A new T helper 17 cytokine in hidradenitis suppurativa: antimicrobial and proinflammatory role of interleukin‐26

Background Interleukin (IL)-26 is a signature T helper 17 cytokine described as aproinflammatory and antimicrobial mediator. So far, IL-26 has been reported inseveral immune-mediated inflammatory diseases, but its involvement in inflammatoryskin disorders is poorly known.Objectives To investigate the role of IL-26 in hidradenitis suppurativa (HS),through its involvement in antimicrobial activity.Methods IL-26 was assessed in patients with HS through gene expression and proteinanalysis at skin and circulating levels. Ex vivo HS organ skin cultures, together withIL-26 antibody treatment, were performed to determine the IL-26 activity. Peripheralblood mononuclear cells (PBMCs) from patients with HS and healthy controlswere either silenced or not with IL-26 small interfering (si)RNA in order to measureits antimicrobial, cytotoxic and phagocytic activities against Staphylococcus aureus.Results Firstly, we observed that IL-26 is able to modulate the proinflammatoryresponse at the immune cell level. IL-26 was increased in the plasma of patientswith HS compared with healthy controls. Subsequently, we explored the bactericidal,cytotoxic and phagocytic activities of PBMCs against S. aureus in patients withHS and healthy controls. These activities were lower in patients with HS than incontrols. Remarkably, the killing activities were reduced when healthy controlPBMCs were transfected with IL-26 siRNA. However, the transfection did not affectthe killing activity of HS PBMCs, supporting the idea that IL-26 lacks efficacy in HS.Conclusions Our findings suggest that infection susceptibility in HS might berelated to IL-26. Although the role of bacteria remains controversial in HS, thispaper supports that there is a defect of antimicrobial response in these patients.