Protein polymorphism of human IL-18 identified by monoclonal antibodies.
Six mAbs were raised against human "functionally inactive" recombinant IL-18, ELISA for determination of "functionally inactive" forms of IL-18 were established using two of these mAbs (#21 and #132), and inactive species of IL-18 protein were examined with human blood plasma and macrophages (Mp). In 6-day GM-CSF-treated monocytes, namely Mp, the mAb #21 recognized the IL-18 proform (24 kDa) and a 48 kDa dimer by immunoblotting. In contrast, only the 24 kDa species was detected as a relatively faint band with a commercial mAb against "active" IL-18. No IL-18 species was detected in premature monocytes. Thus, the dimeric IL-18 was produced in Mp and detectable with the mAb we established. In blood plasma of normal subjects and patients, the #21-recognizable IL-18 was also detected by ELISA, the levels of which were not consistent with those obtained with the commercially available kit for determination of "functionally active" IL-18. We designated the former as type 2 and the latter as type 1. Strikingly, IL-18 type 1 was detected in all volunteers while type 2 was detected in approximately 30% of healthy subjects, and the levels of type 2 were high (10-100 ng/ml) compared to those of type 1 (0.02-0.55 ng/ml) in their blood plasma. In patients with atopic dermatitis, the mean value of type 1 was high (200 ng/ml) compared to those of normal subjects (0.122 ng/ml) and patients with lung cancer (0.113 ng/ml). Production of high type 1 may be associated with an immunomodulatory state in atopic dermatitis. The levels and frequencies of IL-18 type 2 were not significantly changed among these populations. Hence, large amounts of type 2 species are produced in monocyte-Mp differentiation, and their levels and frequencies are unchanged in blood plasma irrespective of the levels of type 1.
Seya
T
T
Department of Immunology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Higashinari-ku, Osaka 537-8511, Japan. seya-tu@mc.pref.osaka.jp
Matsumoto
M
M
Shiratori
I
I
Fukumori
Y
Y
Toyoshima
K
K
D000293:Adolescent; D000328:Adult; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000918:Antibody Specificity; D003876:Dermatitis, Atopic / Q000097:blood / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D015151:Immunoblotting; D020382:Interleukin-18 / Q000097:blood / Q000235:genetics / Q000276:immunology*; D008175:Lung Neoplasms / Q000097:blood / Q000276:immunology; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000276:immunology; D011110:Polymorphism, Genetic; D020033:Protein Isoforms / Q000097:blood / Q000235:genetics / Q000276:immunology
D000911:Antibodies, Monoclonal; D020382:Interleukin-18; D020033:Protein Isoforms