High serum levels of additional IL-18 forms may be reciprocally correlatedwith IgE levels in patients with atopic dermatitis

We established an ELISA system for determination of as yet unidentified spe cies or interleukin 18 (IL-18), named IL-18 type 2, in human serum. Serum I L-18 levels and their effect on IgE levels were examined in 18 patients wit h atopic dermatitis (AD) with no other allergic symptoms. Three of these pa tients showed high IL-18 type 2 concentrations (25-100 ng/ml) in their bloo d serum, and this IL-19 type 2 was detectable only with our established ELI SA system. In contrast, the level of the conventional form of IL-18 (type I ) was found to be 50-400 pg/ml in all patients by the commercially availabl e ELISA. The levels of type I IL-18 showed no correlation with. those of ty pe 2 and similar to 2-fold higher in AD patients than in normal subjects. I L-12 p40 and IgE levels were correlated in the patients with no IL-18 type 2, and interestingly, relatively low IgE concentrations were detected in th e three IL-18 type 2-positive patients. They showed considerable levels of IL-12 p40 unlike normal subjects. The IFN gamma -inducing activity of IL-18 type 2 was > 100-fold less potent by weight ratio than that of a recombina nt 'active' IL-18 preparation, even after the treatment with Caspase I. Alt hough the relationship between AD and serum IgE levels is not clear cut, IL -18 type 2 appears to play some roles in the Th2-polarization involving IgE production in association with immune responses occurring in local inflamm atory milieu such as atopic lesions. (C) 2001 Published by Elsevier Science B.V.