Erythrocyte membrane proteins reactive with human (warm-reacting) anti-red cell autoantibodies

The Clinical Pictures of Autoimmune Hemolytic Anemia

Autoimmune hemolytic anemia is characterized by shortened red blood cell survival and a positive Coombs test. The responsible autoantibodies may be either warm reactive or cold reactive. The rate of hemolysis and the severity of the anemia may vary from mild to severe and life-threatening. Diagnosis is made in the laboratory by the findings of anemia, reticulocytosis, a positive Coombs test, and specific serologic tests. The prognosis is generally good but renal failure and death sometimes occur, especially in cases mediated by drugs.

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.

Lethal autoimmune hemagglutination due to an immunoglobulin A autoagglutinin with Band 3 specificity

BACKGROUND

We describe a patient with a high-titer warm immunoglobulin (Ig)A autoantibody resulting in death due to hemagglutination rather than to hemolysis.

CASE REPORT

A 47-year-old male patient presented with an intriguing pronounced vascular erythema of the skin. A livedo reticularis associated with cold agglutinin of high thermal amplitude was suspected. The patient's condition unexpectedly and abruptly deteriorated resulting in death 3 days after admission.

STUDY DESIGN AND METHODS

Conventional serologic procedures and immunochemical methods were used.

RESULTS

Serologic and immunochemical examinations revealed a warm IgA autoantibody of high titer with anti-Band 3 specificity. Although the patient presented with severe anemia, only mild signs of hemolysis were observed, with no evidence of complement activation. The autopsy revealed an enormous accumulation of agglutinated red blood cells in liver and spleen and a B-cell lymphoma and cerebral edema. Thus, the patient's death was largely caused by hypoxia related to hemagglutination rather than to hemolysis and/or anemia per se.

CONCLUSION

Strongly hemagglutinating antibodies may not only cause immune hemolysis but also hypoxia due to intravascular hemagglutination.

Characterization of a novel hemolytic activity of human IgG fractions arising from diversity in protein and oligosaccharide components

Human IgG is a well-established multifunctional antigen specific immunoglobulin molecule of the adaptive immune system. However, an antigen nonspecific immunological function of human IgG has never been reported. In this study, human IgG was isolated using ammonium sulfate fractional precipitation and diethylaminoethanol (DEAE) cellulose 52 ion exchange chromatography, from which h-IgG and hs-IgG fractions were purified on the basis of their differential binding to rabbit anti-shrimp hemocyanin antibody (h) and rabbit anti-shrimp hemocyanin's small subunit antibody (hs), respectively. We found that h-IgG had a higher hemolytic activity than hs-IgG against erythrocytes from humans, rabbits, mice and chickens, whereas the control IgG showed negligible activity. h-IgG could interact directly with erythrocyte membranes, and this interaction was suppressed by high molecular weight osmoprotectants, showing that it may follow a colloid-osmotic mechanism. In comparative proteomics and glycomics studies, h-IgG and hs-IgG yielded 20 and 5 significantly altered protein spots, respectively, on a 2-D gel. The mean carbohydrate content of h-IgG and hs-IgG was approximately 3.6- and 2-fold higher than that of IgG, respectively, and the α-d-mannose/α-d-glucose content was in the order of h-IgG>hs-IgG>IgG. In this study, a novel antigen nonspecific immune property of human IgG was investigated, and the diversity in the protein constituents and glycosylation levels may have functional signficance.

Immunotherapy treatments of warm autoimmune hemolytic anemia

Warm autoimmune hemolytic anemia (WAIHA) is one of four clinical types of autoimmune hemolytic anemia (AIHA), with the characteristics of autoantibodies maximally active at body temperature. It produces a variable anemia—sometimes mild and sometimes severe. With respect to the absence or presence of an underlying condition, WAIHA is either idiopathic (primary) or secondary, which determines the treatment strategies in practice. Conventional treatments include immune suppression with corticosteroids and, in some cases, splenectomy. In recent years, the number of clinical studies with monoclonal antibodies and immunosuppressants in the treatment of WAIHA increased as the knowledge of autoimmunity mechanisms extended. This thread of developing new tools of treating WAIHA is well exemplified with the success in using anti-CD20 monoclonal antibody, Rituximab. Following this success, other treatment methods based on the immune mechanisms of WAIHA have emerged. We reviewed these newly developed immunotherapy treatments here in order to provide the clinicians with more options in selecting the best therapy for patients with WAIHA, hoping to stimulate researchers to find more novel immunotherapy strategies.

A case of autoimmune hemolytic anemia with anti-D specificity in a 1-year-old child

Although antibodies to antigens in the Rh blood group system are common causes of warm autoimmune hemolytic anemia, specificity for only the D antigen is rare in autoimmune hemolysis in pediatric patients. This case reports an anti-D associated with severe hemolytic anemia (Hb = 2.1 g/dL) in a previously healthy 14-month-old child who presented with a 3-day history of low-grade fevers and vomiting. Because of his severe anemia, on admission to the hospital he was found to have altered mental status, metabolic acidosis, abnormal liver function tests, and a severe coagulopathy. He was successfully resuscitated with uncrossmatched units of group O, D- blood, and after corticosteroid therapy he had complete resolution of his anti-D-mediated hemolysis.

A major target for warm immunoglobulin G autoantibodies: the third external loop of Band 3

BACKGROUND

Rh proteins and the Wr(b) antigen, which results from an interaction between Band 3 and glycophorin A, are the most common targets for warm immunoglobulin (Ig)G autoantibodies. Apart from autoanti-Di(b) , a scarce specificity, IgG warm autoantibodies specific for Band 3 have never been characterized by serologic methods.

STUDY DESIGN AND METHODS

Blood samples from 120 patients with autoimmune hemolytic anemia (AIHA) and IgG-coated red blood cells (RBCs) were studied by serologic methods. Some autoantibodies were investigated by immunochemical methods.

RESULTS

Autoantibodies against the third external loop of Band 3 have a distinctive pattern of reactivity in that they fail to react after RBC treatment with α-chymotrypsin and pronase, whereas papain, ficin, and trypsin have no effect. Eleven (9%) patients had pure anti-Band 3 autoantibodies. Autoanti-Band 3 antibodies were associated with other specificities in 66 (55%) patients. Immunoprecipitation and rare RBCs from a Wu+ homozygote, known to have an unusual pattern of reactivity after protease treatment, were used to confirm the Band 3 specificity. Treatment with sodium hypochlorite, believed to oxidize the Met residue at Position 559 in the third loop, showed that these autoantibodies were heterogeneous. Most antibodies reacted optimally at 37 °C, but two patients had incomplete cold IgG autoantibodies. Unlike autoantibodies to Rh proteins, warm autoanti-Band 3 activate complement and are almost totally bound to autologous RBCs.

CONCLUSION

We describe the first cases of warm IgG autoantibodies specific for the third loop of Band 3. This external loop also appears as a major target in patients with warm antibody AIHA.

Storage-induced changes in erythrocyte membrane proteins promote recognition by autoantibodies

Physiological erythrocyte removal is associated with a selective increase in expression of neoantigens on erythrocytes and their vesicles, and subsequent autologous antibody binding and phagocytosis. Chronic erythrocyte transfusion often leads to immunization and the formation of alloantibodies and autoantibodies. We investigated whether erythrocyte storage leads to the increased expression of non-physiological antigens. Immunoprecipitations were performed with erythrocytes and vesicles from blood bank erythrocyte concentrates of increasing storage periods, using patient plasma containing erythrocyte autoantibodies. Immunoprecipitate composition was identified using proteomics. Patient plasma antibody binding increased with erythrocyte storage time, while the opposite was observed for healthy volunteer plasma, showing that pathology-associated antigenicity changes during erythrocyte storage. Several membrane proteins were identified as candidate antigens. The protein complexes that were precipitated by the patient antibodies in erythrocytes were different from the ones in the vesicles formed during erythrocyte storage, indicating that the storage-associated vesicles have a different immunization potential. Soluble immune mediators including complement factors were present in the patient plasma immunoprecipitates, but not in the allogeneic control immunoprecipitates. The results support the theory that disturbed erythrocyte aging during storage of erythrocyte concentrates contributes to transfusion-induced alloantibody and autoantibody formation.

Partial tolerance of autoreactive B and T cells to erythrocyte-specific self-antigens in mice

BACKGROUND

Breakdown of humoral tolerance to RBC antigens may lead to autoimmune hemolytic anemia, a severe and sometimes fatal disease. The underlying mechanisms behind the breakdown of humoral tolerance to RBC antigens are poorly understood.

DESIGN AND METHODS

In order to study the pathogenesis of autoimmune hemolytic anemia, we developed a murine model with RBC-specific expression of a model antigen carrying epitopes from hen egg lysozyme and ovalbumin.

RESULTS

Humoral tolerance was observed; this was not broken even by strong immunogenic stimulation (lysozyme or ovalbumin with adjuvant). Autoreactive CD4(+) T cells were detected by tetramer enrichment assays, but failed to activate or expand despite repeat stimulation, indicating a nonresponsive population rather than deletion. Adoptive transfer of autoreactive CD4(+) T cells (OT-II mice) led to autoantibody (anti-lysozyme) production by B cells in multiple anatomic compartments, including the bone marrow.

CONCLUSIONS

These data demonstrate that B cells autoreactive to RBC antigens survive in healthy mice with normal immune systems. Furthermore, autoreactive B cells are not centrally tolerized and are receptive to T-cell help. As the autoreactive T cells are present but non-responsive, these data indicate that factors that reverse T-cell non-responsiveness may be central to the pathogenesis of autoimmune hemolytic anemia.

Production of the effector cytokine interleukin-17, rather than interferon-γ, is more strongly associated with autoimmune hemolytic anemia

BACKGROUND

Interleukin-17A is the signature cytokine of the Th17 subset and drives inflammatory pathology, but its relevance to autoantibody-mediated diseases is unclear. Th1 cells secreting interferon-γ have been implicated in autoimmune hemolytic anemia, so the aim was to determine which cytokine is more closely associated with disease severity.

DESIGN AND METHODS

Interferon-γ and interleukin-17A were measured in the sera of patients with autoimmune hemolytic anemia and healthy donors, and in peripheral blood mononuclear cell cultures stimulated with autologous red blood cells, or a panel of peptides spanning red blood cell autoantigen.

RESULTS

Serum interleukin-17A, but not interferon-γ, was significantly raised in patients with autoimmune hemolytic anemia (P<0.001), and correlated with the degree of anemia. Interleukin-17A was also more prominent in the responses of peripheral blood mononuclear cells from patients with autoimmune hemolytic anemia to red blood cells, and, again unlike interferon-γ, significantly associated with more severe anemia (P<0.005). There were no interleukin-17A responses to red blood cells by peripheral blood mononuclear cells from healthy donors. Specific autoantigenic peptides were identified that elicit patients' interleukin-17A responses.

CONCLUSIONS

Interleukin-17A makes a previously unrecognized contribution to the autoimmune response in autoimmune hemolytic anemia, challenging the model that the disease is driven primarily by Th1 cells. This raises the possibility that Th17, rather than Th1, cells should be the target for therapy.

Serum and organ-associated anti-hemoglobin humoral autoreactivity: association with anti-Sm responses and inflammation

The release of hemoglobin (Hb) occurs in some infectious and autoimmune diseases characterized by inflammation. As levels of haptoglobin (Hp) fall, free Hb can cause pathology. Humoral autoreactivity to human Hb was demonstrated in the sera of systemic lupus erythematosus (SLE), leishmania and malaria patients. Serum anti-murine Hb antibody levels in lupus-prone mice also exhibited an age-dependent increase, with progressive organ sequestration; significant isotypic correlation was observed with anti-dsDNA antibodies. A suggestive link between anti-Hb and anti-Sm responses was observed: Human lupus sera expressing anti-Sm antibody reactivity preferentially contained heightened levels of anti-Hb autoantibodies, and immunization of lupus-prone mice with Sm led to enhanced anti-murine Hb reactivity. Human and murine anti-Hb monoclonal antibodies were generated, some of which were preferentially reactive toward disease-associated methemoglobin. Epitope-mapping studies revealed evidence of intra-molecular cross-reactivity. One such autoantibody synergized with Hb to enhance the secretion of pro-inflammatory cytokines while eliciting the increased production of monocyte migratory signals from endothelial cells. Preferential usage of specific variable region gene segments was not observed, although somatic mutations were documented. These studies reveal that, while the etiology, specificity and sequences of anti-Hb autoreactive antibodies can vary, they occur quite frequently and can have inflammatory consequences.

The neonatal Fc receptor as therapeutic target in IgG-mediated autoimmune diseases

Therapy approaches based on lowering levels of pathogenic autoantibodies represent rational, effective, and safe treatment modalities of autoimmune diseases. The neonatal Fc receptor (FcRn) is a major factor regulating the serum levels of IgG antibodies. While FcRn-mediated half-life extension is beneficial for IgG antibody responses against pathogens, it also prolongs the serum half-life of IgG autoantibodies and thus promotes tissue damage in autoimmune diseases. In the present review article, we examine current evidence on the relevance of FcRn in maintaining high autoantibody levels and discuss FcRn-targeted therapeutic approaches. Further investigation of the FcRn-IgG interaction will not only provide mechanistic insights into the receptor function, but should also greatly facilitate the design of therapeutics combining optimal pharmacokinetic properties with the appropriate antibody effector functions in autoimmune diseases.

Autoimmune complications in chronic lymphocytic leukaemia (CLL)

Patients with B-chronic lymphocytic leukaemia /small lymphocytic lymphoma (CLL) have a 5-10% risk of developing autoimmune complications, which primarily cause cytopaenia. These autoimmune cytopaenias can occur at any stage of CLL and do not have independent prognostic significance. The most common autoimmune complication is autoimmune haemolytic anaemia with a lower frequency of immune thrombocytopaenia and pure red blood cell aplasia and only rarely, autoimmune granulocytopaenia (AIG). Autoimmune cytopaenia should always be considered in the differential diagnosis of cytopaenia in patients with CLL. Patients with CLL can also have more than one form of autoimmune cytopaenia, which can occur together with bone-marrow failure. Treatment is usually effective but rarely curative for autoimmune cytopaenia complicating CLL. Optimal therapy will depend on a timely and accurate diagnosis of autoimmune cytopaenia and should be individualised according to the severity of the cytopaenia and the presence or absence of concomitant progressive CLL requiring therapy.

Chronic lymphocytic leukemia cells bind and present the erythrocyte protein band 3: possible role as initiators of autoimmune hemolytic anemia

The mechanisms underlying the frequent association between chronic lymphocytic leukemia (CLL) and autoimmune hemolytic anemia are currently unclear. The erythrocyte protein band 3 (B3) is one of the most frequently targeted Ags in autoimmune hemolytic anemia. In this study, we show that CLL cells specifically recognize B3 through a still unidentified receptor. B3 interaction with CLL cells involves the recognition of its N-terminal domain and leads to its internalization. Interestingly, when binding of erythrocyte-derived vesicles as found physiologically in blood was assessed, we observed that CLL cells could only interact with inside-out vesicles, being this interaction strongly dependent on the recognition of the N-terminal portion of B3. We then examined T cell responses to B3 using circulating CLL cells as APCs. Resting B3-pulsed CLL cells were unable to induce T cell proliferation. However, when deficient costimulation was overcome by CD40 engagement, B3-pulsed CLL cells were capable of activating CD4(+) T cells in a HLA-DR-dependent fashion. Therefore, our work shows that CLL cells can specifically bind, capture, and present B3 to T cells when in an activated state, an ability that could allow the neoplastic clone to trigger the autoaggressive process against erythrocytes.

Hemolytic anemia due to warm autoantibodies

The diagnosis of autoimmune hemolytic anemia (AHA) requires evidence of shortened red blood cell (RBC) survival mediated by autoantibodies directed against autologous RBCs. About 80 percent of patients with AHA have warm-reactive antibodies of the IgG isotype; the remainder exhibit cold-reactive autoantibodies. Typical patients exhibit anemia, reticulocytosis, spherocytes and polychromasia on the blood film and a positive direct antiglobulin test (DAT). Increased indirect serum bilirubin, urinary urobilinogen and serum lactate dehydrogenase (LDH), and decreased serum haptoglobin are not required for the diagnosis, but are frequently present. Patients with AHA and no underlying associated disease are said to have primary or idiopathic AHA. AHA in patients with associated autoimmune disease and certain malignant or infectious diseases is classified as secondary. The etiology of AHA is unknown. Patients with symptomatic anemia require transfusion of RBCs. Prednisone and splenectomy may provide long term remission. Rituximab, intravenous immunoglobulin, immunosuppressive drugs and danazol have been effective in refractory cases and for patients who are poor candidates for surgery.

Deletion of the dominant autoantigen in NZB mice with autoimmune hemolytic anemia: effects on autoantibody and T-helper responses

The mechanisms underlying apparently spontaneous autoimmune diseases, such as autoimmune hemolytic anemia (AIHA) in New Zealand Black (NZB) mice, are unknown. Here, we determine the contribution of the dominant red blood cell (RBC) autoantigen, the anion exchanger protein Band 3, to the development of NZB autoimmune responses. The approach was to prevent Band 3 expression in NZB mice by disrupting the AE1 gene. AE1(-/-) NZB mice produced RBC autoantibodies at the same levels as the wild-type strain, but they differed in recognizing antigens that correspond to glycophorins, rather than Band 3. Splenic T-helper (Th) cells from wild-type NZB mice proliferated strongly against multiple Band 3 peptides, particularly the dominant epitope within aa861-874. This helper response was severely attenuated in AE1(-/-) animals, leaving only weak proliferation to peptide aa861-874. The results demonstrate that the defect in self-tolerance in NZB AIHA is directed to the RBC type, and is not specific for, or dependent on, Band 3. However, the predisposition to RBC autoimmunity may be focused onto Band 3 by weak Th cell cross-reactivity between the helper dominant epitope and an exogenous antigen. The redundancy of the major autoantigen illustrates the requirement for specific therapy to induce dominant forms of tolerance, such as T-cell regulation.

Controlling autoimmunity—Lessons from the study of red blood cells as model antigens

The characterization of human and animal red blood cell (RBC) autoantigens in autoimmune hemolytic anemia (AIHA) has provided an opportunity study the control of specific autoimmune responses of unequivocal pathogenic relevance. The results reveal that censorship of the autoimmune helper T (Th) cell repertoire by deletion and anergy is very incomplete in healthy individuals, even for widely distributed, abundant self-antigens on RBC. There is strong evidence that autoaggression by surviving Th cells is normally held in check by other mechanisms, including failure to display the epitopes that they recognize, and active immunoregulation. AIHA is one of the first human autoimmune diseases in which regulatory T (Tr) cells that are specific for the major autoantigens have been identified. These Tr cells recognize the dominant naturally processed epitopes, and recent studies suggest that disease develops when other determinants, to which such tolerance is less secure, and which are normally inefficiently presented, are displayed at higher levels. Together, the results raise the possibility that therapy for diseases such as AIHA could be based on switching the balance of the response back towards regulation, in particular by the administration of the dominant peptides recognized by specific Tr cells.

Cell-derived anaphylatoxins as key mediators of antibody-dependent type II autoimmunity in mice

Complement C5a, a potent anaphylatoxin, is a candidate target molecule for the treatment of inflammatory diseases, such as myocardial ischemia/reperfusion injury, RA, and the antiphospholipid syndrome. In contrast, up until now, no specific contribution of C5a and its receptor, C5aR, was recognized in diseases of antibody-dependent type II autoimmunity. Here we identify C5a as a novel key mediator of autoimmune hemolytic anemia (AIHA) and show that mice lacking C5aR are partially resistant to this IgG autoantibody-induced disease model. Upon administration of anti-erythrocyte antibodies, upregulation of activating Fcgamma receptors (FcgammaRs) on Kupffer cells, as observed in WT mice, was absent in C5aR-deficient mice, and FcgammaR-mediated in vivo erythrophagocytosis was impaired. Surprisingly, in mice deficient in FcgammaRI and FcgammaRIII, anti-erythrocyte antibody-induced C5 and C5a production was abolished, demonstrating the existence of a previously unidentified FcgammaR-mediated C5a-generating pathway. These results show that the development of a full-blown antibody-dependent autoimmune disease requires C5a--produced by and acting on FcgammaR--and may suggest therapeutic benefits of C5 and/or C5a/C5aR blockade in AIHA and other diseases closely related to type II autoimmune injury.

Warm autoimmune hemolytic anemia is an IgM–IgG immune complex disease

Warm autoimmune hemolytic anemia (WAIHA) is characterized by polyclonal IgG autoantibodies binding to red blood cells (RBC). The characterization of the autoantigen in WAIHA has not yet led to definitive results, and the etiology of RBC autoantibodies remains unclear. An altered control of self-reactive IgG by autologous IgM has been proposed as the underlying mechanism of disease in WAIHA, suggesting that IgM-IgG immune complexes contribute to the pathophysiology of the disease. In the present study, we purified and characterized IgM from plasma of WAIHA patients and from healthy controls using FPLC-based protocols and optical biosensor technology, and investigated IgG present within the IgM fractions. We provide evidence that IgM-IgG immune complexes in plasma and associated with the RBC membrane are the characteristic feature of WAIHA, independent of the etiology of the disease. IgM-IgG immune complexes of WAIHA patients differ from IgM-IgG immune complexes of healthy individuals with regard to quantity and to structural composition. The data suggest that self-immunoglobulin is the original autoantigen underlying WAIHA. The molecular characterization of IgM-IgG immune complexes may define new targets for therapeutic intervention in WAIHA.

Anaemia in systemic lupus erythematosus: from pathophysiology to clinical assessment

Haematological abnormalities are common in systemic lupus erythematosus. Anaemia is found in about 50% of patients, with anaemia of chronic disease being the most common form. Impaired erythropoietin response and presence of antibodies against erythropoietin may contribute to the pathogenesis of this type of anaemia. Patients with autoimmune haemolytic anaemia usually belong to a distinct category, which is associated with anticardiolipin antibodies, thrombosis, thrombocytopenia, and renal disease, often in the context of secondary antiphospholipid syndrome. Autoantibodies, T lymphocytes, and deregulation of the cytokine network can affect bone marrow erythropoiesis, leading to anaemia.

Rh autoantigen presentation to helper T cells in chronic lymphocytic leukemia by malignant B cells

Chronic lymphocytic leukemia (CLL) is frequently associated with autoimmune diseases directed against constituents of the blood, including hemolytic anemia (AIHA). We hypothesized that CLL cells predispose to hematologic autoimmunity by acting as aberrant antigen-presenting cells (APCs). Initially, it was confirmed that all studied patients with AIHA secondary to CLL harbored activated helper T (TH) cells specific for epitopes on the dominant red blood cell (RBC) autoantigens in primary AIHA, the Rh proteins. Rh-specific TH cells were also detected in a number of patients with CLL who, although they did not have AIHA, had low levels of anti-RBC antibody in their sera. Fractionation of putative APC populations from the peripheral blood of patients by negative selection showed that CD5+ CLL cells are the most effective cell type in processing and presenting purified Rh protein to autoreactive TH cells. This ability was confirmed using positively selected CD5+ CLL cells. Thus, our study provides the first evidence for malignant cells driving an autoimmune response by acting as aberrant APCs.

Autoantibody explosion in systemic lupus erythematosus: more than 100 different antibodies found in SLE patients

OBJECTIVE

Description of the various autoantibodies that can be detected in patients with systemic lupus erythematosus (SLE).

METHODS

A literature review, using the terms "autoantibody" and "systemic lupus erythematosus", was conducted to search for articles on autoantibodies in SLE, their target antigens, association with disease activity, or other clinical associations.

RESULTS

One hundred sixteen autoantibodies were described in SLE patients. These include autoantibodies that target nuclear antigens, cytoplasmic antigens, cell membrane antigens, phospholipid-associated antigens, blood cells, endothelial cells, and nervous system antigens, plasma proteins, matrix proteins, and miscellaneous antigens. The target of autoantibody, the autoantigen properties, autoantibody frequencies in SLE, as well as clinical associations, and correlation with disease activity are described for all 116 autoantibodies.

CONCLUSIONS

SLE is the autoimmune disease with the largest number of detectable autoantibodies. Their production could be antigen-driven, the result of polyclonal B cell activation, impaired apoptotic pathways, or the outcome of idiotypic network dysregulation.

Autoimmune hemolytic anemia occurred prior to evident nephropathy in a patient with chronic hepatitis C virus infection: case report

BACKGROUND

Renal involvement in patients with chronic hepatitis C virus infection has been suggested to be due to a variety of immunological processes. However, the precise mechanism by which the kidneys are damaged in these patients is still unclear.

CASE PRESENTATION

A 66 year old man presented with the sudden onset of autoimmune hemolytic anemia. Concomitant with a worsening of hemolysis, his initially mild proteinuria and hemoglobinuria progressed. On admission, laboratory tests revealed that he was positive for hepatitis C virus in his blood, though his liver function tests were all normal. The patient displayed cryoglobulinemia and hypocomplementemia with cold activation, and exhibited a biological false positive of syphilic test. Renal biopsy specimens showed signs of immune complex type nephropathy with hemosiderin deposition in the tubular epithelial cells.

CONCLUSIONS

The renal histological findings in this case are consistent with the deposition of immune complexes and hemolytic products, which might have occurred as a result of the patient's underlying autoimmune imbalance, autoimmune hemolytic anemia, and chronic hepatitis C virus infection.

Interleukin-10-mediated regulatory T-cell responses to epitopes on a human red blood cell autoantigen

Regulatory T cells have been shown to control animal models of immune-mediated pathology by inhibitory cytokine production, but little is known about such cells in human disease. Here we characterize regulatory T-cell responses specific for a human red blood cell autoantigen in patients with warm-type autoimmune hemolytic anemia. Peripheral blood mononuclear cells from patients with autoimmune hemolytic anemia were found either to proliferate and produce interferon-gamma or to secrete the regulatory cytokine interleukin 10 when stimulated in vitro with a major red blood cell autoantigen, the RhD protein. Flow cytometric analysis confirmed that the majority of the responding cells were of the CD4(+) phenotype. Serial results from individual patients demonstrated that this bias toward proliferative or interleukin-10 responses was unstable over time and could reverse in subsequent samples. Epitope mapping studies identified peptides from the sequence of the autoantigen that preferentially induced interleukin-10 production, rather than proliferation, and demonstrated that many contain naturally processed epitopes. Responses to such peptides suppressed T-cell proliferation against the RhD protein, an inhibition that was mediated largely by interleukin 10 and dependent on cytotonic T lymphocyte-associated antigen (CTLA-4) costimulation. Antigenic peptides with the ability to stimulate specific regulatory cells may represent a new class of therapeutic agents for immune-mediated disease.

Severe autoimmune hemolytic anemia caused by a warm IgA autoantibody directed against the third loop of band 3 (RBC anion-exchange protein 1)

BACKGROUND

Autoimmune hemolytic anemia associated with only IgA autoantibodies reacting optimally at 37 degrees C (WAIHA) is exceedingly rare. When identified, warm IgA autoantibodies specificities are usually directed to antigens of the Rh system. However, like IgG autoantibodies, the specificity of the majority of these antibodies is not identified.

CASE REPORT

A case of a 3-year-old boy in whom a life-threatening IgA WAIHA occurred suddenly is reported. Following initial RBC transfusions and treatment with steroids at a dose of 3 mg per kg, which was slowly tapered, stabilization to a state of compensated hemolysis was achieved, persisting 4 months before complete resolution. There was no recurrence within a 16-month follow-up.

STUDY DESIGN AND METHODS

The standard DAT in a gel column method with anti-IgG and anticomplement reagents was negative. However, the same method with an anti-IgA was strongly positive.

RESULTS

The serum and the eluate obtained after acid elution reacted with all normal RBCs tested. Enzymatic treatment of panel RBCs by alpha-chymotrypsin and pronase abolished the reactivity. The reaction was completely inhibited by RBC incubation with four different MoAbs directed against the third extracellular loop of band 3, the RBC anion-exchange protein 1 (AE1), whereas MoAbs against other specificities showed no effect.

CONCLUSIONS

This is the first report of an IgA autoantibody directed against the band 3 (AE1) protein and, more specifically, against the third loop. Moreover, this case underlines the importance of including IgA research in the initial diagnostic evaluation when a hemolytic anemia is suspected to be autoimmune and when IgG and complement are not detected on the patient's RBCs.

Detection of lupus anticoagulant identifies patients with autoimmune haemolytic anaemia at increased risk for venous thromboembolism

Venous thromboembolism (VTE) is a well-recognized complication of autoimmune haemolytic anaemia (AIHA), and is a major cause of morbidity and mortality in this disorder. However, the incidence, pathogenesis and risk-factors for VTE in AIHA remain poorly defined. Lupus anticoagulants (LA) and anticardiolipin (ACA) antibodies are autoantibodies directed against epitopes on prothrombin or beta2 glycoprotein I (beta2-GPI). Both LA and ACA (together called antiphospholipid antibodies, APLA) are associated with VTE. We have prospectively studied the occurrence of VTE and APLA in 30 patients with AIHA. VTE was objectively documented in eight (27%) patients. APLA were detected in 19 (63%) patients with AIHA, of whom nine (30%) had a LA and 17 (57%) ACA. Seven patients had both LA and ACA. Among the eight patients with VTE, LA was detected in five (63%) and ACA in four (50%). There was a statistically significant association between presence of LA and occurrence of VTE (RR: 7.50, 95% CI: 1.25-45.2, P = 0.03). VTE is a frequent and life-threatening complication of AIHA. Detection of the lupus anticoagulant in patients with AIHA identifies individuals at significantly increased risk for VTE. Future studies should address the role of prophylactic anticoagulation in patients with AIHA.

T-cell specificity in murine autoimmune haemolytic anaemia induced by rat red blood cells

Autoimmune haemolytic anaemia (AIHA) can be induced in mice by repeated injections with rat red blood cells (RBC). Here we describe the identification of rat and murine RBC antigens recognized by T-cells from mice with this disease. Splenic T-cells from mice with AIHA proliferated in response to multiple murine RBC membrane components, each of which is recognized by rat RBC induced autoantibodies. Thus, there were responses to murine autoantigen fractions that correspond in apparent molecular mass with the anion channel Band 3, with spectrin from the membrane skeleton and with the high and low molecular mass glycophorins, and the equivalent fractions from rat RBC also stimulated proliferation by T-cells. It was confirmed that purified Band 3 from murine and rat RBC also elicited responses. In contrast with the results in AIHA, T-cells from healthy control mice failed to respond to the antigens from either species, with the exception of proliferation induced by murine spectrin in one experiment and weak responses elicited by rat Band 3. It is suggested that T-cells activated by multiple cross-reactions between rat and murine RBC proteins, and by epitope spreading, are necessary to drive autoantibody production in this model of AIHA.

Autoimmune hemolytic anemia

Red blood cell (RBC) autoantibodies are a relatively uncommon cause of anemia. However, autoimmune hemolytic anemia (AIHA) must be considered in the differential diagnosis of hemolytic anemias, especially if the patient has a concomitant lymphoproliferative disorder, autoimmune disease, or viral or mycoplasmal infection. Classifications of AIHA include warm AIHA, cold agglutinin syndrome, paroxysmal cold hemoglobinuria, mixed-type AIHA, and drug-induced AIHA. Characteristics of the autoantibodies are responsible for the various clinical entities. As a result, diagnosis is based on the clinical presentation and a serologic work-up. For each classification of AIHA, this review discusses the demographics, etiology, clinical presentation, laboratory evaluation, and treatment options.

Reactivity of autoantibodies of autoimmune hemolytic anemia with recombinant rhesus blood group antigens or anion transporter band3

The specificity of autoantibodies in autoimmune hemolytic anemia (AIHA) has been studied using the serological procedure and immunoprecipitation technique with rare phenotype red cells. We attempted to analyze specificity using recombinant rhesus (Rh) blood group and band3 antigens expressed on erythroleukemic cell lines, KU812E. The autoantibody eluates were isolated by the acid elution procedure from the red cells of 20 AIHA patients. The recombinant Rh antigens, RhD, cE, ce, CE, and chimera antigens CE-D and D-CE, were obtained by retroviral cDNA transduction into KU812E cells, and the cell line expressing the antigens was cloned. Band3 cDNA was also obtained and introduced into KU812E and cloned KU812 expressing RhcE. The reactivities of AIHA eluates with recombinant Rh and band3 antigens were studied by flow cytometry. Fifteen eluates reacted with at least one of the RhcE, ce, or CE antigens, and four eluates reacted with RhD. Seven eluates with strong Rh specificity were studied further using chimera antigen. Five eluates showed reduced or lost reactivity, although two eluates reacted identically with the chimera antigens as wild type. These results indicated that conformational epitopes constituted by RhD or CE specific exofacial peptide loops are important for autoantibodies in most cases. Seven eluates reacted with band3, five exclusively. The coexpression study of RhcE and band3 did not enhance the expression of either antigen nor the reactivity with patient eluates, indicating that association of Rh and band3 was not involved in the appearance of autoantigen.

Helper T cells in antibody-mediated, organ-specific autoimmunity

The production of pathogenic autoantibodies in organ-specific autoimmune diseases is largely T cell dependent. For many of these diseases, the precise specificities and cytokine profiles of the T cells that respond to the corresponding autoantigens have now been identified. This knowledge has been exploited to treat some models of antibody-mediated autoimmunity using peptides corresponding to the dominant helper epitopes, giving impetus to the development of a similar approach in the equivalent human diseases.

Polyreactivity of disease-associated anti-RBC IgG autoantibodies of patients with warm autoimmune haemolytic anaemia and natural anti-RBC IgG autoantibodies of healthy individuals

Anti-red blood cell (RBC) immunoglobulin G (IgG) autoantibodies are present in patients with warm autoimmune haemolytic anaemia (WAIHA), and, as natural autoantibodies, in healthy individuals. This study investigated whether the feature of polyreactivity discriminates disease-associated from natural anti-RBC IgG autoantibodies. The patterns of reactivity of purified anti-RBC IgG eluted from the RBC of WAIHA patients and from the RBC of healthy individuals were analysed using quantitative immunoblotting on a panel of whole human tissue or bacterial cell extracts as antigen sources. In parallel, the reactivity patterns of IgG purified from plasma were analysed. Anti-RBC IgG of WAIHA patients and of healthy individuals recognized a wide range of self- and nonself-antigens. The reactivity patterns of anti-RBC IgG were homogeneous among patients and controls, did not differ between patients and controls, and were similar to those of IgG purified from plasma in the case of both patients and healthy individuals. The data demonstrate that the anti-RBC IgG autoantibodies of WAIHA patients share extensive similarity with those of healthy individuals. Polyreactivity is a common feature of both disease-associated and natural anti-RBC IgG autoantibodies.

Altered control of self-reactive IgG by autologous IgM in patients with warm autoimmune hemolytic anemia

Warm autoimmune hemolytic anemia (WAIHA) is characterized by an accelerated clearance of red blood cells (RBCs) associated with the presence of anti-RBC immunoglobulin (Ig)G autoantibodies. In the present study, we analyzed the self-reactive IgG and IgM antibody repertoires of patients with WAIHA using a technique of quantitative immunoblotting on a panel of whole tissue extracts as sources of self-antigens. Data were compared by means of multiparametric statistical analysis. We demonstrate that self-reactive antibody repertoires of IgG purified from plasma and of IgG purified from RBC eluates do not differ between healthy donors and patients with WAIHA, whereas autoreactive repertoires of IgM from patients exhibit broadly altered patterns of reactivity as compared with those of healthy controls. We further demonstrate that IgG purified from eluates of RBCs of healthy donors induces agglutination of RBCs in an indirect Coombs assay to a similar extent as IgG purified from eluates of RBCs of patients with WAIHA. The capability of IgG to induce agglutination of RBCs is suppressed in unfractionated eluates of healthy donors' cells, whereas it is readily found in unfractionated eluates of patients' RBCs. IgM is an essential factor in controlling the ability of IgG in unfractionated RBC eluates to induce agglutination of RBCs. These observations indicate that anti-RBC IgG autoantibodies of patients with WAIHA share extensive similarity with natural antiRBC autoantibodies of healthy donors and suggest that defective control of IgG autoreactivity by autologous IgM is an underlying mechanism for autoimmune hemolysis in WAIHA. (Blood. 2000;95:328-335)

Altered control of self-reactive IgG by autologous IgM in patients with warm autoimmune hemolytic anemia

Warm autoimmune hemolytic anemia (WAIHA) is characterized by an accelerated clearance of red blood cells (RBCs) associated with the presence of anti-RBC immunoglobulin (Ig)G autoantibodies. In the present study, we analyzed the self-reactive IgG and IgM antibody repertoires of patients with WAIHA using a technique of quantitative immunoblotting on a panel of whole tissue extracts as sources of self-antigens. Data were compared by means of multiparametric statistical analysis. We demonstrate that self-reactive antibody repertoires of IgG purified from plasma and of IgG purified from RBC eluates do not differ between healthy donors and patients with WAIHA, whereas autoreactive repertoires of IgM from patients exhibit broadly altered patterns of reactivity as compared with those of healthy controls. We further demonstrate that IgG purified from eluates of RBCs of healthy donors induces agglutination of RBCs in an indirect Coombs assay to a similar extent as IgG purified from eluates of RBCs of patients with WAIHA. The capability of IgG to induce agglutination of RBCs is suppressed in unfractionated eluates of healthy donors' cells, whereas it is readily found in unfractionated eluates of patients' RBCs. IgM is an essential factor in controlling the ability of IgG in unfractionated RBC eluates to induce agglutination of RBCs. These observations indicate that anti-RBC IgG autoantibodies of patients with WAIHA share extensive similarity with natural antiRBC autoantibodies of healthy donors and suggest that defective control of IgG autoreactivity by autologous IgM is an underlying mechanism for autoimmune hemolysis in WAIHA. (Blood. 2000;95:328-335)

Identification of T-Cell Epitopes on the Rhesus Polypeptides in Autoimmune Hemolytic Anemia

We have shown previously that the Rhesus (Rh) polypeptides are the commonest targets for pathogenic anti-red blood cell (RBC) autoantibodies in patients with autoimmune hemolytic anemia (AIHA). The aim of the current work was to determine whether activated T cells from such patients also mount recall responses to epitopes on these proteins. Two panels of overlapping 15-mer peptides, corresponding to the sequences of the 30-kD Rh proteins associated with expression of the D and Cc/Ee blood group antigens, were synthesized and screened for the ability to stimulate the in vitro proliferation of mononuclear cells from the peripheral blood or spleen of nine AIHA cases. Culture conditions were chosen that favor recall proliferation by previously activated T cells, rather than primary responses. In seven of the patients, including all four cases with autoantibody to the Rh proteins, two or more peptides elicited proliferation, but cells from eight of nine patients with other anemias and seven of nine healthy donors failed to respond to the panels. Multiple peptides were also stimulatory in two positive control donors who had been alloimmunized with Rh D-positive RBCs. Six different profiles of peptides elicited responses in the AIHA patients, and this variation may reflect the different HLA types in the group. Stimulatory peptides were identified throughout domains shared between, or specific to, each of the related 30-kD Rh proteins, but T cells that responded to nonconserved regions did not cross-react with the alternative sequences. Anti-major histocompatibility complex class II antibodies blocked the responses and depletion experiments confirmed that the proliferating mononuclear cells were T cells. Notably, splenic T cells that proliferated against multiple Rh peptides also responded to intact RBCs. We propose that pathogenic autoantibody production in many cases of AIHA is driven by the activation of T-helper cells specific for previously cryptic epitopes on the Rh proteins.

Identification of T-Cell Epitopes on the Rhesus Polypeptides in Autoimmune Hemolytic Anemia

We have shown previously that the Rhesus (Rh) polypeptides are the commonest targets for pathogenic anti-red blood cell (RBC) autoantibodies in patients with autoimmune hemolytic anemia (AIHA). The aim of the current work was to determine whether activated T cells from such patients also mount recall responses to epitopes on these proteins. Two panels of overlapping 15-mer peptides, corresponding to the sequences of the 30-kD Rh proteins associated with expression of the D and Cc/Ee blood group antigens, were synthesized and screened for the ability to stimulate the in vitro proliferation of mononuclear cells from the peripheral blood or spleen of nine AIHA cases. Culture conditions were chosen that favor recall proliferation by previously activated T cells, rather than primary responses. In seven of the patients, including all four cases with autoantibody to the Rh proteins, two or more peptides elicited proliferation, but cells from eight of nine patients with other anemias and seven of nine healthy donors failed to respond to the panels. Multiple peptides were also stimulatory in two positive control donors who had been alloimmunized with Rh D-positive RBCs. Six different profiles of peptides elicited responses in the AIHA patients, and this variation may reflect the different HLA types in the group. Stimulatory peptides were identified throughout domains shared between, or specific to, each of the related 30-kD Rh proteins, but T cells that responded to nonconserved regions did not cross-react with the alternative sequences. Anti-major histocompatibility complex class II antibodies blocked the responses and depletion experiments confirmed that the proliferating mononuclear cells were T cells. Notably, splenic T cells that proliferated against multiple Rh peptides also responded to intact RBCs. We propose that pathogenic autoantibody production in many cases of AIHA is driven by the activation of T-helper cells specific for previously cryptic epitopes on the Rh proteins.

The anti-erythrocyte autoimmune response of NZB mice. Identification of two distinct autoantigens

With age, New Zealand black (NZB) mice spontaneously develop anti-mouse red blood cell (RBC) autoantibodies resulting in the development of autoimmune haemolytic anemia (AIHA). Previously, we characterized a panel of monoclonal autoantibodies derived from unimmunized, adult NZB mice. One of these antibodies (G8) was shown to be pathogenic, inducing AIHA in a non-autoimmune-prone mouse strain (BALB/c). Using G8, and two other antibodies from our panel, we have characterized two distinct autoantigens on the surface of mouse RBCs. The autoantigen, historically referred to as antigen X (AgX), was found to be partially hidden on the surface of the mouse RBC because glycosidase treatment or mild digestion with proteinase K resulted in increased reactivity with autoantibodies. One of the monoclonal antibodies (3H5G1) was found to immunoprecipitate a 110,000 MW protein identified as the erythrocyte anion transporter (band 3) whereas the pathogenic antibody (G8) as well as a third monoclonal antibody (2E6m) were shown to immunoprecipitate a 60,000 MW protein that was not reactive with the anti-band 3 serum. Finally, we show that the autoantigen recognized by G8 is expressed on differentiated mouse erythroleukaemia (MEL) cells. The results suggest that a protein distinct from band 3 can serve as a target for AIHA in NZB mice.

Reduced frequency of HLA-DQ6 in individuals with a positive direct antiglobulin test

BACKGROUND

The association between HLA class II antigens and the production of red cell autoantibodies was investigated in this study.

STUDY DESIGN AND METHODS

Thirty-one individuals with a positive direct antiglobulin test (DAT) and 85. DAT-negative controls (cadaveric organ donors) were typed using a DNA-based method for class II HLA typing, that is, the polymerase chain reaction with sequence-specific primers. Amplified HLA alleles corresponding to the serologic specificities DR 1-18 and DQ 1-9 were identified.

RESULTS

Analysis of DR and DQ frequencies showed that HLA-DQ6 was less frequent in DAT-positive individuals (19% vs. 53% in the control population), with a p value of 0.0014 and a corrected p value of 0.059, and relative risk of 0.23 (95% Cl = 0.09-0.58). The frequency of HLA-DQ6 was higher in asymptomatic DAT-positive blood donors (n = 8, 38% DQ6 positive, p = 0.48) than in DAT-positive hospital and clinic patients (n = 23, 13% DQ6 positive, corrected p value = 0.030, relative risk = 0.13, 95% Cl = 0.04-0.41), 96 percent of whom had evidence of clinical hemolysis.

CONCLUSION

This study demonstrates that HLA-DQ6 may have a negative association with a positive DAT result in patients with evidence for hemolysis, and may be a resistance antigen for clinically relevant red cell autoantibodies.