Abstract Body: Hypertension affects roughly half of adults in the U.S. and is caused by several factors, including elevated angiotensin II (Ang II). Studies in mice suggest that T cells may contribute to this pathology. While Ang II is known to affect other immune cells, effects on T cell activation, including cytokine secretion and expression of activation markers like interleukin (IL)-2 receptor a (CD25), C-type lectin protein (CD69), and co-stimulatory receptor 4-1BB (CD137), are only partially characterized. This study investigated the hypothesis that Ang II affects T cell activation, as indicated by altered cytokine secretion and expression of surface markers associated with activation. To test this, 11-week-old C57Bl/6J male mice received saline vehicle or Ang II (490 ng/kg/min) via osmotic pump for 14 days (n=10/group). Following euthanasia, splenocytes were isolated, treated with a polyclonal T cell activation cocktail (1.5mg/mL anti-CD3, anti-CD28, and crosslinker), and cultured for 24/120 h prior to flow cytometry and Luminex cytokine analysis. Flow cytometry revealed splenic T cells from Ang II-infused mice had increased expression of CD25 (CD4: p=0.024, CD8: p=0.007), CD69 (CD4: p=0.017, CD8: p=0.032), and CD137 (CD8: p=0.022) 24 h post-activation, as measured by median fluorescent intensity. Notably, the Ang II group had higher secreted levels of IFNg (interferon-g) at 120 h (p=0.012), as well as increased IP-10 (IFNg-induced protein 10) at 24 h (p=0.011) and 120 h (p=0.013). The increases in CD25 and CD69 are evidence that in vivo Ang II exposure facilitates a stronger ex vivo T cell response to polyclonal activation. This is further supported by the elevated levels of cytokines in the supernatants in these samples, which indicate increased activity through IFNg pathway . Higher expression of CD137 in CD8 T cells in the Ang II group is especially interesting, and indicate that these cells might be more responsive to co-stimulatory activation signals. Taken together, the data suggest Ang II promotes T cell adaptation and functional preparedness that ultimately increases responsiveness to activation stimuli.