IL-17 and IL-22 in atopic allergic disease.

A long standing paradigm is that antigen-specific Th2 cells and their cytokines such as IL-4, IL-5, and IL-13 orchestrate the characteristic features of atopic allergy. The discovery of a role for IL-17-producing (Th17) and IL-22-producing (Th22) T helper cells in inflammatory diseases has added an additional layer of complexity to the understanding of the pathogenesis of allergic diseases. Here we re-evaluate the role of T helper cells, with special focus on the Th17 and Th22 subsets in allergic asthma and atopic dermatitis. Whereas sparse data point to a protective role of the increasing amounts of Th22 cells that are found in chronic stages of both allergies, the data on Th17 cells paint different pictures for the contribution of Th17 cells during subsequent stages of these two forms of allergy.