Distinction of macrophage subpopulations: measurement of functional cell parameters by flow cytometry.

Abstract

Macrophages represent a functionally heterogeneous group of cells which belong to the mononuclear phagocyte system (1). Heterogeneity may exist between macrophages from different organs as well as among macrophages within one organ (2,3). Heterogeneity has been defined by differences of Ia-antigen expression (4,3); monoclonal antibodies (5,6) against cell surface determinants; receptors for the C3 complement component or the Fc part of IgG molecules; cell size (7,3); enzyme activities e.g. phosphatase, nucleotidase (8) peroxidase (9) and transglutaminase (10); wheat germ lectin binding (11); tumor cytoxicity (12); or phagocytosis (13) and adherence. Classification according to several parameters is necessary to identify small subpopulations of macrophages (1). Flow cytometry is a particularly useful method for this purpose, especially because functional parameters of living cells can be measured simultaneously at the single cell level in a fast and accurate way. Such parameters include cytoplasmic (14,15) or lysosomal (16) enzyme activities, transmembrane potential (17,18), intracellular pH (19) and phagocytosis. The use of vital stains also permits cell sorting. Sorted cells can be recultivated and further analyzed. Macrophages are often characterized as cells with high esterase activity (20,21,22), although there are some reports on low esterase activity in macrophages (23,24,25). It was the purpose of this study to characterize the low activity macrophages in more detail.