A method for the ultrastructural demonstration of non-specific esterase in human blood and lymphoid tissue.

Using the substrate 2-naphthylthiol acetate (NTA), we developed a reproducible method of demonstrating a non-specific esterase while retaining nuclear and cytoplasmic details at the ultrastructural level. The NTA esterase had a distribution and pattern of staining similar to those of esterases demonstrable at the light microscopic level by the alpha-naphthyl acetate or naphthol AS-D acetate esterase reaction. The NTA esterase appeared as intensely electron-dense granules of varying size and shape in the cytoplasm. The granules were most abundant in the cells of the histiomonocytic series. The large number of diffusely scattered granules in the cytoplasm of the histiocytes and monocytes made it possible to separate these cells from other haematopoietic elements. There was usually no direct relationship between the NTA esterase positivity and the amount or the location of lysosomes or mitochondria, although in some histiocytes the granules appeared to be associated with lysosomes. The NTA esterase-positive granules were usually more numerous than lysosomes and were located outside the lysosomal granules. Some of the lymphocytes outside the germinal centres and most of the lymphocytes in the blood showed a punctate positivity in the form of 1--4 electron-dense dots. Plasma cells were usually negative but, in rare cases, contained an occasional single dot-like reaction product similar to that in some of the lymphocytes. Granulocytes were always negative. The method described in this paper can be used effectively for identification and study of human haematopoietic cells lines at the ultrastructural level.