Abstract 131: Delayed Egress of CD8 T Cells Contributes to Long-Term Pathology After Ischemic Stroke in Mice

Abstract

Introduction: T cells are recruited to the ischemic brain within hours after stroke onset and can exhibit either protective or detrimental effects on recovery. Recent studies, including our data, confirm the persistence of immune cells in the brain weeks after stroke onset, including cytotoxic CD8 T cell egress, suggesting a longer-term role for the adaptive immune system during functional recovery after stroke. Hypothesis: We hypothesize that a delayed secondary egress of CD8 T cells into the ischemic brain negatively impacts functional recovery after transient ischemic stroke in mice. Methods: Male C57BL/6 mice (Jackson Labs, 8-14 wks) received a 60-min transient middle cerebral artery occlusion (tMCAo) and sacrificed 8, 14, or 30 days (d) post-tMCAo. Neuroinflammation was quantified using flow cytometry, infarct volume determined using MRI, and functional recovery quantified using rotarod behavioral test. In a second cohort, mice were randomized to CD8 T cell depletion (CD8 α -specific antibodies; 400ug; 2.43 clone) or control (isotype antibodies; 400ug) treatment beginning 10d after tMCAo, with booster injections (200ug) every 3d thereafter. Mice were euthanized at 30d post-stroke. Results: Post-stroke mice exhibit a secondary influx of leukocytes at 14 and 30d after tMCAo. Ipsilesional CD4 T cell and CD8 T cell numbers were increased over the contralateral hemisphere at 14d (19-fold, p<0.0001 and 8-fold, p<0.001) and 30d (8-fold, p<0.01 and 7-fold, p<0.01) after stroke, respectively. Moreover, mice with higher ipsilesional CD4 T cells (R 2 =0.33, p=0.05) and CD8 T cells (R 2 =0.52, p<0.01) exhibited worse functional recovery. CD8 T cell-depleted mice had 2.5-fold (p=0.05) reduced leukocyte infiltration at 30d post-tMCAo. Specifically, macrophage, neutrophil, and CD4 T cell numbers were reduced in the ipsilesional hemisphere of the CD8 T cell-depleted mice. There were no significant differences between immune cell numbers in spleen. Conclusions: Our data confirm long-term CD4 T cell and CD8 T cell recruitment into the ipsilesional hemisphere that affect both immune cell numbers present in the brain and functional recovery through one month after stroke onset in mice.