Cytokine expression pattern in the aqueous humor, in contrast to that in serum, may reflect intraocular immune reactions during active inflammation in patients with AAU. Both Th1 and Th17 are involved in immunopathogenesis of HLA-B27 associated and idiopathic AAU, but a different cytokine pattern was identified in these two clinical entities. A predominant Th17-driven immune response may play an important role in the immunopathogenesis of idiopathic AAU, while Th1 dominant immune response may be responsible for the inflammation in HLA-B27 associated AAU.