Specific binding of interleukin 1 (IL-1) beta and IL-1 receptor antagonist (IL-1ra) to human serum. High-affinity binding of IL-1ra to soluble IL-1 receptor type I.
Molecules that bind recombinant interleukin 1 (rIL-1) beta and rIL-1 receptor antagonist (rIL-1ra) with high affinity were detected in sera of healthy individuals. rIL-1 beta bound with dissociation constants in the nanomolar range, and the serum binding capacity was 40-50 ng/ml. rIL-1ra bound with 30 times higher affinity, and the serum binding capacity was 0.7-1 ng/ml. Rabbit antibodies against the recombinant-derived extracellular part of human IL-1 receptor type I (rsIL-1RI) selectively inhibited the binding of 125I-rIL-1ra to the serum factor(s). Almost 70% of the high-affinity IL-1ra-binding capacity was recovered after immunosorption with these antibodies. Binding of 125I-rIL-1ra to rsIL-1RI was blocked by rIL-1 alpha and by rIL-1 beta. In contrast, the purified rIL-1ra-binding factor (IL-1raBF) failed to bind rIL-1 alpha and rIL-1 beta. Gel filtration chromatography indicated a 1:1 binding of rIL-1 beta and rIL-1ra to their respective serum factors. The apparent molecular size of both serum factors was 70-80 kDa. Using SDS-PAGE and autoradiography, IL-1raBF had a molecular size of 60 kDa. We conclude that IL-1raBF, a serum factor which selectively and with high affinity binds IL-1ra (Kd = 70 pM), is related to or identical with a soluble form of IL-1RI. If upregulated during disease, IL-1raBF may constitute yet another level of natural regulation of IL-1 bioactivities.
Svenson
M
M
Dept. Inf. Dis. M7641, Rigshospitalet University Hospital, Copenhagen, Denmark.
Hansen
M B
MB
Heegaard
P
P
Abell
K
K
Bendtzen
K
K
D000906:Antibodies / Q000097:blood; D000937:Antigen-Antibody Reactions; D006801:Humans; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1 / Q000097:blood*; D017472:Receptors, Interleukin-1 / Q000276:immunology / Q000378:metabolism*; D011994:Recombinant Proteins / Q000097:blood; D012016:Reference Values; D012795:Sialoglycoproteins / Q000097:blood*; D012995:Solubility
D000906:Antibodies; C507763:IL1RN protein, human; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1; D017472:Receptors, Interleukin-1; D011994:Recombinant Proteins; D012795:Sialoglycoproteins