Interaction between Ilantide, interleukin 1β, and interleukin 1 receptor antagonist and soluble IL-1 receptor type I. Binding was studied using surface plasmon resonance analysis. Approximately 2,500 to 3,000 resonance units (RUs) of interleukin 1β (IL-1β) (A), IL-1 receptor antagonist (IL-Ra) (B) and Ilantide-t (C) were immobilized on a sensor chip. Binding is expressed as the response difference between the binding of IL-1 receptor type I (IL-1RI) to the sensor chip with the immobilized peptide, IL-1β, or IL-Ra and a blank sensor chip. No binding of any of the tested proteins and Ilantide-t was observed to the double-immunoglobulin (Ig) module (Ig1-Ig2) of the neural cell adhesion molecule (NCAM) (negative control). (D) Binding of the IL-1RI ectodomain to immobilized IL-1β in the presence of the indicated concentrations of Ilantide-t. The results from three experiments are expressed as mean RU ± SEM. **P < 0.01 and ***P < 0.001 compared with binding of IL-1RI alone to IL-1β (one-way analysis of variance followed by the Newman-Keuls post hoc test).