Is cytokine expression responsible for differences between allergens and irritants?

Irritant and allergic contact dermatitis are two very similar diseases, and differentiating between these two can be difficult clinically. Recently, cytokines have been identified as useful tools for differentiation. Thus, our laboratory has identified an early cytokine pattern in the induction phase of contact sensitivity that is specific for allergens and is not found after epicutaneous application of irritants or tolerogens. The up-regulation of the Langerhans' cell-derived signal interleukin (IL)-1 beta early after allergen application especially seems to be highly specific for contact allergens. This cytokine was also found to be essential for the development of epicutaneous sensitization because injection of an anti-IL-1 beta monoclonal antibody before epicutaneous application of an allergen prevented sensitization. Additionally, cytokines also seem to be involved in down-modulating an ongoing inflammatory reaction such as contact sensitivity. IL-10 especially was shown to inhibit the LC accessory functions and to down-modulate inflammatory cytokines. The homeostasis of proinflammatory and counterregulatory cytokines and their clinical implications are discussed in this review.