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

Photomedicine based on heme-derived compounds

Photoimaging and phototherapy have become major platforms for the diagnosis and treatment of various health complications. These applications require a photosensitizer (PS) that is capable of absorbing light from a source and converting it into other energy forms for detection and therapy. While synthetic inorganic materials such as quantum dots and gold nanorods have been widely explored for their medical diagnosis and photodynamic (PDT) and photothermal (PTT) therapy capabilities, translation of these technologies has lagged, primarily owing to potential cytotoxicity and immunogenicity issues. Of the various photoreactive molecules, the naturally occurring endogenous compound heme, a constituent of red blood cells, and its derivatives, porphyrin, biliverdin and bilirubin, have shown immense potential as noteworthy candidates for clinically translatable photoreactive agents, as evidenced by previous reports. While porphyrin-based photomedicines have attracted significant attention and are well documented, research on photomedicines based on two other heme-derived compounds, biliverdin and bilirubin, has been relatively lacking. In this review, we summarize the unique photoproperties of heme-derived compounds and outline recent efforts to use them in biomedical imaging and phototherapy applications.

Transfusion-related immunomodulation: a reappraisal

PURPOSE OF REVIEW

This review summarizes current and prior observations regarding transfusion-related immunomodulation (TRIM) and puts these ideas into a modern immunological context, incorporating concepts from innate, adaptive, and nutritional immunity. We propose that TRIM research focus on determining whether there are specific, well-defined immunosuppressive effects from transfusing 'pure' red blood cells (RBCs) themselves, along with the by-products produced by the stored RBCs as a result of the 'storage lesion.' Macrophages are a key cell type involved in physiological and pathological RBC clearance and iron recycling. The plasticity and diversity of macrophages makes these cells potential mediators of immune suppression that could constitute TRIM.

RECENT FINDINGS

Recent reports identified the capacity of macrophages and monocytes to exhibit 'memory.' Exposure to various stimuli, such as engulfment of apoptotic cells and interactions with ß-glucan and lipopolysaccharide, were found to induce epigenetic, metabolic, and functional changes in certain myeloid cells, particularly macrophages and monocytes.

SUMMARY

Macrophages may mediate the immunosuppressive aspects of TRIM that arise as a result of transfused RBCs and their storage lesion induced by-products.

Diminished organelle motion in murine Kupffer cells during the erythrocytic stage of malaria

Parasitized erythrocytes are ingested by murine hepatic macrophages during malaria infection. We non-invasively monitored how this altered the motion of intracellular phagosomes in Kupffer cells using magnetometry. Submicrometric γFe(2)O(3) particles were injected prior to malaria infection. They were cleared from the blood, primarily by Kupffer cells, and retained within their phagosomes. The mice were periodically magnetized. After removing this external magnet, the aligned iron particles created a remnant magnetic field (RMF) which then decayed (relaxation), reflecting the motion of particle-containing phagosomes. After baseline measurements of relaxation, the mice were injected intravenously with Plasmodium chabaudi-parasitized or normal murine red blood cells (RBCs). During the next 15 days, relaxation measurements, parasitaemia and haematocrit values were monitored. At 6 days post injection with 3 × 10(7) parasitized RBCs, relaxation rates had decreased. At this time, all mice had parasitaemias greater than 58 per cent and haematocrits less than 20 per cent. At day 7, while the parasitaemias were declining, the rate of relaxation continued to decrease. Throughout the experiment, relaxation remained constant in animals injected with normal RBCs. Electron microscopy revealed Kupffer cells filled with damaged and parasitized erythrocytes, and haemoglobin degradation pigment. We conclude that ingestion and metabolism of parasitized erythrocytes by liver macrophages during malaria infection decreases their organelle motion with likely consequences of compromised host defences.

Robust erythrophagocytosis leads to macrophage apoptosis via a hemin-mediated redox imbalance: role in hemolytic disorders

MP from the RES are responsible for the clearance of senescent RBC. Although the frequency of senescent RBC is low under steady-state conditions, it increases dramatically during hemolytic disorders, resulting in enhanced erythrophagocytosis. As erythrophagocytosis has been involved in MP dysfunction and as certain hemolytic disorders associate to MP apoptosis, a possible link between erythrophagocytosis and the viability of phagocytes was investigated herein. To mimic hemolytic disorders, two distinct in vitro models, artificially oxidized RBC and DSRBC, were chosen to study the erythrophagocytosis impact on the viability of J774A.1 MP. Although CRBC were weakly phagocytosed and did not affect MP viability significantly, erythrophagocytosis of oxidized RBC and DSRBC was robust and resulted in a sharp decrease of MP viability via apoptosis. Under these conditions, Hb-derived HE was shown to be involved in the induction of apoptosis. Moreover, oxidized RBC, DSRBC, and HE generated ROS species, which were responsible for the apoptosis of MP. Furthermore, HO-1, strongly induced in response to treatment with oxidized RBC, DSRBC, or HE, was shown to protect MP partially against apoptosis, suggesting that robust erythro-phagocytosis may exceed the detoxification capabilities of MP. Taken together, these results suggest that enhanced erythrophagocytosis associated to hemolytic disorders leads to MP apoptosis in vitro and may have critical implications for the control of malaria infection and for the exacerbated susceptibility to bacterial infections during hemolytic disorders.

Dual effect of Plasmodium-infected erythrocytes on dendritic cell maturation

Background

Infection with Plasmodium is the cause of malaria, a disease characterized by a high inflammatory response in the blood. Dendritic cells (DC) participate in both adaptive and innate immune responses, influencing the generation of inflammatory responses. DC can be activated through different receptors, which recognize specific molecules in microbes and induce the maturation of DC.

Methods

Using Plasmodium yoelii, a rodent malaria model, the effect of Plasmodium-infected erythrocytes on DC maturation and TLR responses have been analysed.

Results

It was found that intact erythrocytes infected with P. yoelii do not induce maturation of DC unless they are lysed, suggesting that accessibility of parasite inflammatory molecules to their receptors is a key issue in the activation of DC by P. yoelii. This activation is independent of MyD88. It was also observed that pre-incubation of DC with intact P. yoelii-infected erythrocytes inhibits the maturation response of DC to other TLR stimuli. The inhibition of maturation of DC is reversible, parasite-specific and increases with the stage of parasite development, with complete inhibition induced by schizonts (mature infected erythrocytes). Plasmodium yoelii-infected erythrocytes induce a broad inhibitory effect rendering DC non-responsive to ligands for TLR2, TLR3, TLR4, TLR5, TLR7 and TLR9.

Conclusions

Despite the presence of inflammatory molecules within Plasmodium-infected erythrocytes, which are probably responsible for DC maturation induced by lysates, intact Plasmodium-infected erythrocytes induce a general inhibition of TLR responsiveness in DC. The observed effect on DC could play an important role in the pathology and suboptimal immune response observed during the disease. These results help to explain why immune functions are altered during malaria, and provide a system for the identification of a parasite-derived broad inhibitor of TLR-mediated signaling pathways.

Red blood cell dysfunction in septic glucose-6-phosphate dehydrogenase-deficient mice

Glucose-6-phosphate dehydrogenase (G-6-PDH) deficiency is the most common known human genetic polymorphism. This study tested the hypothesis that G-6-PDH deficiency worsens sepsis-induced erythrocyte dysfunction. Sepsis (24 h) was induced by cecal ligation and puncture in wild-type (WT) and G-6-PDH-deficient (G-6-PDH activity 15% of WT) mice. Erythrocyte responses were tested in whole blood as well as in subpopulations of circulating erythrocytes. Whereas erythrocyte deformability was similar in unchallenged deficient and WT animals, sepsis decreased erythrocyte deformability that was more pronounced in deficient than WT animals. Sepsis also resulted in anemia and hemolysis in deficient compared with WT animals. Mean corpuscular hemoglobin content and erythrocyte deformability decreased in younger erythrocyte subpopulations from septic deficient compared with WT animals. Sepsis decreased the reduced-to-oxidized glutathione ratio in erythrocytes from both deficient and WT animals; however, plasma glutathione increased more in deficient than in WT animals. Erythrocyte content of band 3 associated with the cytoskeleton was elevated in deficient compared with WT erythrocytes. The antioxidant N-acetyl-l-cysteine in vivo alleviated the sepsis-induced decrease in erythrocyte deformability in deficient animals compared with sham-operated control animals. This study demonstrates that a mild degree of G-6-PDH deficiency (comparable to the human class III G-6-PDH deficiencies) worsens erythrocyte dysfunction during sepsis. Increased erythrocyte rigidity and tendency for hemolysis together with alterations in band 3-spectrin interactions may contribute to the immunomodulatory effects of G-6-PDH deficiency observed after major trauma and infections in humans.

Appearance of an erythrocyte population with decreased deformability and hemoglobin content following sepsis

With the use of the cecal ligation and puncture model in mice, this study tested whether sepsis-induced decreased erythrocyte deformability is restricted to a subpopulation of cells. Erythrocyte subpopulations were isolated by centrifugal elutriation. Lineweaver-Burk conversion of deformability-response curves to shear stress was used to determine the shear stress at half-maximal cell elongation (K(EI)) and maximal cell elongation (EI(max)). Sepsis decreased erythrocyte deformability in whole blood. K(EI) values were elevated (2.7 vs. 2.1 Pa) and EI(max) values decreased (0.56 vs. 0.50) in sepsis compared with sham mice. K(EI) values for cells eluted at 7 ml/min (smallest and oldest cells) were similar; however, K(EI) values for cells eluted at 8 ml/min were greater in septic than sham animals (2.50 vs. 2.10). Younger and larger subpopulations of erythrocytes (eluted at 9, 10, and 11 ml/min) also showed a tendency of decreased deformability in sepsis. Mean corpuscular hemoglobin content was decreased in cells eluted at 7 and 8 ml/min in sepsis (4.5 and 10.2 pg) compared to sham (7.4 and 11.4 pg) mice. This study indicates that an erythrocyte subpopulation that represents 20% of circulating cells shows the most pronounced decrease in cell deformability during sepsis. Increased rigidity together with decreased corpuscular hemoglobin content in these cells may contribute to microcirculatory dysfunction and immune modulation during sepsis.

The effect of strenuous exercise on mRNA concentrations of interleukin-12, interferon-gamma and interleukin-4 in equine pulmonary and peripheral blood mononuclear cells

The effect of strenuous exercise on the mRNA concentrations of interleukin-12p35 subunit (IL-12p35), interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) in equine pulmonary and peripheral blood mononuclear cells (PBMCs) was investigated. We hypothesized that strenuous exercise would suppress the expression of IL-12p35, IFN-gamma and augment the expression of IL-4. Eleven horses were randomly divided into two groups, a stall-confined control group (n=5) and an exercise-conditioned treatment group (n=6). Bronchoalveolar and PBMCs were obtained from horses in the treatment group prior to the commencement of a 9-week conditioning program and 24h after the completion of a maximum exercise test conducted in week 12. Samples were obtained simultaneously from control horses. Differential counts were performed on the bronchoalveolar lavage cells. Real-time PCR was performed on the pulmonary and PBMCs to quantitate cytokine expression using equine-specific primers and Taqman probes. Target gene expression was normalized to 18s rRNA expression. With the exception of IL-4 in the BALF cells, mRNA for the three cytokines was detected in the mononuclear cells from all horses at both sampling times. There were no significant differences in the cytokine mRNA concentrations between the two groups of horses at either of the sampling times. These findings demonstrate that strenuous treadmill exercise does not exert a deleterious effect on gene expression for IL-12p35, IFN-gamma or IL-4 when assessed in horses 24h following the intense physical activity.

The effect of high intensity exercise on the functional capacity of equine pulmonary alveolar macrophages and BAL-derived lymphocytes

The effect of strenuous exercise on the functional capacity of pulmonary alveolar macrophages (PAM) and bronchoalveolar lavage-derived lymphocytes was determined in eight horses prior to and after 7 weeks of training. Strenuous exercise had no effect on the total cell count or the percentage of live cells in bronchoalveolar lavage (BAL) samples prior to or following training. However, training was associated with a significant increase in the total cell count of pre-exercise BAL samples and a significant reduction in the percentage of live cells in post-exercise samples. Strenuous exercise was associated with impaired phagocytosis by PAM after 7 weeks of training but had no effect on similar samples obtained from untrained horses. The oxidative burst activity of PAM was significantly increased following strenuous exercise for both untrained and trained horses. BAL -derived lymphocyte oxidative burst was similarly affected following training. These results suggest that strenuous exercise and training may influence pulmonary immune cell function.

IgG-coated erythrocytes augment LPS-stimulated TNF-alpha secretion, TNF-alpha mRNA levels, and TNF-alpha mRNA stability in macrophages

Previous studies have shown that IgG-coated erythrocytes (EIgG) augment the LPS-stimulated increase in serum TNF-alpha levels in animals and the LPS-stimulated secretion of TNF-alpha by isolated macrophages. The present study evaluated the mechanism for the effect of EIgG on LPS-stimulated TNF-alpha secretion in the murine macrophage cell line, RAW 264.7. Incubation of the macrophages with EIgG or IgG-coated glass beads caused a dose-dependent augmentation of LPS-stimulated TNF-alpha secretion. The addition of EIgG increased the rate of LPS-stimulated TNF-alpha protein secretion between 2 and 4 hr after LPS. Accordingly, EIgG increased the levels of TNF-alpha mRNA at 2 and 3 hr after LPS. The increase in the LPS-stimulated TNF-alpha mRNA levels caused by EIgG was associated with an increase in TNF-alpha mRNA stability. Thus, the augmentation of LPS-stimulated TNF-alpha secretion by EIgG was associated with an increase in TNF-alpha mRNA levels which at least partly resulted from an increase in the stability of TNF-alpha mRNA.

Role of an oxidative stress in the macrophage dysfunction caused by erythrophagocytosis

A phagocytic challenge with immunoglobulin G (IgG)-coated erythrocytes (EIgGs) has been shown to cause a subsequent depression of macrophage respiratory burst capacity and phagocytic function. The present study evaluated the hypothesis that this macrophage dysfunction is caused by an oxidative stress. An oxidative stress induced by ferric ammonium citrate (FAC) plus cumene hydroperoxide (CHP) caused a depression of macrophage function that was attenuated by antioxidants and iron chelators. In contrast, the same antioxidants and iron chelators did not alter changes caused by a challenge with EIgGs. EIgG challenge caused an increase in lipid peroxidation but failed to deplete glutathione (GSH) or decrease the activity of glyceraldehyde-3-phosphate dehydrogenase (GA-3-PD), suggesting that there was only a slight oxidative stress. Inhibition of the Fc gamma receptor (Fc gammaR) stimulated respiratory burst by removing calcium during the challenge did not attenuate the changes caused by an EIgG challenge. A phagocytic challenge with nonerythrocyte particles, IgG-coated beads (BIgGs), did not depress the respiratory burst capacity but did depress phagocytic function. Fc gammaR expression was depressed following a phagocytic challenge but not an oxidative stress. Thus, an oxidative stress can depress macrophage function, but the dysfunction caused by a phagocytic challenge with EIgGs involves Fc gammaR depletion and the erythrocyte contents rather than an oxidative stress.

IgG-coated erythrocytes augment the lipopolysaccharidestimulated increase in serum tumor necrosis factor-alpha

Previous studies have shown that the injection of IgG-coated erythrocytes (EIgG) caused an increase in the mortality rate due to bacterial lipopolysaccharide (LPS). This observation led to the present evaluation of the effect of EIgG on the LPS-stimulated increase in serum tumor necrosis factor-alpha (TNF-alpha) levels and TNF-alpha secretion by macrophages. The prior injection of EIgG augmented the increase in LPS-stimulated serum TNF-alpha levels ninefold at 1 h after LPS. Serum TNF-alpha levels were augmented when LPS was injected 2 or 6 h after EIgG but not at 0.5 or 12 h after EIgG. Complement activation caused by EIgG may contribute to the priming for TNF-alpha, because activation of complement with cobra venom factor caused a threefold augmentation of the LPS-stimulated serum TNF-alpha levels. Isolated macrophages that had ingested EIgG or were adherent to immobilized IgG showed augmented TNF-alpha secretion in response to LPS. Thus clearance of immune complexes from the blood can augment the LPS-stimulated increase in serum TNF-alpha levels that is due, in part, to complement activation and signaling via FcgammaR.

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.

Chemiluminescence activity of phagocytes from tracheal aspirates of premature infants after surfactant therapy

The effect of surfactant on the respiratory burst of phagocytic cells was studied in the tracheobronchial tract of 40 mechanically ventilated neonates (gestational age 24-37 weeks) over the first week of life. We measured the luminol-dependent chemiluminescence (CL) activity of granulocytes and macrophages isolated from tracheal aspirates in 23 preterm infants 1-6 days after administration of bovine surfactant and in 17 untreated controls. Following stimulation by the chemotactic peptide N-formylmethionylleucylphenylalanine, CL activity was not or only slightly impaired in the surfactant group. In contrast, treatment with exogenous surfactant significantly reduced CL response to opsonized zymosan (OPZ), which involves phagocytosis, for up to 6 days (p < 0.05). The impairment of CL activity seemed to be dose dependent, as repeated surfactant applications (cumulative phospholipid dose of 200 mg/kg) reduced OPZ-elicited CL activity to a greater extent than application of a single dose of 100 mg/kg. In agreement with in vitro studies, our data suggest that high-dose application of exogenous surfactant may affect the antibacterial function of phagocytic cells in the lung.

Simultaneous detection of free radical release and membrane current during phagocytosis

Stimulation of macrophages induces the "respiratory burst" response which is associated with the generation of superoxide (O2-), a drop in cytoplasmic pH, and a pronounced depolarization of the membrane potential. The purpose of the present studies was to determine whether an increase in O2- was temporally related to changes in membrane potential and transmembrane current. Release of O2- at the single cell level was photometrically monitored during phagocytosis of immune complexes while simultaneously measuring whole-cell current. Membrane depolarization and the generation of a non-selective current followed an increase in O2- production with a variable lag time which was correlated with the state of cellular maturation in culture. In the absence of phagocytosis, the exposure of macrophages to O2- generated by a xanthine-xanthine oxidase reaction activated a non-selective current similar to that seen after phagocytosis. These results provide the first demonstration of the relationship between free radical release and the ensuing electrophysiological signaling events which are linked to particle engulfment in phagocytic cells.

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 gamma for 72 h. IFN gamma treatment caused a four to fivefold increase in phorbol myristate acetate (PMA)-triggered H2O2 production, but Fc receptor phagocytic function was unaltered. IFN gamma-activated macrophages were able to phagocytize a greater number of EIgG before a decrease in PMA-triggered 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 gamma treatment may be effective in preventing the impairment of host defense against bacterial infection that is associated with erythrocyte phagocytosis.

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 micrograms/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.

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.

Macrophage hydrogen peroxide production and phagocytic function are decreased following phagocytosis mediated by Fc receptors but not complement receptors

Previous in vivo and in vitro studies have shown that the phagocytosis of IgG-coated erythrocytes results in a depression of macrophage function. The present study compared the effect of phagocytosis mediated by Fc receptors with that mediated by complement receptors. The phagocytosis of IgG-coated erythrocytes by elicited peritoneal macrophages depressed their capacity to produce hydrogen peroxide as well as phagocytic function. Phagocytosis of erythrocytes coated with IgM and complement had neither of these effects. These results implicate the intracellular signaling that results from Fc receptor mediated phagocytosis in the depression of macrophage function that is caused by phagocytosis.