Oxidative damage and inflammation are both implicated in the genesis of hypertension; however, the mechanisms by which these stimuli promote hypertension are not fully understood. Here, we have described a pathway in which hypertensive stimuli promote dendritic cell (DC) activation of T cells, ultimately leading to hypertension. Using multiple murine models of hypertension, we determined that proteins oxidatively modified by highly reactive gamma-ketoaldehydes (isoketals) are formed in hypertension and accumulate in DCs. Isoketal accumulation was associated with DC production of IL-6, IL-1beta, and IL-23 and an increase in costimulatory proteins CD80 and CD86. These activated DCs promoted T cell, particularly CD8+ T cell, proliferation; production of IFN-gamma and IL-17A; and hypertension. Moreover, isoketal scavengers prevented these hypertension-associated events. Plasma F2-isoprostanes, which are formed in concert with isoketals, were found to be elevated in humans with treated hypertension and were markedly elevated in patients with resistant hypertension. Isoketal-modified proteins were also markedly elevated in circulating monocytes and DCs from humans with hypertension. Our data reveal that hypertension activates DCs, in large part by promoting the formation of isoketals, and suggest that reducing isoketals has potential as a treatment strategy for this disease.