Cytologic characterization of pulmonary alveolar macrophages by enzyme histochemistry in plastic

Quantitative morphometric analyses of macrophages should facilitate a more precise definition of the role of macrophages in neoplastic diseases and inflammatory diseases of lymphoid and hemopoietic tissues. The usefulness of the available phenotypic markers is affected by the extent to which they are expressed by macrophages in tissue sections. For our study of phenotypic markers for macrophages in human tissue sections, we selected lung, since pulmonary alveolar macrophages are more readily identified morphologically in tissue sections than macrophages in most other tissues. In 1-2 micron sections of freshly fixed lung embedded in methacrylate, 89.7% of pulmonary alveolar macrophages had histochemically demonstrable acid phosphatase; 86.2%, nonspecific esterase with naphthol ASD chloroacetate as the substrate; 86.2%, nonspecific esterase with alpha-naphthyl butyrate as the substrate; 80.5%, peroxidase; and 75.8%, iron. With respect to their expression of markers, the observed heterogeneity among pulmonary alveolar macrophages is interesting; this heterogeneity may reflect the degree to which they have been activated, the different periods of time since they arrived in the lung, and differences in their local environments. Except for peroxidase, all examined markers were as well demonstrated when tissues were fixed after storage over liquid nitrogen as when fixation was carried out with fresh tissue. Acid phosphatase and nonspecific esterase with the chloroactetate substrate gave bright colors that would facilitate morphometric analyses. The storage of tissue over liquid nitrogen will be equally satisfactory for the characterization of macrophages with histochemical markers and monoclonal antibodies.