Identification of T lymphocytes by a histochemical stain for alpha naphthyl acetate esterase activity

Lymphocyte suspensions and peripheral blood smears from 20 normal individuals were examined for nonspecific esterase activity, using alpha naphthyl acetate as substrate and hexazotized pararosanilin stain. Lymphocytes show intense, focal, red "dot-like" activity; monocytes show diffuse reddish granulation. B lymphocytes do not react. Critical variables of the procedure include: use of proper anticoagulant; fixation for 30-180 seconds; incubation with substrate 3-5 hours; and pH 5.8. Comparison of results with conventional E rosette methodology showed 53-63% rosettes; 50-58% esterase-positive lymphocytes in cytocentrifuge preparations and 47-59% esterase-positive lymphocytes on peripheral blood films. Technical advantages of the procedure favor it as an alternative method for assessing T lymphocytes.