Pathogenic autoantibodies in the NZB mouse are specific for erythrocyte band 3 protein

Induction of IL-10 cytokine and the suppression of T cell proliferation by specific peptides from red cell band 3 and in vivo effects of these peptides on autoimmune hemolytic anemia in NZB mice

PURPOSE

The anion channel protein band 3 is the main target of the pathogenic red blood cells (RBC) autoantibodies in New Zealand black (NZB) mice. CD4 T cells from NZB mice with autoimmune hemolytic anemia respond to band 3. Previously, we have shown that IL-10 and peptides containing a dominant T cell epitope from red cell band 3 modulate autoimmune hemolytic anemia in NZB mice. Because of the immunoregulatory role of IL-10 in autoimmune diseases, we aim to identify individual band 3 peptides that induce high IL-10 production and simultaneously suppress CD4 T cell proliferation and to investigate the effect intranasal administration of IL-10 producing band 3 peptides on autoantibody responses of NZB mice.

METHODS

Splenic CD4 T cells of NZB mice were isolated and stimulated by co-culture of T cells with individual band 3 peptides. IL-10 production was measured by enzyme-linked immunosorbent assay and proliferative response of CD4 T cells was estimated by incorporation of [³H] thymidine assay. NZB mice were given either PBS, or peptides 25 (241-251) and 29 (282-296) or both peptides intranasally on three occasions at 2-day intervals. The mice were bled at 6, 10 and 18 weeks after peptide inhalation, and the number of RBC auto-antibodies was measured by DELAT and hematocrit values were assessed.

RESULTS

Peptides 25 (241-251) and 29 (282-296) induced the highest IL-10 production by CD4 T cells. These peptides also inhibited the peak T cell proliferative response. 6 and 10 weeks after peptide inhalation, the total IgG, IgG1 and IgG2a in mice treated with both peptides 241-251 and 282-296 were significantly higher than control (P < 0.05). However, no significant difference in the mean hematocrit between of the peptide-treated mice and the control group was found.

CONCLUSIONS

Although band 3 peptides 241-251 and 282-296 induced to the highest IL-10 production by CD4 T cells in vitro but fail to reverse the RBC autoantibody response in vivo. Modifications to improve solubility these peptides might help to modulate the immune response toward a T helper-2 profile and decrease the severity of anemia.

Haematological manifestations of lupus

Our purpose was to compile information on the haematological manifestations of systemic lupus erythematosus (SLE), namely leucopenia, lymphopenia, thrombocytopenia, autoimmune haemolytic anaemia (AIHA), thrombotic thrombocytopenic purpura (TTP) and myelofibrosis. During our search of the English-language MEDLINE sources, we did not place a date-of-publication constraint. Hence, we have reviewed previous as well as most recent studies with the subject heading SLE in combination with each manifestation. Neutropenia can lead to morbidity and mortality from increased susceptibility to infection. Severe neutropenia can be successfully treated with granulocyte colony-stimulating factor. While related to disease activity, there is no specific therapy for lymphopenia. Severe lymphopenia may require the use of prophylactic therapy to prevent select opportunistic infections. Isolated idiopathic thrombocytopenic purpura maybe the first manifestation of SLE by months or even years. Some manifestations of lupus occur more frequently in association with low platelet count in these patients, for example, neuropsychiatric manifestation, haemolytic anaemia, the antiphospholipid syndrome and renal disease. Thrombocytopenia can be regarded as an important prognostic indicator of survival in patients with SLE. Medical, surgical and biological treatment modalities are reviewed for this manifestation. First-line therapy remains glucocorticoids. Through our review, we conclude glucocorticoids do produce a response in majority of patients initially, but sustained response to therapy is unlikely. Glucocorticoids are used as first-line therapy in patients with SLE with AIHA, but there is no conclusive evidence to guide second-line therapy. Rituximab is promising in refractory and non-responding AIHA. TTP is not recognised as a criteria for classification of SLE, but there is a considerable overlap between the presenting features of TTP and SLE, and a few patients with SLE have concurrent TTP. Myelofibrosis is an uncommon yet well-documented manifestation of SLE. We have compiled the cases that were reported in MEDLINE sources.

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.

Indoleamine 2,3 dioxygenase contributes to transferable tolerance in rat red blood cell inducible model of experimental autoimmune haemolytic anaemia

Autoimmune haemolytic anaemia (AIHA) is caused by autoantibodies against red blood cell (RBC) surface antigens that render RBC susceptible to Fc-mediated phagocytosis and complement-mediated lysis. Experimental AIHA can be induced by injection of rat RBC to naive mice, but a lymphocyte-mediated regulatory mechanism eventually suppresses the production of autoantibodies specific for mouse RBC. Critically, this tolerogenic response can be transferred to naive mice by splenocytes from the rat RBC-immunized mouse. Here we investigate whether indoleamine 2,3 dioxygenase (IDO) or the initiators of IDO cascade, including the cytotoxic T lymphocyte antigen (CTLA)-4 receptor and its soluble isoform, contribute to this tolerogenic mechanism. Splenocytes from experimental AIHA mice were transferred adoptively to naive mice under the cover of anti-CTLA-4, anti-soluble CTLA-4 antibodies or IDO inhibitor 1-methyl tryptophan (1-MT). Recipient mice were immunized with rat RBC and levels of antibody against self-RBC and rat-RBC were monitored. Our results indicate that transfer of tolerance to naive recipients is dependent upon IDO-mediated immunosuppression, as mice receiving previously tolerized splenocytes under the cover of 1-MT were refractory to tolerance and developed haemolytic disease upon further challenge with rat RBC. Initiators of IDO activity, CTLA-4 or soluble CTLA-4 did not mediate this tolerogenic process but, on their blockade, boosted antigen-specific effector immune responses.

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.

Increased red cell turnover in a line of CD22-deficient mice is caused by Gpi1c: a model for hereditary haemolytic anaemia

CD22, an inhibitory co-receptor of the BCR, has been identified as a potential candidate gene for the development of autoimmune haemolytic anaemia in mice. In this study, we have examined Cd22(tm1Msn) CD22-deficient mice and identified an increase in RBC turnover and stress erythropoiesis, which might be consistent with haemolysis. We then, however, eliminated CD22 deficiency as the cause of accelerated RBC turnover and established that enhanced RBC turnover occurs independently of B cells and anti-RBC autoanti-bodies. Accelerated RBC turnover in this particular strain of CD22-deficient mice is red cell intrinsic and appears to be the consequence of a defective allele of glucose phosphate isomerase, Gpi1(c). This form of Gpi1 was originally derived from wild mice and results in a substantial reduction in enzyme activity. We have identified the polymorphism that causes impaired catalytic activity in the Gpi1(c) allele, and biochemically confirmed an approximate 75% reduction of GPI1 activity in Cd22(-/-) RBCs. The Cd22(-/-).Gpi1(c) congenic mouse provides a novel animal model of GPI1-deficiency, which is one of the most common causes of chronic non-spherocytic haemolytic anaemia in humans.

Regulatory T cells essential to prevent the loss of self-tolerance in murine models of erythrocyte-specific autoantibody responses

The spontaneous appearance of anti-erythrocyte autoantibodies resulting in autoimmune hemolytic anemia described in NZB mice more than 40 years ago provided a model for the study of mechanisms behind the loss of self-tolerance. We developed an in vitro model of this anti-MRBC response in which CD8(+) suppressor T cells were shown to be a controlling element. CD8(+) T cells from young NZB mice co-cultured with spleen cells from old, actively autoimmune NZB mice suppressed the anti-MRBC responses of the old mice. Eliminating the CD8(+) cells from young NZB spleen cells or even from non-autoimmune BALB/c spleen cells prior to culture removed the controlling influence of these CD8(+) cells and allowed the development of anti-MRBC-secreting cells. This review will consider the role of the CD8(+) suppressive cells in the anti-self-erythrocyte model in light of insights provided by current 'regulatory T cell' literature.

The Lbw2 locus promotes autoimmune hemolytic anemia

The lupus-prone New Zealand Black (NZB) strain uniquely develops a genetically imposed severe spontaneous autoimmune hemolytic anemia (AIHA) that is very similar to the corresponding human disease. Previous studies have mapped anti-erythrocyte Ab (AEA)-promoting NZB loci to several chromosomal locations, including chromosome 4; however, none of these have been analyzed with interval congenics. In this study, we used NZB.NZW-Lbw2 congenic (designated Lbw2 congenic) mice containing an introgressed fragment of New Zealand White (NZW) on chromosome 4 encompassing Lbw2, a locus previously linked to survival, glomerulonephritis, and splenomegaly, to investigate its role in AIHA. Lbw2 congenic mice exhibited marked reductions in AEAs and splenomegaly but not in anti-nuclear Abs. Furthermore, Lbw2 congenics had greater numbers of marginal zone B cells and reduced expansion of peritoneal cells, particularly the B-1a cell subset at early ages, but no reduction in B cell response to LPS. Analysis of a panel of subinterval congenic mice showed that the full effect of Lbw2 on AEA production was dependent on three subloci, with splenomegaly mapping to two of the subloci and expansions of peritoneal cell populations, including B-1a cells to one. These results directly demonstrated the presence of AEA-specific promoting genes on NZB chromosome 4, documented a marked influence of background genes on autoimmune phenotypes related to Lbw2, and further refined the locations of the underlying genetic variants. Delineation of the Lbw2 genes should yield new insights into both the pathogenesis of AIHA and the nature of epistatic interactions of lupus-modifying genetic variants.

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.

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.

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.

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.

IL-4 and IL-10 modulate autoimmune haemolytic anaemia in NZB mice

New Zealand Black (NZB) mice spontaneously develop autoimmune haemolytic anaemia (AIHA). Here the effect of injecting NZB mice with plasmids encoding IL-4 (pIL-4) or IL-10 (pIL-10) on NZB disease was tested. Both constructs delayed the development of anaemia as judged by increased haematocrit values as compared with controls, but neither altered the IgG1 to IgG2 red blood cell (RBC) bound autoantibody levels. The increased haematocrit value was associated temporally with increased RBC bound IgG in NZB mice treated with pIL-10, but not pIL-4. By contrast, up-regulation of splenic macrophage FcgammaRIIb2 mRNA was associated temporally with increased haematocrit values in NZB mice given pIL-4. However, no such increase occurred in NZB mice that inhaled a peptide containing a dominant T-cell epitope, although this treatment is known to bias the autoimmune response towards Th2 and to reduce the severity of anaemia. It is considered that IL-4 treatment, in part, ameliorates NZB anaemia by increasing the expression of the inhibitory FcgammaRIIb2 and thereby reducing the capacity of splenic macrophages to phagocytose autoantibody coated RBC, but that this mechanism does not explain the beneficial effects of the inhaled peptide.

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.

Peptides containing a dominant T-cell epitope from red cell band 3 have in vivo immunomodulatory properties in NZB mice with autoimmune hemolytic anemia

The major target of the pathogenic red blood cell (RBC) autoantibodies in New Zealand black (NZB) mice is the anion channel protein band 3, and CD4+ T cells from NZB mice respond to band 3. Here, we demonstrate that a band 3 peptide 861-875, which is the predominant sequence recognized by NZB T cells in vitro, bears a dominant helper epitope able to modulate the autoimmune hemolyic anemia in vivo. The development of RBC-bound autoantibodies and anemia was accelerated in NZB mice injected with peptide 861-874, which is relatively insoluble, and inhalation of the peptide primed T cells for both peptide 861-874 and band 3 responses. By contrast, inhalation of a soluble analog (Glu861, Lys875) of peptide 861-874 deviated the autoimmune response toward a T helper-2 (Th2) profile, with marked increases in the ratio of interleukin-4 to interferon-gamma produced by splenic T cells responding in vitro to either peptide 861-874 or band 3. Moreover, in mice that had received such treatment, the proportion of RBC-bound immunoglobulin G (IgG) molecules that were of the Th2-associated IgG1 isotype was also increased, and anemia was less severe. It is concluded that NZB autoimmune hemolytic anemia is helper dependent and that nasal administration of different peptides containing the dominant T-cell epitope can have potentially detrimental or beneficial effects on the disease.

Regulatory T cells secreting IL-10 dominate the immune response to EBV latent membrane protein 1

Viruses exploit a number of strategies to evade immune recognition. In this study, we describe a novel mechanism by which EBV, rather than avoiding detection, subverts the immune response by stimulating regulatory T cells that secrete IL-10. Human PBMC from all EBV-seropositive, but not -seronegative, donors responded to both purified latent membrane protein 1 and the corresponding immunodominant peptides with high levels of IL-10 secretion by CD4(+) T cells. These IL-10 responses, characteristic of T regulatory 1 cells, inhibited T cell proliferation and IFN-gamma secretion induced by both mitogen and recall Ag. It was confirmed that the inhibition was IL-10 dependent by the use of neutralizing Ab. The deviation of the immune response toward suppression is likely to be important in maintaining latency and EBV-associated tumors.

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.

Characterization of the dominant autoreactive T-cell epitope in spontaneous autoimmune haemolytic anaemia of the NZB mouse

NZB mice spontaneously develop autoimmune haemolytic anaemia (AIHA) due to a T helper-dependent autoantibody response against the erythrocyte anion channel protein, Band 3. Here, we characterize the recognition of the Band 3 sequence 861-874, which carries the dominant, I-E(d)-restricted T cell epitope. The ability of N and C-terminal truncated versions of peptide 861-874 to elicit NZB splenic T-cell proliferation indicated that the core epitope spans residues 862-870. Next, a set of alanine substitution analogues was tested to determine which residues functioned either as MHC anchor or TCR contact residues. A combination of proliferation and MHC:peptide binding assays identified residues 862(L), 864(V), 865(L), and 869(K) as I-E(d) anchor residues, and 868(V) as the only TCR contact residue. The ability of the wild-type sequence 861-874 to compete with a high affinity reference peptide for binding to I-E(d) indicates that the escape of pathogenic NZB T cells from purging of the autoreactive repertoire cannot be attributed to ineffective presentation of peptide 861-874 by its restricting element. It will now be possible to design altered peptide ligands of Band 3 861-874, in order to further dissect the mechanisms responsible for the maintenance and loss of T cell tolerance to RBC autoantigens, and to modulate the immune response in AIHA.

Selective increase of autoimmune epitope expression on aged erythrocytes in mice: implications in anti-erythrocyte autoimmune responses

We investigated the impact of changes occurring during red blood cell (RBC) ageing on the RBC-binding activity of pathogenic anti-erythrocyte monoclonal antibodies derived from autoimmune-prone New Zealand black (NZB) mice. As assessed by flow cytometric analysis on in vivo biotinylated RBCs, all five NZB-derived anti-RBC mAb exhibited more efficient binding to aged RBCs than to young RBCs, and resulted in a selective elimination of more aged RBCs from the circulating blood. In addition, treatment of RBCs with proteases markedly enhanced the binding of all five anti-RBC mAb, raising the possibility that increased exposure of autoimmune epitopes on aged RBCs may be in part, a result of contacts with proteolytic enzymes during the lifetime of circulating RBCs. In marked contrast, the binding activity of mAb raised in non-autoimmune animals against antigens expressed on RBCs, such as CD44, CD47, CD147 and TER-119, was either decreased or unchanged with RBC ageing, and these epitopes, except for that recognized by anti-CD47 mAb, were highly sensitive to mild treatment with proteases. Our data unravel the unique molecular feature of RBC epitopes involved in autoimmune haemolytic anaemia, suggesting that membrane alterations in aged RBCs might play a significant role in the development of the autoantibody response to RBCs.

Antigen specificity in canine autoimmune haemolytic anaemia

Autoimmune haemolytic anaemia (AIHA) is the most common clinical manifestation of autoimmunity in the dog and generally presents as a profound, regenerative, Coombs' positive anaemia of acute or chronic onset. The disease pathogenesis involves formation of erythrocyte-specific autoantibodies of the IgG and IgM class that may fix complement resulting in intra- or extravascular haemolysis. Western blotting and immunoprecipitation studies using autoantibody eluted from the erythrocytes of dogs with AIHA have demonstrated specificity for erythrocyte glycophorins and the membrane anion-exchange molecule (band 3). Autoantibodies specific for the cytoskeletal molecule spectrin have been identified in serum by ELISA. The specificity of autoreactive T-cells has been examined in vitro using bulk cultures stimulated with a panel of autoantigens including intact erythrocyte membranes, purified glycophorin and spectrin fractions and a panel of overlapping 15-mer glycophorin peptides. Control responses to ConA and recall (vaccine antigens) and non-recall (KLH) antigens were measured in the same system. PBMC obtained from dogs that had recovered from AIHA consistently proliferated in response to erythrocyte membranes, with occasional responses to spectrin or glycophorin. PBMC from sone clinically normal dogs also responded to erythrocyte membranes. PBMC obtained from dogs closely related to AIHA cases gave the most consistent responses, including proliferation when stimulated by the glycophorin peptides. These data suggest that normal dogs harbour erythrocyte autoreactive lymphocytes, and that these cells may be primed in dogs recovered from AIHA or having genetic susceptibility to the disease.

Splenic but not thymic autoreactive T cells from New Zealand Black mice respond to a dominant erythrocyte Band 3 peptide

Previous work from our laboratory suggested that erythrocyte Band 3 peptide 861-874 is the dominant epitope recognized by splenic T cells from adult New Zealand Black (NZB) mice that are developing autoimmune haemolytic anaemia (AIHA). Here, it is shown that splenic T cells from 6-week-old NZB mice mount a vigorous in vitro proliferative response to peptide 861-874 and some other selected Band 3 peptides. As the donors grow older, splenic T cells respond to an increasing number of Band 3 peptides and the magnitude of their response also becomes greater. Splenic T cells from 3-week-old NZB mice still responded vigorously to peptide 861-874 and Band 3. By contrast, neither thymocytes nor single-positive CD4-enriched thymus cells from NZB mice responded to peptide 861-874 or Band 3, although they responded to concanavalin A (Con A). However, thymocytes from mice expressing a transgenic T-cell receptor (TCR)-specific for myelin basic protein (MBP) peptide Ac 1-9 responded vigorously to Ac 1-9. It is considered that the T-cell response of NZB mice to Band 3 is initially focused on peptide 861-874 and later spreads to other Band 3 peptides as the disease progresses and that peptide 861-874-reactive T cells are primed in the periphery rather than the thymus.

Proliferative responses of peripheral blood mononuclear cells from normal dogs and dogs with autoimmune haemolytic anaemia to red blood cell antigens

Autoimmune haemolytic anaemia (AIHA), one of the most common autoimmune diseases of the dog, is characterised by binding of autoantibody to erythrocyte membrane antigens leading to a decreased red blood cell (RBC) life-span. Failure of self-tolerance with activation of autoreactive T-lymphocytes is thought to play a key role in the initiation of such autoimmune events. Peripheral blood mononuclear cells (PBMC) were obtained from 11 clinically normal dogs, six clinically normal relatives of two littermate dogs which died from AIHA, and four dogs which had recovered from primary AIHA. Cells were stimulated in vitro with a panel of canine RBC-derived antigens (RBC membranes, glycophorin, spectrin, five 15-mer glycophorin peptides), the non-recall antigen keyhole limpet haemocyanin (KLH), and the mitogen concanavalin A (Con A). The kinetics of the proliferative responses to specific antigens were assessed by serially sampling the cultures from days 4 to 10. PBMC from all dogs responded strongly to Con A (day 2) and to KLH (maximal response on days 7 to 10) under appropriate culture conditions. Two of 11 normal dogs responded weakly to RBC membranes (mean stimulation index = 4.25). In contrast, PBMC from all dogs recovered from AIHA responded to RBC membranes (mean SI = 9.2 +/- 2.5) and occasionally to other erythrocyte antigens. Similar responses were recorded with PBMC from dogs related to AIHA cases. It is considered that although normal individuals harbour erythrocyte-reactive lymphocytes, such cells are primed in dogs with AIHA or a genetic susceptibility to this disease.

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.

Altered response to and production of TGF-beta by B cells from autoimmune NZB mice

New Zealand Black (NZB) mice spontaneously develop immune dysfunction manifested as autoimmune hemolytic anemia and systemic lupus erythematosus. In later life, a subset of these mice develop clonal CD5+ B cell tumors analogous to human chronic lymphocytic leukemia (CLL). NZB disease is marked by B cell hyperactivity characterized by spontaneous immunoglobulin secretion and proliferation. Elimination of autoreactive lymphocytes by apoptosis is a vital mechanism to prevent expansion of self-reactive lymphocyte population. TGF-beta appears to be an important factor in normal and abnormal immune regulation and this cytokine may play a role in the development of chronic human B cell tumors. We asked whether the response to or production of TGF-beta by NZB B cells was aberrant and could contribute to disease development. In this study, we demonstrated that the apoptotic response to TGF-beta was increased in B cells from NZB mice compared to B cells from normal BALB/c mice. The increased apoptosis was related to endogenous activation and was possibly mediated through increased expression of the TGF-beta Type II receptor. Despite functional differences between CD5-negative B cells and CD5-positive B cells, TGF-beta induced apoptosis in both populations to a similar extent. NZB B cells also secrete increased active TGF-beta compared to BALB/c B cells. We suggest that the aberrant secretion of active TGF-beta and the increased response to the apoptotic effects of TGF-beta by NZB B cells may play a role in the disease process of these mice, perhaps attempting to limit the autoimmune phenomena, but possibly also contributing to generalized immunosuppression. We also suggest that the CD5(+) tumors in the NZB mouse may not be a fully appropriate model of human CLL, since CLL B cells are abnormally resistant to the apoptotic effects of TGF-beta.

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.

Infection of C3HeB/FeJ mice with the docile strain of lymphocytic choriomeningitis virus induces autoantibodies specific for erythrocyte Band 3

C3HeB/FeJ mice infected with the docile strain of lymphocytic choriomeningitis virus (LCMV-d) develop a persistent infection with a transient haemolytic anaemia. Immunoglobulin can be eluted from the red blood cells (RBC) of these mice but it cannot be detected on the RBC by a conventional antiglobulin test. The present study demonstrates that RBC from such mice bear erythrocyte autoantibodies which are predominantly of the IgG2a subclass, with lower levels of autoantibodies of the IgG1, IgG2b and IgG3 subclasses. To identify the target antigen the autoantibodies were eluted from the RBC of LCMV-infected mice. The eluted autoantibody bound to intact normal RBC and precipitated a 105000 MW component that corresponds to murine Band 3 protein. A monoclonal antibody derived from mice infected with LCMV-d also precipitated mouse Band 3, and reacted specifically by enzyme-linked immunosorbent assay against a purified preparation of Band 3. This study has shown that in C3H mice infected with LCMV-d which develop autoimmune haemolytic anaemia, the target autoantigen is erythrocyte membrane Band 3.

T-helper 1 dominated responses to erythrocyte Band 3 in NZB mice

Band 3, the red blood cell (RBC) anion channel protein, is the target autoantigen for the pathogenic RBC autoantibodies and T-helper (Th) cells in New Zealand Black (NZB) mice with autoimmune haemolytic anaemia (AIHA). To determine the subpopulation of these Th cells, they were stimulated with Band 3 and the profile of the cytokines elaborated by the responding cells was measured. NZB T cells stimulated with Band 3 produced high levels of the Th1 cytokine, interferon-gamma (IFN-gamma), but little or no interleukin-4 (IL-4), IL-5 or IL-10. Similar patterns were produced by NZB T cells responding to a spectrin preparation from the RBC membrane skeleton, or to mycobacterial heat-shock protein (hsp) 65 following immunization of mice with hsp 65 in incomplete adjuvant. By contrast, T cells from CBA mice similarly immunized with hsp 65 produced high levels of IL-4 and IL-5 in response to hsp 65. Examination of the isotype of the RBC-bound immunoglobulins in NZB mice revealed that immunoglobulin G2a (IgG2a) autoantibodies were the first to be detected in most mice and that later in the disease, IgG3 autoantibodies were often prominent. It is concluded that, contrary to expectation, the development of RBC autoantibodies in NZB mice is associated with Th1 cytokine-dominated responses.

Origin of blood-group antigens: a self-declaration mechanism in somatic cell society

Blood-group antigens have been developed as a self-declaration mechanism in higher organisms, since blood cells carry different DNA from that of germ-line cells, and their selfishness must be strictly limited. If not, symbiosis between somatic DNA and germ-line DNA cannot be maintained since blood cells can express autonomy programmed within themselves. For the sake of maintenance of symbiosis, this self-declaration is not limited to blood cells and all somatic cells need a self-plural declaration mechanism such as blood-group antigens. Differentiation and development including induction and inhibition also depend on the self-declaration--recognition mechanism.

Autoreactive T cell specificity in autoimmune hemolytic anemia of the NZB mouse

Splenic T cells from Coombs'-positive New Zealand Black (NZB) mice proliferated consistently in vitro in response to the integral red blood cell (RBC) membrane protein Band 3, the antigen previously shown to be the target for the pathogenic RBC autoantibodies. The responding cells predominantly express CD4 and the proliferative response is blocked by antibodies to the NZB major histocompatibility complex class II but not by antibodies to an irrelevant H-2 haplotype. NZB splenic T cells also proliferated in response to the internal membrane skeleton protein spectrin. By contrast, T cells from BALB/c and DBA2 mice, which bear the same H-2 haplotype as NZB mice, but which do not develop autoimmune hemolytic anemia (AIHA), fail to respond to Band 3. It is considered that these results support the hypothesis that Band 3-reactive T cells provide help for the production of pathogenic anti-Band 3 autoantibodies in NZB mice. T cells from Coombs'-negative NZB mice as young as 3 weeks old proliferated in response to Band 3; moreover, the RBC from Coombs'-negative mice bore elevated levels of autoantibody as judged by a sensitive direct enzyme-linked anti-globulin test. Thus, the pathology of AIHA develops at a much earlier age than was thought previously.

Autoimmune hemolytic anemia

Autoimmune hemolytic anemia (AHA) is characterized by the production of Coombs' antibodies, which are responsible for the destruction of red blood cells (RBCs). Analysis of both monoclonal anti-RBC autoantibodies derived from autoimmune New Zealand black mice and transgenic mice expressing a pathogenic IgM anti-RBC autoantibody has considerably improved our understanding of the B-cell responses involved in AHA, although our knowledge of T-cell immunity in AHA is still limited. The identification of the major T-cell epitope in the context of MHC class II molecules would be of paramount importance in helping to elucidate the cellular and molecular basis central to the development of AHA.

Affinity maturation and isotype switch in clonally related anti-erythrocyte autoantibodies

The NZB mouse is genetically predisposed to develop, at approximately 6 months of age, a spontaneous and severe autoimmune anaemia caused by production of pathogenic anti-mouse erythrocyte autoantibodies. Molecular analysis of a panel of five anti-erythrocyte monoclonal antibodies (MoAb) derived from splenocytes of unimmunized NZB mice revealed that these autoantibodies all had functionally rearranged genes from the VH J558 family of immunoglobulin genes with closest homology to germline genes H10 and H30. Owing to clustering of nucleotide differences within the CDRs, compared with the germline, it was concluded that these antibodies were most likely generated by an antigen-driven mechanism. We report here further molecular analysis of two (4.16.1 and B4.13.2) of the panel of five anti-mouse erythrocyte producing hybridomas which are apparently clonally related. Nucleotide analysis of the light chain cDNA indicated that both antibodies had closest homology to germline gene V kappa 24 and use J kappa 2 gene. Determination of the functional affinities of the MoAb reveal that B4.13.2 (IgG2a) has a > 10-fold higher affinity for mouse erythrocytes when compared to 4.16.1 (IgG1). This finding supports the view that these two autoantibodies are generated by an antigen-driven mechanism. The proposed mechanism would involve the selection and expansion of a small population of B-lymphocytes by antigen leading to isotype switch, somatic mutation and increased affinity. Our data also point to the possibility that some framework residues may be involved in the binding to antigen.

Production of erythrocyte autoantibodies in NZB mice is inhibited by CD4 antibodies

NZB mice spontaneously develop haemolytic anaemia as the result of production of erythrocyte autoantibodies. The mechanisms leading to breakdown in tolerance to erythrocyte autoantigens are unknown. Antibodies to CD4 have been successfully used to treat several murine models of autoimmune disease. In this study we injected NZB mice with non-depleting CD4 antibodies and were able to prevent and abrogate erythrocyte autoantibody production in young (Coombs' negative) and old (Coombs' positive) mice, respectively. Our data indicate the dependency of autoantibody production on CD4+ T cells. However, withdrawal of anti-CD4 antibodies resulted in the appearance of erythrocyte autoantibodies, showing that under these conditions we were unable to re-establish tolerance to autoantigens on erythrocytes using anti-CD4 treatment.

IgG glycosylation in autoimmune-prone strains of mice

The relationship between increased levels of IgG oligosaccharide chains lacking galactose (G0) and the development of rheumatoid arthritis is unclear. In order to further our understanding of the observed correlation between raised serum G0 and arthritis, we have studied G0 levels in arthritis-prone and non-susceptible (i.e. non-arthritis-prone) mice and the effects on G0 of mycobacterial antigens, which have been postulated to play a role in the early events leading to the development of arthritis. We have shown that different age-matched mouse strains have characteristic 'resting' levels of G0 which (in six out of seven strains of mice) increase with age. We have also shown that these increases can be enhanced by immunization of arthritis-prone strains of mice with an adjuvant containing mycobacteria (Freund's complete adjuvant (FCA)), suggesting that deflects in the ability to regulate these G0 changes may be related to susceptibility to arthritis.