Naturally occurring anti-band-3 antibodies and complement together mediate phagocytosis of oxidatively stressed human erythrocytes

What is the role of complement in bystander hemolysis? Old concept, new insights

INTRODUCTION

Bystander hemolysis occurs when antigen-negative red blood cells (RBCs) are lysed by the complement system. Many clinical entities including passenger lymphocyte syndrome, hyperhemolysis following blood transfusion, and paroxysmal nocturnal hemoglobinuria are complicated by bystander hemolysis.

AREAS COVERED

The review provides data about the role of the complement system in the pathogenesis of bystander hemolysis. Moreover, future perspectives on the understanding and management of this syndrome are described.

EXPERT OPINION

Complement system can be activated via classical, alternative, and lectin pathways. Classical pathway activation is mediated by antigen-antibody (autoantibodies and alloantibodies against autologous RBCs, infectious agents) complexes. Alternative pathway initiation is triggered by heme, RBC microvesicles, and endothelial injury that is a result of intravascular hemolysis. Thus, C5b is formed, binds with C6-C9 compomers, and MAC (C5b-9) is formulated in bystander RBCs membranes, leading to cell lysis. Intravascular hemolysis, results in activation of the alternative pathway, establishing a vicious cycle between complement activation and bystander hemolysis. C5 inhibitors have been used effectively in patients with hyperhemolysis syndrome and other entities characterized by bystander hemolysis.

P. falciparum Invasion and Erythrocyte Aging

Plasmodium parasites need to find red blood cells (RBCs) that, on the one hand, expose receptors for the pathogen ligands and, on the other hand, maintain the right geometry to facilitate merozoite attachment and entry into the red blood cell. Both characteristics change with the maturation of erythrocytes. Some Plasmodia prefer younger vs. older erythrocytes. How does the life evolution of the RBC affect the invasion of the parasite? What happens when the RBC ages? In this review, we present what is known up until now.

Biomimetic Nanomaterials for the Immunomodulation of the Cardiosplenic Axis Postmyocardial Infarction

The spleen is an important mediator of both adaptive and innate immunity. As such, attempts to modulate the immune response provided by the spleen may be conducive to improved outcomes for numerous diseases throughout the body. Here, biomimicry is used to rationally design nanomaterials capable of splenic retention and immunomodulation for the treatment of disease in a distant organ, the postinfarct heart. Engineered senescent erythrocyte-derived nanotheranostic (eSENTs) are generated, demonstrating significant uptake by the immune cells of the spleen including T and B cells, as well as monocytes and macrophages. When loaded with suberoylanilide hydroxamic acid (SAHA), the nanoagents exhibit a potent therapeutic effect, reducing infarct size by 14% at 72 h postmyocardial infarction when given as a single intravenous dose 2 h after injury. These results are supportive of the hypothesis that RBC-derived biomimicry may provide new approaches for the targeted modulation of the pathological processes involved in myocardial infarction, thus further experiments to decisively confirm the mechanisms of action are currently underway. This novel concept may have far-reaching applicability for the treatment of a number of both acute and chronic conditions where the immune responses are either stimulated or suppressed by the splenic (auto)immune milieu.

Warm autoimmune hemolytic anemia: new insights and hypotheses

PURPOSE OF REVIEW

Warm autoimmune hemolytic anemia (wAIHA) is the most common of the immune hemolytic anemias. Although there are numerous case reports and reviews regarding this condition, some of the unusual and more recent findings have not been fully defined and may be contentious. This review will provide insight into the common specificity of the warm autoantibodies and hypothesize a novel mechanism of wAIHA, that is proposed to be linked to the controversial subject of red blood cell senescence.

RECENT FINDINGS AND HYPOTHESES

It is now well established that band 3 on the red blood cell is the main target of autoantibodies in wAIHA. wAIHA targets the older red blood cells (RBCs) in about 80% of cases and, recently, it has been shown that the RBCs in these patients are aging faster than normal. It has been proposed that in these 80% of patients, that the autoantibody recognizes the senescent red blood cell antigen on band 3. It is further hypothesized that this autoantibody's production and potency has been exacerbated by hypersensitization to the RBC senescent antigen, which is processed through the adaptive immune system to create the pathogenic autoantibody. Recent publications have supported previous data that the senescent RBC antigen is exposed via a dynamic process, wherein oscillation of a band 3 internal loop flipping to the cell surface, creates a conformational neoantigen that is the RBC senescent antigen. It has also recently been shown that the cytokine profile in patients with wAIHA favors production of inflammatory cytokines/chemokines that includes interleukin-8 which can activate neutrophils to increase the oxidative stress on circulating RBCs to induce novel antigens, as has been postulated to favour exposure of the senescent RBC antigen.

SUMMARY

This manuscript reviews new findings and hypotheses regarding wAIHA and proposes a novel mechanism active in most wAIHA patients that is due to an exacerbation of normal RBC senescence.

Methodologies and tools to shed light on erythrophagocytosis

Red blood cells (RBC) are the most abundant circulating cell of the human body. RBC are constantly exposed to multiple stresses in the circulation, leading to molecular and structural impairments and death. The physiological process of RBC senescence or ageing is referred to as eryptosis. At the end of their lifespan, aged RBC are recognized and removed from the blood by professional phagocytes via a phenomenon called erythrophagocytosis (EP); the phagocytosis of RBC. Some genetic and acquired diseases can influence eryptosis, thereby affecting RBC lifespan and leading to hemolytic anemia. In some diseases, such as diabetes and atherosclerosis, eryptosis and EP can participate in disease progression with both professional and non-professional phagocytes. Therefore, investigating the process of EP in vivo and in vitro, as well as in different cell types, will not only contribute to the understanding of the physiological steps of EP, but also to the deciphering of the specific mechanisms involving RBC and EP that underlie certain pathologies. In this review, the process of EP is introduced and the different methods for studying EP are discussed together with examples of the experimental procedures and materials required.

Crosstalk between Heme Oxygenase-1 and Iron Metabolism in Macrophages: Implications for the Modulation of Inflammation and Immunity

Heme oxygenase-1 (HO-1) is an enzyme that catalyzes the degradation of heme, releasing equimolar amounts of carbon monoxide (CO), biliverdin (BV), and iron. The anti-inflammatory and antioxidant properties of HO-1 activity are conferred in part by the release of CO and BV and are extensively characterized. However, iron constitutes an important product of HO-1 activity involved in the regulation of several cellular biological processes. The macrophage-mediated recycling of heme molecules, in particular those contained in hemoglobin, constitutes the major mechanism through which living organisms acquire iron. This process is finely regulated by the activities of HO-1 and of the iron exporter protein ferroportin. The expression of both proteins can be induced or suppressed in response to pro- and anti-inflammatory stimuli in macrophages from different tissues, which alters the intracellular iron concentrations of these cells. As we discuss in this review article, changes in intracellular iron levels play important roles in the regulation of cellular oxidation reactions as well as in the transcriptional and translational regulation of the expression of proteins related to inflammation and immune responses, and therefore, iron metabolism represents a potential target for the development of novel therapeutic strategies focused on the modulation of immunity and inflammation.

Improving packed red blood cell storage with a high-viscosity buffered storage solution

BACKGROUND

Massive transfusion with older packed red blood cells is associated with increased morbidity and mortality. As packed red blood cells age, they undergo biochemical and structural changes known as the storage lesion. We developed a novel solution to increase viscosity in stored packed red blood cells. We hypothesized that packed red blood cell storage in this solution would blunt storage lesion formation and mitigate the inflammatory response after resuscitation.

METHODS

Blood was obtained from 8- to 10-week-old C57BL/6 male donor mice or human volunteers and stored as packed red blood cell units for 14 days for mice or 42 days for humans in either standard AS-3 storage solution or EAS-1587, the novel packed red blood cell storage solution. Packed red blood cells were analyzed for microvesicles, cell-free hemoglobin, phosphatidylserine, band-3 protein, glucose utilization, and osmotic fragility. Additional mice underwent hemorrhage and resuscitation with packed red blood cells stored in either AS-3 or EAS-1587. Serum was analyzed for inflammatory markers.

RESULTS

Murine packed red blood cells stored in EAS-1587 demonstrated reductions in microvesicle and cell-free hemoglobin accumulation as well as preserved band-3 expression, increase glucose utilization, reductions in phosphatidylserine expression, and susceptibility to osmotic stress. Serum from mice resuscitated with packed red blood cells stored in EAS-1587 demonstrated reduced proinflammatory cytokines. Human packed red blood cells demonstrated a reduction in microvesicle and cell-free hemoglobin as well as an increase in glucose utilization.

CONCLUSION

Storage of packed red blood cells in a novel storage solution mitigated many aspects of the red blood cell storage lesion as well as the inflammatory response to resuscitation after hemorrhage. This modified storage solution may lead to improvement of packed red blood cell storage and reduce harm after massive transfusion.

The regulation roles of Ca2+ in erythropoiesis: What have we learned?

Calcium (Ca²⁺) is an important second messenger molecule in the body, regulating cell cycle and fate. There is growing evidence that intracellular Ca²⁺ levels play functional roles in the total physiological process of erythroid differentiation, including the proliferation and differentiation of erythroid progenitor cells, terminal enucleation, and mature red blood cell aging and clearance. Moreover, recent research on the pathology of erythroid disorders has made great progress in the past decades, indicating that calcium ion hemostasis is closely related to ineffective erythropoiesis and increased sensitivity to stress factors. In this review, we summarized what is known about the functional roles of intracellular Ca²⁺ in erythropoiesis and erythrocyte-related diseases, with an emphasis on the regulation of the intracellular Ca²⁺ homeostasis during erythroid differentiation. An understanding of the regulation roles of Ca²⁺ homeostasis in erythroid differentiation will facilitate further studies and eventually molecular identification of the pathways involved in the pathological process of erythroid disorders, providing new therapeutic opportunities in erythrocyte-related disease.

Novel concepts in red blood cell clearance

PURPOSE OF REVIEW

Red blood cell (RBC) clearance has been studied for decades in many different pathologies, which has revealed different routes of RBC degradation, depending on the situation. This review summarizes the latest mechanistic insights on RBC clearance in different contexts; during homeostatic removal, immune-mediated destruction, and systemic inflammation.

RECENT FINDINGS

Besides the recognition of a variety of potential 'eat me' signals on RBCs, recent evidence suggests that normal RBC degradation is driven by the increase of the adhesive properties of RBCs, mediating the retention in the spleen and leading to RBC hemolysis. Furthermore, immune-mediated degradation of RBCs seems to be fine-tuned by the balance between the density of the antigens expressed on RBCs and the presence of 'don't eat me' signals. Moreover, besides RBC clearance by macrophages, neutrophils seem to play a much more prominent role in immune-mediated RBC removal than anticipated. Lastly, RBC clearance during systemic inflammation appears to be driven by a combination of extreme macrophage activity in response to proinflammatory cytokines as well as direct damage of RBC by the inflammation or inflammatory agent.

SUMMARY

Recent studies on RBC clearance have expanded our knowledge on their destruction in different contexts.

Large conformational dynamics in Band 3 protein: Significance for erythrocyte senescence signalling

Band 3 (Anion Exchanger 1, AE1), the predominant protein of erythrocyte membranes, facilitates Cl^-/HCO₃^- exchange and anchors the plasma membrane to the cytoskeleton. The Band 3 crystal structure revealed the amino acid 812-830 region as intracellular, conflicting with protein chemical data that suggested extracellular disposition. Further, circulating senescent cell auto-antibody that cannot enter erythrocytes, binds two regions of Band 3: residues 538-554 and 812-830. To reconcile this discrepancy, we assessed localization of residues 812-830 with Band 3 expressed in HEK293 cells and human erythrocytes, using chemical labeling probes and an antibody against residues 812-830. Antibody and chemical probes revealed reorientation of 812-830 region between extracellular and intracellular. This dramatic conformational change is an intrinsic property of the Band 3 molecule, occurring when expressed in HEK293 cells and without the damage that occurs during erythrocyte circulation. Conditions used to crystallize Band 3 for structural determination did not alter conformational dynamics. Collectively, these data reveal large Band 3 conformational dynamics localized to a region previously identified as an erythrocyte senescence epitope. Surface exposure of the senescence epitope (812-830), limited by conformational dynamics, may act as the "molecular clock" in erythrocyte senescence.

Erythrocytes: Central Actors in Multiple Scenes of Atherosclerosis

The development and progression of atherosclerosis (ATH) involves lipid accumulation, oxidative stress and both vascular and blood cell dysfunction. Erythrocytes, the main circulating cells in the body, exert determinant roles in the gas transport between tissues. Erythrocytes have long been considered as simple bystanders in cardiovascular diseases, including ATH. This review highlights recent knowledge concerning the role of erythrocytes being more than just passive gas carriers, as potent contributors to atherosclerotic plaque progression. Erythrocyte physiology and ATH pathology is first described. Then, a specific chapter delineates the numerous links between erythrocytes and atherogenesis. In particular, we discuss the impact of extravasated erythrocytes in plaque iron homeostasis with potential pathological consequences. Hyperglycaemia is recognised as a significant aggravating contributor to the development of ATH. Then, a special focus is made on glycoxidative modifications of erythrocytes and their role in ATH. This chapter includes recent data proposing glycoxidised erythrocytes as putative contributors to enhanced atherothrombosis in diabetic patients.

Quantifying dynamic range in red blood cell energetics: Evidence of progressive energy failure during storage

BACKGROUND

During storage, red blood cells (RBCs) undergo significant biochemical and morphologic changes, referred to collectively as the "storage lesion". It was hypothesized that these defects may arise from disrupted oxygen-based regulation of RBC energy metabolism, with resultant depowering of intrinsic antioxidant systems.

STUDY DESIGN AND METHODS

As a function of storage duration, the dynamic range in RBC metabolic response to three models of biochemical oxidant stress (methylene blue, hypoxanthine/xanthine oxidase, and diamide) was assessed, comparing glycolytic flux by NMR and UHPLC-MS methodologies. Blood was processed/stored under standard conditions (AS-1 additive solution) with leukoreduction. Over a 6-week period, RBC metabolic and antioxidant status were assessed at baseline and following exposure to the three biochemical oxidant models. Comparison was made of glycolytic flux (¹ H-NMR tracking of [2-¹³ C]-glucose and metabolomic phenotyping with [1,2,3-¹³ C₃ ] glucose), reducing equivalent (NADPH/NADP⁺ ) recycling, and thiol-based (GSH/GSSG) antioxidant status.

RESULTS

As a function of storage duration, we observed the following: (1) a reduction in baseline hexose monophosphate pathway (HMP) flux, the sole pathway responsible for the regeneration of the essential reducing equivalent NADPH; with (2) diminished stress-based dynamic range in both overall glycolytic as well as proportional HMP flux. In addition, progressive with storage duration, RBCs showed (3) constraint in reducing equivalent (NADPH) recycling capacity, (4) loss of thiol based (GSH) recycling capacity, and (5) dysregulation of metabolon assembly at the cytoplasmic domain of Band 3 membrane protein (cdB3).

CONCLUSION

Blood storage disturbs normal RBC metabolic control, depowering antioxidant capacity and enhancing vulnerability to oxidative injury.

The role of complement in brain injury following intracerebral hemorrhage: A review

Intracerebral hemorrhage (ICH) is a significant cause of death and disability and current treatment is limited to supportive measures to reduce brain edema and secondary hematoma expansion. Current evidence suggests that the complement cascade is activated early after hemorrhage and contributes to brain edema/injury in multiple ways. The aim of this review is to summarize the most recent literature about the role of the complement cascade after ICH. Primary literature demonstrating complement mediated brain edema and neurologic injury through the membrane attack complex (MAC) as well as C3a and C5a are reviewed. Further, attenuation of brain edema and improved functional outcomes are demonstrated after inhibition of specific components of the complement cascade. Conversely, complement also plays a significant role in neurologic recovery after ICH and in other neurologic disorders. We conclude that the role of complement after ICH is complex. Understanding the role of complement after ICH is essential and may elucidate possible interventions to reduce brain edema and injury.

C2 IgM Natural Antibody Enhances Inflammation and Its Use in the Recombinant Single Chain Antibody-Fused Complement Inhibitor C2-Crry to Target Therapeutics to Joints Attenuates Arthritis in Mice

Natural IgM antibodies (NAbs) have been shown to recognize injury-associated neoepitopes and to initiate pathogenic complement activation. The NAb termed C2 binds to a subset of phospholipids displayed on injured cells, and its role(s) in arthritis, as well as the potential therapeutic benefit of a C2 NAb-derived ScFv-containing protein fused to a complement inhibitor, complement receptor-related y (Crry), on joint inflammation are unknown. Our first objective was to functionally test mAb C2 binding to apoptotic cells from the joint and also evaluate its inflammation enhancing capacity in collagen antibody-induced arthritis (CAIA). The second objective was to generate and test the complement inhibitory capacity of C2-Crry fusion protein in the collagen-induced arthritis (CIA) model. The third objective was to demonstrate in vivo targeting of C2-Crry to damaged joints in mice with arthritis. The effect of C2-NAb on CAIA in C57BL/6 mice was examined by inducing a suboptimal disease. The inhibitory effect of C2-Crry in DBA/1J mice with CIA was determined by injecting 2x per week with a single dose of 0.250 mg/mouse. Clinical disease activity (CDA) was examined, and knee joints were fixed for analysis of histopathology, C3 deposition, and macrophage infiltration. In mice with suboptimal CAIA, at day 10 there was a significant (p < 0.017) 74% increase in the CDA in mice treated with C2 NAb, compared to mice treated with F632 control NAb. In mice with CIA, at day 35 there was a significant 39% (p < 0.042) decrease in the CDA in mice treated with C2-Crry. Total scores for histopathology were also 50% decreased (p < 0.0005) in CIA mice treated with C2-Crry. C3 deposition was significantly decreased in the synovium (44%; p < 0.026) and on the surface of cartilage (42%; p < 0.008) in mice treated with C2-Crry compared with PBS treated CIA mice. Furthermore, C2-Crry specifically bound to apoptotic fibroblast-like synoviocytes in vitro, and also localized in the knee joints of arthritic mice as analyzed by in vivo imaging. In summary, NAb C2 enhanced arthritis-related injury, and targeted delivery of C2-Crry to inflamed joints demonstrated disease modifying activity in a mouse model of human inflammatory arthritis.

Differential red blood cell age fractionation and Band 3 phosphorylation distinguish two different subtypes of warm autoimmune hemolytic anemia

Warm autoimmune hemolytic anemia (wAIHA) is a blood disorder characterized by the increased destruction of autologous red blood cells (RBCs) due to the presence of opsonizing pathogenic autoantibodies. Preliminary reports published more than three decades ago proposed the presence of two wAIHA subtypes: Type I, in which autoantibodies preferentially recognize the oldest, most dense RBCs; and Type II, characterized by autoantibodies that show no preference.

STUDY DESIGN AND METHODS

We evaluated patients having wAIHA for Type I and II subtype using discontinuous Percoll gradient age fractionation and direct antiglobulin test (DAT). We performed Western immunoblotting and mass spectrometry to show autoantibody specificity for Band 3. We investigated Band 3 tyrosine phosphorylation in different Percoll fractions to determine aging associated with oxidative stress.

RESULTS

We confirm the existence of two subtypes of wAIHA, Type I and Type II, and that autoantibodies recognize Band 3. Type I patients were characterized by five Percoll fractions, with a DAT showing IgG opsonization F₁ < F₅ and elevated Band 3 phosphorylation compared to healthy controls (HCs). In contrast, Type II wAIHA patients were characterized by three to four Percoll fractions, where the DAT IgG opsonization shows F₁ ≥ F_3/4 and Band 3 phosphorylation was absent or significantly decreased compared to HC.

CONCLUSIONS

Type I patients have increased Band 3 tyrosine phosphorylation that may represent accelerated aging of their RBCs resulting in exacerbation of a pathologic form of RBC senescence. Type II patients show decreased Band 3 tyrosine phosphorylation and lack the oldest, most dense RBCs suggesting premature RBC clearance and a more severe wAIHA.

Red Blood Cell Dysfunction in Critical Illness

Oxygen (O2) delivery, which is fundamental to supporting patients with critical illness, is a function of blood O2 content and flow. This article reviews red blood cell (RBC) physiology and dysfunction relevant to disordered O2 delivery in the critically ill. Flow is the focus of O2 delivery regulation: O2 content is relatively fixed, whereas flow fluctuates greatly. Thus, blood flow volume and distribution vary to maintain coupling between O2 delivery and demand. This article reviews conventional RBC physiology influencing O2 delivery and introduces a paradigm for O2 delivery homeostasis based on coordinated gas transport and vascular signaling by RBCs.

Band 3 ectopic expression in colorectal cancer induces an increase in erythrocyte membrane-bound IgG and may cause immune-related anemia

Autoimmune hemolytic anemia (AIHA) is a rare comorbidity in colorectal cancer (CRC) and has an unknown etiology. Previously, we described an AIHA case secondary to CRC with ectopic band 3 expression. Herein, we investigated ectopic band 3 expression and erythrocyte membrane-bound IgG in a CRC cohort. Between September 2016 and August 2018, 50 patients with CRC and 26 healthy controls were enrolled in the present study. The expression of band 3 and SLC4A1 mRNA was observed in 97% of CRC surgical specimens. Although clinical AIHA was not observed in any patient with CRC, a direct antiglobulin test was positive in 10 of the patients in the CRC group (p = 0.01). Flow cytometry revealed significantly increased erythrocyte membrane-bound IgG among patients with CRC compared to healthy controls (mean ± standard deviation; 38.8 ± 4.7 vs. 29.9 ± 15.6, p = 0.012). Normocytic anemia was observed, including in cases negative for fecal occult blood, suggesting a shortened erythrocyte life-span due to increased membrane-bound IgG. Immunoprecipitation revealed increased anti-band 3 autoantibodies in patients' sera. Mouse experiments recapitulated this phenomenon. We also confirmed that band 3 expression is controlled by 5'AMP-activated protein kinase under hypoxic conditions. These findings increase our understanding of the etiology of cancer-related anemia.

Sensing of red blood cells with decreased membrane deformability by the human spleen

The current paradigm in the pathogenesis of several hemolytic red blood cell disorders is that reduced cellular deformability is a key determinant of splenic sequestration of affected red cells. Three distinct features regulate cellular deformability: membrane deformability, surface area-to-volume ratio (cell sphericity), and cytoplasmic viscosity. By perfusing normal human spleens ex vivo, we had previously showed that red cells with increased sphericity are rapidly sequestered by the spleen. Here, we assessed the retention kinetics of red cells with decreased membrane deformability but without marked shape changes. A controlled decrease in membrane deformability (increased membrane rigidity) was induced by treating normal red cells with increasing concentrations of diamide. Following perfusion, diamide-treated red blood cells (RBCs) were rapidly retained in the spleen with a mean clearance half-time of 5.9 minutes (range, 4.0-13.0). Splenic clearance correlated positively with increased membrane rigidity (r = 0.93; P < .0001). To determine to what extent this increased retention was related to mechanical blockade in the spleen, diamide-treated red cells were filtered through microsphere layers that mimic the mechanical sensing of red cells by the spleen. Diamide-treated red cells were retained in the microsphilters (median, 7.5%; range, 0%-38.6%), although to a lesser extent compared with the spleen (median, 44.1%; range, 7.3%-64.0%; P < .0001). Taken together, these results have implications for understanding the sensitivity of the human spleen to sequester red cells with altered cellular deformability due to various cellular alterations and for explaining clinical heterogeneity of RBC membrane disorders.

A case-control analysis of hyperhemolysis syndrome in adults and laboratory correlates of complement involvement

BACKGROUND

Hyperhemolysis syndrome (HS) is a poorly understood, severe hemolytic anemia provoked by transfusion. Both host and donor RBCs are destroyed in HS; thus, transfusion paradoxically worsens anemia. Risk factors and mechanism of HS are unknown.

STUDY DESIGN AND METHODS

A retrospective case-control analysis was performed on adults with HS. Patients with HS were matched 1:1 with matched, transfused controls, and HS risk factors were analyzed with multivariable logistic regression. HS samples were analyzed for complement deposition by flow cytometry, and an in vitro model of bystander hemolysis was developed.

RESULTS

Forty-one patients with 54 episodes of HS were identified in a 26-year period from 1992 to 2018. Of the HS episodes, only 18.5% were associated with a new alloantibody, and such patients were more tolerant of additional transfusion in the acute episode (p = 0.005). Thirteen percent of episodes were fatal, and HS recurred in 52.6%. Alloimmunization (odds ratio [OR], 17.3), non-B blood type (OR, 9.8), D antigen (OR, 9.1), and infection (OR, 5.5) were associated with HS on multivariable analysis. Hyperbilirubinemia was predictive of fatal HS (OR, 33.6). Increased complement was observed on RBCs during HS episodes, and the in vitro model of bystander hemolysis recapitulated complement decoration of sickled RBCs.

CONCLUSIONS

HS is associated with significant morbidity, mortality, and recurrence. Risk factors such as known alloimmunization, blood group, and infection predispose to HS. Bystander complement activation may drive HS. These factors may help physicians refine risk-benefit assessments for transfusion and guide further therapeutic development.

What can we learn from ineffective erythropoiesis in thalassemia?

Erythropoiesis is a dynamic process regulated at multiple levels to balance proliferation, differentiation and survival of erythroid progenitors. Ineffective erythropoiesis is a key feature of various diseases, including β-thalassemia. The pathogenic mechanisms leading to ineffective erythropoiesis are complex and still not fully understood. Altered survival and decreased differentiation of erythroid progenitors are both critical processes contributing to reduced production of mature red blood cells. Recent studies have identified novel important players and provided major advances in the development of targeted therapeutic approaches. In this review, β-thalassemia is used as a paradigmatic example to describe our current knowledge on the mechanisms leading to ineffective erythropoiesis and novel treatments that may have the potential to improve the clinical phenotype of associated diseases in the future.

Molecular mechanism for the red blood cell senescence clock

Lacking protein synthesis machinery and organelles necessary for autophagy or apoptosis, aged red blood cells (RBCs) are marked by circulating auto-antibodies for macrophage-mediated clearance. The antigen recognized by these auto-antibodies is the major protein of the RBC membrane, Band 3. To ensure regulation and specificity in clearance, the molecular "clock" must mark senescent cells in a way that differentiates them from younger cells, to prevent premature clearance. Predominant models of Band 3 senescence signaling are reviewed, and merits are discussed in light of the recently published crystal structure of the Band 3 membrane domain. © 2017 IUBMB Life, 70(1):32-40, 2018.

Glucose-6-Phosphate Dehydrogenase Deficiency Mimicking Atypical Hemolytic Uremic Syndrome

A 4-year-old boy presented with nonimmune hemolysis, thrombocytopenia, and acute kidney injury. Investigations for an underlying cause failed to identify a definitive cause and a putative diagnosis of complement-mediated atypical hemolytic uremic syndrome (aHUS) was made. The patient was started initially on plasma exchange and subsequently eculizumab therapy, after which his kidney function rapidly improved. While on eculizumab therapy, despite adequate complement blockade, he presented 2 more times with hemolytic anemia and thrombocytopenia, but without renal involvement. Genetic analysis did not uncover a mutation in any known aHUS gene (CFH, CFI, CFB, C3, CD46, THBD, INF2, and DGKE) and anti-factor H antibodies were undetectable. Whole-exome sequencing was undertaken to identify a cause for the eculizumab resistance. This revealed a pathogenic variant in G6PD (glucose-6-phosphate dehydrogenase), which was confirmed by functional analysis demonstrating decreased erythrocyte G6PD activity. Eculizumab therapy was withdrawn. Complement-mediated aHUS is a diagnosis of exclusion and this case highlights the diagnostic difficulty that remains without an immediately available biomarker for confirmation. This case of G6PD deficiency presented with a phenotype clinically indistinguishable from complement-mediated aHUS. We recommend that G6PD deficiency be included in the differential diagnosis of patients presenting with aHUS and suggest measuring erythrocyte G6PD concentrations in these patients.

On the Mechanism of Human Red Blood Cell Longevity: Roles of Calcium, the Sodium Pump, PIEZO1, and Gardos Channels

In a healthy adult, the transport of O₂ and CO₂ between lungs and tissues is performed by about 2 · 10¹³ red blood cells, of which around 1.7 · 10¹¹ are renewed every day, a turnover resulting from an average circulatory lifespan of about 120 days. Cellular lifespan is the result of an evolutionary balance between the energy costs of maintaining cells in a fit functional state versus cell renewal. In this Review we examine how the set of passive and active membrane transporters of the mature red blood cells interact to maximize their circulatory longevity thus minimizing costs on expensive cell turnover. Red blood cell deformability is critical for optimal rheology and gas exchange functionality during capillary flow, best fulfilled when the volume of each human red blood cell is kept at a fraction of about 0.55-0.60 of the maximal spherical volume allowed by its membrane area, the optimal-volume-ratio range. The extent to which red blood cell volumes can be preserved within or near these narrow optimal-volume-ratio margins determines the potential for circulatory longevity. We show that the low cation permeability of red blood cells allows volume stability to be achieved with extraordinary cost-efficiency, favouring cell longevity over cell turnover. We suggest a mechanism by which the interplay of a declining sodium pump and two passive membrane transporters, the mechanosensitive PIEZO1 channel, a candidate mediator of P_sickle in sickle cells, and the Ca²⁺-sensitive, K⁺-selective Gardos channel, can implement red blood cell volume stability around the optimal-volume-ratio range, as required for extended circulatory longevity.

The Action of Red Cell Calcium Ions on Human Erythrophagocytosis in Vitro

In the present work we have studied in vitro the effect of increasing red cell Ca²⁺ ions on human erythrophagocytosis by peripheral monocyte-derived autologous macrophages. In addition, the relative contribution to phagocytosis of phosphatidylserine exposure, autologous IgG binding, complement deposition and Gárdos channel activity was also investigated. Monocytes were obtained after ficoll-hypaque fractionation and induced to transform by adherence to glass coverslips, for 24 h at 37°C in a RPMI medium, containing 10% fetal calf serum. Red blood cells (RBC) were loaded with Ca²⁺ using 10 μM A23187 and 1 mM Ca-EGTA buffers, in the absence of Mg²⁺. Ca²⁺-loaded cells were transferred to above coverslips and incubated for 2 h at 37°C under various experimental conditions, after which phagocytosis was assessed by light microscopy. Confirming earlier findings, phagocytosis depended on internal Ca²⁺. Accordingly; it was linearly raised from about 2–15% by increasing the free Ca²⁺ content of the loading solution from 0.5 to 20 μM, respectively. Such a linear increase was virtually doubled by the presence of 40% autologous serum. At 7 μM Ca²⁺, the phagocytosis degree attained with serum was practically equal to that obtained with either 2 mg/ml affinity-purified IgG or 40% IgG-depleted serum. However, phagocytosis was reduced to levels found with Ca²⁺ alone when IgG-depleted serum was inactivated by heat, implying an involvement of complement. On the other hand, phagocytosis in the absence of serum was markedly reduced by preincubating macrophages with phosphatidylserine-containing liposomes. In contrast, a similar incubation in the presence of serum affected it partially whereas employing liposomes made only of phosphatidylcholine essentially had no effect. Significantly, the Gárdos channel inhibitors clotrimazole (2 μM) and TRAM-34 (100 nM) fully blocked serum-dependent phagocytosis. These findings show that a raised internal Ca²⁺ promotes erythrophagocytosis by independently triggering phosphatidylserine externalization, complement deposition and IgG binding. Serum appeared to stimulate phagocytosis in a way dependent on Gárdos activity. It seems likely that Ca²⁺ promoted IgG-binding to erythrocytes via Gárdos channel activation. This can be an important signal for clearance of senescent human erythrocytes under physiological conditions.

Antibodies to Senescent Antigen and C3 Are Not Required for Normal Red Blood Cell Lifespan in a Murine Model

Red blood cells (RBCs) have a well-defined lifespan, indicating a mechanism by which senescent cells of a certain age are removed from circulation. However, the specifics by which senescent cells are recognized and removed are poorly understood. There are multiple competing hypotheses for this process, perhaps the most commonly cited is that senescent RBCs expose neoantigens [or senescent antigen(s)] that are then recognized by naturally occurring antibodies, which opsonize the senescent cells and result in clearance from circulation. While there are a large volume of published data to indicate that older RBCs accumulate increased levels of antibody on their surface, to the best of our knowledge, the causal role of such antibodies in clearance has not been rigorously assessed. In the current report, we demonstrate that RBC lifespan and clearance patterns are not altered in mice deficient in antibodies, in C3 protein, or missing both. These data demonstrate that neither antibody nor C3 is required for clearance of senescent RBCs, and questions if they are even involved, in a murine model of RBC lifespan.

Diversity and Versatility of Phagocytosis: Roles in Innate Immunity, Tissue Remodeling, and Homeostasis

Phagocytosis, a critical early event in the microbicidal response of neutrophils, is now appreciated to serve multiple functions in a variety of cell types. Professional phagocytes play a central role in innate immunity by eliminating pathogenic bacteria, fungi and malignant cells, and contribute to adaptive immunity by presenting antigens to lymphocytes. In addition, phagocytes play a part in tissue remodeling and maintain overall homeostasis by disposing of apoptotic cells, a task shared by non-professional phagocytes, often of epithelial origin. This functional versatility is supported by a vast array of receptors capable of recognizing a striking variety of foreign and endogenous ligands. Here we present an abbreviated overview of the different types of phagocytes, their varied modes of signaling and particle engulfment, and the multiple physiological roles of phagocytosis.

Single amino acid fingerprinting of the human antibody repertoire with high density peptide arrays

The antibody species that patrol in a patient's blood are an invaluable part of the immune system. While most of them shield us from life-threatening infections, some of them do harm in autoimmune diseases. If we knew exactly all the antigens that elicited all the antibody species within a group of patients, we could learn which ones correlate with immune protection, are irrelevant, or do harm. Here, we demonstrate an approach to this question: First, we use a plethora of phage-displayed peptides to identify many different serum antibody binding peptides. Next, we synthesize identified peptides in the array format and rescreen the serum used for phage panning to validate antibody binding peptides. Finally, we systematically vary the sequence of validated antibody binding peptides to identify those amino acids within the peptides that are crucial for binding "their" antibody species. The resulting immune fingerprints can then be used to trace them back to potential antigens. We investigated the serum of an individual in this pipeline, which led to the identification of 73 antibody fingerprints. Some fingerprints could be traced back to their most likely antigen, for example the immunodominant capsid protein VP1 of enteroviruses, most likely elicited by the ubiquitous poliovirus vaccination. Thus, with our approach, it is possible, to pinpoint those antibody species that correlate with a certain antigen, without any pre-information. This can help to unravel hitherto enigmatic diseases.

From the Cradle to the Grave: The Role of Macrophages in Erythropoiesis and Erythrophagocytosis

Erythropoiesis is a highly regulated process where sequential events ensure the proper differentiation of hematopoietic stem cells into, ultimately, red blood cells (RBCs). Macrophages in the bone marrow play an important role in hematopoiesis by providing signals that induce differentiation and proliferation of the earliest committed erythroid progenitors. Subsequent differentiation toward the erythroblast stage is accompanied by the formation of so-called erythroblastic islands where a central macrophage provides further cues to induce erythroblast differentiation, expansion, and hemoglobinization. Finally, erythroblasts extrude their nuclei that are phagocytosed by macrophages whereas the reticulocytes are released into the circulation. While in circulation, RBCs slowly accumulate damage that is repaired by macrophages of the spleen. Finally, after 120 days of circulation, senescent RBCs are removed from the circulation by splenic and liver macrophages. Macrophages are thus important for RBCs throughout their lifespan. Finally, in a range of diseases, the delicate interplay between macrophages and both developing and mature RBCs is disturbed. Here, we review the current knowledge on the contribution of macrophages to erythropoiesis and erythrophagocytosis in health and disease.

Neuroprotective effects of antibodies on retinal ganglion cells in an adolescent retina organ culture

Glaucoma, a neurodegenerative disease, is characterized by a progressive loss of retinal ganglion cells (rgc). Up- and down-regulated autoantibody immunoreactivities in glaucoma patients have been demonstrated. Previous studies showed protective effects of down-regulated antibodies [gamma (γ)-synuclein and glial fibrillary acidic protein [GFAP]) on neuroretinal cells. The aim of this study was to test these protective antibody effects on rgc in an organ culture model and to get a better understanding of cell-cell interactions of the retina in the context of the protective effect. We used an adolescent retinal organ culture (pig) with an incubation time of up to 4 days. Retinal explants were incubated with different antibodies for 24 h (anti-GFAP, anti-γ-synuclein and anti-myoglobin antibody as a control). Brn3a and TUNEL staining were performed. We also conducted glutamine synthetase staining and quantification of the retinal explants. Mass spectrometry analyses were performed as well as protein analyses via microarray. We detected a continuous decrease of rgc/mm in the retinal explants throughout the 4 days of incubation with increased TUNEL rgc staining. Immunohistochemical analyses showed a protective effect of anti-γ-synuclein (increased rgc/mm of 41%) and anti-GFAP antibodies (increased rgc/mm of 37%). Mass spectrometric, microarray and immunohistochemical analyses demonstrated Müller cell involvement and decreased endoplasmic reticulum stress response in the antibody-treated retinae. We could detect that the tested antibodies have a protective effect on rgc which seems to be the result of reduced stress levels in the retina as well as a shift of glutamine synthetase localization in the endfeet of the Müller cells towards the inner retinal layer. Loss of retinal ganglion cells (rgc) in glaucoma leads to blindness. Several antibodies are down-regulated in glaucoma patients. Our aim was to test if these antibodies have a protective effect of rgc in a retinal organ culture. This could be shown with an increase of rgc numbers. This effect results through reduced stress levels and the shift of glutamine synthetase localization.

Single Molecule Studies of the Diffusion of Band 3 in Sickle Cell Erythrocytes

Sickle cell disease (SCD) is caused by an inherited mutation in hemoglobin that leads to sickle hemoglobin (HbS) polymerization and premature HbS denaturation. Previous publications have shown that HbS denaturation is followed by binding of denatured HbS (a.k.a. hemichromes) to band 3, the consequent clustering of band 3 in the plane of the erythrocyte membrane that in turn promotes binding of autologous antibodies to the clustered band 3, and removal of the antibody-coated erythrocytes from circulation. Although each step of the above process has been individually demonstrated, the fraction of band 3 that is altered by association with denatured HbS has never been determined. For this purpose, we evaluated the lateral diffusion of band 3 in normal cells, reversibly sickled cells (RSC), irreversibly sickled cells (ISC), and hemoglobin SC erythrocytes (HbSC) in order to estimate the fraction of band 3 that was diffusing more slowly due to hemichrome-induced clustering. We labeled fewer than ten band 3 molecules per intact erythrocyte with a quantum dot to avoid perturbing membrane structure and we then monitored band 3 lateral diffusion by single particle tracking. We report here that the size of the slowly diffusing population of band 3 increases in the sequence: normal cells<HbSC<RSC<ISC. We also demonstrate that the size of the compartment in which band 3 is free to diffuse decreases roughly in the same order, with band 3 diffusing in two compartments of sizes 35 and 71 nm in normal cells, but only a single compartment in HbSC cells (58 nm), RSC (45 nm) and ISC (36 nm). These data suggest that the mobility of band 3 is increasingly constrained during SCD progression, suggesting a global impact of the mutated hemoglobin on erythrocyte membrane properties.

Iron deficiency or anemia of inflammation? : Differential diagnosis and mechanisms of anemia of inflammation

Iron deficiency and immune activation are the two most frequent causes of anemia, both of which are based on disturbances of iron homeostasis. Iron deficiency anemia results from a reduction of the body’s iron content due to blood loss, inadequate dietary iron intake, its malabsorption, or increased iron demand. Immune activation drives a diversion of iron fluxes from the erythropoietic bone marrow, where hemoglobinization takes place, to storage sites, particularly the mononuclear phagocytes system in liver and spleen. This results in iron-limited erythropoiesis and anemia. This review summarizes current diagnostic and pathophysiological concepts of iron deficiency anemia and anemia of inflammation, as well as combined conditions, and provides a brief outlook on novel therapeutic options.

The Redox Cycler Plasmodione Is a Fast-Acting Antimalarial Lead Compound with Pronounced Activity against Sexual and Early Asexual Blood-Stage Parasites

Previously, we presented the chemical design of a promising series of antimalarial agents, 3-[substituted-benzyl]-menadiones, with potent in vitro and in vivo activities. Ongoing studies on the mode of action of antimalarial 3-[substituted-benzyl]-menadiones revealed that these agents disturb the redox balance of the parasitized erythrocyte by acting as redox cyclers-a strategy that is broadly recognized for the development of new antimalarial agents. Here we report a detailed parasitological characterization of the in vitro activity profile of the lead compound 3-[4-(trifluoromethyl)benzyl]-menadione 1c (henceforth called plasmodione) against intraerythrocytic stages of the human malaria parasite Plasmodium falciparum We show that plasmodione acts rapidly against asexual blood stages, thereby disrupting the clinically relevant intraerythrocytic life cycle of the parasite, and furthermore has potent activity against early gametocytes. The lead's antiplasmodial activity was unaffected by the most common mechanisms of resistance to clinically used antimalarials. Moreover, plasmodione has a low potential to induce drug resistance and a high killing speed, as observed by culturing parasites under continuous drug pressure. Drug interactions with licensed antimalarial drugs were also established using the fixed-ratio isobologram method. Initial toxicological profiling suggests that plasmodione is a safe agent for possible human use. Our studies identify plasmodione as a promising antimalarial lead compound and strongly support the future development of redox-active benzylmenadiones as antimalarial agents.

Agglutination of human erythrocytes by the interaction of Zn(2+)ion with histidine-651 on the extracellular domain of band 3

Clustering of band 3, chloride/bicarbonate exchanger, has been reported in Zn(2+)-treated human erythrocytes. However, the agglutination of human erythrocytes is also induced by the interaction of Zn(2+)ion with histidine on band 3. Identification of histidine that interacts with Zn(2+)ion remains to be determined. The Zn(2+)-induced agglutination of human erythrocytes was unaffected by chymotrypsin cleavage of the small loop region containing His-547 in the extracellular domain of band 3. On the other hand, papain digestion of the large loop region containing His-651 in band 3 inhibited such Zn(2+)-induced agglutination. Moreover, Zn(2+)-induced erythrocyte agglutination was inhibited by the peptide (ARGWVIHPLG) containing His-651, but not by the peptide such as ARGWVIRPLG, which His-651 was substituted by arginine. Among 10 kinds of animal erythrocytes tested, interestingly, no agglutination by Zn(2+)ions was observed in cow cells only that the forth amino acid in the upstream from His-669 on the large loop of cow band 3 is aspartate (Asp-665) instead of glycine. As expected, the agglutination of human erythrocytes by Zn(2+) ions was inhibited in the presence of aspartate. These data indicate that the interaction of Zn(2+) ion with His-651 residue of band 3 plays an important role in the Zn(2+)-induced agglutination of human erythrocytes.

Band 3 Erythrocyte Membrane Protein Acts as Redox Stress Sensor Leading to Its Phosphorylation by p (72) Syk

In erythrocytes, the regulation of the redox sensitive Tyr phosphorylation of band 3 and its functions are still partially defined. A role of band 3 oxidation in regulating its own phosphorylation has been previously suggested. The current study provides evidences to support this hypothesis: (i) in intact erythrocytes, at 2 mM concentration of GSH, band 3 oxidation, and phosphorylation, Syk translocation to the membrane and Syk phosphorylation responded to the same micromolar concentrations of oxidants showing identical temporal variations; (ii) the Cys residues located in the band 3 cytoplasmic domain are 20-fold more reactive than GSH; (iii) disulfide linked band 3 cytoplasmic domain docks Syk kinase; (iv) protein Tyr phosphatases are poorly inhibited at oxidant concentrations leading to massive band 3 oxidation and phosphorylation. We also observed that hemichromes binding to band 3 determined its irreversible oxidation and phosphorylation, progressive hemolysis, and serine hyperphosphorylation of different cytoskeleton proteins. Syk inhibitor suppressed the phosphorylation of band 3 also preventing serine phosphorylation changes and hemolysis. Our data suggest that band 3 acts as redox sensor regulating its own phosphorylation and that hemichromes leading to the protracted phosphorylation of band 3 may trigger a cascade of events finally leading to hemolysis.

The influence of host genetics on erythrocytes and malaria infection: is there therapeutic potential?

As parasites, Plasmodium species depend upon their host for survival. During the blood stage of their life-cycle parasites invade and reside within erythrocytes, commandeering host proteins and resources towards their own ends, and dramatically transforming the host cell. Parasites aptly avoid immune detection by minimizing the exposure of parasite proteins and removing themselves from circulation through cytoadherence. Erythrocytic disorders brought on by host genetic mutations can interfere with one or more of these processes, thereby providing a measure of protection against malaria to the host. This review summarizes recent findings regarding the mechanistic aspects of this protection, as mediated through the parasites interaction with abnormal erythrocytes. These novel findings include the reliance of the parasite on the host enzyme ferrochelatase, and the discovery of basigin and CD55 as obligate erythrocyte receptors for parasite invasion. The elucidation of these naturally occurring malaria resistance mechanisms is increasing the understanding of the host-parasite interaction, and as discussed below, is providing new insights into the development of therapies to prevent this disease.

Red cell physiology and signaling relevant to the critical care setting

PURPOSE OF REVIEW

Oxygen (O2) delivery, the maintenance of which is fundamental to supporting those with critical illness, is a function of blood O2 content and flow. Here, we review red blood cell (RBC) physiology relevant to disordered O2 delivery in the critically ill.

RECENT FINDINGS

Flow (rather than content) is the focus of O2 delivery regulation. O2 content is relatively fixed, whereas flow fluctuates by several orders of magnitude. Thus, blood flow volume and distribution vary to maintain coupling between O2 delivery and demand. The trapping, processing and delivery of nitric oxide (NO) by RBCs has emerged as a conserved mechanism through which regional blood flow is linked to biochemical cues of perfusion sufficiency. We will review conventional RBC physiology that influences O2 delivery (O2 affinity & rheology) and introduce a new paradigm for O2 delivery homeostasis based on coordinated gas transport and vascular signaling by RBCs.

SUMMARY

By coordinating vascular signaling in a fashion that links O2 and NO flux, RBCs couple vessel caliber (and thus blood flow) to O2 need in tissue. Malfunction of this signaling system is implicated in a wide array of pathophysiologies and may be explanatory for the dysoxia frequently encountered in the critical care setting.

Treatment with garlic restores membrane thiol content and ameliorates lead induced early death of erythrocytes in mice

Sequelae of chronic lead (Pb(2+) ) toxicity includes anemia that is partially due to early death of erythrocytes characterized by excess accumulation of ROS and downregulation of antioxidant system causing oxidative stress and externalization of phosphatidylserine. In this study, pathophysiological based therapeutic application of garlic was evaluated against erythrocyte death. Results suggest that garlic administration prevents oxidative stress, restored the antioxidant balance in erythrocytes of Pb(2+) exposed mice. Moreover, in vitro studies revealed that activity of both scramblase and aminophospholipid translocase could be changed by modifying the critical sulfhydryl groups in presence of dithiothreitol during Pb(2+) exposure. Data also indicated that garlic treatment in Pb(2+) exposed mice exhibited sharp decline in PS exposure and increase in erythrocyte membrane thiol group followed by increase in aminophospholipid translocase activity and decline in scramblase activity. Findings indicated that garlic has the ability to restore the lifespan of erythrocytes during Pb(2+) exposure.

On the dark side of therapies with immunoglobulin concentrates: the adverse events

Therapy by human immunoglobulin G (IgG) concentrates is a success story ongoing for decades with an ever increasing demand for this plasma product. The success of IgG concentrates on a clinical level is documented by the slowly increasing number of registered indication and the more rapid increase of the off-label uses, a topic dealt with in another contribution to this special issue of Frontiers in Immunology. A part of the success is the adverse event (AE) profile of IgG concentrates which is, even at life-long need for therapy, excellent. Transmission of pathogens in the last decade could be entirely controlled through the antecedent introduction by authorities of a regulatory network and installing quality standards by the plasma fractionation industry. The cornerstone of the regulatory network is current good manufacturing practice. Non-infectious AEs occur rarely and mainly are mild to moderate. However, in recent times, the increase in frequency of hemolytic and thrombotic AEs raised worrying questions on the possible background for these AEs. Below, we review elements of non-infectious AEs, and particularly focus on hemolysis and thrombosis. We discuss how the introduction of plasma fractionation by ion-exchange chromatography and polishing by immunoaffinity chromatographic steps might alter repertoire of specificities and influence AE profiles and efficacy of IgG concentrates.

Mechanisms tagging senescent red blood cells for clearance in healthy humans

This review focuses on the analysis and evaluation of the diverse senescence markers suggested to prime red blood cells (RBC) for clearance in humans. These tags develop in the course of biochemical and structural alterations accompanying RBC aging, as the decrease of activities of multiple enzymes, the gradual accumulation of oxidative damage, the loss of membrane in form of microvesicles, the redistribution of ions and alterations in cell volume, density, and deformability. The actual tags represent the penultimate galactosyl residues, revealed by desialylation of glycophorins, or the aggregates of the anion exchanger (band 3 protein) to which anti-galactose antibodies bind in the first and anti-band 3 naturally occurring antibodies (NAbs) in the second case. While anti-band 3 NAbs bind to the carbohydrate-free portion of band 3 aggregates in healthy humans, induced anti-lactoferrin antibodies bind to the carbohydrate-containing portion of band 3 and along with anti-band 3 NAbs may accelerated clearance of senescent RBC in patients with anti-neutrophil cytoplasmic antibodies (ANCA). Exoplasmically accessible phosphatidylserine (PS) and the alterations in the interplay between CD47 on RBC and its receptor on macrophages, signal regulatory protein alpha (SIRPalpha protein), were also reported to induce erythrocyte clearance. We discuss the relevance of each mechanism and analyze the strength of the data.

Thalassemic erythrocytes release microparticles loaded with hemichromes by redox activation of p72Syk kinase

High counts of circulating microparticles, originated from the membrane of abnormal erythrocytes, have been associated with increased thrombotic risk in hemolytic disorders. Our studies indicate that in thalassemia intermedia patients the number of circulating microparticles correlates with the capability of the thalassemic erythrocytes to release microparticles. The microparticles are characteristically loaded with hemichromes formed by denatured α-chains. This finding was substantiated by the positive correlation observed in thalassemia intermedia patients between the amount of hemichromes measured in erythrocytes, their capability to release microparticles and the levels of plasma hemichromes. We observed that hemichromes, following their binding to the cytoplasmic domain of band 3, induce the formation of disulfide band 3 dimers that are subsequently phosphorylated by p72Syk kinase. Phosphorylation of oxidized band 3 appears to be relevant for the formation of large hemichromes/band 3 clusters that, in turn, induce local membrane instability and the release of microparticles. Proteomic analysis of microparticles released from thalassemia intermedia erythrocytes indicated that, besides hemichromes and clustered band 3, the microparticles contain a characteristic set of proteins that includes catalase, heat shock protein 70, peroxiredoxin 2 and carbonic anhydrase. High amounts of immunoglobulins and C3 have also been found to be associated with microparticles, accounting for their intense phagocytosis. The effect of p72Syk kinase inhibitors on the release of microparticles from thalassemia intermedia erythrocytes may indicate new perspectives for controlling the release of circulating microparticles in hemolytic anemias.

Membrane peroxidation and methemoglobin formation are both necessary for band 3 clustering: mechanistic insights into human erythrocyte senescence

Oxidative damage and clustering of band 3 in the membrane have been implicated in the removal of senescent human erythrocytes from the circulation at the end of their 120 day life span. However, the biochemical and mechanistic events leading to band 3 cluster formation have yet to be fully defined. Here we show that while neither membrane peroxidation nor methemoglobin (MetHb) formation on their own can induce band 3 clustering in the human erythrocytes, they can do so when acting in combination. We further show that binding of MetHb to the cytoplasmic domain of band 3 in peroxidized, but not in untreated, erythrocyte membranes induces cluster formation. Age-fractionated populations of erythrocytes from normal human blood, obtained by a density gradient procedure, have allowed us to examine a subpopulation, highly enriched in senescent cells. We have found that band 3 clustering is a feature of only this small fraction, amounting to ∼0.1% of total circulating erythrocytes. These senescent cells are characterized by an increased proportion of MetHb as a result of reduced nicotinamide adenine dinucleotide-dependent reductase activity and accumulated oxidative membrane damage. These findings have allowed us to establish that the combined effects of membrane peroxidation and MetHb formation are necessary for band 3 clustering, and this is a very late event in erythrocyte life. A plausible mechanism for the combined effects of membrane peroxidation and MetHb is proposed, involving high-affinity cooperative binding of MetHb to the cytoplasmic domain of oxidized band 3, probably because of its carbonylation, rather than other forms of oxidative damage. This modification leads to dissociation of ankyrin from band 3, allowing the tetrameric MetHb to cross-link the resulting freely diffusible band 3 dimers, with formation of clusters.

Red blood cell clearance in inflammation

SUMMARY

Anemia is a frequently encountered problem in the critically ill patient. The inability to compensate for anemia includes several mechanisms, collectively referred to as anemia of inflammation: reduced production of erythropoietin, impaired bone marrow response to erythropoietin, reduced iron availability, and increased red blood cell (RBC) clearance. This review focuses on mechanisms of RBC clearance during inflammation. We state that phosphatidylserine (PS) expression in inflammation is mainly enhanced due to an increase in ceramide, caused by an increase in sphingomyelinase activity due to either platelet activating factor, tumor necrosis factor-α, or direct production by bacteria. Phagocytosis of RBCs during inflammation is mediated via RBC membrane protein band 3. Reduced deformability of RBCs seems an important feature in inflammation, also mediated by band 3 as well as by nitric oxide, reactive oxygen species, and sialic acid residues. Also, adherence of RBCs to the endothelium is increased during inflammation, most likely due to increased expression of endothelial adhesion molecules as well as PS on the RBC membrane, in combination with decreased capillary blood flow. Thereby, clearance of RBCs during inflammation shows similarities to clearance of senescent RBCs, but also has distinct entities, including increased adhesion to the endothelium.

Naturally occurring anti-band 3 antibodies in clearance of senescent and oxidatively stressed human red blood cells

SUMMARY

Naturally occurring anti-band 3 antibodies (anti-band 3 NAbs) are directed against the 55-kDa chymotryptic fragment of the anion transport protein (band 3) of red blood cells (RBCs). They bind to senescent and oxidatively stressed RBCs and induce their selective clearance. These IgG NAbs exist at low concentrations, and have a weak affinity that prevents them from actively recruiting second binding sites. Cellular senescence or oxidative damage induces a cascade of biochemical events that results in the detachment of band 3 from the cytoskeleton and in clustering of band 3 protein by bound hemichromes and Syk kinase. Clustered band 3 proteins allow bivalent binding of anti-band 3 NAbs. Bivalently bound anti-band 3 NAbs have the unique capacity to stimulate C3b deposition by preferentially generating C3b2-IgG complexes, which act as potent C3 convertase precursors of the alternative complement pathway. Antibody binding not only to clustered, but also to oligomerized band 3 protein further increases if the human plasma also contains induced anti-lactoferrin antibodies. These bind to the polylactosaminyl oligosaccharide, a carbohydrate that exists in lactoferrin and in the 38-kDa fragment of band 3 protein. Anti-lactoferrin antibodies are found primarily in plasma of patients with autoimmune diseases and who have anti-neutrophil cytoplasmic antibodies (ANCA).

Immunoregulation by naturally occurring and disease-associated autoantibodies : binding to cytokines and their role in regulation of T-cell responses

The role of naturally occurring autoantibodies (NAbs) in homeostasis and in disease manifestations is poorly understood. In the present chapter, we review how NAbs may interfere with the cytokine network and how NAbs, through formation of complement-activating immune complexes with soluble self-antigens, may promote the uptake and presentation of self-molecules by antigen-presenting cells. Both naturally occurring and disease-associated autoantibodies against a variety of cytokines have been reported, including NAbs against interleukin (IL)-1α, IL-6, IL-8, IL-10, granulocyte-macrophage colony-stimulating factor, interferon (IFN)-α, IFN-β, IFN-γ, macrophage chemotactic protein-1 and IL-21. NAbs against a variety of other self-antigens have also been reported, and using thyroglobulin as an example we discuss how NAbs are capable of promoting uptake of immune complexes via complement receptors and Fc-receptors on antigen-presenting cells and thereby regulate T-cell activity. Knowledge of the influence of NAbs against cytokines on immune homeostasis is likely to have wide-ranging implications both in understanding pathogenesis and in treatment of many immunoinflammatory disorders, including a number of autoimmune and autoinflammatory diseases.

Human red blood cell aging: correlative changes in surface charge and cell properties

Red blood cells (RBCs) during microcirculation, aging and storage, lose N-acetylneuraminic acid (NANA) and other biomaterials thereby altering cell structures, some properties and functions. Such cell damage very likely underlies the serious adverse effects of blood transfusion. However, a controversy has remained since 1961–1977 as to whether with aging, the RBCs, suffering loss of NANA, do have a decreased charge density. Any correlation between the changes in the cell properties with cell aging is also not clear. Therefore, to remove the ambiguity and uncertainty, we carried out multiparameteric studies on Percoll fractions of blood of 38 volunteers (lightest-young-Y-RBCs, densest-old-O-RBCs, two middle fractions).We found that there were striking differences between the properties of Y-RBCs and O-RBCs. The ζ-potential of Y-RBCs decreased gradually with aging. Studies in parallel on RBC fractions incubated with both positively charged quantum dots and Sambucus Nigra-fluorescein isothiocyanate (FITC) along with their ζ-potentials provide for the first time direct visual evidence about the lesser amount of charge density and NANA on O-RBCs, and a collinear decrease in their respective ζ-potentials. Close correlation was found between the surface charge on an aging RBC and its structure and functions, from the cell morphology, the membrane deformability to the intracellular Hb structure and oxidation ability. This quantitative approach not only clarifies the picture but also has implications in biology and medicine.