Human macrophages produce dimeric forms of IL-18 which can be detected with monoclonal antibodies specific for inactive IL-18.
We established two monoclonal antibodies (mAbs) which specifically recognize human 'functionally inactive' recombinant IL-18, and IL-18 protein polymorphism was examined using human monocytes and macrophages (M phi). In 6 day GM-CSF-treated M phi, an 'inactive' IL-18-recognizing mAb 21 detected the IL-18 proform (24 kDa) and a 48-kDa protein, which were gradually increased concomitant with maturation stage. Majority of the 24- and 48-kDa forms were barely detectable with other mAbs recognizing 'active' IL-18. No reagents including Toll stimulators up-regulated these IL-18 populations in M phi. The 21-recognizable IL-18 species were separated using an anion-exchanger column and their IFN gamma-inducing activity was assessed with human lymphocytes plus IL-12. Virtually no as yet known activity was detected with these IL-18 species. After processed with M phi proteases, an 18-kDa form was generated to express the IFN gamma-inducing activity, although the activity was far weaker than that of control 'active' IL-18. These observations suggested that large amounts of various IL-18 species are produced with monocyte-M phi differentiation and most of these IL-18 species are functionally 'inactive' in terms of the reported IL-18 function even after proteolytic 18-kDa conversion.
Kikkawa
S
S
Department of Immunology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Higashinari-ku, Osaka 537-8511, Japan.
Matsumoto
M
M
Shida
K
K
Fukumori
Y
Y
Toyoshima
K
K
Seya
T
T
D000911:Antibodies, Monoclonal / Q000032:analysis* / Q000276:immunology; D000918:Antibody Specificity; D002851:Chromatography, High Pressure Liquid; D019281:Dimerization; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D007371:Interferon-gamma / Q000187:drug effects / Q000378:metabolism; D018664:Interleukin-12 / Q000494:pharmacology; D020382:Interleukin-18 / Q000032:analysis* / Q000737:chemistry / Q000276:immunology; D007694:Killer Cells, Natural / Q000187:drug effects / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000378:metabolism; D008264:Macrophages / Q000737:chemistry* / Q000187:drug effects; D008970:Molecular Weight; D020033:Protein Isoforms / Q000032:analysis / Q000276:immunology / Q000494:pharmacology; D013696:Temperature; D013997:Time Factors
D000911:Antibodies, Monoclonal; D020382:Interleukin-18; D020033:Protein Isoforms; D018664:Interleukin-12; D007371:Interferon-gamma; D016178:Granulocyte-Macrophage Colony-Stimulating Factor