A SENSITIVE ASSAY OF CYTO-TOXICITY APPLICABLE TO MIXED CELL-POPULATIONS

The fluorescent vital dye, Hoechst 33342, was used to stain cultured cells prior to assay of antibody dependent complement mediated cytotoxicity. The fluorescence of nonviable dye stained cell is quenched by cellular uptake of trypan bue, but trypan blue excluding cells remain intensely fluorescent. Detection by fluorescence microsocpy of one viable prestained cell per 105 unstained cells was accurate and reliable. The technique was found to have sensitivity equal to a clonogenic assay for measuring cytotoxicity. The dye stained cell assay may be used to measure depletion of a selected cell type, when those cells are stained prior to mixing with another cell population. This technique may prove useful to study model systems for depletion of tumor cells or T-cells from bone marrow.