Flow cytometric measurement of non-specific esterase activity.

alpha-Naphthyl acetate esterase (alpha-NAE) is primarily found in mononuclear phagocytes and may be used to distinguish them from other leucocytes. Conventional cytochemical techniques are subjective and may be difficult to interpret, especially with cells which express only low levels of activity. This has caused difficulties in the classification of non-lymphoblastic leukaemias. This paper describes the adaptation of a cytochemical assay for use with the flow cytometer. The alpha-NAE activity of peripheral blood mononuclear cells was examined and found to be associated with the expression of the surface antigen CD14. The reaction could be inhibited by sodium fluoride. A series of human cell lines were also compared for alpha-NAE activity. Distinct differences in staining observed between the cell lines correlated with the number of cell-associated granules observed under the microscope.