Gb3 expression on HUVECs and GMVECs by flow cytometry. Labeling HUVECs (A) and GMVECs (D) with an isotype-matched irrelevant antibody (mouse IgM-FITC) determined the background FITC (FL1) fluorescence and is indicated by the horizontal line. HUVECs (B) and GMVECs (E) labeled with mouse IgM anti-Gb3 (CD77)-FITC expressing higher FITC fluorescence than background were considered positive. Burkitt lymphoma cells were used as positive controls (data not shown). The x-axis indicates increasing cell size and the y-axis indicates increasing FITC fluorescence. Overlay histograms of HUVECs (C) and GMVECs (F) show the background FITC fluorescence (cells labeled with irrelevant mouse IgM-FITC; first peak) and the increased FITC fluorescence due to Gb3 expression when cells were labeled with mouse IgM anti-Gb3 (CD77)-FITC (second peak). The x-axis indicates increasing FITC fluorescence and the y-axis indicates the events counted.