A novel IL-18BP ELISA shows elevated serum IL-18BP in sepsis and extensive decrease of free IL-18.
IL-18 binding protein (IL-18BP) is a circulating antagonist of the proinflammatory Th1 cytokine IL-18. It effectively blocks IL-18 by forming a 1:1 high affinity (Kd=400 pM) complex, exhibiting a very low dissociation rate. We have developed a sandwich ELISA for IL-18BPa and determined its limit of detection (62 pg/ml). Interference by IL-18 and related cytokines, as well as cross reactivity with other IL-18BP isoforms (b, c, and d) were determined. Using this ELISA, we measured serum IL-18BPa in large cohorts of healthy individuals and in septic patients. Serum IL-18BPa in healthy individuals was 2.15+/-0.15 ng/ml (range 0.5-7 ng/ml). In sepsis, the level rose to 21.9+/-1.44 ng/ml (range 4-132 ng/ml). Total IL-18 was measured in the same sera by an electrochemiluminescence assay and free IL-18 was calculated based on the mass action law. Total IL-18 was low in healthy individuals (64+/-17 pg/ml) and most of it ( approximately 85%) was in its free form. Total IL-18 and IL-18BPa were both elevated in sepsis patients upon admission (1.5+/-0.4 ng/ml and 28.6+/-4.5 ng/ml, respectively). At these levels, most of the IL-18 is bound to IL-18BPa, however the remaining free IL-18 is still higher than in healthy individuals. We conclude that IL-18BPa considerably inhibits circulating IL-18 in sepsis. Yet, exogenous administration of IL-18BPa may further reduce circulating IL-18 activity.
Novick
D
D
Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, 76100, Israel.
Schwartsburd
B
B
Pinkus
R
R
Suissa
D
D
Belzer
I
I
Sthoeger
Z
Z
Keane
W F
WF
Chvatchko
Y
Y
Kim
S H
SH
Fantuzzi
G
G
Dinarello
C A
CA
Rubinstein
M
M
D017398:Alternative Splicing; D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D001665:Binding Sites; D019556:COS Cells; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005982:Glutathione Transferase / Q000378:metabolism; D006023:Glycoproteins / Q000097:blood* / Q000652:urine; D006801:Humans; D006825:Hybridomas / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D020382:Interleukin-18 / Q000097:blood*; D007700:Kinetics; D008024:Ligands; D051379:Mice; D020033:Protein Isoforms; D011863:Radioimmunoassay; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D018805:Sepsis / Q000097:blood*
D000911:Antibodies, Monoclonal; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D020382:Interleukin-18; D008024:Ligands; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; C118370:interleukin-18 binding protein; D005982:Glutathione Transferase