Changes in the levels of cytokines in the circulating blood and skin have been reported in patients with atopic dermatitis (AD). We determined IFN-γ, IL-2, IL-4, IL-5 and IL-10 in both the serum and plasma of 45 AD patients and 20 healthy donors. Since differences in the levels of these cytokines between serum and plasma were found, the roles of Ca2+ and proteolytic enzymes were examined. Levels of IL-2 and IL-10 were measured in citrated plasma to which various amounts of CaCl2, protease inhibitors, and proteases had been added. All cytokine determinations were carried out using a standard ELISA. The plasma levels of IFN-γ, IL-2, and IL-5 were significantly elevated, but the serum levels of these cytokines were not significantly changed. The levels of IL-2 in the plasma of the AD patients averaged 4.25-fold higher than in the serum of the AD patients, and 2.5-fold higher than in the plasma of healthy controls (P < 0.001). CaCl2 produced a dose-dependent decrease in IL-2 and IL-10 in citrated plasma. The protease inhibitors PMSF, aprotinin and leupeptin produced a dose-dependent increase in measurable levels of IL-2 and IL-10 in plasma. A decrease in IL-2 levels was also seen in CaCl2-supplemented serum-free medium, and this was accentuated by the addition of the proteases thrombin, trypsin, chymotrypsin and elastase. These findings suggest that although significant changes in cytokine levels have been reported not to occur in circulating blood but have been reported to occur in the skin of AD patients both in vivo and in vitro, cytokines can indeed also be found to be elevated in circulating blood when assessed carefully by statistically valid methods. Further, it is suggested that during the preparation of serum, some circulating cytokines are degraded by calcium-dependent proteases, and that Ca2+ itself can also affect the measurement of cytokines. The measurement of circulating cytokines needs to be carefully reassessed.
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