Experimental autoimmune encephalomyelitis (EAE), a common model of multiple sclerosis (MS), is mainly mediated by CD4(+) T cells with demyelination and neurodegeneration of central nervous system (CNS). The loss of P2Y(12) receptor might be associated with the pathogenesis of MS/EAE, but its potential mechanism is still not clear. In this study, more severe EAE developed in P2Y(12)-knockout (P2Y(12)-KO) mice compared to WT mice. Knockout of P2Y(12) increased expression of IL-17A in the sera and proportion of Th17 cells in spleen and CNS. However, in vitro studies showed that P2Y(12) did not influence cell differentiation and proliferation of CD4(+) T cells. In bone marrow-derived dendritic cells (BMDCs), loss of P2Y(12) significantly increased the production of IL-23 in contrast to the wild-type (WT) BMDCs. FACS analysis indicated that the culture supernatant from P2Y(12)-deficient DCs promoted more naive CD4(+) T cells to differentiate into Th17 cells. Our finding demonstrated that genetic deletion of P2Y(12) receptor broke the balance of Th subtypes by affecting the cytokine profile of BMDCs and resulted in the aggravated EAE, which suggested that P2Y(12) may be a potential target in treating MS. (C) 2016 Elsevier Inc. All rights reserved.