Flow cytometric analysis of IL-4, IL-13 and IFN-gamma expression in peripheral blood mononuclear cells and detection of circulating IL-13 in patients with atopic dermatitis provide evidence for the involvement of type 2 cytokines in the disease.

Recent studies have shown increased T-helper (Th) 2 cytokine expression and decreased IFN-gamma expression in peripheral blood from patients with atopic dermatitis (AD). In the present study, we examined the cytokine expression in peripheral blood mononuclear cells in patients with AD and tested how the cytokine profile correlated with the patients' age, severity and laboratory findings. Peripheral blood mononuclear cells obtained from 20 patients with AD were stimulated with phorbol 12-myristate 13-acetate and ionomycin, and were examined for the frequencies of CD4+ cells expressing IL-4, IL-13 and IFN-gamma at the single cell level using intracellular cytokine staining and flow cytometry. There was a significant positive correlation between IL-4 and IL-13 expression in CD4+ cells. Expression levels of both IL-4 and IL-13 in CD4+ cells were significantly correlated with peripheral blood eosinophilia. These findings suggest that CD4+ cells producing IL-4 and IL-13 play important roles in the pathogenesis of AD. IFN-gamma expression did not correlate with either IL-4 or IL-13 expression, or with blood eosinophilia. We also measured serum levels of IL-13 in 144 patients with AD using enzyme-linked immunosorbent assay, and found 16 patients with detectable levels of serum IL-13. IL-13+ patients had significantly higher serum IgE levels than IL-13- patients, suggesting a direct association between serum levels of IL-13 and IgE. It was also shown that the IL-13+ group was significantly younger in age than the IL-13- group, although the implication of this finding is not clear at present. The sum of these findings suggested that the predominance of Th2 cells and the consequent overexpression of IL-4 and IL-13 in peripheral blood may be deeply involved in the pathogenetic process of AD.