<b><i>Background:</i></b> Atopic diseases constitute a major health challenge for industrialized countries, and elevated levels of interleukin 4 (IL-4) frequently characterize these disorders. Previous in vitro<i></i>analyses have indicated that IL-4 strongly upregulates the expression of IL-4-sensitive genes in human monocytes. <b><i>Objective:</i></b> To explore whether similar expression alterations may contribute to the pathomechanisms of atopic diseases in vivo we carried out a small-scale case-control clinical study (<i>n</i> = 43), in which we quantified the plasma levels of IgE and IL-4 as well as the expression of selected IL-4-sensitive genes in blood leukocytes. <b><i>Methods:</i></b> 34 allergic patients suffering from allergic rhinitis (<i>n</i> = 11), atopic eczema (<i>n</i> = 11) and allergic asthma (<i>n</i> = 12) as well as 9 healthy control individuals were recruited. IgE and IL-4 plasma levels were determined by ELISA, and the expression of selected IL-4-sensitive gene products in blood leukocytes was quantified by qRT-PCR. In addition, the fatty acid oxygenase activity of isolated monocytes was measured by RP-HPLC analysis of the arachidonic acid oxygenation products (ex vivo activity assays). <b><i>Results:</i></b> We found that plasma levels of IgE and IL-4 were significantly elevated in atopic patients but the degree of elevation was not sufficient to upregulate the expression of the selected IL-4-sensitive genes in circulating leukocytes. Moreover, the arachidonic acid oxygenase activity of blood monocytes was not significantly altered in atopic patients. <b><i>Conclusion:</i></b> Our data suggest that the IL-4 plasma levels of atopic patients are not high enough to impact the expression of IL-4-sensitive genes.

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