Macrophage heterogeneity in prostaglandins and thromboxane synthesis: differential activation by Fc- and C3b-dependent bacterial phagocytosis

Comparative assessment of metabolic enzyme levels in macrophage populations of the F344 rat

The immune system is a direct target for toxic insult by a number of drugs and other chemicals, many of which require activation to toxic metabolites by drug-metabolizing enzymes. We compared the induction of drug-metabolizing enzymes, including cytochrome P450 1A1 (CYP1A1) and aldehyde dehydrogenase (ALDH), which are differentially expressed in various macrophage populations following treatment of F344 rats with the inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Kupffer cells, alveolar macrophages and splenic macrophages from TCDD-treated animals expressed elevated levels of inducible CYP1A1 as compared to other macrophage subpopulations or cells from control rats. TCDD treatment also resulted in increased ethoxyresorufin-O-deethylase (EROD) activity and total cytochrome P450 content in tissue-derived macrophages. Immunoreactive protein and mRNA transcripts for CYP1A1 were not detectable in resident peritoneal macrophages or peripheral blood monocytes. Examination of aromatic hydrocarbon receptor (AhR) levels in macrophage populations suggests that the ability of TCDD to induce metabolic enzymes in specific cell types correlates well with AhR expression. In vivo activation of macrophages, using either Bacillus of Calmette and Guérin, Mycobacterium tuberculosis (BCG) or polyinosinic:polycytidylic acid (Poly I:C), caused no significant alteration in the levels of induction of CYP1A1. ALDH-3 induction was similar in all macrophage populations examined. These studies indicate that macrophages, particularly those from portals of entry, may be induced to produce increased levels of specific enzymes, and the induction is dependent upon their maturational stage rather than their activation state. The metabolism of xenobiotics to toxic intermediates by immune cells and its role in immunosuppression are discussed.

Immunophenotyping of murine peritoneal macrophages and lymphocytes by flow cytometry

Peritoneal cells include mainly macrophages and both T and B lymphocytes. We describe a simple procedure to analyze by flow cytometry the antigens expressed on macrophage and/or lymphocyte membranes. F4/80 and CR3 macrophage antigens were detected with anti-F4/80 and anti-Mac-1 monoclonal antibodies (mAb) respectively, CD4 and THY1.2 T lymphocyte antigens with GK1.5 and J1j mAbs respectively, B CD5 lymphocytes were identified with LY1.2 mAb and Fc gamma RII/Fc gamma RIII were detected with 2.4G2 mAb.

Separation of murine peritoneal macrophages using Percoll density gradients

Macrophages harvested from the murine peritoneal cavity are functionally and morphologically heterogeneous. Here, we describe a procedure which permits the determination of specific cell densities using a continuous density gradient of Percoll (analytical step). Subsequently, discontinuous density gradients are used in routine (preparative step) to isolate all the cell subpopulations according to their actual specific density. This procedure has been successfully used for both mouse and rat peritoneal macrophages.

Quantification of bacterial phagocytosis by flow cytometry and spectrofluorimetry

Bacterial phagocytosis is a cardinal function of phagocytes. We describe a simple procedure to easily quantify this function using fluoresceinated bacteria. Non-ingested bacteria and those adsorbed to the cell membrane are eliminated by an enzymatic procedure. Only macrophages with ingested fluorescent bacteria are detected, thereby permitting an accurate quantification of the phagocytic process by both spectrofluorimetric measurement and flow cytometric analysis.

Interferon-gamma-activated immature macrophages exhibit a high Trypanosoma cruzi infection rate associated with a low production of both nitric oxide and tumor necrosis factor-alpha

Murine peritoneal macrophages (MPM) can be subdivided into two subpopulations of mature and immature macrophages. In contrast to mature macrophages, immature ones were highly susceptible to Trypanosoma cruzi infection. This highly susceptibility was associated with a low production of alpha 2-macroglobulin. Interferon-gamma (IFN-gamma)-activated immature macrophages also exhibited a higher infection rate than did IFN-gamma-activated mature ones. This higher rate of infection was associated with a low production of both nitric oxide (N = O) and tumor necrosis factor-alpha (TNF-alpha). In contrast, mature MPM showed a lower rate of infection and produced higher levels of N = O and TFN-alpha. Taken together, these results show a clear-cut difference in the course of T. cruzi infection in relation to the macrophage maturation state.

Mouse peritoneal macrophages: characterization of functional subsets following Percoll density gradients

Mouse resident peritoneal cells were separated into twelve fractions on Percoll gradients according to their specific density and were thoroughly characterized by Giemsa staining, some biochemical assays, immunophenotyping and phagocytic tests. Among these fractions, the macrophages were mainly represented in 7 subsets of 1.073 to 1.104 g/ml densities. The results of this study emphasize that resident peritoneal macrophages of primo-explantation can be divided into two distinct subpopulations with separate functions, related to the stage of cell maturity. In fact, our results show that one macrophage subpopulation is rich in immature cells, characterized by their peroxidative activity, the expression of F4/80 antigen, Mac-1 and Fc receptors, in correlation with their high specific density; the second subpopulation contains mature macrophages (lower percentage of peroxidase-positive cells) with lower densities and a lower level of expression of the above-mentioned molecules. Antibody-dependent and antibody-independent bacterial phagocytosis, the phagocytic index and Fc gamma RII rosetting increased together with the cell density, and were elevated in the immature cell subpopulation. T and B lymphocytes were also identified in all the macrophage subsets, but in a low proportion.

Inverse relation in the de novo arginase synthesis and nitric oxide production in murine and rat peritoneal macrophages in long-term cultures in vitro

1. The de novo synthesis of arginase was much higher in murine than in rat peritoneal macrophages. This process was inhibited irreversibly by protein synthesis inhibitors and reversibly by glycolysis blockers. 2. Rat macrophages produce more nitric oxide (NO) than murine cells. NO production was inhibited by the inhibitors of protein synthesis or glycolysis. 3. The loading of macrophages by exogenous arginine for 24 hr in vitro resulted in the increase of arginase and nitrite in macrophages to different extents. 4. No great differences in lysozyme production was observed. 5. The proportion of arginine taken up and incorporated is contrasted in murine and rat macrophages.

Metabolism of benzo[a]pyrene by murine splenic cell types

The objective of the present study was to determine which splenic cell type(s) of B6C3F1 mice was capable of metabolizing B(a)P. Separation of splenocytes based on density by centrifugation through discontinuous Percoll gradients along with immunomagnetic negative selection or antibody-mediated complement lysis was utilized to obtain highly enriched populations of splenocytes for B(a)P metabolism studies. Immunofluorescent cell staining in conjunction with flow cytometry and examination of Giemsa-stained cytospin cell preparations indicated that B- or T-cell populations of greater than 95% purity and an 80-90% pure population of splenic macrophages were routinely attained. Splenic cell populations were incubated with [3H]B(a)P for 24 hr. High-pressure liquid chromatography was used to separate and quantitate the B(a)P metabolites generated by the enriched splenic cell populations. The results of these studies demonstrate that the macrophage is the cell type responsible for the metabolism of B(a)P within the spleen. The major metabolites of B(a)P produced were as follows: an unidentified peak of polar metabolites containing polyhydroxylated metabolites, B(a)P-9,10-dihydroxy-9,10-dihydrodiol, and B(a)P-7,8-dihydroxy-7,8- dihydrodiol. Other splenic cell types examined, including B and T cells, polymorphonuclear cells, or the spleen capsule did not produce amounts of B(a)P metabolites significantly above background levels. Based on these findings, macrophages are the splenic cell types which metabolize B(a)P. As a result, macrophages may be the cell type targeted by B(a)P resulting in suppression of splenic humoral immune responses.

Eicosanoids modulate CR1- and Fc-dependent bacterial phagocytosis

It is known that macrophages produce large amounts of eicosanoids during phagocytosis and that pharmacological concentrations of prostaglandin E2 (PGE2) inhibit phagocytosis in several models. However, the physiological effect on phagocytosis of endogenous prostaglandins, produced during CR1- or FcR-mediated bacterial phagocytosis, remains unclear. In this study, we show that indomethacin inhibits the CR1- but not the FcR-dependent phagocytosis of bacteria by rat peritoneal cells in the same range of concentrations that inhibit the synthesis of PGE2, PGI2 and thromboxane A2. An exogenous supply of PGE2 and PGE1 (10(-10) to 10(-8) M) restored the CR1-mediated phagocytosis; higher concentrations were inhibitory. Our data indicate that PGE2 and/or PGI2, produced by rat peritoneal cells, are involved in CR1-dependent bacterial phagocytosis.

Trypanosoma cruzi but not Trypanosoma brucei fails to induce a chemiluminescent signal in a macrophage hybridoma cell line

Macrophage-Trypanosoma cruzi interactions were studied by using a newly generated macrophage hybridoma cell line (2C11-12) that was selected for its capacity to produce high levels of reactive oxygen intermediates. This cell line was found to be a suitable host cell for T. cruzi, and intracellular parasitic development could be inhibited by activation with gamma interferon. When exposed to opsonized Trypanosoma brucei, Micrococcus lysodeikticus, or Legionella pneumophila, the activated macrophage cell line produces a high chemiluminescent signal, indicating the release of reactive oxygen intermediates. Alternatively, when opsonized T. cruzi was added to these activated macrophages, this parasite failed to stimulate a chemiluminescent response, suggesting an impairment in the triggering of the respiratory burst.