The adaptive immune system in atopic dermatitis and implications on therapy

In atopic dermatitis (AD), the skin inflammation is believed to occur due to a misdirected immune reaction against harmless antigens on the one hand, and to a disturbed skin barrier on the other. In recent years, vast efforts have been made to investigate the relevance and details of the immune response to allergens. Clinically, it was demonstrated for the first time that aeroallergen exposure leads to worsening of AD symptoms. An overexpression of Th2 cytokines has been observed in acute and subacute lesions of AD. The clinical impact of the key Th2 cytokines IL-4 and IL-13 on atopic dermatitis has recently been shown in clinical studies with dupilumab, a monoclonal antibody which blocks the IL-4/IL-13 receptor. In vitro data indicate, however, that the T cell response is not solely Th2-polarized but may lead to heterogeneous cytokine production involving IFN-gamma and IL-17 in an allergen-dependent manner. Classical thymus-derived Foxp3 T cells have interestingly been detected in elevated numbers in the circulation of AD patients. Therapeutic approaches with allergen specific immunotherapy aim to induce regulatory T cells of the Tr1 type. The strikingly altered microbiome of AD skin with diminished diversity of bacteria on lesional skin but increases of S. aureus colonization and the sensitization against microbial allergens and homologue self-proteins deserve special attention. For the treatment of itch symptoms, which still represent a challenge in daily practice, promising data have been published on the relevance of the H(histamine)4-receptor and on mediators such as IL-31, TSLP.