IL-31 and IL-31 receptor alpha in pemphigus: Contributors to more than just itch?

Pemphigus is an autoimmune blistering disorder with four major subtypes: pemphigus vulgaris (PV), pemphigus vegetans (PVe), pemphigus foliaceus (PF), and pemphigus herpetiformis (PH). Among them, PF and PH present itching as a clinical feature; however, the mechanisms behind the pruritus are still unclear. In this report, we sought to investigate the expression of a type 2 inflammation-related pruritogenic cytokine IL-31 and its receptor subunit IL-31RA through immunofluorescence staining analysis. The number of eosinophils, basophils, and mast cells, and the expression levels of thymic stromal lymphopoietin (TSLP) and periostin were also investigated. Evaluation showed an increase in the number of dermal IL-31⁺ cells and IL-31RA⁺ cells in PH and PVe. Epidermal expression of IL-31RA increased in PV, PF, and PVe, but not in PH, compared to healthy individuals. The number of dermal eosinophils and basophils was also increased in PVe and PH. The number of dermal mast cells and expression levels of TSLP and periostin did not change among pemphigus subtypes and healthy controls. Collectively, enhanced IL-31/IL-31RA signaling and the increased numbers of dermal eosinophils and basophils may participate in itching in PH. On the other hand, IL-31/IL-31RA signaling seemed unable to provoke itching in PVe, a non-pruritic subtype of pemphigus, although it might contribute to epidermal thickening and dermal fibrosis.