In vitro differential effects of the antiglucocorticoid RU486 on the release of lymphokines from mitogen-activated normal human lymphocytes

Abstract

The synthetic antiglucocorticoid RU486 has multiple effects on the immune system. We have recently reported that RU486 suppresses normal lymphocyte proliferation and downregulates interleukin-2 receptors (IL-2R) by decreasing the accumulation of the β-chain IL-2R mRNA in normal human lymphocytes in culture. To further explore the mechanism of the immunoregulatory actions of RU486, in the present study, we investigated the effects of this molecule on the release of lymphokines from phytohemagglutinin (PHA)-activated normal human peripheral blood lymphocytes (NPBL) in culture. We have found that RU486 differentially regulates the release of lymphokines from PHA-activated NPB lymphocytes. Specifically, RU486 (at concentrations of 1–100 nM) exerts pure antagonist actions by almost completely reversing the inhibitory effects of the glucocorticoid dexamethasone (Dex) on the release of monocyte/macrophages-derived lymphokines, such as IL-1, IL-6, IL-8 and tumor necrosis factor-alpha (TNF-α). Dex decreased in a dose-dependent manner the release of the above four lymphokines, with an ID 50 of 0.9±0.1, 4.76±0.4, 9.8±1.8, and 1.16±0.2 nM for IL-1, IL-6, IL-8 and TNF-α, respectively. Conversely, RU486 exhibits both agonist and antagonist effects on the release of T-lymphocyte-derived lymphokines. RU486 given alone, exerts agonist/glucocorticoid effects, by decreasing in a dose-dependent manner the release of IL-2 and −3. The maximal inhibitory effect of RU486 was observed at 10 nM and was 64.5±4.3% of the control value, ( n=6, P<0.02) for IL-2 and 59.2±6.3% ( n=6, P<0.02) for IL-3. The ID 50 of RU486 for the release of IL-2 and −3 were 14.6±2.0 and 11.6±1.9 nM, respectively, i.e. almost similar with those of Dex. Interestingly, when high doses of RU486 (1 μM) were combined with Dex RU486 exhibited antagonist actions by significantly counteracting the inhibitory effects of Dex on IL-2 and −3 release. In conclusion, the antiglucocorticoid RU486 exhibits complex regulatory actions on lymphokine secretion, dependent upon the type of the lymphokine-producing cell. A pure antagonist effect was observed on the release of monocyte-derived IL-1, IL-6, IL-8 and TNF-α. However, when RU486 was given alone it acted as a glucocorticoid agonist on the secretion of T-lymphocyte-derived IL-2 and −3, while combined with the agonist (Dex) it exhibits antagonist effects on the release of the above lymphokines. This molecule still remains unexplored as an immunoregulatory agent. Further studies are needed in order to assess its relevance on pharmacological intervention in the immune system.