Protocol uses specific antibodies coupled to one of four fluorochromes: fluorescein isothiocyanate (FITC), R-phycoerythrin (PE), peridinin chlorophyll-a (PcP),
and allophycocyanin (APC). These fluorochromes can be used simultaneously to stain and analyze the expression patterns of four different proteins in the same sample. The
fluorochrome stained cell populations are analyzed using a FACSCalibur dual-laser flow cytometer.