Chronic inflammation can associate with autoreactive immune responses, including CD4(+) T cell responses to self-Ags. In this paper, we show that the adipocyte-derived proinflammatory hormone leptin can affect the survival and proliferation of autoreactive CD4(+) T cells in experimental autoimmune encephalomyelitis, an animal model of human multiple sclerosis. We found that myelin olygodendrocyte glycoprotein peptide 35-55 (MOG(35-55))-specific CD4(+) T cells from C57BL/6J wild-type mice could not transfer experimental autoimmune encephalomyelitis into leptin-deficient ob/ob mice. Such a finding was associated with a reduced proliferation of the transferred MOG(35-55)-reactive CD4(+) T cells, which had a reduced degradation of the cyclin-dependent kinase inhibitor p27(kip1) and ERK1/2 phosphorylation. The transferred cells displayed reduced Th1/Th17 responses and reduced delayed-type hypersensitivity. Moreover, MOG(35-55)-reactive CD4(+) T cells in ob/ob mice underwent apoptosis that associated with a downmodulation of Bcl-2. Similar results were observed in transgenic AND-TCR- mice carrying a TCR specific for the pigeon cytochrome c 88-104 peptide. These molecular events reveal a reduced activity of the nutrient/energy-sensing AKT/mammalian target of rapamycin pathway, which can be restored in vivo by exogenous leptin replacement. These results may help to explain a link between chronic inflammation and autoimmune T cell reactivity.