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An interleukin-1 (IL-1) inhibitor produced by the M20 myelomonocytic cell line has been shown to be active in various in vitro and in vivo IL-1 induced parameters. This inhibitor has been purified from the conditioned medium by gel filtration through a Sephacryl S-300 column or dye ligand chromotography on Affi-Gel blue column, followed by isoelectric focusing in free solution in the pH range 3–5 using the Rotofor cell. When gel filtration by FPLC with the Superose 12 column was used as the final step, the combined sequence of purification procedures resulted in a 1600-fold purification of the IL-1 inhibitor. The purified IL-1 inhibitor has a molecular weight of approximately 52±4 kDa and a p I of 4.15±0.1. By SDS-PAGE analysis the inhibitor preparation thus obtained showed the presence of two protein bands, while a few closely spaced protein bands were seen by analytical isoelectric focusing in polyacrylamide gels (pH 3–6). Some of these bands in PAGIF might correspond to different degrees of glycosylation of the inhibitory protein. Although the M20 IL-1 inhibitor has not yet been purified to homogeneity, it should be stressed that the procedures used, allowed us to remove the great majority of the proteins present in the medium in which the M20 cells were cultured, and to recover in satisfactory yield the inhibitor which we consider likely to be present in the conditioned medium in subnanomolar concentrations.

Interleukin-1 (IL-1) is an important mediator in inflammation and immunological processes. The findings of native IL-1 inhibitors suggest a negative feedback mechanism to down-regulate IL-1 mediated acute inflammation. IL-1 inhibitors were also found elevated in disease states associated with high IL-1 levels. We have previously described one such IL-1 inhibitor derived from the human M20 myelomonocytic cell line. In this paper we present several biological and biochemical characteristics of the M20 IL-1 inhibitor. Various in vitro activities of the inhibitor are described and its IL-1 specificity in these assays is demonstrated. Purification of the inhibitor was performed by DEAE-high performance liquid chromatography, isoelectric focusing, gel filtration and dye ligand chromatography column. This protein factor has a MW of 52 ± 4 kDa and a pI of 4.15 ± 0.1. The inhibitor has no cross-reactivity against a panel of known cytokines (IL-1α, IL-1β, IL-2, sIL-2R, IL-6, tumor necrosis factor (TNF), interferon-γ (IFN-γ)) and is distinct from the IL-1 receptor antagonist (IL-1ra). The purified IL-1 inhibitor was destroyed by trypsin, 2-mercaptoethanol, sodium dodecyl sulfate and extremes in pH and in temperature. Only IL-1 induced (but not the IL-2, IL-6, or TNF induced) thymocyte proliferation and PGE2 production by fibroblasts were inhibited by the inhibitor, thus showing specifity to IL-1 in these assays.