Binding of IL-1 alpha, IL-1 beta, and IL-1 receptor antagonist by soluble IL-1 receptors and levels of soluble IL-1 receptors in synovial fluids.
These studies have examined the binding of the three IL-1 ligands, IL-1 alpha, IL-1 beta, and IL-1 receptor antagonist (IL-1 ra), to soluble forms of types I and II IL-1Rs (sIL-1RI and sIL-1RII). This interaction was measured in direct binding experiments, in which the ligands bound to immobilized sIL-1R, and in inhibition experiments, in which sIL-1R in solution inhibited the binding of IL-1 ligands to immobilized sIL-1R. In addition, the effects of sIL-1R on the detection of IL-1 ligands by ELISA were examined. Finally, levels of sIL-1R in synovial fluid samples were determined, and their effects on measurement of IL-1 in these samples were estimated. IL-1 beta bound more avidly to sIL-1RII than IL-1 alpha or IL-1ra, primarily because of a slow dissociation rate. In contrast, IL-1 ra bound more avidly than IL-1 alpha or IL-1 beta to sIL-1RI, again because of a slow dissociation rate. sIL-1RII and sIL-1RI inhibited the detection of IL-1 beta and IL-1ra, respectively, by ELISA. Low levels of sIL-1RI (approximately 1.0-2.5 ng/ml) were present in all synovial fluids, irrespective of the degree of inflammation, and were correlated inversely with the levels of measured IL-1ra. In contrast, higher levels of sIL-1RII (approximately 10-20 ng/ml) were found in inflammatory synovial fluids and were not correlated with IL-1ra levels. IL-1 beta could not be detected in any synovial fluid. These results suggest that some IL-1 beta and IL-1ra may be bound in vivo to sIL-1RII and sIL-1RI, respectively, leading to underestimations of cytokine concentrations in body fluids when measured by ELISA.
Department of Medicine, University of Colorado Health Sciences Center, CO 80262.
W P
WP
Arend
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M
Malyak
M F
MF
Smith
T D
TD
Whisenand
J L
JL
Slack
J E
JE
Sims
J G
JG
Giri
S K
SK
Dower
D000818:Animals; D000911:Antibodies, Monoclonal; D001667:Binding, Competitive; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1 / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D017472:Receptors, Interleukin-1 / Q000032:analysis* / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012795:Sialoglycoproteins / Q000378:metabolism*; D012995:Solubility; D013582:Synovial Fluid / Q000276:immunology*
D000911:Antibodies, Monoclonal; C507763:IL1RN protein, human; C507764:Il1rn protein, mouse; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1; D017472:Receptors, Interleukin-1; D011994:Recombinant Proteins; D012795:Sialoglycoproteins