Abstract 5448: Regulatory T Cells Control Post-Ischemic Neovascularization

CD4+ and CD8+ T lymphocytes are key regulators of post-ischemic neovascularization. T cell activation is promoted by two major costimulatory signalings: the CD28/B7 and the CD40ligand-CD40 pathways. Interestingly, CD28 interactions with the structurally related ligands B7–1 and B7–2 are also required for the generation and homeostasis of CD4+CD25+ regulatory T cells (Treg), which play a critical role in the suppression of immune responses and the control of T-cell homeostasis. We hypothesized that Treg cell activation may modulate the immuno-inflammatory response to ischemic injury, leading to alteration of post-ischemic vessel growth. Ischemia was induced by right femoral artery ligation in CD28-, B7–1/2- or CD40-deficient mice (n=10 per group). CD40 deficiency did not affect Treg levels and led to significant reduction in post-ischemic inflammatory response and vessel growth. In contrast, at day 21 after ischemia, angiographic score, foot perfusion, and capillary density were increased by 2.0-, 1.2-, and 1.8-fold respectively in CD28-deficient mice, which show profound reduction in Treg, compared to controls. Similarly, disruption of B7–1/2 signaling and subsequent Treg deletion significantly enhanced post-ischemic neovascularization. These effects were associated with enhanced accumulation of CD3-positive T cells and Mac-3 positive macrophages in the ischemic leg of CD28−/− or B7−/− mice compared with controls. Proinflammatory cytokines, IL-1β, TNF-α and IL-6, were also upregulated and antiinflammatory mediators, IL-10 and TGF-β1 downregulated in the ischemic legs of CD28−/− or B7−/− mice. Finally, treatment of CD28−/− mice with the nonmitogenic anti-CD3 monoclonal antibody enhanced expression of the regulatory T-cell marker Foxp3 in blood and ischemic tissue of CD28−/− mice, led to reduction in post-ischemic inflammatory response and neovascularization in CD28-deficient mice. In conclusion, endogenous Treg cell response controls post-ischemic neovascularization.