FACScan histogram plots showing peripheral blood neutrophils from patient no. PNH046 stained with anti–CD16-PE (phycoerythrin). The upper two plots are before G-CSF treatment and show a large PNH population (CD16−ve) and a small, normal, CD16+ve population. The CD16 is cleaved off by PI-PLC in the upper right plot but this enzyme has no effect on the negative peak. In the lower two plots, after G-CSF treatment, the negative peak has shifted to the right but this apparent increase in CD16 expression is not affected by PI-PLC (see text).