The Asian atopic dermatitis phenotype combines features of atopic dermatitis and psoriasis with increased TH17 polarization

Atopic dermatitis (AD) is the most common inflammatory skin disease, with a large and currently unmet need for effective therapeutics. AD and psoriasis, another common skin disease, are recognized as polar inflammatory skin diseases. Psoriasis is emerging as an IL-23/T_H17-skewed disease, whereas AD is considered to be T_H2-centered. These distinctions are relevant to emerging therapies for each. To date, the characterization of AD in different patient populations has made the assumption that disease mechanisms are similar across them. Noda et al present evidence that this is not so (J Allergy Clin Immunol 2015; 136: 1254-1264).

The prevalence of AD among adults in Asia is 7% to 10%, which is considerably higher than in other populations. In addition, prominent T_H17 activation has been observed in blood and acute AD lesions of Asian AD patients. The high prevalence and increased IL-17⁺ T-cell expansion suggest that an Asian AD phenotype may have different immune and barrier characteristics than the European American (EA) one. The authors have thus directly compared AD in European American (EA) and Asian (Japanese and Korean) populations. Their report classifies an Asian AD phenotype that is mixed between the EA AD and psoriasis phenotypes, with features atypical to AD such as parakeratosis and a unique cytokine profile with co-activation of the T_H2 and T_H17 axes. Even in the presence of increased IgE levels, Asian AD shows significantly higher induction of T_H17 and T_H22-related cytokines. Interestingly, psoriasis has a very low prevalence in Asian populations.

Further studies are needed to clarify the extent to which these differences are genetic, environmental, and/or microbiome related; for example, a similar study of Asian AD patients and Asian American AD patients. Additionally, FLG mutation status was unknown for all of the patients the current study includes. Regardless, the differences in the phenotype of Asian AD presented here call for similar description of other racial groups, and they provide a rationale for testing of IL-17/IL-23-targeted therapeutic strategies that have been successfully used in the treatment of psoriasis, in addition to those that are T_H2-specific.