Interleukin-18 as a severity marker and novel potential therapeutic target for epidermolytic ichthyosis

Serum interleukin (IL)-18 levels were significantly higher in patients with epidermolytic ichthyosis than in healthy controls, and IL-18 levels correlated with the severity of ichthyosis, as measured by the Ichthyosis Scoring System. Immunoblotting analysis revealed that mature IL-18 levels were increased in the supernatant of mutant KRT1-expressing HaCaT cells, and these cells showed NLRP3 aggregation in the cytoplasm and ASC protein clustered around mutant keratin aggregations. Mutant keratin might promote the activation of the NLRP3 inflammasome and its downstream caspase-1-mediated IL-18 release in keratinocytes from patients with epidermolytic ichthyosis. Background Epidermolytic ichthyosis (EI) is a major form of nonsyndromic inherited ichthyosis, characterized by erythroderma, marked hyperkeratosis and scale, bulla and erosion at birth, associated with KRT1/KRT10 mutations. The cytokine and chemokine profiles in EI are poorly understood, and specific treatment options have not been established. Aim To explore novel biomarkers and therapeutic targets in patients with EI. Methods We analysed cytokine levels in serum and skin samples from 10 patients with inherited ichthyosis, including seven patients with EI. Wild-type and mutant KRT1 constructs were established and transfected into HaCaT cells, an immortalized keratinocyte cell line, for in vitro immunoblotting and immunocytochemistry analyses. Results Multiplex cytokine/chemokine analysis revealed that 10 cytokines/chemokines [interleukin (IL)-1 beta, IL-4, IL-17A, IL-16, IL-18, IL-1 receptor-alpha, macrophage colony-stimulating factor, interferon-alpha 2, basic fibroblast growth factor and monocyte chemotactic protein-3] were significantly increased in patients with EI. Furthermore, IL-18 levels were significantly higher in patients with EI [n = 7; 2714.1 (1438.0) pg mL(-1)] than in healthy controls [n = 11; 218.4 (28.4) pg mL(-1), P < 0.01]. Immunohistochemical analyses showed that IL-18 expression was elevated in skin samples from patients with EI. Serum IL-18 levels correlated with the severity of ichthyosis, as measured by the Ichthyosis Scoring System. Immunoblotting analysis revealed that mature IL-18 levels were increased in the supernatant of mutant KRT1 expressing HaCaT cells. Additionally, these cells showed NLRP3 aggregation in the cytoplasm and ASC clustered around mutant keratin aggregations. These findings suggest that mutant keratin might promote the activation of the NLRP3 inflammasome and its downstream caspase-1-mediated IL-18 release in keratinocytes from patients with EI. Conclusions Our results suggest that serum IL-18 is a severity marker released from the skin of patients with EI. Blockade of IL-18 may be a useful novel therapeutic option for patients with EI.