Polymorphonuclear neutrophils promote rFGF-2-induced angiogenesis in Vivo

Background. The role of neutrophils in angiogenesis remains largely unknown. Recent evidence has shown that polymorphonuclear neutrophils (PMNs) produce several proangiogenic cytokines, including VEGF, TNF-α, IL-1, IL-6, and IL-8. In addition, PMN-derived proteinases promote endothelial cell migration. We hypothesized that PMNs may facilitate angiogenesis and that reducing circulating PMNs might alter the host angiogenic response. Materials and methods. We utilized a corneal pocket assay to compare rFGF-2-induced vessel formation in the corneas of mice with normal levels of circulating neutrophils to those in a neutropenic state. Circulating PMNs were reduced using serial intraperitoneal injections of monoclonal antibody to Gr-1. Slow release rFGF2 pellets were implanted into the corneas of neutropenic mice and controls. Corneal neovascularization, measured as vessel length and area of vessel in-growth, was quantified using slit-lamp microscopy on day 7. Results. The average number of circulating PMNs was significantly reduced in the experimental group compared to the control group on days 1-7 (P < 0.05). No statistical differences in circulating monocytes or lymphocytes were observed from days 0 to 6. Mice in the experimental group had a vascular area of 2.58 ± 0.2 mm² compared to 3.55 ± 0.3 mm² in the control group (P < 0.05). Conclusions. Corneal neovascularization in response to rFGF-2 is diminished by PMN depletion. PMNs play an important role in facilitating rFGF-2-induced angiogenesis.