An antibody to a 17 amino acid synthetic peptide of the type I interleukin-1 receptor preferentially blocks interleukin-1β binding

On the basis of their relative hydropathy and α-helical structure, we prepared antibodies to four synthetic peptides with amino acid sequences homologous to four hydrophilic, extracellular regions of the murine 80 kDa type I interleukin-1 receptor (IL-1RI). Antibodies to each of the four peptides recognized their specific immunogen. Human [¹²⁵I]-IL-1α or -β was crosslinked to murine EL4 and D10S cells. Antiserum to peptide 150-166 precipitated the IL-1/IL-1R complex, whereas antibodies to peptide 66-84, 190-200, or 266-285 did not. Antibody to peptide 150-166 did not precipitate the type II IL-1R. Anti-IL-1RI^150-166 blocked 71% of the binding of radiolabeled human IL-1β to EL4 cells and 50% of the binding to D10S cells. Using affinity-purified anti-IL-1RI^150-166, we compared the ability of this antibody to inhibit the binding of murine or human IL-1α to that of murine or human IL-1β. At a concentration of 20 ng/ml, affinity-purified anti-IL-1RI^150-166 blocked 50% binding of murine IL-1β. At 1 μg/ml, 90% blockage was observed. In contrast, no significant blockade of IL-1α binding was observed at concentrations as high as 3 μg/ml of anti-IL- 1RI^150-166. The selective blockade of IL-1β forms was not due to differences in the affinities of these ligands for receptors on these cells. The antibody also blocked the binding of human IL-1β but not human IL-1α to EL4 cells. The biologic activity of murine IL-1β but not IL-1α on EL4 cells was also inhibited by this antibody. These data suggest (1) that antibody to a specific epitope on the extracellular domain interferes with the binding of IL-1β but not IL-1α, (2) the differential inhibition of binding of IL-1β but not IL-1α by anti-IL-1RI^150-166 also blocks biologic activity, and (3) IL-1α and IL-1β may transduce different signals by binding to separate loci on the IL-1RI.