Effects of IL‐1 receptor accessory protein on IL‐1 binding

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Abstract
Interleukin‐1 (IL‐1) is an important pro‐inflammatory cytokine that exerts its diverse biological functions by binding to a receptor complex consisting of two transmembrane proteins, type I IL‐1 receptor (IL‐1RI) and IL‐1 receptor accessory protein (IL‐1RAcP). Both receptor chains are indispensable for IL‐1 signaling, but only IL‐1RI is able to bind the cytokine. The effects of IL‐1RAcP on IL‐1 binding are unclear. This study shows that although expression of IL‐1RAcP does not alter the equilibrium dissociation constant of IL‐1, it has an effect on the non‐equilibrium binding modus, most likely due to changes in on/off rates. This defines an additional function of IL‐1RAcP: it stabilizes the active IL‐1 receptor complex.