Heterogeneity of human peritoneal macrophages: cytochemical and flow cytometric studies

Human peritoneal macrophages obtained from females undergoing laparoscopic examination have been investigated. Morphologic heterogeneity as well as a wide variation in the content of nonspecific esterase, acid phosphatase (AP), and myeloperoxidase (MP) were observed with standard cytochemical stains. This heterogeneity was evident within the same sample as well as between different individuals. Phagocytic activity was also highly variable. In only 3 cases out of 85 samples screened could human peritoneal macrophages be characterized as resident (peroxidase negative, acid phosphatase negative) by the criteria used in rodent systems, thus indicating that female peritoneal macrophages are continuously responding to stimuli/irritation. A newly developed flow cytofluorometric method was used to quantitatively document the macrophage heterogeneity in enzyme expression and phagocytic activity. Population distributions derived from single-cell analysis of various enzyme activities and phagocytic levels further emphasized the spread in expression of these parameters both within the individual peritoneal samples as well as between donors. Simultaneous determination of two markers such as leucine aminopeptidase (LAP) and zymosan ingestion indicated that the association between these features varied markedly between individuals. It is hoped that the use of this multiparameter flow cytometric technique on in vitro differentiating blood monocytes, subjected to different stimuli, will give us a better understanding not only of the development of monocytes to macrophages but also of the sources of heterogeneity in normal human resident macrophages.