Autoimmune hemolytic anemia

The SOD1 transgene expressed in erythroid cells alleviates fatal phenotype in congenic NZB/NZW-F1 mice

Oxidative stress due to a superoxide dismutase 1 (SOD1) deficiency causes anemia and autoimmune responses, which are phenotypically similar to autoimmune hemolytic anemia (AIHA) and systemic lupus erythematosus (SLE) in C57BL/6 mice and aggravates AIHA pathogenesis in New Zealand black (NZB) mice. We report herein on an evaluation of the role of reactive oxygen species (ROS) in a model mouse with inherited SLE, that is, F1 mice of the NZB × New Zealand white (NZW) strain. The ROS levels within red blood cells (RBCs) of the F1 mice were similar to the NZW mice but lower compared to the NZB mice throughout adult period. Regarding SLE pathogenesis, we examined the effects of an SOD1 deficiency or the overexpression of human SOD1 in erythroid cells by establishing corresponding congenic F1 mice. A SOD1 deficiency caused an elevation in ROS production, methemoglobin content, and hyperoxidation of peroxiredoxin in RBC of the F1 mice, which were all consistent with elevated oxidative stress. However, while the overexpression of human SOD1 in erythroid cells extended the life span of the congenic F1 mice, the SOD1 deficiency had no effect on life span compared to wild-type F1 mice. It is generally recognized that NZW mice possess a larval defect in the immune system and that NZB mice trigger an autoimmune reaction in the F1 mice. Our results suggest that the oxidative insult originated from the NZB mouse background has a functional role in triggering an aberrant immune reaction, leading to fatal responses in F1 mice.

Oxidative stress as a potential causal factor for autoimmune hemolytic anemia and systemic lupus erythematosus

The kidneys and the blood system mutually exert influence in maintaining homeostasis in the body. Because the kidneys control erythropoiesis by producing erythropoietin and by supporting hematopoiesis, anemia is associated with kidney diseases. Anemia is the most prevalent genetic disorder, and it is caused by a deficiency of glucose 6-phosphate dehydrogenase (G6PD), for which sulfhydryl oxidation due to an insufficient supply of NADPH is a likely direct cause. Elevated reactive oxygen species (ROS) result in the sulfhydryl oxidation and hence are another potential cause for anemia. ROS are elevated in red blood cells (RBCs) under superoxide dismutase (SOD1) deficiency in C57BL/6 mice. SOD1 deficient mice exhibit characteristics similar to autoimmune hemolytic anemia (AIHA) and systemic lupus erythematosus (SLE) at the gerontic stage. An examination of AIHA-prone New Zealand Black (NZB) mice, which have normal SOD1 and G6PD genes, indicated that ROS levels in RBCs are originally high and further elevated during aging. Transgenic overexpression of human SOD1 in erythroid cells effectively suppresses ROS elevation and ameliorates AIHA symptoms such as elevated anti-RBC antibodies and premature death in NZB mice. These results support the hypothesis that names oxidative stress as a risk factor for AIHA and other autoimmune diseases such as SLE. Herein we discuss the association between oxidative stress and SLE pathogenesis based mainly on the genetic and phenotypic characteristics of NZB and New Zealand white mice and provide insight into the mechanism of SLE pathogenesis.

Reactive oxygen species exacerbate autoimmune hemolytic anemia in New Zealand Black mice

Elevated reactive oxygen species (ROS) and oxidative damage occur in the red blood cells (RBCs) of SOD1-deficient C57BL/6 mice. This leads to autoimmune responses against RBCs in aged mice that are similar to autoimmune hemolytic anemia (AIHA). We examined whether a SOD1 deficiency and/or the human SOD1 transgene (hSOD1) would affect phenotypes of AIHA-prone New Zealand Black (NZB) mice by establishing three congenic strains: those lacking SOD1, those expressing hSOD1 under a GATA-1 promoter, and those lacking mouse SOD1 but expressing hSOD1. Levels of intracellular ROS and oxidative stress markers increased, and the severity of the AIHA phenotype was aggravated by a SOD1 deficiency. In contrast, the transgenic expression of hSOD1 in an erythroid cell-specific manner averted most of the AIHA phenotype evident in the SOD1-deficient mice and also ameliorated the AIHA phenotype in the mice possessing intrinsic SOD1. These data suggest that oxidative stress in RBCs may be an underlying mechanism for autoimmune responses in NZB mice. These results were consistent with the hypothetical role of reactive oxygen species in triggering the autoimmune reaction in RBCs and may provide a novel approach to mitigating the progression of AIHA by reducing oxidative stress.

Galactosylation of IgG1 modulates FcγRIIB-mediated inhibition of murine autoimmune hemolytic anemia

Murine immune effector cells express three different stimulatory FcγRs (FcγRI, FcγRIII and FcγRIV) and one inhibitory receptor, FcγRIIB. Competitive engagement of stimulatory and inhibitory FcγRs has been shown to be critical for the development of immune complex-mediated inflammatory disorders. Because of the previous demonstration that FcγRIIB was unable to inhibit FcγRIII-mediated autoimmune hemolytic anemia induced by 105-2H IgG1 anti-RBC mAb, we reevaluated the regulatory role of FcγRIIB on the development of anemia using two additional IgG1 anti-RBC mAbs (34-3C and 3H5G1) and different 34-3C IgG subclass-switch variants. We were able to induce a more severe anemia in FcγRIIB-deficient mice than in FcγRIIB-sufficient mice after injection of 34-3C and 3H5G1 IgG1, but not 105-2H IgG1. Structural analysis of N-linked oligosaccharides attached to the CH2 domain revealed that 105-2H was poorly galactosylated as compared with the other mAbs, while the extent of sialylation was comparable between all mAbs. In addition, we observed that a more galactosylated 105-2H variant provoked more severe anemia in FcγRIIB-deficient mice than FcγRIIB-sufficient mice. In contrast, the development of anemia induced by three non-IgG1 subclass variants of the 34-3C mAb was not down-regulated by FcγRIIB, although they were more galactosylated than its IgG1 variant. These data indicate that FcγRIIB-mediated inhibition of autoimmune hemolytic anemia is restricted to the IgG1 subclass and that galactosylation, but not sialylation, of IgG1 (but not other IgG subclasses) is critical for the interaction with FcγR, thereby determining the pathogenic potential of IgG1 autoantibodies.

Rescue of anaemia and autoimmune responses in SOD1-deficient mice by transgenic expression of human SOD1 in erythrocytes

Oxidative stress has been implicated as a cause of various diseases such as anaemia. We found that the SOD1 [Cu,Zn-SOD (superoxide dismutase)] gene deficiency causes anaemia, the production of autoantibodies against RBCs (red blood cells) and renal damage. In the present study, to further understand the role of oxidative stress in the autoimmune response triggered by SOD1 deficiency, we generated mice that had the hSOD1 (human SOD1) transgene under regulation of the GATA-1 promoter, and bred the transgene onto the SOD1(-/-) background (SOD1(-/-);hSOD1(tg/+)). The lifespan of RBCs, levels of intracellular reactive oxygen species, and RBC content in SOD1(-/-);hSOD1(tg/+) mice, were approximately equivalent to those of SOD1(+/+) mice. The production of antibodies against lipid peroxidation products, 4-hydroxy-2-nonenal and acrolein, as well as autoantibodies against RBCs and carbonic anhydrase II were elevated in the SOD1(-/-) mice, but were suppressed in the SOD1(-/-);hSOD1(tg/+) mice. Renal function, as judged by blood urea nitrogen, was improved in the transgenic mice. These results rule out the involvement of a defective immune system in the autoimmune response of SOD1-deficient mice, because SOD1(-/-);hSOD1(tg/+) mice carry the hSOD1 protein only in RBCs. Metabolomic analysis indicated a shift in glucose metabolism to the pentose phosphate pathway and a decrease in the energy charge potential of RBCs in SOD1-deficient mice. We conclude that the increase in reactive oxygen species due to SOD1 deficiency accelerates RBC destruction by affecting carbon metabolism and increasing oxidative modification of lipids and proteins. The resulting oxidation products are antigenic and, consequently, trigger autoantibody production, leading to autoimmune responses.

Differential contribution of three activating IgG Fc receptors (FcgammaRI, FcgammaRIII, and FcgammaRIV) to IgG2a- and IgG2b-induced autoimmune hemolytic anemia in mice

Murine phagocytes express three different activating IgG FcgammaR: FcgammaRI is specific for IgG2a; FcgammaRIII for IgG1, IgG2a, and IgG2b; and FcgammaRIV for IgG2a and IgG2b. Although the role of FcgammaRIII in IgG1 and IgG2a anti-RBC-induced autoimmune hemolytic anemia (AIHA) is well documented, the contribution of FcgammaRI and FcgammaRIV to the development of IgG2a- and IgG2b-induced anemia has not yet been defined. In the present study, using mice deficient in FcgammaRI, FcgammaRIII, and C3, in combination with an FcgammaRIV-blocking mAb, we assessed the respective roles of these three FcgammaR in the development of mild and severe AIHA induced by two different doses (50 and 200 microg) of the IgG2a and IgG2b subclasses of the 34-3C anti-RBC monoclonal autoantibody. We observed that the development of mild anemia induced by a low dose of 34-3C IgG2a autoantibody was highly dependent on FcgammaRIII, while FcgammaRI and FcgammaRIV additionally contributed to the development of severe anemia induced by a high dose of this subclass. In contrast, the development of both mild and severe anemia induced by 34-3C IgG2b was dependent on FcgammaRIII and FcgammaRIV. Our results indicate differential roles of the three activating FcgammaR in IgG2a- and IgG2b-mediated AIHA.

IgM and IgA anti-erythrocyte autoantibodies induce anemia in a mouse model through multivalency-dependent hemagglutination but not through complement activation

By generating IgM and IgA switch variants of the 34-3C IgG2a anti-red blood cell (RBC) autoantibody, we evaluated the pathogenic activity of these 2 isotypes in view of the Fc-associated effector functions (ie, complement activation and polyvalency-dependent agglutination). We found that polymeric forms of 34-3C IgM and IgA anti-RBC autoantibody were as pathogenic as IgG2a, which was the most pathogenic among 4 different IgG subclasses, whereas their monomeric variants completely lacked pathogenic effects. Histological examination showed that 34-3C IgM and IgA autoantibodies caused anemia as a result of multivalency-dependent hemaggultination and subsequent sequestration of RBC in the spleen, in contrast to Fc receptor- and complement receptor-mediated erythrophagocytosis by Kupffer cells with IgG isotypes. In addition, the development of anemia induced by IgM and IgA isotypes of 34-3C antibody and by 2 additional IgM anti-RBC monoclonal autoantibodies was not inhibited at all in C3-deficient mice, indicating the lack of involvement of complement activation in the pathogenesis of IgM- and IgA-induced anemia. Our data demonstrate a remarkably high pathogenic potential of polymeric forms of IgM and IgA anti-RBC autoantibodies due to their ability to induce hemagglutination but completely independent of complement activation.

Evaluation of liposomal clodronate in experimental spontaneous autoimmune hemolytic anemia in dogs

OBJECTIVES

Liposomal clodronate (dichloromethylene diphosphonate) has been used to deplete macrophages and block clearance of opsonized cells in mouse models of autoimmune disease. However, liposomal clodronate (LC) has not been previously evaluated in a large-animal spontaneous autoimmune disease model. Therefore, the safety and efficacy of LC treatment was assessed in normal dogs and in dogs with spontaneous autoimmune hemolytic anemia (AIHA).

METHODS

LC was administered intravenously first to healthy dogs and then to dogs with spontaneous, severe AIHA to determine if the treatment was safe and could block clearance of opsonized red blood cells (RBCs) in vivo. Studies were also conducted to assess the in vitro effects of LC on dog macrophages and dendritic cells.

RESULTS

Intravenous infusion of low doses of LC was well tolerated and blocked clearance of opsonized RBCs in normal dogs in vivo. LC was taken up by splenic macrophages and dendritic cells in vivo, and induced killing of macrophages and dendritic cells in vitro. Seven dogs with severe, spontaneous AIHA were treated with LC in a pilot study. Treatment was well tolerated, 2 of 7 LC-treated dogs with AIHA had a decrease in RBC clearance, and LC-treated dogs had significantly increased survival times compared to historical control dogs matched for disease severity.

CONCLUSIONS

These results indicate that LC can be safely administered intravenously to dogs and that even relatively low doses are capable of blocking RBC clearance and improving outcomes in a spontaneous large-animal model of AIHA. Therefore, additional studies of LC for treatment of autoantibody-mediated cytopenias in dogs and humans may be warranted.

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.

Multiple loci are linked with anti-red blood cell antibody production in NZB mice -- comparison with other phenotypes implies complex modes of action

The New Zealand Black (NZB) mouse strain is a model of autoimmune haemolytic anaemia (AHA) and systemic lupus erythematosus (SLE), characterized by the production of anti-red blood cell (RBC) antibodies and anti-nuclear antibodies (ANA), respectively. A linkage analysis was carried out in an (NZB x BALB/c) F(2) cross in order to identify loci involved in the production of both anti-RBC IgM and IgG antibodies. These regions of linkage were compared with linkage data to ANA from the same cohort and other linkage analyses involving New Zealand mice. Four previously described NZB loci linked to anti-RBC antibodies were confirmed, and eight novel loci linked to this trait were also mapped: five of which were of NZB origin, and three derived from the non-autoimmune BALB/c background. A comparison between loci linked with anti-RBC antibodies and ANA demonstrated many that co-localize, suggesting the presence of genes that result in the general breaking of tolerance to self-antigen. Furthermore, the observation that some loci were associated only with the anti-RBC response suggests an antigen specific mechanism in addition to a general breaking of tolerance. A locus linked with anti-RBC antibodies and ANA on distal chromosome 7 in this cohort is orthologous to one on the q arm of human chromosome 11, a region linked to AHA and ANA in human SLE.

Autoantibody formation after alloimmunization: are blood tranfusions a risk factor for autoimmune hemolytic anemia?

BACKGROUND

The development of RBC autoantibodies resulting from or associated with allogeneic blood transfusions (i.e., RBC autoimmunization) is not a well-recognized complication of RBC transfusions.

STUDY DESIGN AND METHODS

T: he presentation, laboratory evaluation, clinical course, and management of two patients whose autoimmune hemolytic anemia followed allogeneic blood transfusion and occurred in association with the development of one or more alloantibodies is described. A retrospective analysis was performed of our blood-bank records over 1 year to determine the frequency of RBC autoimmunization associated with alloimmunization.

RESULTS

Out of 2618 patients who had a positive DAT or IAT, 121 were identified with RBC autoantibodies; 41 of these patients had both allo- and autoantibodies to RBC antigens, whereas the remainder, 80, had only autoantibodies. At least 34 percent (12/41) of these patients (none with hemoglobinopathy) developed their autoantibodies in temporal association with alloimmunization after recent blood transfusion(s).

CONCLUSION

RBC autoimmunization and the development of autoimmune hemolytic anemia should be recognized as a complication of allogeneic blood transfusion. The need for additional blood transfusion was successfully avoided in one patient by treatment with recombinant human EPO and corticosteroid therapy. Once RBC autoimmunization is identified, subsequent management should incorporate a strategy that minimizes subsequent exposure to allogeneic blood.

Treatment of childhood autoimmune haemolytic anaemia with rituximab

Autoimmune haemolytic anaemia commonly has a severe course in young children, thus requiring multiple immunosuppressive treatments. Five children with refractory idiopathic autoimmune haemolytic anaemia, and one child with the disease after bone-marrow transplantation, were treated with rituximab-a monoclonal antibody against CD20. Tolerance of the treatment was good. However, circulating Bcells were absent and hypogammaglobulinaemia was seen for 9 months after treatment. All patients remained in complete remission 15-22 months after the start of rituximab therapy. Corticosteroids and immunosuppressive drugs were stopped or their dose markedly reduced. We suggest that rituximab could be a valuable treatment for autoimmune haemolytic anaemia, although a long-lasting but transient B-cell deficiency develops.

Immune complex-like moieties in immunoglobulin for intravenous use (i.v.Ig) bind complement and enhance phagocytosis of human erythrocytes

Treatment with i.v.Ig can, on rare occasions, lead to detrimental effects such as enhanced erythrocyte sequestration and an increase in serum immune complexes with inflammatory sequellae such as exacerbation of glomerular nephritis. In this study, i.v.Ig (Sandoglobin) was examined for complement binding moieties which resemble immune complexes and can mediate the binding of IgG and C'3b to human erythrocytes via CR1 and enhance erythrocyte susceptibility to sequestration. Sephacryl S-200 HR separated i.v.Ig into two fractions: monomeric IgG (74%) and larger complexes of the molecular weight of an IgG dimer or greater (> or = 300 kD) (26%). In the presence of complement, the 'dimers' bound to human erythrocytes, rendering them susceptible to phagocytosis in vitro. Removal of erythrocyte-specific isoantibodies from the i.v.Ig had no effect on 'dimer' binding to the erythrocytes. Monomeric IgG contained virtually no complement-activating, erythrocyte-binding activity. Erythrocyte binding of complement-bearing IgG 'dimers' and subsequent phagocytosis resembles the binding of complement-bearing immune complexes to erythrocyte CR1. Exposure to Factor I leads to the release of complement-bearing IgG 'dimers' from erythrocyte CR1 and to the abrogation of erythrophagocytosis. Binding of complement-bearing IgG 'dimers' to the erythrocyte is blocked by To5, a CR1-specific monoclonal antibody.

The pathologic significance of the immunoglobulins expressed by chronic lymphocytic leukemia B-cells in the development of autoimmune hemolytic anemia

The increased number of CD5+ B-cells in some human autoimmune diseases, the frequent commitment of CD5+ B-cells to the production of natural autoantibodies, and the apparent involvement of these cells in the pathogenesis of the autoimmune hemolytic anemia (AIHA) in certain mouse models suggests a causal relationship between the CD5+ chronic lymphocytic leukemia (CLL) B-cell and the AIHA which frequently develops in this malignant disorder. In support of this conclusion is our recent finding that the VH region gene repertoire of the leukemic B-cells from CLL patients with AIHA is rather biased and characterised by the over-representation of the 51p1 VH gene. On the other hand, it appears relatively certain that the pathogenic anti-erythrocyte antibodies in CLL patients with AIHA are produced by remnant normal B-cells, and that the antibodies expressed by the leukemic CD5+ B-cells do not directly bind red blood cells (RBC). Of interest, the antibodies produced by the leukemic B-cells from CLL patients with AIHA might have in common rheumatoid factor (RF) activity. These data indicate that the antibodies produced by the leukemic B-cells from CLL patients with AIHA are not directly involved in red blood cell destruction, but may be involved in the induction or amplification of a polyclonal anti-RBC response. Finally, we discuss the possible clinical implications of our finding that CLL patients with leukemic cells expressing the 51p1 VH gene may be at a higher risk to develop autoimmune hemolytic anemia.

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.