Abstract 16273: Ecto-5’-Nucleotidase Suppression of T Cell Trafficking to the Ischemic Brain
Background. Ischemic strokes account for 87% of all strokes in the United States. We studied ecto-5’-nucleotidase (CD73), an ectoenzyme present on brain tissue and leukocytes, which we have shown to mitigate tissue injury following cerebral ischemia through its hydrolysis of adenosine monophosphate to the anti-inflammatory nucleoside adenosine. Here we test the hypothesis that CD73 suppresses leukosequestration into ischemic brain tissue. After infiltrating brain tissue, leukocytes, specifically T cells, can exacerbate through direct cytotoxicity, the secretion of pro-inflammatory cytokines or capillary plugging. While T cell populations can be broadly defined, the roles of specific subpopulations and their regulation by CD73 remain unknown.
Methods. Wild-type (WT, n=5) and CD73 null (CD73KO, n=5) mice underwent permanent occlusion of the left middle cerebral artery (MCA) through the retro-orbital injection of Rose Bengal and subsequent application of a neon laser to an oval bony window opened to the MCA. Occlusion was defined as a >80% reduction in blood flow maintained for 25 minutes. Two days following the induction of thrombosis, mice were sacrificed and their brains harvested for analysis. Flow cytometry was used to identify populations of helper (CD4+/CD45+) and cytotoxic (CD8+/CD45+) T cells found in the ischemic and contralateral hemispheres of each group.
Results. There was a 42% relative increase in T cells in CD73KO mice vs. WT mice following MCA occlusion (4.1x105 ± 8.0x104 vs. 1.6x105 ± 2.0x104, p=0.02; for CD73KO vs. WT, respectively). When T cell subsets were examined, there was an increase in both CD4+ and CD8+ T cells infiltrating into the ischemic brain tissue. The ischemic hemisphere of CD73KO mice contained significantly more helper T cells (230x104 ± 6.1x104 vs. 6.2x104 ± 0.9x104, p=0.03) and cytotoxic T cells (1.8x105 ± 2.9x104 vs. 1.0x105 ± 1.3x104, p=0.03) than their WT counterparts.
Conclusion. These data are the first to show that the presence of CD73 suppresses T cell trafficking into ischemic brain, resulting in fewer CD4 + and CD8+ cells in the ischemic tissue. As T cell flux can contribute to ischemic damage, these findings have implications for the treatment of stroke.
- © 2011 by American Heart Association, Inc.