Supplementary Material for: Serum Concentration and Skin Expression of S100A7 (Psoriasin) in Patients Suffering from Hidradenitis Suppurativa

<b><i>Background:</i></b> Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease. An important role of innate immune dysregulation in the pathogenesis of HS has been highlighted. S100A7 (psoriasin) is an innate, antimicrobial protein that exerts proinflammatory and chemotactic action. <b><i>Objectives:</i></b> The objective of the study was to investigate serum concentrations of S100A7 in individuals with HS as compared to healthy controls. Further, we evaluated the expression of S100A7 in lesional HS skin as compared to perilesional (clinically uninvolved) HS skin and normal skin. <b><i>Methods:</i></b> Serum concentrations of S100A7 were evaluated with a commercially available ELISA kit. The expression of S100A7 in the skin was assessed using qRT-PCR and immunofluorescence staining. <b><i>Results:</i></b> We found increased expression of S100A7 in lesional HS skin as compared to perilesional HS skin (<i>p</i> = 0.0017). The expression of S100A7 in lesional HS skin was positively associated with serum C-reactive protein concentration and the severity of disease according to Hurley staging. The serum concentration of S100A7 in individuals with HS was decreased as compared to healthy controls and patients with psoriasis. <b><i>Conclusions:</i></b> Upregulated in lesional HS skin, S100A7 may enhance the inflammatory process and contribute to the HS pathogenesis.