Effect of phagocytosis of erythrocytes and erythrocyte ghosts on macrophage phagocytic function and hydrogen peroxide production

Our previous studies have shown that an in vivo phagocytic challenge with IgG-coated erythrocytes can depress Kupffer cell complement and Fc receptor function, as well as decrease the survival rate following endotoxemia and bacteremia. In an effort to better understand the mechanism underlying these in vivo findings, the present study evaluated the in vitro effects of a phagocytic challenge with either IgG-coated erythrocytes (EIgG) or erythrocyte ghosts (GIgG) on macrophage phagocytic and respiratory burst activity. Elicited rat peritoneal macrophage (PM) monolayers were challenged with varying doses of EIgG, then the noninternalized EIgG were lysed hypotonically and the monolayers incubated for an additional hour prior to determining phagocytic function and PMA-stimulated hydrogen peroxide production. Challenge of PM with 1×10⁶ EIgG per well had no effect, but challenge with 1×10⁷ or 1×10⁸ EIgG per well caused a dose-dependent depression of phagocytic function or hydrogen peroxide production. GIgG were formed by hypotonically lysing EIgG bound to PM at 4°C. The bound GIgG were phagocytized during a subsequent incubation at 37°C. Challenge with GIgG depressed phagocytic function only with the highest challenge dose tested (1×10⁸ per well) and did not depress hydrogen peroxide production. The observation that prior phagocytic challenge with EIgG depressed macrophage function to a greater extent than challenge with GIgG supports our previous in vivo observations. Furthermore, these studies suggest that the internalization of erythrocyte contents, and not phagocytosis per se, plays an important role in determining macrophage host defense function.     

Depressing hepatic macrophage complement receptor function causes increased susceptibility to endotoxemia and infection.

Previous work has demonstrated that in vivo hepatic macrophage complement receptor clearance function is depressed after thermal injury. To determine whether impairment of complement receptor function is important in host defense, the present study evaluated the effect of the depression of complement receptor function in uninjured animals on susceptibility to endotoxin shock and bacterial infection. Hepatic complement receptor clearance function was evaluated by measuring the hepatic uptake of a test dose (2.9 X 10(8)/100 g) of rat erythrocytes coated with anti-erythrocyte immunoglobulin M (EIgM) or EIgG in rats. Depression of hepatic complement receptor function was induced by the injection of EIgG. The hepatic uptake of the test dose of EIgM or EIgG was depressed after the injection of 8.7 X 10(8) EIgG per 100 g and 17.4 X 10(8) EIgG per 100 g but not after the injection of 2.9 X 10(8) EIgG per 100 g. This effect was shown not to be due to a decrease in hepatic blood flow or a depletion of serum C3 and was, therefore, due to a depression in hepatic macrophage complement receptor clearance function. Susceptibility to endotoxin shock was increased with the dose of 8.7 X 10(8) EIgG per 100 g, and susceptibility to infection with Pseudomonas aeruginosa was increased with the dose of 17.4 X 10(8) EIgG per 100 g. Therefore, depression of hepatic macrophage complement receptor clearance function with EIgG is associated with depressed host defense.     

Scavengers of reactive oxygen intermediates do not mediate the depression of macrophage hydrogen peroxide production caused by erythrocyte phagocytosis

Our previous studies have shown that a phagocytic challenge with IgG-coated erythrocytes (EIgG) depressed macrophage triggered H₂O₂ production in vitro, and in vivo there was a decrease in the survival rate following bacteremia. The phagocytosis of an equal number of IgG-coated erythrocyte ghosts had none of these effects, indicating that the contents of the erythrocytes are important for these effects. The present study evaluated the role of the scavengers of reactive oxygen intermediates within erythrocytes in the depression of H₂O₂ production triggered with phorbol myristate acetate following a phagocytic challenge with EIgG. Elicited rat peritoneal macrophages (PM) were challenged with EIgG prepared from normal E or E with inactivated catalase, depleted glutathione, hemoglobin converted to methemoglobin, or fixed with formaldehyde. The depression of triggered H₂O₂ production was similar when equal numbers of normal EIgG and EIgG with inactivated scavengers were phagocytized. When the phagocytic challenge with normal EIgG was carried out in the presence of cytochalasin B, no depression of triggered H₂O₂ production was observed. Cytochalasin B partially blocked the phagocytosis of EIgG, so that with larger doses of EIgG there was sufficient ingestion of EIgG to depress H₂O₂ production in untreated PM. These results indicate that the scavengers of reactive oxygen intermediates present in erythrocytes are neither required nor sufficient to depress H₂O₂ production by macrophages.     

In vivo microscopic studies of the responses of the liver to endotoxin

Summary In vivo microscopic methods concomitant with electron microscopic and histochemical procedures are being used to explore the sequelae of responses of Kupffer cells and the hepatic microvasculature to endotoxins. To gain further insight into the role of the liver in host defense and nonspecific resistance, the effects of endotoxin also are being studied in animals sensitized to endotoxin (BCG infection) or tolerant to endotoxin (pretreated with detoxified endotoxin, low doses of endotoxin, or in C3H/HeJ mice). The results to date, have demonstrated that endotoxin induces significant alterations in the hepatic microcirculation due to swelling of Kupffer and endothelial cells and the adhesion of leukocytes and platelets to the sinusoid wall. Lymphocytes frequently are associated with the Kupffer cells. Phagocytosis also is affected; following a brief period of stimulation, the rate of phagocytosis by Kupffer cells is depressed. In BCG infected animals all of these responses are exaggerated but can be minimized by pretreatment with detoxified endotoxin or minute concentrations of endotoxin 24 h prior to the challenge dose of endotoxin. The responses are not seen in the endotoxin low-responder, C3H/HeJ mouse which was found to have a deficiency in lysosomal enzymes and a paucity of functional Kupffer cells. The results provide some insight into the sequelae of cellular and microvascular events that occur in the liver during endotoxemia, endotoxin-related host defense mechanisms and non-specific resistance. In addition, support is provided for the central role of Kupffer cells in these events and that lysosomal enzymes participate in the toxic response elicited by endotoxin.Supported in part by the National Institutes of Health (HL-23604), the American Heart Association (77–1802; 81–601) and the Deutsche Forschungsgemeinschaft (SFB 90, Heidelberg)     

In vivo microscopic observations of the responses of Kupffer cells and the hepatic microcirculation to Mycobacterium bovis BCG alone and in combination with endotoxin.

Kupffer cell function and hepatic microvascular hemodynamics were studied by in vivo microscopy in Mycobacterium bovis BCG-infected NMRI mice before and after treatment with minute (0.01 mu mg) tolerance-producing doses and doses causing 70% lethality (0.5 micrograms) of Escherichia coli 0111:B5 endotoxin alone and in combination. BCG-induced granulomas distorted the hepatic microvasculature and impeded blood flow in many sinusoids; flow also was altered further by leukocytes adhering to the sinusoidal walls and by enlarged Kupffer cells that bulged into the lumen. Nevertheless, in BCG-infected mice, the ratio of Kupffer cells which phagocytosed latex to sinusoids containing blood flow and capable of delivering these particulates to Kupffer cells was significantly greater than that in uninfected mice. The phagocytosis of single latex particles by individual Kupffer cells also was more rapid. This indicated an expansion of the numbers and activation of Kupffer cells. In this hyperreactive state, the tolerance-inducing dose of endotoxin produced no change in the rate of phagocytosis after 2 h. In contrast, the 70% lethal dose reduced the rate by 123%, unless tolerance was induced, in which case there was no reduction in the rate of phagocytosis. Twenty-four hours after injection of the tolerance-inducing dose, however, the rate of phagocytosis was accelerated slightly (17%). This suggested that the Kupffer cells had been activated and perhaps were more effective in clearing subsequent endotoxin from the blood but without sufficient release of toxic substances to be lethal. That some mediators were released, however, was suggested by the microvascular alterations that accompanied the above phagocytic responses. These results further support the concept of a central role for Kupffer cells in endotoxin-mediated, nonspecific host defense mechanisms.     

Lysosomotropic Agents Ameliorate Macrophage Dysfunction Following the Phagocytosis of IgG-Coated Erythrocytes: A Role for Lipid Peroxidation

Phagocytosis of IgG-coated erythrocytes (EIgG) can depress several macrophage functions. Our previous studies have suggested that this macrophage dysfunction may be due to an oxidative stress caused by the interaction of hemoglobin-derived iron with superoxide and/or hydrogen peroxide. Since lysosomotropic agents are capable of altering iron handling by macrophages, the present study evaluated the ability of these agents to prevent the macrophage dysfunction and lipid peroxidation caused by a phagocytic challenge with EIgG. Elicited rat peritoneal macrophages showed a depression of PMA-stimulated hydrogen peroxide production, calcium ionophore-stimulated arachidonate release and Fc receptor-mediated phagocytosis. The lysosomotropic agents; chloroquine, quinacrine, ammonium chloride and methylamine all prevented the depression of hydrogen peroxide production and arachidonate release but did not alter the depression of phagocytic function. These agents also prevented the increase in lipid peroxidation products caused by a phagocytic challenge with EIgG. These results suggest that the ability of lysosomotropic agents to prevent some aspects of macrophage dysfunction after a phagocytic challenge may be due to their ability to block the oxidative stress caused by the challenge.     

Alteration of rat Kupffer cell function following mitomycin-C administration

Cancer chemotherapeutic agents modify the human immune system in diverse ways including both immunosuppression and immunostimulation. We evaluated the effects of mitomycin-C on rat Kupffer cell phagocytosis, C3b receptor binding, and lysosomal enzyme activity. Kupffer cell cultures were greater than 95% pure. Phagocytosis of IgG-coated sheep red blood cells was demonstrated by 84% of control cells but by only 25% of cells isolated two weeks following mitomycin-C administration (p less than 0.0005). This depression in phagocytic ability had returned to control levels by four weeks posttreatment. Similarly, C3b receptor binding of IgM and complement coated sheep red blood cells was observed in 88% of control Kupffer cells, but declined to 47% at two weeks after drug administration (p less than 0.005) and returned to normal after four weeks. Lysosomal enzyme activity was not impaired by mitomycin-C. Histologically severe ulceration of the colon of treated animals was seen one and two weeks after drug administration, but healed by four weeks post-mitomycin-C treatment. Depression of macrophage function as a consequence of cancer chemotherapy may have important clinical consequences in host defense against bacteria and tumor metastases.     

A phagocytic challenge with IgG-coated erythrocytes depresses macrophage respiratory burst and phagocytic function by different mechanisms

A phagocytic challenge with IgG-coated erythrocytes (EIgG) previously has been shown to cause impaired macrophage respiratory burst capacity and FcgammaR-mediated phagocytic function. Because both the respiratory burst and FcgammaR-mediated phagocytosis are dependent on the release of arachidonate (AA), we evaluated the effects of impaired AA release on the depression of macrophage function caused by a phagocytic challenge. Challenge with EIgG caused a depression of A23187-stimulated AA release that was associated with impaired phorbol myristate acetate (PMA)-stimulated H2O2 production and FcgammaR-mediated phagocytic function. In contrast, challenge with IgG-coated glass beads (BIgG) had no effect on either AA release or H2O2 production but did depress phagocytic function. Exogenous AA prevented the depression of H2O2 production but had no effect on phagocytic function. Phospholipase A2 (PLA2) activity was depressed under conditions where AA release was impaired. The depression of phagocytic function was correlated with a depression of both EIgG binding and FcgammaR expression. Thus, a phagocytic challenge with EIgG results in macrophage dysfunction by depressing PLA2 activity and depleting FcgammaR.     

Respiratory burst capacity of activated macrophages is resistant to depression by erythrocyte phagocytosis

The present study evaluated whether macrophage activation would reduce the depression in the capacity of macrophages to produce H₂O₂ following EIgG phagocytosis. Macrophage activation was accomplished by exposing inflammatory rat peritoneal macrophages to 10 units of IFN for 72 h. IFN treatment caused a four to fivefold increase in phorbol myristate acetate (PMA)-triggered H₂O₂ production, but Fc receptor phagocytic function was unaltered. IFN-activated macrophages were able to phagocytize a greater number of EIgG before a decrease in PMAtriggered H₂O₂ production was observed and the level of H₂O₂ production did not fall below that of untreated-inflammatory macrophages that had not received an EIgG phagocytic challenge. The depression in Fc receptor phagocytic function was unaltered with macrophage activation. These results indicate that activated macrophages are resistant to the depression of respiratory burst capacity caused by erythrocyte phagocytosis and suggests that IFN treatment may be effective in preventing the impairment of host defense against bacterial infection that is associated with erythrocyte phagocytosis.     

Effect of red blood cells and red blood cell ghosts on reticuloendothelial system function

Previous studies have shown that hepatic phagocytosis of red blood cell (RBC) stroma can depress reticuloendothelial system (RES) phagocytic function and increase susceptibility to shock. Since the RBC stroma used in these experiments contained substantial amounts of adherent hemoglobin, the present study was carried out to evaluate the role of the hepatic uptake of RBC membrane material on RES phagocytic function and susceptibility to endotoxin shock in rats. Neuraminidase-treated RBC which contained normal amounts of hemoglobin and RBC ghosts which were hemoglobin-free were used. Both preparations were removed from the circulation primarily by the liver. RES phagocytic function was depressed following the hepatic uptake of 29 X 10(8) neuraminidase-treated RBC and 26 X 10(8) RBC ghosts. RES uptake of neuraminidase-treated RBC was associated with an increase in susceptibility to endotoxin shock, but RBC ghosts did not affect shock susceptibility. Thus, RBC ghosts and intact RBC are equally effective in depressing RES phagocytic function, but RBC ghosts did not affect susceptibility to endotoxin shock.     

Effect of anti-kupffer cell serum on phagocytosis and humoral antibody formation

To ascertain the effects of selective impairment of the fixed macrophage compartment on host defense, rabbit anti-rat Kupffer cell serum was raised and tested for its ability to depress phagocytosis and to serve as an immunosuppressant. The ability of the anti-Kupffer cell serum (AKS) to depress intravascular clearance rates of gelatinized RE test lipid emulsion indicated that the antiserum can functionally impair overt phagocytic activity. The phagocytic impairment was manifested by a significantly decreased liver phagocytosis of the lipid emulsion, whereas only a slight decrease in phagocytosis by the spleen was noted. When titered in vitro, AKS was cytotoxic to hepatic and splenic macrophages. Although AKS induced some degree of immunosuppressive activity, it was not as effective as antilymphocytic serum in suppressing the humoral immune response of rats to sheep red blood cells. Selectivity in the cytotoxic activity of AKS was manifested by toxicity for macrophages but not toxicity for thymocytes or splenic lymphocytes. It is suggested that AKS as a specific antimacrophage serum may be useful for assessing the contribution of the reticuloendothelial system to host defense physiology and metabolism.     

Effect of infectious bovine rhinotracheitis virus infection on bovine alveolar macrophage function.

Bovine alveolar macrophages isolated in culture were assessed for immunological activity in assays for Fc and complement receptors, for phagocytosis, and for effector cell function in antibody-dependent cell cytotoxicity. In the case of uninfected alveolar macrophages, Fc receptors were detected on approximately 94% of macrophages and complement receptors were detected on 39%. Phagocytosis of immunoglobulin G-coated sheep erythrocytes occurred in 58% of macrophages, and phagocytosis of opsonized Candida parapsilosis, mediated by the complement receptor, was observed in 68% of cells. Alveolar macrophages were efficient effector cells in antibody-dependent cell cytotoxicity. Infection of macrophages with infectious bovine rhinotracheitis (IBR) virus resulted in reductions in Fc-mediated receptor activity and phagocytosis after approximately 12 and 6 h, respectively. Complement receptor activity was initially elevated and then markedly reduced. Macrophages retrieved from IBR-immune and -susceptible donors were affected to a similar extent. The ability of macrophages to participate in antibody-dependent cell cytotoxicity was reduced dramatically from 2 h after IBR virus infection, suggesting that IBR virus-infected alveolar macrophages undergo alterations in immunological activity long before morphological changes in the cells become apparent.     

Fc-mediated endocytosis by human neutrophils. Ultrastructural studies

Fc Receptors (FcR) mediate the binding and uptake by polymorphonuclear leukocytes (PMN) of antibody-coated particles and soluble immune complexes. We have studied Fc-mediated endocytosis by PMN ultrastructurally using a gold-conjugated monoclonal antibody (3G8) to block or to mark the location of FcR. Phagocytosis of antibody-coated erythrocytes (EIgG) was initiated rapidly after binding to discrete foci on the PMN plasma membrane. After the phagocytosis of EIgG, we examined the distribution of FcR remaining on the PMN plasma membrane. 3G8-Colloidal gold continued to bind to PMN after ingestion of up to three EIgG, demonstrating that all PMN FcR are not utilized during a brief phagocytic event. The endocytosis of soluble immune complexes was examined by labeling plasma membrane-bound rabbit immune complexes with goat anti-rabbit IgG conjugated to colloidal gold. Gold was found in clusters randomly distributed over the plasma membrane at 4 degrees C. When cells were warmed to 37 degrees C, numerous endocytic vesicles were observed as early as 2.5 minutes after warming. After 30 minutes at 37 degrees C, large vesicles, 1 micron in diameter, were found to contain 20 to 30 gold particles. The endocytosis of 3G8 was also examined using colloidal gold. After binding of 3G8-gold at 4 degrees C, clusters of large vesicles, up to 2 micron in diameter, were rapidly formed at 37 degrees C.     

Trypanosoma congolense infections: antibody-mediated phagocytosis by Kupffer cells

Immunohistochemical double-label technique was used to detect trypanosomal antigen in macrophages. Immunoglobulin (Ig)M as well as IgG2a monoclonal antibodies (mAb) specific for the variant surface glycoprotein (VSG) mediated phagocytosis of Trypanosoma congolense variant antigenic type (VAT) TC13 by macrophages [bone marrow-derived macrophage cell line from BALB/c (BALB.BM)] in vitro. Administration of these IgM or IgG2a antibodies to BALB/c mice 30 min after injection of 3 x 10(8) T. congolense mediated phagocytosis of trypanosomes by Kupffer cells of the liver within 1 h. Plasma levels of the monokines interleukin (IL)-1beta, IL-10, and IL-12p40 were significantly increased 6-48 h after phagocytosis. In BALB/c mice infected with 10(3) T. congolense, a small degree of phagocytosis of trypanosomes by Kupffer cells, mediated by actively synthesized antibodies, was detected as early as 5 days after infection. Phagocytosis of trypanosomes was dramatically enhanced on day 6. Concomitantly, the Kupffer cells trippled in size. In BALB/c mice infected for 6 days, treatment with IgM or IgG2a mAb specific for T. congolense VSG led to clearance of VAT TC13 parasitemia but did not prevent death at the second parasitemia of a different VAT. We conclude that IgM as well as IgG antibody mediate phagocytosis of trypanosomes by Kupffer cells.     

Corynebacterium parvum can Reverse the Depression of Macrophage Hydrogen Peroxide Production Caused by Erythrocyte Phagocytosis

Our previous studies have shown that the phagocytosis of IgG-coated erythrocytes (EIgG) in vivo increases the mortality rate with bacterial infection, and EIgG phagocytosis in vitro depresses phorbol myristate acetate (PMA)-triggered H₂O₂ production. The present study was undertaken to determine if the depression of H₂O₂ production caused by EIgG phagocytosis could be reversed by exposing macrophages to priming agents. Macrophages exposed to 100 μg/ml of C. parvum, it's pyridine-soluble extract (PE), or the pyridine extract residue (PER) for 1 hr showed an enhanced production of H₂O₂ in response to PMA triggering. The priming effect of C. parvum, PE, and PER lasted for 3-6 hr. 18 hr after exposure to C parvum or PER, PMA-triggered H₂O₂ production was depressed, however PE did not have this effect. The priming effect of C parvum was not prevented by cycloheximide. EIgG phagocytosis caused a dose dependent depression of PMA-triggered H₂O₂ production. When macrophages were exposed to C. parvum, PE, or PER following EIgG phagocytosis, the priming of PMA-triggered H₂O₂ production was reduced but H₂O₂ production was maintained at levels equal to or greater than that of control macrophages. These results show that phagocytosis did not prevent the action of priming agents on macrophage respiratory burst capacity, and suggests that such agents may preserve macrophage bactericidal function following phagocytosis.     

Effects of acute moderate exercise on the phagocytosis of Kupffer cells in rats

AIM: This study investigated the function of Kupffer cells, and particularly their role as immunocompetent cells that come into contact with gut-derived endotoxin, in the acute exercise of rats. METHODS: Female Fischer 344 rats were run on a treadmill at 21 m min(-1) for 60 min on a 15% grade. RESULTS: Afterwards, the number of latex particles in the liver was higher in the exercising rats than that in resting rats and an increase in the number of latex particles phagocytosed by each Kupffer cell was noted. The plasma endotoxin concentration was significantly higher in the exercise group than in the resting rats, and the small intestine was damaged by the exercise. Plasma corticosterone and thyroxine 4 levels were unchanged. Although the number of Kupffer cells was unchanged by acute exercise, the number of CD14-positive Kupffer cells increased. Plasma liver enzyme activities were slightly increased by acute exercise, whereas plasma tumour necrosis factor-alpha was not detected. CONCLUSION: These results suggest that moderately intense exercise increases the phagocytosis of Kupffer cells, and that it might be induced by endotoxemia of portal blood caused by intestinal mucosal lesions resulting from acute exercise.     

Effect of extravascular hemolysis on the RES depression following thermal injury

This study was carried out to determine if the reticuloendothelial system (RES) uptake of damaged red blood cells (RBC) following thermal injury is sufficient to depress hepatic and splenic clearance function or to increase susceptibility to endotoxin shock. This was approached by determining the extent of the RES uptake of intact RBC (extravascular hemolysis) following thermal injury in rats, and by determining the effect on RES function of a similar degree of extravascular hemolysis induced in uninjured animals by the injection of heat damaged RBC. The RES uptake of three doses of heated RBC was characterized and the second largest dose caused a degree of extravascular hemolysis which was comparable to that associated with thermal injury. This latter dose of heated RBC depressed splenic clearance function but did not depress hapatic clearance function as determined using the smallest dose of heated RBC or formalinized sheep red blood cells as the test particles. Susceptibility to endotoxin shock was increased following the injection of the dose of heated RBC which stimulated the degree of extravascular hemolysis associated with thermal injury. Thus, the extravascular hemolysis associated with thermal injury is sufficient to depress splenic clearance function but not hepatic clearance function, and may contribute to the increased susceptibility to endotoxin shock following thermal injury. These findings further support the hypothesis that the hemolysis induced by thermal injury contributes to the depression of host defense associated with this form of injury.     

Effect of methylprednisolone on bacterial clearance and endotoxin liberation during experimental sepsis induced by gram-negative bacteria.

To determine the effect of methylprednisolone administration on the clearance of bacteremia and the release and clearance of endotoxin during antibiotic therapy of gram-negative bacterial sepsis, Escherichia coli K1 sepsis was induced in paired rabbits. Moxalactam and either methylprednisolone or placebo were administered to infected rabbits 1.5 h after intraperitoneal administration of live bacteria. Serial blood samples were obtained for quantitation of bacteremia and endotoxemia, arterial blood gases, and complete blood count. Arterial blood pressure, heart rate, and core body temperature were also monitored. There were no significant differences between the methylprednisolone-treated and placebo-treated groups in either the levels of bacteremia or endotoxemia or in the physiologic, metabolic, or hematologic parameters that were measured. We conclude that methylprednisolone administration has no acute effect on bacterial clearance or on the kinetics of endotoxin release and clearance during antibiotic therapy of gram-negative bacterial sepsis in this experimental model.     

A modified colorimetric method for the measurement of phagocytosis and antibody-dependent cell cytotoxicity using 2,7-diaminofluorene.

A sensitive and rapid colorimetric method for the in vitro determination of phagocytic activity and antibody-dependent cell-mediated cytotoxicity (ADCC) is described. The assay uses red blood cells (RBC) as target cells and relies on the specific oxidation of 2,7-diaminofluorene (DAF) by the pseudoperoxidase activity of hemoglobin (Hb). Generation of fluorene blue (FB), the chromophore formed upon oxidation of DAF, was a linear function of erythrocyte concentration. The oxidation of DAF by peritoneal macrophages (M phi) containing myeloperoxidase was negligible, confirming that the development of color was exclusively due to the pseudoperoxidase activity of Hb. A positive correlation was observed between FB formation and increased phagocytosis of opsonized erythrocytes. Phagocytosis increased as a function of time, reaching a maximum at 90 min of incubation. The phagocytosis of IgG-opsonized erythrocytes was greater than non-opsonized erythrocytes and was inhibited by high concentrations of non-specific human or mouse IgG, showing that phagocytosis was mediated by the Fc gamma receptor of macrophages. The interaction between opsonized RBC and macrophages also evoked an antibody-dependent extracellular lysis, however this process was slower than ingestion. The DAF phagocytosis assay has shown to be very sensitive, simple, rapid and safe.     

Age dependent phagocytosis of red cell membranes by the reticulohistiocytary system of the isolated perfused rat liver

Isolated rat livers were perfused with a medium free of immune globulins, protein and hemoglobin to investigate age-dependent differences in the phagocytosis of erythrocyte membranes. Membranes of young erythrocytes were phagocyted significantly more than those of old ones. The control parameters of the liver function also were significantly higher during the increased phagocytosis of the young cells than for the old cells and the control group. In the aged animals the characteristic of the elimination curve is changing. The old livers eliminated less ghosts than the young ones. These results are significant.