Soluble human interleukin-6 receptor. Expression in insect cells, purification and characterization

Eur J Biochem. 1995 Dec 1;234(2):661-9. doi: 10.1111/j.1432-1033.1995.661_b.x.


The extracellular domain of the human interleukin-6 (IL-6) receptor, comprising 339 amino acids following the signal peptide, has been expressed in baculovirus-infected insect cells (Sf158). When the soluble receptor secreted into the culture medium was purified by affinity chromatography, using IL-6 immobilized on Sepharose, 6 mg soluble receptor was isolated from 1 l conditioned medium of Sf158 suspension cultures. A molar absorption coefficient of 9.3 x 10(4) was calculated from the ultraviolet spectrum of the soluble IL-6 receptor. After SDS/PAGE and silver staining, an apparent molecular mass of 48 kDa was estimated for the purified protein. Deglycosylation with peptide N-glycosidase F resulted in an increase in electrophoretic mobility and a decrease in the apparent molecular mass from 48 kDa to about 41-44 kDa. As expected, the soluble human IL-6 receptor bound human 125I-labeled IL-6 with low affinity (Kd = 500 pM). Furthermore, the binding of soluble human IL-6 receptor to immobilized IL-6 was studied using real-time interaction analysis. The recombinant soluble receptor showed biological activity on HepG2 cells stably transfected with a cDNA coding for IL-6 (HepG2-IL-6 cells). Haptoglobin mRNA synthesis was induced by the soluble IL-6 receptor at concentrations as low as 10 ng/ml. Five monoclonal antibodies were generated. Two groups of antibodies were identified mapping to amino acids 1-67 and 68-143 of the soluble IL-6 receptor, respectively. The plasma clearance of soluble 125I-labeled IL-6 receptor in the absence and presence of IL-6 was studied in rats as a model system. The kinetics was biphasic. Soluble IL-6 receptor/IL-6 complexes were cleared more rapidly than the soluble receptor alone. Intravenously injected soluble 125I-labeled IL-6 receptor, as well as complexes with IL-6, rapidly accumulated in liver and to a lesser extent in skeletal muscle, skin and kidneys. Subsequently, the radioactivity appeared in the gut content.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal / immunology
  • Antigens, CD / isolation & purification
  • Antigens, CD / metabolism*
  • Base Sequence
  • Glycosylation
  • Humans
  • Male
  • Metabolic Clearance Rate
  • Mice
  • Mice, Inbred BALB C
  • Molecular Sequence Data
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Interleukin / isolation & purification
  • Receptors, Interleukin / metabolism*
  • Receptors, Interleukin-6
  • Recombinant Proteins / metabolism
  • Spodoptera
  • Tissue Distribution


  • Antibodies, Monoclonal
  • Antigens, CD
  • Receptors, Interleukin
  • Receptors, Interleukin-6
  • Recombinant Proteins