Evidence for a role of autoinflammation in early‐phase psoriasis

Summary Psoriasis is a common, inflammatory immune‐mediated skin disease mainly presenting with plaques whose pathogenesis is based on the central role of the interleukin (IL)‐23/IL‐17 axis. However, the mechanisms acting in papular lesions of early‐phase psoriasis are not fully understood. The aim of this study was to assess the involvement of autoinflammation, a state of sterile inflammation mainly driven by IL‐1 over‐production that has been recently hypothesized to act in the early phase of disease. Lesional skin of 10 patients with recent onset, untreated psoriasis has been investigated for expression of IL‐1β, IL‐17, IL‐23 and other cytokines involved in the disease in comparison with normal skin of 10 healthy controls using a protein array method. Immunohistochemical phenotyping of inflammatory infiltrate and co‐localization experiments with immunofluorescence confocal microscopy were conducted. IL‐1β was significantly more expressed in psoriasis than in normal skin ( P  < 0·0001). The chemokine IL‐8 was also over‐expressed in psoriasis ( P  = 0·03) while IL‐12, IL‐17, IL‐23, tumour necrosis factor‐α and interferon‐γ were only slightly more expressed in psoriasis than in normal skin, without reaching statistical significance. The inflammatory infiltrate consisted mainly of neutrophils with a relevant number of macrophages and dendritic cells and only scattered, predominantly T helper 1 lymphocytes. IL‐1β co‐localized mainly with CD66b, a neutrophil marker, suggesting that neutrophils were the major source of this cytokine. IL‐1β over‐expression in combination with low expression of cytokines that are predominant in late‐phase plaque psoriasis may support the role of autoinflammation in early‐phase disease, possibly paving the way to randomized trials with IL‐1 antagonists.