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Figure 4 Incorporation of mobilized peripheral mononuclear cells into vascular wall and differentiation to vascular smooth muscle cell (SMC). Peripheral blood mononuclear cells were isolated from rabbit after 6 days of granulocyte-colony stimulating factor (G-CSF) or placebo injection and tagged with DiI (red color). In another rabbit, these cells were infused systemically after balloon injury to the iliac artery. Two weeks after injury, frozen sections were stained with alpha-smooth muscle actin (SMA) (green color). Peripheral blood mononuclear cells from placebo-injected animals (A) revealed no double-positive (DiI+/alpha-SMA+) cells, implying that the infused cells did not differentiate to SMC but remained as mono-macrophage lineage cells. But the mobilized mononuclear cells from G-CSF–injected animals were observed as DiI+/alpha-SMA+ double positive cells within both media (B) and neointima (C), implying that the cells mobilized by G-CSF incorporated into vascular wall and differentiated to SMC. Some of the mobilized cells incorporated into neointima but did not differentiate into SMC (D). Such infiltration of the cells mobilized by G-CSF into vascular wall led to the increased neointimal thickness at 2 weeks (B, C, and D) compared with control animals infused with non-mobilized peripheral mononuclear cells (A).