Atopic Patients Show Increased Interleukin 4 Plasma Levels but the Degree of Elevation Is Not Sufficient to Upregulate Interleukin-4-Sensitive Genes

BACKGROUND: Atopic diseases constitute a major health challenge for industrialized countries, and elevated levels of interleukin 4 (IL-4) frequently characterize these disorders. Previous in vitroanalyses have indicated that IL-4 strongly upregulates the expression of IL-4-sensitive genes in human monocytes. OBJECTIVE: 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 (n = 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. METHODS: 34 allergic patients suffering from allergic rhinitis (n = 11), atopic eczema (n = 11) and allergic asthma (n = 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). RESULTS: 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. CONCLUSION: 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.