T-helper 17 cells expand in multiple sclerosis and are inhibited by interferon-β

Objective T‐helper 1 (Th1) and Th17 lymphocytes are involved in experimental autoimmune encephalomyelitis, the model of multiple sclerosis (MS). We characterized the Th1/Th17 cell populations in peripheral blood (PB), their interferon (IFN) receptor expression sensitivity to IFN‐β in MS patients. Methods In 30 untreated patients with active MS (AMS) and 32 with inactive MS (IMS), and in 22 healthy subjects, we measured intracellular cytokine expression, interleukin‐17–producing myelin basic protein–stimulated PB lymphocytes, surface IFN type I receptor chain1 (IFN‐αR1) expression, IFN‐β‐dependent signal transducer and activator of transcription 1 (STAT1) phosphorylation, and apoptosis of anti‐CD3 monoclonal antibody–stimulated PB lymphocytes. Results Th17 cell percentage increased around sevenfold in AMS compared with IMS or healthy subjects, but there was no change in Th1 cells. Th17 cells in AMS were myelin basic protein specific. The longitudinal follow‐up of 18 MS patients shifting between AMS and IMS showed that the percentage of Th17 but not Th1 cells always increased in AMS. IFN‐αR1 expression, IFN‐β–induced STAT1 activation, and apoptosis were significantly greater in Th17 than Th1 cells. IFN‐αR1 expression and IFN‐β–dependent STAT1 activation progressively increased in vitro with a highly significant positive correlation only in developing Th17 but not in Th0 or Th1 cells. Interpretation Evidence that an expansion of peripheral Th17 cells, a Th subset that can infiltrate brain parenchyma and damage cells, is associated with disease activity in MS. The greater IFN‐αR1 level expressed by Th17 compared with Th1 cells might make them a selective target for IFN‐β therapy. Ann Neurol 2009;65:499–509