Engineering human interleukin-6 to obtain variants with strongly enhanced bioactivity

Carlo Toniatti, Andrea Cabibbo, Elisabetta Sporeno, Anna Laura Salvati, Mauro Cerretani, Sergio Serafini, Armin Lahm, Riccardo Cortese, Gennaro Ciliberto

Research output: Contribution to journalArticlepeer-review


Interleukin-6 (IL-6) triggers the formation of a high affinity receptor complex with the ligand binding subunit IL-6Rα and the signal transducing chain gp130. Since the intracytoplasmic region of the IL-6Rα does not contribute to signaling, soluble forms of the extracytoplasmic domain (sIL-6Rα), potentiate IL-6 bioactivity and induce a cytokine-responsive status in cells expressing gp130 only. This observation, together with the detection of high levels of circulating soluble human IL-6Rα (shIL-6Rα) in sera, suggests that the hIL-6-shIL-6Rα complex is an alternative form of the cytokine. Here we describe the generation of human IL-6 (hIL-6) variants with strongly enhanced shIL-6Rα binding activity and bioactivity. Homology modeling and site-directed mutagenesis of hIL-6 suggested that the binding interface for hIL-6Rα is constituted by the C-terminal portion of the D-helix and residues contained in the AB loop. Four libraries of hIL-6 mutants were generated by each time fully randomizing four different amino acids in the predicted AB loop. These libraries were displayed monovalently on filamentous phage surface and sorted separately for binding to immobilized shIL-6Rα. Mutants were selected which, when expressed as soluble proteins, showed a 10- to 40-fold improvement in shIL-6Rα binding; a further increase (up to 70-fold) was achieved by combining variants isolated from different libraries. Interestingly, high affinity hIL-6 variants show strongly enhanced bioactivity on cells expressing gp130 in the presence of shIL-6Rα at concentrations similar to those normally found in human sera.

Original languageEnglish
Pages (from-to)2726-2737
Number of pages12
JournalEMBO Journal
Issue number11
Publication statusPublished - 1996


  • BAF cells
  • IL-6
  • IL-6 receptor superagonists
  • IL-6R
  • Phage display

ASJC Scopus subject areas

  • Genetics
  • Cell Biology


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