Glycophorin A-mediated haemolysis of normal human erythrocytes: evidence for antigen aggregation in the pathogenesis of immune haemolysis

Alpha hemolysin of E. coli induces hemolysis of human erythrocytes independently of toxin interaction with membrane proteins

Alpha hemolysin (HlyA) is a hemolytic and cytotoxic protein secreted by uropathogenic strains of E. coli. The role of glycophorins (GPs) as putative receptors for HlyA binding to red blood cells (RBCs) has been debated. Experiments using anti-GPA/GPB antibodies and a GPA-specific epitope nanobody to block HlyA-GP binding on hRBCs, showed no effect on hemolytic activity. Similarly, the hemolysis induced by HlyA remained unaffected when hRBCs from a GPAnull/GPBnull variant were used. Surface Plasmon Resonance experiments revealed similar values of the dissociation constant between GPA and either HlyA, ProHlyA (inactive protoxin), HlyAΔ914-936 (mutant of HlyA lacking the binding domain to GPA) or human serum albumin, indicating that the binding between the proteins and GPA is not specific. Although far Western blot followed by mass spectroscopy analyses suggested that HlyA interacts with Band 3 and spectrins, hemolytic experiments on spectrin-depleted hRBCs and spherocytes, indicated these proteins do not mediate the hemolytic process. Our results unequivocally demonstrate that neither glycophorins, nor Band 3 and spectrins mediate the cytotoxic activity of HlyA on hRBCs, thereby challenging the HlyA-receptor hypothesis. This finding holds significant relevance for the design of anti-toxin therapeutic strategies, particularly in light of the growing antibiotic resistance exhibited by bacteria.

RBC membrane biomechanics and Plasmodium falciparum invasion: probing beyond ligand-receptor interactions

A critical step in malaria blood-stage infections is the invasion of red blood cells (RBCs) by merozoite forms of the Plasmodium parasite. Much progress has been made in defining the parasite ligands and host receptors that mediate this critical step. However, less well understood are the RBC biophysical determinants that influence parasite invasion. In this review we explore how Plasmodium falciparum merozoites interact with the RBC membrane during invasion to modulate RBC deformability and facilitate invasion. We further highlight RBC biomechanics-related polymorphisms that might have been selected for in human populations due to their ability to reduce parasite invasion. Such an understanding will reveal the translational potential of targeting host pathways affecting RBC biomechanical properties for the treatment of malaria.

Ligation of Glycophorin A Generates Reactive Oxygen Species Leading to Decreased Red Blood Cell Function

Acute, inflammatory conditions associated with dysregulated complement activation are characterized by significant increases in blood concentration of reactive oxygen species (ROS) and ATP. The mechanisms by which these molecules arise are not fully understood. In this study, using luminometric- and fluorescence-based methods, we show that ligation of glycophorin A (GPA) on human red blood cells (RBCs) results in a 2.1-fold, NADPH-oxidase-dependent increase in intracellular ROS that, in turn, trigger multiple downstream cascades leading to caspase-3 activation, ATP release, and increased band 3 phosphorylation. Functionally, using 2D microchannels to assess membrane deformability, GPS-ligated RBCs travel 33% slower than control RBCs, and lipid mobility was hindered by 10% using fluorescence recovery after photobleaching (FRAP). These outcomes were preventable by pretreating RBCs with cell-permeable ROS scavenger glutathione monoethyl ester (GSH-ME). Our results obtained in vitro using anti-GPA antibodies were validated using complement-altered RBCs isolated from control and septic patients. Our results suggest that during inflammatory conditions, circulating RBCs significantly contribute to capillary flow dysfunctions, and constitute an important but overlooked source of intravascular ROS and ATP, both critical mediators responsible for endothelial cell activation, microcirculation impairment, platelet activation, as well as long-term dysregulated adaptive and innate immune responses.

A monoclonal antibody with anti-D-like activity in murine immune thrombocytopenia requires Fc domain function for immune thrombocytopenia ameliorative effects

BACKGROUND

The mechanism of action of anti-D in ameliorating immune thrombocytopenia (ITP) remains unclear. The monoclonal antibody (MoAb) Ter119, which targets murine red blood cells (RBCs), has been shown to mimic the effect of anti-D in improving antibody-mediated murine ITP. The mechanism of Ter119-mediated ITP amelioration, especially the role of the antigen-binding and Fc domains, remains untested. A functional Fc domain is crucial for many therapeutic MoAb activity; therefore, the requirement of Ter119 Fc domain in ITP amelioration is investigated using outbred CD-1 mice.

STUDY DESIGN AND METHODS

Ter119 variants, including Ter119 F(ab')2 fragments, deglycosylated Ter119, and afucosylated Ter119, were generated to test their effect in ameliorating antibody-induced murine ITP. In vivo inhibition of FcγRIII and FcγRIIB was achieved using the Fab fragment of the FcγRIII/FcγRIIB-specific MoAb 2.4G2.

RESULTS

Ter119 F(ab')2 fragments and deglycosylated Ter119 were unable to ameliorate murine ITP or mediate phagocytosis of RBCs by RAW264.7 macrophages in vitro. Inhibition of FcγRIII and FcγRIIB, as well as Ter119 defucosylation, do not affect Ter119-mediated ITP amelioration.

CONCLUSION

The Fc domain of Ter119, as well as its Fc glycosylation, is required for Ter119-mediated ITP amelioration. Moreover, both Fc and Fc glycosylation are required for Ter119-mediated phagocytosis in vitro. These findings demonstrate the importance of the Fc domain in a therapeutic MoAb with anti-D-like activity.

Autoimmune haemolytic anaemia: a review and report of four cases

Treatment of autoimmune haemolytic anaemia is still a challenge to clinicians. Even today it may be lethal. Half of the cases are secondary due to an underlying disease, and the others are primary or idiopathic cases. According to the specificity and type of autoantibodies there are warm and cold type forms of autoimmune haemolytic anaemia. The hallmark of the diagnosis is to detect the presence of haemolysis by clinical and laboratory signs and detect the underlying autoantibodies. Treatment of autoimmune haemolytic anaemia is still a challenge to clinicians. We still loose patients due to excessive haemolysis or severe infections caused by immunosuppression. First line treatment is corticosteroids. Other immunosuppressive agents like: cyclophosphamide, azathioprine, cyclosporine or the off label rituximab can be used in case of corticosteroid refractoriness. Splenectomy is a considerable option in selective cases. The authors discuss treatment options and highlight difficulties by presenting 4 cases. Orv. Hetil., 2015, 156(11), 449–456.

Membrane damages under high pressure of human erythrocytes agglutinated by concanavalin A

Human erythrocytes are agglutinated by lectins such as concanavalin A (Con A). The behaviors of agglutinated erythrocytes under pressure are less well understood. Here, we report the effects of erythrocyte agglutination on pressure-induced membrane damages. Small clumps of intact erythrocytes by Con A were dissociated by a pressure of 200 MPa. Further, the observation by scanning electron microscopy demonstrated the generation of vesicles, fragmented particles, and membrane hole. On the other hand, large clumps of trypsin-digested erythrocytes by Con A seemed to be stable against 200 MPa. However, the erythrocytes dissociated from such pressure-treated clumps by methyl α-mannopyranoside also showed the existence of vesicles and fragmented particles except for the membrane hole. Pressure-induced hemolysis was greatly suppressed in such large clumps. Similar suppressive effects were observed in erythrocytes packed by centrifugation. However, the hemolysis occurred when the erythrocytes dissociated from 200 MPa-treated large clumps by methyl α-mannopyranoside were incubated at 0°C and atmospheric pressure. Pyrene excimer fluorescence due to spectrin denaturation was observed in Con A-agglutinated ghosts that were exposed to a pressure of 200 MPa. These results suggest that upon pressure treatment of tightly agglutinated erythrocytes, the hemolysis is greatly suppressed, but membrane damages occur such as spectrin denaturation and vesiculation.

Antibody specific for the glycophorin A complex mediates intravenous immune globulin-resistant anemia in a murine model

BACKGROUND

Therapy for patients with autoimmune hemolytic anemia (AHA) remains a major challenge. Patients with glycophorin A (GPA)-specific immunoglobulin G antibodies can have severe hemolysis, which may occur by mechanisms independent from traditional macrophage-dependent Fcγ receptor (FcγR)-mediated extravascular hemolysis. As intravenous immune globulin (IVIG) is known to display its beneficial effects in FcγR-mediated cytopenias, and IVIG responses in AHA are inconsistent at best, we sought to gain insight into the mechanism of anemia by a GPA complex-specific monoclonal antibody (TER119) in a mouse model of immune hemolytic anemia and evaluate the therapeutic effect of IVIG.

STUDY DESIGN AND METHODS

The anemic effect of the TER119 antibody was studied in vitro by incubation of mouse RBC with the antibody and in vivo by infusing the antibody into normal mice versus mice genetically deficient for the Fc receptor γ chain (Fcγ), complement C3, mice naturally deficient in complement C5, and splenectomized mice. IVIG efficacy in anemia was determined by treating mice with an intensive IVIG dosing regimen.

RESULTS

The TER119-mediated anemia was independent of classical FcγR-, C3-, and C5-dependent mechanisms, but occurred by a mechanism consistent with RBC agglutination. In accordance with agglutination, the presence of the spleen accelerated the anemia observed but anemia could still occur in splenectomized mice. IVIG did not significantly affect the induction of anemia by TER119.

CONCLUSION

The mechanism of anemia induced by AHA-causing antibodies may be an important factor to consider in the response to therapy with IVIG.

The James Blundell Award Lecture 2007: do we really understand immune red cell destruction?

We have learned a great deal about immune red blood cell (RBC) destruction since the elaboration of biochemical/immunological interactions of antibodies, complement and macrophages during the past 50 years. We first learned about the direct lysis of RBCs involving complement. We then learned of the role of the macrophage (particularly in the spleen and the liver) in initiating phagocytosis and antibody-dependent cytotoxicity of antibody-coated RBCs. Later, as the complexities of the human complement system were unravelled, we learned that complement-coated RBCs that were not directly haemolysed could interact with macrophages and that specific complement molecules on the RBC membrane could lead to a phagocytic event or the RBC (although heavily coated with complement) could survive normally. The application of isotope-labelling procedures (e.g. (51)Cr) for RBC survival (starting in the 1950s) advanced our knowledge considerably. Advances in knowledge in immunology helped us understand the complexity of the immunoglobulins (e.g. subclasses) and the specific receptors on macrophages and their role in immune haemolysis. Nevertheless, after more than 30 years researching this area, I am sometimes embarrassed to realize how much I cannot explain. Why do some patients have severe haemolytic transfusion reactions because of antibodies that are only detectable by one technique or not detectable by any? How do we explain autoimmune haemolytic anaemia with negative direct antiglobulin tests (DATs)? Why do RBCs strongly coated with immunoglobulin (Ig)G1 or IgG3 sometimes have normal survival? Are cells, other than macrophages, involved in immune RBC destruction? Could the relative amount of cytotoxicity vs. phagocytosis explain different clinical findings and response to treatment? How do we explain 'hyperhaemolysis' in sickle cell disease? Could novel mechanisms involving IgG glycosylation, CD47, 'armed' macrophages, bystander lysis, antibody activated reactive oxygen species, natural killer cells or antibody perturbation of RBC membrane be involved? Why do RBCs die after circulating for 100-120 days in healthy individuals? How should we define a 'clinically significant' antibody; how do we evaluate this? So many questions, so little time!

Cytokine storm in a mouse model of IgG-mediated hemolytic transfusion reactions

Cytokines are hypothesized to play a central role in the pathophysiology of IgG-mediated hemolytic transfusion reactions (HTRs), and deeper understanding is required for improving therapy for these events. After establishing well-defined mouse models of HTRs, we tested whether cytokines were involved. Red blood cells (RBCs) from human glycophorin A transgenic (hGPA-Tg) or wild-type (WT) mice were transfused into non-Tg recipients passively immunized with monoclonal antibodies (Mabs). Only transfusions of incompatible RBCs induced IgG-mediated HTRs, exemplified by rapid clearance and hemoglobinuria. Very high plasma levels of monocyte chemoattractant protein-1 (MCP-1) and interleukin-6 (IL-6), and lower levels of tumor necrosis factor-alpha (TNF-alpha), were induced after incompatible transfusion. No significant changes in IL-10, IL-12, or interferon-gamma (IFN-gamma) levels were observed. The proinflammatory cytokines elaborated in this in vivo mouse model are also implicated in the systemic inflammatory response syndrome (SIRS) and confirm the hypothesis that cytokine storm occurs as a result of HTRs.

A novel mechanism of erythrocyte capture from circulation in humans

OBJECTIVE

The capture of blood cells from the circulation is mediated by highly specialized adhesion molecules. These molecules contribute to the specificity of recruitment for various subsets. Here, we used a simple substrate of hyaluronic acid to investigate the specificity of CD44-mediated recruitment from human whole blood under shear conditions.

MATERIALS AND METHODS

Human whole blood was perfused through a parallel-plate flow chamber, which mimics intravascular conditions. Microscopy was used to directly observe blood-cell interactions with adhesion molecule substrates.

RESULTS

Erythrocytes, but not leukocytes, efficiently tethered to and rolled on the hyaluronic acid substrate. These interactions were demonstrated to be mediated by CD44 and regulated by the sialic acid content of the cells. Inflammatory stimuli did not result in enhanced erythrocyte rolling. Rather, interactions were restricted to aged erythrocytes approaching senescence. This mechanism of erythrocyte capture from the blood flow was found to be restricted to primates and not conserved across mammalian species.

CONCLUSION

This is the first report of erythrocyte tethering and rolling under shear conditions, a behavior, until now, thought to be exclusive to leukocytes. It may represent an important mechanism to identify, capture, and clear old erythrocytes during normal homeostasis or clot formation.

Mouse models of IgG- and IgM-mediated hemolysis

Well-characterized mouse models of allo-immune antibody-mediated hemolysis would provide a valuable approach for gaining greater insight into the pathophysiology of hemolytic transfusion reactions. To this end, mouse red blood cells (mRBCs) from human glycophorin A transgenic (hGPA-Tg) donor mice were transfused into non-Tg recipients that had been passively immunized with IgG or IgM hGPA-specific monoclonal antibodies (mAbs). In this novel murine "blood group system," mRBCs from hGPA-Tg mice are "antigen positive" and mRBCs from non-Tg mice are "antigen negative." Passive immunization of non-Tg mice with the IgG1 10F7 and IgG3 NaM10-2H12 anti-hGPA mAbs each induced rapid clearance of incompatible transfused hGPA-Tg-mRBCs in a dose-response manner. Using various knockout mice as transfusion recipients, both the complement system and activating Fcgamma receptors were found to be important in the clearance of incompatible mRBCs by each of these IgG mAbs. In addition, the IgM E4 anti-hGPA mAb induced complement-dependent intravascular hemolysis of transfused incompatible hGPA-Tg-mRBCs accompanied by gross hemoglobinuria. These initial studies validate the relevance of these new mouse models for addressing important questions in the field of transfusion medicine.

Immune hemolytic anemia associated with negative routine serology

Immune hemolytic anemia can occur in patients who have no antibodies detectable by routine procedures (direct [DAT] and indirect [IAT] antiglobulin tests). DAT-negative autoimmune hemolytic anemias (AIHAs) represent 5% to 10% of all AIHAs. Three causes have been identified: (1) small numbers of red blood cell (RBC)-bound IgG molecules below the threshold of the DAT; (2) IgA and IgM autoantibodies; and (3) low-affinity autoantibodies. Antibody-independent cytotoxic events caused by natural killer (NK) cells have also been implicated. DATs are sometimes found to be positive when tested by reference laboratories, due to poor technique in reading antiglobulin tests in hospital laboratories. Hemolytic transfusion reactions also can occur when no alloantibodies are detectable by routine procedures. In some cases antibodies can be detected by special serologic procedures (such as the Polybrene test); in other instances phenotypically matched RBCs survive well and a specific antigen can be shown to be involved, suggesting a specificity (like anti-C) that is undetectable by any technique. Antibodies other than to blood group antigens, such as human leukocyte antigen (HLA) antibodies, may sometimes be involved.

Hemolysis of erythrocytes by granulysin-derived peptides but not by granulysin

Granulysin, a 9-kDa protein localized in human cytolytic T lymphocytes and natural killer cell granules, is cytolytic against tumors and microbes but not against red blood cells. Synthetic peptides corresponding to the central region of granulysin recapitulate the lytic activity of the intact molecule, and some peptides cause hemolysis of red blood cells. Peptides in which cysteine residues were replaced by serine maintain their activity against microbes but lose activity against human cells, suggesting their potential as antibiotics. Studies were undertaken to determine the mechanism of resistance of red blood cells to granulysin and sensitivity to a subset of granulysin-derived peptides. Granulysin lyses immature reticulocytes, which have mitochondria, but not red blood cells. Granulysin lyses U937 cells but not U937 cells lacking mitochondrial DNA and a functional respiratory chain (U937rho(o) degrees cells), further demonstrating the requirement of intact mitochondria for granulysin-mediated death. Peptide G8, which corresponds to helix 2/loop 2/helix 3, lyses red blood cells, while peptide G9, which is identical except that the cysteine residues were replaced by serine, does not lyse red blood cells. Granulysin peptide-induced hemolysis is markedly inhibited by an anion transporter inhibitor and by Na(+), K(+), and Ca(2+) channel blockers but not by Na(+)/K(+) pump, cotransport, or Cl(-) channel blockers. Although recombinant granulysin and G9 peptide do not induce hemolysis, they both competitively inhibit G8-induced hemolysis. The finding that some derivatives of granulysin are hemolytic may have important implications for the design of granulysin-based antimicrobial therapeutics.

Evidence for a mechanosensitive calcium influx into red cells

Red cells exposed to glycophorin A reactive antibodies and lectins develop a non-specific cation permeability. To determine if this might be due to the activation of a non-selective mechanosensitive channel we have subjected red cells, loaded with a calcium responsive fluorescent probe, to filtration through 5 and 3 microm pores. Calcium entered 28% of normal red cells at the moment of deformation when 3 microm filtered, a finding consistent with the transient activation of a mechanosensitive channel. Red cells containing hemoglobin AC and AS had enhanced calcium responses to filtration. An increased influx of calcium in hemoglobin disorders might play a role in providing protection against Falciparum malaria.