title: IL-1 beta is secreted by activated murine macrophages as biologically inactive precursor.
abstract: IL-1 alpha and IL-beta are distinct cytokines, produced by activated macrophages. The temporal sequence in the processing and secretion as well as the mechanism(s) by which IL-1 is secreted from the cells remain undefined. Here we have studied the production of IL-1 from murine macrophages after stimulation with LPS or Listeria monocytogenes by two distinct methods: i) immunoprecipitation of radio-labeled IL-1 peptides from culture supernatants, and ii) determination of IL-1 activity by neutralization with monospecific antisera to either form of IL-1. We confirmed that precursor and mature forms of both IL-1 alpha and IL-1 beta can be detected in the culture supernatants after stimulation of the macrophages with 10 to 20 micrograms LPS/ml but, in addition, we report the novel finding that IL-1 beta is exclusively secreted in its unprocessed precursor form after stimulation of the cells with either 0.5 to 1 microgram LPS/ml or with L. monocytogenes. Exposure of the cells to increasing amounts of LPS led to the appearance of a 20-kDa IL-1 beta peptide in the culture supernatants concomitant with the release of a processing activity for the IL-1 beta precursor. These data therefore suggest that, in a first step, IL-1 beta is secreted as an unprocessed precursor protein that in a second, postsecretory step is cleaved by a LPS-inducible protease, thus generating the 20-kDa IL-1 beta peptide. The latter represents the biologically active IL-1 beta inasmuch as the generation of IL-1 beta activity in the culture supernatants strictly correlated with the appearance of the 20-kDa IL-1 beta peptide.
authors.affiliation: Institute of Clinical Microbiology, University of Erlangen/Nürnberg, FRG.
authors.forename: H U
authors.initials: HU
authors.lastname: Beuscher
authors.forename: C
authors.initials: C
authors.lastname: Günther
authors.forename: M
authors.initials: M
authors.lastname: Röllinghoff
mesh_terms: D000818:Animals; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D007375:Interleukin-1 / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008262:Macrophage Activation; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008970:Molecular Weight; D011498:Protein Precursors / Q000378:metabolism; D011499:Protein Processing, Post-Translational
chemical_list: D007375:Interleukin-1; D008070:Lipopolysaccharides; D011498:Protein Precursors