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Activated macrophages have various characteristics in common with exudate and resident macrophages, but the ability to inhibit intracellular proliferation of the protozoa Toxoplasma gondii, the expression of Ia antigen and the capacity to produce H2O2 varies among these cells. Assessment of these features of macrophages, which are generally used as criteria for macrophage activation, has certain drawbacks. Since activated murine macrophages, but not exudate or resident macrophages, produce considerable amounts of NO2-, assessment of NO2- production by these cells might serve as a measure of macrophage activation. The aim of the present study was to find out whether NO2- production by murine peritoneal macrophages correlates with the three generally accepted criteria for macrophage activation. Quantitative data on resident, exudate and activated macrophages revealed that the production of NO2- stimulated by a calcium-ionophore correlates best with the ability to inhibit the proliferation of T. gondii, Ia antigen expression, and capacity to produce H2O2. Because it is rapid and easy to perform, measurement of the amount of NO2- produced by murine macrophages stimulated with a calcium-ionophore offers the most practical criterion for distinction between activated macrophages and exudate and resident macrophages.

The aim of the present study was to obtain quantitative data on the expression of seven cell-surface antigens by the murine macrophage-like cell lines WEHI-3, P388-D1, J774.1, and PU5-1.8, and to compare these data with those obtained for various mononuclear phagocytes. Binding of monoclonal antibodies F4/80, M1/70, 2.4.G.2., 30.G.12, M3/38, M3/84, and 59AD2.2 to cells from these four cell lines was detected by the biotin-avidin immunoperoxidase staining method and quantified by cytophotometry. The results are expressed as the percentage cells expressing a given antigen and the mean specific integrated absorbance per 0.25 micron2 cell-surface area. The results revealed that the phenotypes of the four macrophage-like cell lines differ markedly. Expression of the cell antigens by the cells of the various cell lines did not follow a normal distribution. Although the cell lines divide continuously and have certain characteristics in common with mature mononuclear phagocytes, none of the macrophage-like cell lines accurately resembles any of the mononuclear phagocyte populations. The strongest correlations for membrane were found between on the one hand WEHI-3 and P388-D1 cells and monoblasts and promonocytes (P greater than 0.011) on the other. P388-D1, J774.1 and PU5-1.8 cells expressed four of the six antigens to the same extent as skin macrophages (P greater than 0.012). With respect to expression of antigens recognized by antibodies 2.4.G.2., 30.G.12, M3/38, and M3/84 PU5-1.8 cells resembled activated peritoneal macrophages (P greater than 0.031). It is concluded that WEHI-3 is the most immature cell line, followed by the P388-D1 cell line, while J774.1, and PU5-1.8 are the most mature cell lines.