CD8 + T Lymphocytes Regulate the Arteriogenic Response to Ischemia by Infiltrating the Site of Collateral Vessel Development and Recruiting CD4 + Mononuclear Cells Through the Expression of Interleukin-16

Abstract

Background— Previous studies have demonstrated that macrophages and CD4 + T lymphocytes play pivotal roles in collateral development. Indirect evidence suggests that CD8 + T cells also play a role. Thus, after acute cerebral ischemia, CD8 + T cells infiltrate the perivascular space and secrete interleukin-16 (IL-16), a potent chemoattractant for monocytes and CD4 + T cells. We tested whether CD8 + T lymphocytes contribute to collateral vessel development and whether the lack of circulating CD8 + T cells prevents IL-16 expression, impairs CD4 + mononuclear cell recruitment, and reduces collateral vessel growth after femoral artery ligation in CD8 −/− mice . Methods and Results— After surgical excision of the femoral artery, laser Doppler perfusion imaging demonstrated reduced blood flow recovery in CD8 −/− mice compared with C57/BL6 mice (ischemic/nonischemic limb at day 28, 0.66±0.04 versus 0.87±0.04, respectively; P <0.01). This resulted in greater calf muscle atrophy (mean fiber area, 785±68 versus 1067±69 μm 2 , respectively; P <0.01) and increased fibrotic tissue content (10.8±1.2% versus 7±1%, respectively; P <0.01). Moreover, CD8 −/− mice displayed reduced IL-16 expression and decreased CD4 + T-cell recruitment at the site of collateral vessel development. Exogenous CD8 + T cells, infused into CD8 −/− mice immediately after femoral artery ligation, selectively homed to the ischemic hind limb and expressed IL-16. The restoration of IL-16 expression resulted in significant CD4 + mononuclear cell infiltration of the ischemic limb, faster blood flow recovery, and reduced hindlimb muscle atrophy/fibrosis. When exogenous CD8 + T cells deficient in IL-16 (IL-16 −/− ) were infused into CD8 −/− mice immediately after femoral artery ligation, they selectively homed to the ischemic hind limb but were unable to recruit CD4 + mononuclear cells and did not improve blood flow recovery. Conclusions— These results demonstrate that CD8 + T cells importantly contribute to the early phase of collateral development. After femoral artery ligation, CD8 + T cells infiltrate the site of collateral vessel growth and recruit CD4 + mononuclear cells through the expression of IL-16. Our study provides further evidence of the significant role of the immune system in modulating collateral development in response to peripheral ischemia.