The processing of interleukin-1 beta studied with antibodies raised against synthetic peptides from the precursor N-terminal region

The exact sequence of events during processing of human interleukin-1 beta (IL-1 beta) and the fate of the N-terminal region are unknown. We have used anti-peptide sera specific for the precursor and mature regions of IL-1 beta to study biosynthesis. These were raised against peptides corresponding to amino acids 1-15, 17-32, and 43-54 of the precursor and a peptide corresponding to the C-terminal 33 amino acids of mature human IL-1 beta. Antiserum to the mature region peptide immunoprecipitated the 35-kD precursor from cell lysates and 17-kD mature IL-1 beta and a 31-kD protein from the culture supernatants from radiolabeled human peripheral blood monocytes stimulated with lipopolysaccharide (LPS). Antisera to peptides from the precursor region also immunoprecipitated the 35-kD IL-1 beta precursor but not the 31-kD or 17-kD forms. Of the precursor-specific sera, only antiserum to amino acids 1-15 specifically recognized any other proteins; a peptide of 18 kD and a low molecular weight peptide, both of which accumulated in the medium. The 18-kD protein was not recognized by any of the other antisera and is unlikely to be the N-terminal region of the precursor removed during processing. Pulse-chase experiments indicated that the 31-kD protein could be a processing intermediate and also that it was itself an end product along with full-length precursor. Only 17-kD mature IL-1 beta had biological activity.