To quantify circulating and bone marrow EPC by fluorescence-activated cell sorter analysis (FACS), mononuclear cells were isolated using RBC Lysis buffer (Biolegend, San Diego, CA) from either 200 μL of peripheral blood or bone marrow. The cells were incubated for 30 minutes on ice with a FITC-conjugated anti-mouse CD117 (c-Kit) antibody (Biolegend) and PE-conjugated anti-mouse CD202b (Tie-2) antibody (Biolegend). The cells then were washed with PBS and fixed in 4% paraformaldehyde. Data were acquired using a FACS Calibur flow cytometer, and analyzed using Cell Quest software (BD Biosciences, Franklin Lakes, NJ) with a 530-nm filter. In each sample, 20,000 cells were analyzed, and data were analyzed by FlowJo software (Tree Star, Ashland, OR). To quantify EPCs, c-Kit+/Tie-2+ double-positive cells within the monocytic cell population were counted.