Eosinophilic pustulosis folliculitis (EPF) is a disease with unknown etiology, which is characterized by symptoms, including eosinophilic pustules on the face and other hair follicles. The pathophysiology of EPF is thought to be mainly due to Th2 cytokines such as IL-4, IL-5, and IL-13 because of the presence of numerous eosinophils in the pustular contents. Nonetheless, little is known about the pathogenesis of the disease. On the other hand, the clinical features of the disease are known to be significantly responsive to oral indomethacin, which desensitizes and downregulates the CRTH2 on immune cells. Type 2 innate lymphoid cells (ILC2s) serve for innate immunity and are defined by the expression of GATA3 and CRTH2 without any linage markers (Lin). ILC2s are known to respond to external stimuli to produce Th2 cytokines faster than Th2 cells in many diseases. Although ILC2 is known to play an important role, such as in atopic dermatitis, little is known about its contribution to the pathophysiology of EPF. Here we histopathologically analyzed the skin biopsy samples from patients diagnosed with EPF at our clinic and examined whether ILC2s were present and if the pathology is consistent with responsiveness to indomethacin. We collected histology samples from formalin-fixed, paraffin-embedded blocks of 31 EPF patients. For ILC2 staining, a cocktail of lineage markers (Lin), including CD1a, CD3, CD11c, CD14, CD16, CD20, FceR1, S100A9, Calprotectin, and CD56, was used, and therefore, ILC2s were defined as Lin-CRTH2+Gata3+ cells. We observed that the presence of ILC2s in the skin lesion was clinically correlated with responsiveness to indomethacin. We further discuss if CRTH2+ Th2 cells may present in EPF and if the responsibility of indomethacin is independent of CRTH2 ligands, prostaglandin D2. Collectively, our study suggested the possible involvement of ILC2 with EPF. Although further research is needed to clarify the whole picture of the pathogenesis of EPF, the molecules relating to ILC2 might be promising candidates for a novel therapy for EPF.

ESDR383 - The presence of ILC2 may suggest the pathophysiological contribution to eosinophilic pustulosis folliculitis.

The scientific meeting of the European Society for Dermatological Research (ESDR) is held yearly, usually in September. With an international attendance of more than 1000 skin scientists from around the globe, the four-day event includes short oral presentations from peer-reviewed abstracts, keynote lectures from international experts, sponsored symposia, satellite programs, educational events as well as an important focus on posters, networking and building collaborations amongst scientists. For more information about this year’s meeting visit our website.