Indoleamine 2,3 Dioxygenase (IDO) Expression and Activity in Relapsing- Remitting Multiple Sclerosis

BACKGROUND: Interferon gamma (IFN-γ) production induces the transcription of indoleamine 2,3 dioxygenase (IDO) resulting in the reduction of T-cell activation and proliferation through the depletion of tryptophan and the elicitation of Treg lymphocytes. IDO was shown to be involved in the pathogenesis of autoimmune diseases; we investigated whether changes in IDO gene expression and activity could be indicative of onset of relapse in multiple sclerosis (MS) patients. METHODS: IDO and interferon-γ (IFN-γ) gene expression, serum IDO activity (Kynurenine/Tryptophan ratio) and serum neopterin concentration – a protein released by macrophages upon IFN-γ stimulation – were measured in 51 individuals: 36 relapsing remitting (RR)-MS patients (21 in acute phase -AMS, 15 in stable phase -SMS) and 15 healthy controls (HC). PBMCs samples in AMS patients were collected before (BT-AMS) and during glucocorticoids-based therapy (DT-AMS). RESULTS: IDO expression was increased and IFN-γ was decreased (p<0.001) in BT-AMS compared to SMS patients. Glucocorticoids-induced disease remission resulted in a significant reduction of IDO and IFN-γ gene expression, IDO catalytic activity (p<0.001). Serum neopterin concentration followed the same trend as IDO expression and activity. CONCLUSIONS: Measurement of IDO gene expression and activity in blood could be a useful marker to monitor the clinical course of RR-MS. Therapeutic interventions modulating IDO activity may be beneficial in MS.