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.

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 microm2, 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.