The fluorescent staining was analyzed on a FACS Calibur (BD
Bio-sciences) flow cytometer. Electronic gates were set to enable
analysis of the fluorescence of the viable cell population according
to FSC/SSC histograms. The percentage of cells stained with each
monoclonal antibody was determined by comparing each histogram
with one from control cells stained with FITC-, PE-, APC-, or
Cy2-labeled isotype control mono-clonal antibodies