AQP4 and neuromyelitis optica: In this regard, IL-6 is critical for Th17 differentiation.28 Previous studies have indicated that serum IL-6 levels are elevated in NMO patients.7 As we observed that AQP4 p61–80-specific T cells from NMO patients exhibited Th17 polarization, we questioned whether there were alterations in expression of costimulatory molecules or increased production of IL-6 by myeloid APC.