Abstract 5112: Contribution of Th17 Cells, a New Subset of CD4+ T Cells, to Angiogenic Response to Hindlimb Ischemia
Background: Accumulating evidence suggests contribution of T cell to the collateral development in ischemic tissue; however, its mechanism remains unclear. Th17 cells are recently identified as a new subset of CD4+ T cells and specifically secrete interleukin-17 (IL-17). Here, we investigated the role of CD4+ T and Th17 cells in the induction of angiogenesis.
Methods and Results: Unilateral hindlimb ischemia was produced in wild-type mice (WT, C57BL/6). Neutralization using anti-CD4 antibody resulted in complete depletion of CD4+ T cells (flow cytometry) and a significant reduction of blood flow perfusion (laser Doppler perfusion imaging, LDPI: 0.61±0.08 vs. 0.41±0.11 p<0.05) in the ischemic limbs. Since IL-6, inducer of Th17 cells, was upregulated in the ischemic limbs, we next focused on Th17 cells. The expression of IL-17 and RORgt (Th17 regulator) was upregurated in the ischemic limbs, but not in the contralateral limbs. IL-17-deficient (IL-17−/−) mice also showed a significant decrease in angiogenesis, compared with WT mice (LDPI: 0.72±0.26 vs. 0.38±0.27, p<0.01), accompanied with significant reduction of capillary formation (CD31 immunostaining: 1223.3±267.3/mm2 vs. 692.9±165.6/mm2, p<0.01). Immunostaining and flow cytometry showed decreased infiltration of neutrophils, monocyte/macrophages, and CD4+ T cells in the ischemic limbs of IL-17−/− mice (p<0.05). The levels of angiogenic factors such as IL-1b and VEGF-A were also decreased in the ischemic limbs of IL-17−/− mice (p<0.05). To determine the contribution of bone marrow-derived Th17 cells, bone marrow-transplanted mice (BMT) were prepared. BMTIL-17−/− to Wild showed a significant decrease in angiogenic response, compared with BMTWild to Wild (LDPI: 0.60±0.15 vs. 0.24±0.11, p<0.05). To assess the effect of Th17 cells on angiogenesis, spleen-derived CD4+ T cells from IL-17−/− or WT mice were implanted into the ischemic limbs of athymic mice. Implantation of CD4+ T cells from IL-17−/− mice showed a significant reduction of angiogenic response, compared with those from WT mice (LDPI: 0.71±0.17 vs. 0.51±0.13, p<0.05).
Conclusion: CD4+ Th17 cells contribute to the angiogenic response and provide new insights into the mechanism by which T cells promote collateral development.