Calcineurininhibitoren nicht jedoch Rapamycin verhindern die Aktivierung des immunomodulatorischen Enzyms Indoleamine 2,3-dioxygenase

Abstract

Introduction: T-cell costimulatory blockade prevents allograft rejection and can induce peripheral tolerance. However, concomitant use of calcineurin inhibitors but not rapamycin are known to antagonize these effects. Recently, indoleamine 2,3-dioxygenase (IDO) via tryptophan depletion has been demonstrated to be the mediator of CTLA4Ig induced tolerance. An interaction between IDO activity and conventional immunosuppressive agents has not been investigated yet. Methods: Isolated, human peripheral blood mononuclear cells (PBMC) were stimulated with 10 μg/ml phytohaemag- glutinin (PHA) and 10 mg/ml concanavalin A (ConA) in the absence or presence of 0.01 μg/ml — 1 μg/ml cyclosporin-A (CsA), tacrolimus (FK506), rapamycin (Rapa), mycophenolate mofetil (MMF) or methylprednisolone (MP). After 48 hours of incubation tryptophan and kynurenin concentrations in cellculture supernatants were analyzed by high performance liquid chromatography (HPLC). Kynurenine to tryptophan ratios (kyn/trp) were calculated as an indirect estimate of functional IDO activity. Results: PHA and ConA significantly induced IDO activation and thus tryptophan degradation in a dose-dependent manner. CsA, FK506 and MMF revealed profound IDO inhibition in PBMCs as reflected by significantly reduced kyn/trp (all P < 0.01) and by increasing tryptophan concentrations. (P < 0.01) In sharp contrast Rapa and MP, at identical concentrations, had only marginal effects on IDO enzyme activity and did not decrease tryptophan catabolism when compared to mitogen stimulation alone (P = ns). Conclusion: These data provide first evidence that the differential effects of CsA, FK506 and Rapa on IDO activity may explain their capacity to either inhibit, or synergize with tolerance induction, when used in combination with T-cell costimulatory blocking agents.