High circulating levels of biologically inactive IL-6/SIL-6 receptor complexes in systemic juvenile idiopathic arthritis: evidence for serum factors interfering with the binding to gp130.
We previously demonstrated that high levels of IL-6/sIL-6R complexes are present in sera of patients with systemic juvenile idiopathic arthritis (s-JIA) and that the amount of IL-6 estimated in the IL-6/sIL-6R complexes is markedly higher than that measured by the B9 assay. Here, we show that two additional bioassays, employing human myeloma XG-1 cells and human hepatoma Hep3B cells, detected serum IL-6 levels similar to those measured by the B9 assay and approximately 10-fold lower than the IL-6 levels estimated to be present in the IL-6/sIL-6R complex. Using an assay for the measurement of the amount of circulating IL-6 complexed with the sIL-6R and available for binding to gp130 (gp130 binding activity), we show that the IL-6/gp130 binding activity is similar to that detected by the bioassays and again significantly lower than that estimated to be present in the IL-6/sIL-6R complex. Addition of recombinant human IL-6 (rhIL-6) to sera of patients or controls results in a markedly lower increase in the gp130 binding activity in patients than in controls. Moreover, sera from s-JIA patients inhibited in a dose dependent manner the gp130 binding activity assay. These results show that sera from patients with s-JIA contain a factor, or factors, that inhibit(s) the binding of the IL-6/sIL-6R complex to gp130. This inhibitory activity does not appear to be due to soluble gp130, C-reactive protein or autoantibodies to IL-6.
Pignatti
P
P
Paediatria Generale e Reumatologia, IRCCS Policlinico San Matteo, Pavia, Italy.
Ciapponi
L
L
Galle
P
P
Hansen
M B
MB
Massa
M
M
Meazza
C
C
Paonessa
G
G
Novick
D
D
Ciliberto
G
G
Martini
A
A
De Benedetti
F
F
D000293:Adolescent; D015703:Antigens, CD / Q000097:blood*; D001171:Arthritis, Juvenile / Q000097:blood*; D001323:Autoantibodies / Q000097:blood; D001667:Binding, Competitive; D001681:Biological Assay / Q000379:methods; D001685:Biological Factors / Q000097:blood*; D002097:C-Reactive Protein / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D050822:Cytokine Receptor gp130; D006801:Humans; D015850:Interleukin-6 / Q000097:blood* / Q000276:immunology; D008562:Membrane Glycoproteins / Q000097:blood*; D011485:Protein Binding; D019947:Receptors, Interleukin-6 / Q000097:blood*; D015398:Signal Transduction; D012995:Solubility
D015703:Antigens, CD; D001323:Autoantibodies; D001685:Biological Factors; C494199:IL6ST protein, human; D015850:Interleukin-6; D008562:Membrane Glycoproteins; D019947:Receptors, Interleukin-6; D050822:Cytokine Receptor gp130; D002097:C-Reactive Protein