Interleukin-17E, inducible nitric oxide synthase and arginase1 as new biomarkers in the identification of neutrophilic dermatoses.

Neutrophilic dermatoses (ND) are a heterogeneous group of diseases, but can often have a relatively similar histological appearance. To identify a combination of biomarkers allowing a better differentiation of ND types. Biopsies were obtained from normal human skin (NS; n = 4), chronic plaque-type psoriasis (PsO; n = 7), paradoxical psoriasis (PP; n = 8), generalized pustular psoriasis (GPP; n = 9), subcorneal pustular dermatosis of Sneddon-Wilkinson (SPD; n = 3), acute generalized exanthematous pustulosis (AGEP; n = 3), hidradenitis suppurativa (HS; n = 7), Sweet syndrome (SS; n = 8) and pyoderma gangrenosum (PG; n = 8). Samples were analysed by immunofluorescence using three biomarkers, interleukin (IL)-17E, inducible nitric oxide synthase (iNOS) and arginase1, each one in combination with two cell markers, myeloperoxidase (MPO) and CD68, which allow the identification of neutrophils and macrophages, respectively. We found that SS is characterized by high expression of IL-17E and iNOS in the epidermis, while PG exhibits low expression. The density of the neutrophil infiltrate helps to differentiate PP (high-density infiltrate) from PsO (low-density infiltrate). High expression of arginase1 in the granular layer of the epidermis is a hallmark of SPD. Finally, mature neutrophils and proinflammatory macrophages are readily detectable in PP, SPD and PG, whereas immature neutrophils and anti-inflammatory macrophages are more frequent in GPP, AGEP, HS and SS. The analysis of ND by immunofluorescence using IL-17E, iNOS and arginase1 in combination with MPO and CD68 allows for characterization of differential expression patterns in the epidermis as well as the determination of the polarization status of the dermal neutrophils and macrophages. The appropriate markers may help in the differentiation of ND in clinical practice.