We have previously reported that there are sex differences in the renal T cell profile of spontaneously hypertensive rats (SHR), with females having more anti-inflammatory regulatory T cells (Tregs) and males expressing more pro-inflammatory Th17 T cells. High mobility group box 1 protein (HMGB1) is an endogenous danger molecule and when released by necrotic cells it activates pro-inflammatory immune cells. We hypothesized that males have higher HMGB1 mediated renal T cell activation compared to females. Serum and kidneys were isolated from 13 week old male and female SHR and spleens from normotensive male Wistar Kyoto rats (WKY). HMGB1 expression was measured in sera using an ELISA. To quantitate renal T cell activation, we performed a mixed lymphocyte reaction in the presence and absence of HMGB1 neutralizing antibody. For the reaction, T cells were isolated from kidneys using magnetic activated cell sorting and spleens were homogenized to obtain a single cell suspension of antigen presenting cells (APCs). T cells and APCs were plated together, incubated for 96 hours, proliferation was confirmed and T cell activation was assessed by the magnitude of CD71 using flow cytometry. Male SHR had greater serum HMGB1 levels than female SHR (ng/ml: 5.3±1.1 vs. 2.5±0.3; p=0.0225; N=4-6). In male SHR, 92% of T cells were activated by incubation with APCs in contrast to 65% of T cells in females (CD71+ T cells: 92±1% vs. 65±1%; p<0.0001; N=3). HMGB1 neutralization decreased T cell activation in both sexes (males to 74±1%; females to 54±1%; effect of treatment: p<0.0001) but neutralization resulted in a greater decrease in T cell activation in male SHR (interaction: p=0.0012). These data support our hypothesis that male SHR have higher HMGB1 mediated renal T cell activation compared to females. We propose that in male SHR, circulating HMGB1 release promotes the expression of renal Th17 cells to a greater extent than in female SHR.