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A wide range of immune-modulating effects make IL-10 a potential therapeutic option in the treatment of numerous diseases pathophysiological based on a dysregulation of cytokine production. The background of this study was to investigate, whether the beneficial effects of a therapeutic immunosuppression with IL-10 may be countered by an increased risk for infections due to impaired effector cell functions of unspecific immunity. We demonstrated the in vitro effects of IL-10 on phagocytosis (P), intracellular killing (K), and chemotactic activity (C) by human neutrophils (PMN) and monocytes (MON) using Candida albicans as test strain and compared the results to the effects of prednisolone and GM-CSF. IL-10 reduced significantly the intracellular killing rate of PMN compared to untreated phagocytes (60 +/- 16% versus 68 +/- 13%, mean +/- SD, p = 0.0002). High dose IL-10 (100 ng/ml) had a stimulating effect on the percentage of phagocytizing MON (70.2 +/- 12.7% vs. 66.9 +/- 14.2%, p = 0.0436), without impairing intracellular killing. Prednisolone reduced significantly the Candida uptake by MON (57 +/- 18.1% vs. 66. 9 +/- 14.2%, p = 0.0019). In contrast to prednisolone, neither MON nor PMN chemotaxis was suppressed by IL-10. In conclusion, IL-10 had only marginal immunosuppressive effects on the unspecific immunity compared to prednisolone.

Interleukin-10 (IL-10) has potent anti-inflammatory and immunosuppressive properties. The potential therapeutic benefit may be compromised by the down-regulation of the non-specific immune system and an increased risk of infection. We studied the effects of IL-10 on important functions of native and granulocyte-macrophage colony-stimulating factor (GM-CSF) activated neutrophils and monocytes, namely phagocytosis and membrane expression of the beta superset2-integrins and of the intercellular adhesion molecule-1 (ICAM-1). In order to simulate the in vivo situation closely, we used whole blood flowcytometric assays. The effects of IL-10 (0.05, 1, 10, 100 ng/ml) were compared to those of prednisolone (10 superset-8-10 superset-5 Mol/l), an approved immunosuppressive drug which is known to impair phagocyte function. - Incubation with IL-10 for three hours significantly attenuated the ability of neutrophils to phagocytose E.coli, particularly in lower concentrations. On the other hand, high IL-10 concentrations (10, 100 ng/ml) slightly augmented monocyte phagocytosis. Similarly, expression of the beta subset2-integrins and of ICAM-1 on monocytes was markedly enhanced with IL-10 concentrations in the range from 1 to 100 ng/ml and IL-10 showed strong synergistic effects with GM-CSF in the enhancement of monocyte receptor expression. Neutrophil adhesion molecule expression was not affected. Prednisolone suppressed the phagocytosis of both cell types in a dose-dependent fashion but hardly altered the receptor numbers. Our study indicates that IL-10 can behave as a de-activator as well as an activator on the non-specific immune system, depending on the cell type and the concentration.