Deficiency of IL-36 receptor antagonist (DITRA) is associated with decreased homoeostatic CCL27 expression leading to heightened dermal inflammation.

Deficiency of the Interleukin-36 Receptor antagonist (DITRA) is a rare autoinflammatory condition which commonly manifests as severe, recurrent episodes of Generalized Pustular Psoriasis (GPP). Loss-of-function mutations in the IL36RN gene result in unopposed IL-36 cytokine signalling leading to severe psoriatic inflammation, which can be successfully treated with Anti-IL-36 receptor (IL-36R) monoclonal antibodies. Despite such advances, there remain some key questions concerning how loss of a functional IL-36R antagonist predisposes to GPP, including identifying the potential impacts of IL36RN mutations on skin homeostasis. To address this question, we investigated the consequences of IL-36Ra deficiency using Il36rn-/- mice, which recapitulate the severe psoriatic inflammation observed in DITRA patients. Here, we demonstrate, that in overtly healthy Il36rn-/- mice, prior to disease onset, there is disrupted dermal immune homeostasis, characterised by decreased expression of the chemokine CCL27. Altered skin homeostasis occurred in association with dysbiosis of the skin microbiome, characterised by a significant outgrowth of the commensal bacteria, Cutibacterium acnes. Importantly, intradermal administration of recombinant CCL27, prior to disease induction, significantly reduced the enhanced severity of psoriasiform inflammation, demonstrating a central role for this chemokine in regulating predisposition to increased severity. Transcriptomic analysis of GPP patients skin also revealed decreased CCL27 expression in non-lesional, as well as lesional, compared to healthy skin, indicating that this chemokine may also play a key instructive role among DITRA patients. Together, these data identify a novel mechanism through which IL-36Ra deficiency alters dermal homeostasis and predisposes to increased severity of psoriatic disease observed in DITRA patients.