Interleukin-1 receptor antagonist competitively inhibits the binding of interleukin-1 to the type II interleukin-1 receptor

The interleukin-1 receptor antagonist (IL-1ra) inhibits the binding of interleukin-1 (IL-1) to T-cell lines possessing the type I IL-1 receptor; evidence has been published (Carter, D.B., Deibel, M.R.J., Dunn, C.J., Tomich, C.S., Laborde, A.L., Slightom, J.L., Berger, A.E., Bienkowski, M.J., Sun, F.F., McEwan, R.N., Harris, P.K.W., Yem, A.W., Waszak, G.A., Chosay, J.G., Sieu, L.C., Hardee, M.M., Zurcher-Neely, H.A., Reardon, I.M., Heinrickson, R.L., Truesdell, S.E., Shelly, J.A., Eessalu, T.E., Taylor, B.M., and Tracey, D.E. (1990) Nature 344, 633-638; Hannum, C.H., Wilcox, C.J., Arend, W.P., Joslin, F.G., Dripps, D.J., Heimdal, P.L., Armes, L.G., Sommer, A., Eisenberg, S.P., and Thompson, R.C. (1990) Nature 343, 336-340) that IL-Ira does not bind to the type II IL-1 receptor (IL-1RtII). In this study we examined the ability of human recombinant IL-1ra to block the binding of IL-1 to the IL-1RtII on human polymorphonuclear leukocytes (PMN) and Raji human B-lymphoma cells. The binding of ¹²⁵I-IL-1β to PMN was competitively inhibited by IL-1ra. IL-1β was more potent in inhibiting the binding of ¹²⁵I-IL-1β than IL-1ra. Incubating PMN with ¹²⁵I-IL-1ra in the presence of increasing concentrations of IL-1β or IL-1ra showed that IL-1β was an ~40-fold more potent inhibitor of binding of ¹²⁵I-IL-1ra than unlabeled IL-1ra. The IL-1ra was ~500-fold less potent in inhibiting the binding of ¹²⁵I-IL-1α than IL-1α. IL-1ra was also able to competitively inhibit binding of ¹²⁵I-IL-1β to Raji cells. PMN or Raji cells were also incubated with ¹²⁵I-IL-1 in the absence or presence of IL-1 or IL-1ra. After cross-linking of IL-1 to cells followed by specific immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed a band at 85 kDa corresponding to the 68-kDa IL-1RtII. However, in the presence of an excess of either unlabeled IL-1 or IL-1ra, the 85-kDa IL-1·IL-1RtII complex was not present. These findings demonstrate that the IL-1ra recognizes and blocks IL-1 binding to the IL-1RtII.