Monocyte nonspecific esterase: a technique for quantifying activity

During a study comparing the results of leukocyte differential counts obtained from the Hemalog-D with those obtained by manual techniques, discrepancies in monocyte counts were observed in patients with lymphomas. It was postulated that these patients might have monocyte nonspecific esterase (MNSE) deficiency because the Hemalog-D identifies monocytes by their MNSE activity. To confirm this hypothesis, a quantitative assay was developed employing a spectrophotometry technique to measure MNSE activity in suspensions of whole monocytes using a-naphthyl butyrate as the substrate. In this assay, the monocyte concentration correlated directly with the change in absorbance observed during the reaction (r = .998). Serial assays demonstrated reproducibility of MNSE activity in individual patients. This technique for quantitation of esterase activity adds another tool that may be useful in evaluating monocyte abnormalities.