Interleukin 25, thymic stromal lymphopoietin and house dust mites in pathogenesis of atopic dermatitis

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease in the world. It is characterized by recurrent eczematous skin lesions, fluctuating course and chronic pruritus. Increasing evidence suggest that AD is more common in adults than previously thought. The disease is characterized by an impaired skin barrier, aberrant Th2-type cytokine production and intensive pruritus. Epithelial keratinocytes constitute the first physical, chemical and immunological barrier, classified as a part of the innate defense system. These keratinocytes secrete various factors, e.g. alarmins such as thymic stromal lymphopoietin (TSLP) and interleukin 25 (IL-25). Serum levels of substance P (SP) have been reported to be increased in patients with AD and correlated with itch intensity. Several previous studies reported a positive association between AD severity and house dust mites (HDM) sensitization. The aim of the study was to analyze IL-25, TSLP and SP concentrations in blood serum of adult patients with severe AD, depending on the degree of allergy to HDM. There were 31 adult AD patients enrolled into the study and a control group that consisted of 20 healthy subjects. AD was diagnosed on the basis of Hanifin and Rajka criteria. SCORing Atopic Dermatitis (SCORAD) and visual analogue (VAS) scores were used to assess the intensity of pruritus and blood content of specific IgE to HDM, as well as TSLP, IL-25 cytokines and SP was measured. Our study presents the evidence that IL-25 serum concentration is increased in patients with atopic dermatitis and this cytokine plays an important role in pathogenesis of this disease. HDM could stimulate the release of IL-25 which aggravates the disease severity. Our results corroborate previous findings on the role of TSLP in atopic dermatitis.