A test of granulocyte membrane integrity and phagocytic function.

An assay of granulocyte viability has been developed which yields information about rwo important cell parameters, cell membrane integrity and phagocytic activity. The assay is based on the fact that only live cells can accumulate fluorescein, which is enzymatically split from the nonfluorescent substrate fluorescein diacetate. Dead cells, on the other hand, become permeable to the fluorescent red dye ethidium bromide. When cells are exposed first to opsonized zymosan particles, which they can phagocytize, then to a combination of these fluorescent dyes, one can distinguish microscopically between dead cells with fluorescent red nuclei, live cells which fluoresce green, and live cells with phagocytic function which are swollen with the pink zymosan particles in a green fluorescing cytoplasm. This assay takes 20--30 min and can be used to distinguish different degrees of cellular damage after cryopreservation.