening than WT treated mice. This was confirmed at histological level, because, after PPD treatment, IL-22R−/− mice showed less acanthosis than WT mice. In addition, we showed that IL-22R plays a role in induction of chemokine expression as well as neutrophil marker. Along the same line, after PPD treatment, proportion of neutrophils is lower in the skin of IL-22R−/− mice compare to WT mice. We conclude that IL-22R associated cytokines act in ACD mainly by inducing acanthosis, and indirectly by increasing skin neutrophilic infiltrate.