Structural basis of pro-inflammatory signaling via the Interleukin-36 receptor (IL-36R) mediated by IL-36γ and IL-37

Interleukin-36 receptor (IL-36R) is activated by IL-36α, IL-36β, and IL-36γ to elicit pro-inflammatory signaling and is targeted in acute skin inflammation by the approved antibody spesolimab. IL-37 was recently proposed as a new IL-36R agonist. Such diverse agonist repertoire together with the antagonistic IL-36Ra and IL-38 create a fascinating structure-function landscape for IL-36R, albeit one that is poorly understood. Here, we elucidate how IL-36R grapples IL-36γ with low affinity to enable facile recruitment of the shared receptor IL-1RAcP with high-affinity. In contrast, IL-36R interacts with IL-37 via the exact opposite binding signature. Comparative interrogation of IL-36R activation by IL-36γ and IL-37 confirmed their common pro-inflammatory signature and distinguished IL-36γ as markedly more pro-inflammatory. Structural comparisons of cytokine-activated versus spesolimab-antagonized IL-36R revealed spesolimab’s mode of action as an allosteric antagonist. Collectively, our study provides the structural and mechanistic blueprint of IL-36R activation by distinct cytokines and will facilitate its therapeutic targeting.