Interleukin (IL)-18 is a pleiotropic cytokine, which may play a role in autoimmune and allergic disorders. Serum IL-18 levels were measured in 34 patients with chronic ordinary urticaria (COU) and 17 normal subjects. In vivo and in vitro assays for histamine-releasing factors, an autologous serum skin test (ASST) and a basophil histamine release assay were also performed for all patients with COU. Serum IL-18 concentration was not significantly different between patients with COU and normal subjects (mean ± standard error of the mean 246.47 ± 18.40 pg/mL vs. 213.88 ± 22.24 pg/mL), and no significant difference was found between ASST-positive and ASST-negative patients. However, in ASST-positive patients, IL-18 levels paralleled clinical severity scores and showed a tendency to correlate with in vitro histamine release. The increased IL-18 levels in the ASST-positive patients with most active chronic urticaria may reflect stronger immune system activation and possibly an involvement of IL-18 as a direct histamine-releasing factor.
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