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

On the basis of their relative hydropathy and alpha-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 [I-125]-IL-1 alpha or -beta 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-1 beta 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-1 alpha to that of murine or human IL-1 beta, At a concentration of 20 ng/ml, affinity-purified anti-IL-1RI(150-166) blocked 50% binding of murine IL-1 beta. At 1 mu g/ml, 90% blockage was observed, In contrast, no significant blockade of IL-1 alpha binding was observed at concentrations as high as 3 mu g/ml of anti-IL-1RI(150-166). The selective blockade of IL-1 beta 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-1 beta but not human IL-1 alpha to EL4 cells, The biologic activity of murine IL-1 beta but not IL-1 alpha 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-1 beta but not IL-1 alpha, (2) the differential inhibition of binding of IL-1 beta but not IL-1 alpha by anti-IL-1RI(150-166) also blocks biologic activity, and (3) IL-1 alpha and IL-1 beta may transduce different signals by binding to separate loci on the IL-1RI.