Serum soluble interleukin 6 (IL-6) receptor and IL-6/soluble IL-6 receptor complex in systemic juvenile rheumatoid arthritis.
By using a sandwich ELISA, soluble human IL-6 receptor (sIL-6 R) levels were measured in the sera of 20 healthy children and of 25 patients with systemic juvenile rheumatoid arthritis (JRA). In patients with systemic JRA, serum sIL-6 R levels (114.6 +/- 37.7 ng/ml) were significantly lower (P < 0.01) than those of healthy children (161.2 +/- 45.5 ng/ml). Serum sIL-6 R levels were negatively correlated (r = -0.610, P < 0.001) with serum IL-6 levels measured with the B9 cells. The serum IL-6/sIL-6 R complex was detected using an ELISA based on a monoclonal antibody to IL-6 for capture and on a monoclonal antibody to human sIL-6 R for detection. Healthy controls had little, if any, detectable serum IL-6/sIL-6 R complex (OD 0.024 +/- 0.027), while the majority of patients with systemic JRA presented measurable serum IL-6/sIL-6 R complex (OD 0.492 +/- 0.546). IL-6 levels estimated in the circulating IL-6/sIL-6 R complexes were in the range of nanograms per milliliter and approximately 20-fold higher than those measured by the B9 cells. Since serum C-reactive protein concentrations were much more correlated with serum levels of IL-6/sIL-6 R complexes (r = 0.713, r2 = 0.51, P < 0.0001) than with the serum IL-6 levels measured with the B9 cells (r = 0.435, r2 = 0.19, P = 0.05), the large quantities of serum IL-6 present in IL-6/sIL-6 R complexes appear to be biologically relevant in vivo, at least as far as the induction by IL-6 of acute phase protein production.
De Benedetti
F
F
Clinica Pediatrica, Universitá degli Studi di Pavia, Italy.
Massa
M
M
Pignatti
P
P
Albani
S
S
Novick
D
D
Martini
A
A
D000293:Adolescent; D001171:Arthritis, Juvenile / Q000097:blood* / Q000145:classification / Q000209:etiology; D002648:Child; D002675:Child, Preschool; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D006801:Humans; D015850:Interleukin-6 / Q000302:isolation & purification* / Q000378:metabolism; D046911:Macromolecular Substances; D011485:Protein Binding; D018123:Receptors, Interleukin / Q000302:isolation & purification* / Q000378:metabolism; D019947:Receptors, Interleukin-6; D012995:Solubility
D015850:Interleukin-6; D046911:Macromolecular Substances; D018123:Receptors, Interleukin; D019947:Receptors, Interleukin-6