Two forms of soluble human type II interleukin (IL)-1 receptor (shIL-1RII) were generated, one consisting of the complete extracellular three immunoglobulin (Ig)-like domains and one containing only the first two N-terminal Ig-like domains. Both forms bound IL-1β with a dissociation constant (K d) of 200 pM and neutralized IL-1β in a bioassay. They did not bind or neutralize IL-1α. This demonstrates that the two Ig-like domains of shIL-1RII are sufficient to bind IL-1β with an affinity comparable to full length shIL-1RII. This suggests that this short form of shIL-1RII contributes to the anti-inflammatory effect of soluble IL-1 receptors in vivo.
