Immunoadhesins of interleukin-6 and the IL-6 soluble IL-6R fusion protein hyper-IL-6

Signal transduction in response to interleukin-6 (IL-6) results from homodi merization of gp130. This dimerization occurs after binding of IL-6 to its surface receptor (IL-6R) and can also be triggered by the complex of solubl e IL-6R and IL-6. We fused IL-6 to the constant region of a human IgG1 heav y chain (Fc). IL-6Fc was expressed in COS-7 cells and purified via Protein A Sepharose. Using three different assays we found that the biological acti vity of this dimeric IL-6 protein is comparable with monomeric IL-6. Recent ly, we described the designer cytokine Hyper-IL-6 (H-IL-B) in which soluble IL-6R and IL-6 are connected via a flexible peptide linker. This molecule turned out to be 100-1000 times more effective than unlinked IL-6 and solub le IL-6R. Hyper-IL-6 acts on cells only expressing gp130 and is a potent st imulator of in vitro expansion of early hematopoietic precursors. Here we s how that a Fc fusion protein of H-IL-6 (H-IL-6Fc) has the same biological a ctivity on BAF/gp130 cells as H-IL-6. Furthermore, both H-IL-6 forms have a similar ability to induce the synthesis of acute phase proteins in human h epatoma cells HepG2 and in mice in vivo. The introduction of a thrombin cle avage site between H-IL-6 and the Fc portion of H-IL-6Fc made it possible t o specifically recover biologically active monomeric H-IL-6 by Limited prot eolysis of the fusion protein. A more general use of cleavable immunoadhesi ns expressed in mammalian cells is discussed. (C) 1999 Elsevier Science B.V . All rights reserved.