Autoimmune hemolytic anemia and thrombocytopenia in a Chinese patient with heterozygous NBAS mutations: Case report

RATIONALE

Neuroblastoma amplified sequence (NBAS)-associated disease is an autosomal recessive disorder and a broad spectrum of clinical symptoms has been reported. However, autoimmune mediated hemolytic anemia (AIHA) is rarely reported in NBAS disease.

PATIENT CONCERNS

A now 21-year-old male harbors heterozygous variants of c.6840G>A and c.335 + 1G>A and was found had retarded growth, hypogammaglobulinemia, B lymphopenia, optic atrophy, horizontal nystagmus, slight splenomegaly and hepatomegaly since childhood. This case had normal hemoglobin level and platelet count in his childhood. He developed AIHA first in his adulthood and then thrombocytopenia during the treatment of AIHA. The mechanism underlying a case with pronounced hypogammaglobulinemia and B lymphopenia is elusive. In addition to biallelic NBAS mutations, a germline mutation in the ANKRD26 (c.2356C>T) gene was also detected. So either autoimmune or ANKRD26 mutation-mediated thrombocytopenia is possible in this case.

INTERVENTION AND OUTCOME

He was initially managed with steroid and intermittent intravenous immunoglobulin supplement. After treatment, he responded well with a normalization of hemoglobin and serum bilirubin. But the patient subsequently experienced severe thrombocytopenia in addition to AIHA. He was then given daily avatrombopag in addition to steroid escalation. He responded again to new treatment, with the hemoglobin levels and platelet counts went back to the normal ranges. Now he was on de-escalated weekly avatrombopag and low-dose steroids maintenance.

CONCLUSION

The phenotype of this case indicates that c.335 + 1G>A NBAS variant is probably a pathogenic one and c.2356C>T ANKRD26 variant is improbably a pathogenic one. AIHA may respond well to steroid even when happened in patients with NBAS disease.

Gene expression analysis revealed downregulation of complement receptor 1 in clonal B cells in cold agglutinin disease

Cold agglutinin disease (CAD) is a rare B-cell lymphoproliferative disorder of the bone marrow, manifested by autoimmune hemolytic anemia caused by binding of monoclonal IgM autoantibodies to the I antigen. Underlying genetic changes have previously been reported, but their impact on gene expression profile has been unknown. Here, we define differentially expressed genes in CAD B cells. To unravel downstream alteration in cellular pathways, gene expression by RNA sequencing was undertaken. Clonal B-cell samples from 12 CAD patients and IgM-expressing memory B cells from 4 healthy individuals were analyzed. Differential expression analysis and filtering resulted in 93 genes with significant differential expression. Top upregulated genes included SLC4A1, SPTA1, YBX3, TESC, HBD, AHSP, TRAF1, HBA2, RHAG, CA1, SPTB, IL10, UBASH3B, ALAS2, HBA1, CRYM, RGCC, KANK2, and IGHV4-34. They were upregulated at least 8-fold, while complement receptor 1 (CR1/CD35) was downregulated 11-fold in clonal CAD B cells compared to control B cells. Flow cytometry analyses further confirmed reduced CR1 (CD35) protein expression by clonal CAD IgM+ B cells compared to IgM+ memory B cells in controls. CR1 (CD35) is an important negative regulator of B-cell activation and differentiation. Therefore, reduced CR1 (CD35) expression may increase activation, proliferation, and antibody production in CAD-associated clonal B cells.

Evaluating the prevalence of inborn errors of immunity in adults with chronic immune thrombocytopenia or Evans syndrome

Inborn errors of immunity (IEIs) are monogenic disorders that predispose patients to immune dysregulation, autoimmunity, and infection. Autoimmune cytopenias, such as immune thrombocytopenia (ITP) and Evans syndrome (a combination of ITP and autoimmune hemolytic anemia), are increasingly recognized phenotypes of IEI. Although recent findings suggest that IEIs may commonly underlie pediatric ITP and Evans syndrome, its prevalence in adult patients with these disorders remains undefined. This study sought to estimate the prevalence of underlying IEIs among adults with persistent or chronic ITP or Evans syndrome using a next-generation sequencing panel encompassing >370 genes implicated in IEIs. Forty-four subjects were enrolled from an outpatient adult hematology clinic at a tertiary referral center in the United States, with a median age of 49 years (range, 20-83). Fourteen subjects (31.8%) had secondary ITP, including 8 (18.2%) with Evans syndrome. No cases of IEI were identified despite a high representation of subjects with a personal history of autoimmunity (45.5%) and early onset of disease (median age at diagnosis of 40 years [range, 2-77]), including 20.5% who were initially diagnosed as children. Eight subjects (18.2%) were found to be carriers of pathogenic IEI variants, which, in their heterozygous state, are not disease-causing. One case of TUBB1-related congenital thrombocytopenia was identified. Although systematic screening for IEI has been proposed for pediatric patients with Evans syndrome, findings from this real-world study suggest that inclusion of genetic testing for IEI in the routine work-up of adults with ITP and Evans syndrome has a low diagnostic yield.

Purine Nucleoside Phosphorylase Deficiency in Two Unrelated Patients with Autoimmune Hemolytic Anemia and Eosinophilia: Two Novel Mutations

Two Iranian patients with purine nucleoside phosphorylase (PNP) deficiency are described in terms of their clinical and molecular evaluations. PNP deficiency is a rare form of combined immunodeficiency with a profound cellular defect. Patients with PNP deficiency suffer from variable recurrent infections, hypouricemia, and neurological manifestations. Furthermore, patient 1 developed mild cortical atrophy, and patient 2 presented developmental delay, general muscular hypotonia, and food allergy. The two unrelated patients with developed autoimmune hemolytic anemia and T cells lymphopenia and eosinophilia were referred to Immunology, Asthma and Allergy Research Institute (IAARI) in 2019. After taking blood and DNA extraction, genetic analysis of patient 1 was performed by PCR and direct sequencing and whole exome sequencing was applied for patient 2 and the result was confirmed by direct sequencing in the patient and his parents. The genetic result showed two novel variants in exon 3 (c.246_285+9del) and exon 5 (c.569G>T) PNP (NM_000270.4) in the patients, respectively. These variants are considered likely pathogenic based on the American College of Medical Genetics and Genomics (ACMG) guideline. PNP deficiency has a poor prognosis; therefore, early diagnosis would be vital to receive hematopoietic stem cell transplantation (HSCT) as a prominent and successful treatment.

Co-Occurring Thrombotic Thrombocytopenic Purpura and Autoimmune Hemolytic Anemia in a Child Carrying the Pathogenic SHOC2 c.4A>G (p.Ser2Gly) Variant

BACKGROUND RASopathies involve mutations in genes that encode proteins participating in the RAS-mitogen-activated protein kinase pathway and are a collection of multisystem disorders that clinically overlap. Variants in the SHOC2 gene have been reported in Noonan-like syndrome, which include distinct facial features, short stature, congenital cardiac defects, developmental delays, bleeding disorders, and loose anagen hair. This report is of a 7-year-old girl with the c.4A>G (p.Ser2Gly) variant of the SHOC2 gene, consistent with Noonan-like syndrome, with loose anagen hair, presenting with thrombotic thrombocytopenic purpura and autoimmune hemolytic anemia. CASE REPORT The child had a medical history of 7 hospitalizations at our institution. At the age of 2 months, she underwent surgical correction for ventricular and atrial septal defects. At the age of 2 years, tonsil and adenoid removal surgery was performed, followed by surgery for otitis media at age 5 years. At 7 years, she was hospitalized for the simultaneous occurrence of thrombotic thrombocytopenic purpura and autoimmune hemolytic anemia. The patient displayed short stature and mild intellectual disability. Notable facial features included sparse hair, mild frontal bossing, and low-set ears. Antinuclear antibody levels demonstrated a significant gradual shift. Through trio whole-exome sequencing, a c.4A>G (p.Ser2Gly) variation in the SHOC2 gene was identified. CONCLUSIONS Given the clinical information and genetic testing results, the patient's condition appeared to closely be a type of RASopathy. This report has highlighted the importance of physical, developmental, and genetic testing in children presenting with dysmorphism, developmental delay, and hematological abnormalities.

Cytokine polymorphisms in patients with autoimmune hemolytic anemia

Autoimmune hemolytic anemia (AIHA) is due to autoantibodies with or without complement activation and involves cellular and cytokine dysregulation. Here, we investigated cytokine single-nucleotide polymorphisms (SNPs) of TNF-α, TGF-β1, IL-10, IL-6, and IFN-γ, along with their serum levels. The former were related to hematological parameters, therapy, and clinical outcome. The study included 123 consecutive patients with primary AIHA [77 warm AIHA and 46 cold agglutinin disease (CAD)], followed up for a median of 49 months. Results show that the allelic frequency of TNF-α -308 G/A polymorphisms was significantly lower in patients versus controls. Moreover, the genotypic frequency of TNF-α -308G/A and TGF-β gene codon 25 G/C genotypes was significantly lower in patients versus controls. Considering cytokine SNP genotypes associated with different gene expression levels, TNF-α high gene expression was significantly more frequent in patients, TGF-β and IL-10 high gene expression was higher in patients with more severe anemia, and TGF-β high gene expression was higher in patients with active disease. Considering treatment, TNF-α and TGF-β high gene expression was more frequent in multitreated patients and particularly in CAD. It may be speculated that this genetic predisposition to a stronger inflammatory response may result in a greater immune dysregulation and in a relapsed/refractory disease. Regarding cytokine serum levels, TNF-α and TGF-β were significantly lower, and IL-10 and IL-6 were significantly higher in patients versus controls, underlying the complex interplay between genetic background and disease features.

Evans syndrome caused by a deleterious mutation affecting the adaptor protein SASH3

Increasing evidence suggests multilineage cytopenias (also known as Evans syndrome) may be caused by inborn errors of immunity (IEI) with immune dysregulation. We studied a patient with autoimmune haemolytic anaemia and immune thrombocytopenia and identified a germline mutation in SASH3 (c.862C>T;p.Arg288Ter), indicating a recently identified IEI. Immunohistochemistry performed after clinically indicated splenectomy revealed severe hypoplasia/absence of germinal centres. The autoimmune phenotype was associated with an increased CD21low T-bet+ CD11c+ subset along with decreased regulatory T cells, impaired T-cell proliferation and T-cell exhaustion. The younger brother carries the same SASH3 mutation and shares immunophenotypic features but is currently clinical asymptomatic, indicating heterogeneity of SASH3 deficiency.

Common Variable Immunodeficiency, Autoimmune Hemolytic Anemia, and Pancytopenia Associated With a Defect in IKAROS

OBJECTIVE

Mutations in IKZF1, which encodes Ikaros family zinc finger 1 (IKAROS) transcription factor, are associated with recurrent infections, cytopenia, autoimmune diseases, and hematologic malignancies. Diverse clinical phenotypes resulting from IKZF1 mutations include pulmonary fungal infections, cytopenia, autoimmune hemolytic anemia (AIHA), and malignancies. In this study, we aimed to assess the DNA-binding ability and pericentromeric (PC) localization of a variant of IKZF discovered in a patient.

MATERIALS AND METHODS

DNA-binding ability of a pathogenic IKZF variant was tested using electrophoretic mobility shift assay and PC localization of the variant was assessed by immunofluorescent microscopy in NIH3T3 cells.

RESULTS

Clinical features of a 3-month-old male infant who underwent hematopoietic stem cell transplantation because of an IKZF1 mutation-associated common variable immunodeficiency, AIHA, and pancytopenia are described. DNA studies revealed a heterozygous missense variant (IKZF1 NM_006060 c.427C>T; p.R143W). Cotransfection studies revealed that mutant R143W has a partial dominant-negative effect over PC targeting and DNA binding.

CONCLUSIONS

IKZF1 mutation must be kept in mind if neonatal AIHA, common variable immunodeficiency, and pancytopenia are observed.

Breed predispositions, clinical findings, and prognostic factors for death in dogs with nonregenerative immune-mediated anemia

BACKGROUND

Breed predispositions, survival, and prognostic factors have not been evaluated in dogs with nonregenerative immune-mediated anemia (nrIMA).

HYPOTHESIS/OBJECTIVES

To describe clinicopathologic variables, evaluate their associations with survival, and determine breed predispositions for dogs with nrIMA.

ANIMALS

Fifty-nine client-owned dogs with nrIMA.

METHODS

Referral hospital records were reviewed retrospectively for dogs with primary nrIMA (PCV ≤30%, corrected reticulocyte percentage (CR%) ≤1.0, bone marrow sampling with evidence of immune-mediated destruction, and underlying causes excluded). Breed predispositions were evaluated by calculation of odds ratios in a case control study; prognostic factors by logistic regression in a cohort study.

RESULTS

Fifty-nine dogs with nrIMA had a median PCV of 12% (interquartile range [IQR]: 10%-17%) and CR% 0.1 (0%-0.2%). At least ≥1 ACVIM IMHA diagnostic criteria were met by 35 dogs (59%). Whippets, Lurchers, and miniature Dachshunds were predisposed to nrIMA. Median survival time was 277 days (IQR: 37-1925), with 3- and 12-month survival rates 61% and 43%, respectively. Erythroid regeneration and remission were achieved by 88% and 62% of dogs, respectively. Corrected reticulocyte percentage >0.2 was associated with improved survival.

CONCLUSION AND CLINICAL IMPORTANCE

Although there is overlap of clinical features between dogs with IMHA and nrIMA, the prognosis for those with nrIMA depends predominantly on the severity of reticulocytopenia.

RNA sequencing of whole blood in dogs with primary immune-mediated hemolytic anemia (IMHA) reveals novel insights into disease pathogenesis

Immune-mediated hemolytic anemia (IMHA) is a life-threatening autoimmune disorder characterized by a self-mediated attack on circulating red blood cells. The disease occurs naturally in both dogs and humans, but is significantly more prevalent in dogs. Because of its shared features across species, dogs offer a naturally occurring model for studying IMHA in people. In this study, we used RNA sequencing of whole blood from treatment-naïve dogs to study transcriptome-wide changes in gene expression in newly diagnosed animals compared to healthy controls. We found many overexpressed genes in pathways related to neutrophil function, coagulation, and hematopoiesis. In particular, the most highly overexpressed gene in cases was a phospholipase scramblase, which mediates the externalization of phosphatidylserine from the inner to the outer leaflet of cell membranes. This family of genes has been shown to be critically important for programmed cell death of erythrocytes as well as the initiation of the clotting cascade. Unexpectedly, we found marked underexpression of many genes related to lymphocyte function. We also identified groups of genes that are highly associated with the inflammatory response and red blood cell regeneration in affected dogs. We did not find any genes that distinguished dogs that lived vs. those that died at 30 days following diagnosis, nor did we find any relevant genomic signatures of microbial organisms in the blood of affected animals. Future studies are warranted to validate these findings and assess their implication in developing novel therapeutic approaches for dogs and humans with IMHA.

Autoimmune hemolytic anemia and immune thrombocytopenia following hematopoietic stem cell transplant: A critical review of the literature

Autoimmune cytopenias (AIC) post-hematopoietic stem cell transplant (HSCT) are rare but exceptionally challenging complication. We conducted a comprehensive literature review and identified a pooled incidence of post-HSCT autoimmune hemolytic anemia and/or immune thrombocytopenia of 2.66% (SE = 0.27) in pediatric patients. Nonmalignant disease, unrelated donor transplant, peripheral or cord blood stem cell source, conditioning regimen without total body irradiation, and presence of chronic graft-versus-host disease were prominent risk factors. Treatment was highly variable, and cytopenias were commonly refractory. AIC represent a significant post-HSCT complication. We report here the incidence, risk factors, and possible biology behind the development of AIC in pediatric post-HSCT patients.

Warm antibody autoimmune hemolytic anemia

Autoimmune hemolytic anemia (AIHA) is a rare and heterogeneous disease that affects 1 to 3/100 000 patients per year. AIHA caused by warm autoantibodies (w-AIHA), ie, antibodies that react with their antigens on the red blood cell optimally at 37°C, is the most common type, comprising ∼70% to 80% of all adult cases and ∼50% of pediatric cases. About half of the w-AIHA cases are called primary because no specific etiology can be found, whereas the rest are secondary to other recognizable underlying disorders. This review will focus on the postulated immunopathogenetic mechanisms in idiopathic and secondary w-AIHA and report on the rare cases of direct antiglobulin test-negative AIHA, which are even more likely to be fatal because of inherent characteristics of the causative antibodies, as well as because of delays in diagnosis and initiation of appropriate treatment. Then, the characteristics of w-AIHA associated with genetically defined immune dysregulation disorders and special considerations on its management will be discussed. Finally, the standard treatment options and newer therapeutic approaches for this chronic autoimmune blood disorder will be reviewed.

[THE DIFFERENTIAL DIAGNOSTIC OF ANEMIA]

The article presents analysis of the publications' data of the recent years concerning regulation of iron metabolism and possibilities of application of indicators of iron metabolism in differential diagnostic of anemia. The original results of protein detection are described concerning bivalent transporter of metals and ferroportine under iron-deficiency anemia, anemia of chronic inflammatory diseases and autoimmune hemolytic anemia. The significance of these proteins in more profound comprehension of pathogenesis is demonstrated

Solving a cold case of haemolysis: back to the basics

Membrane disorders comprise an important group of inherited haemolytic anaemias. Diagnostic work-up starts with examination of the blood smear, followed by osmotic gradient ektacytometry. In special cases DNA analysis is performed to confirm the diagnosis. For this purpose a next-generation sequencing-based method has been developed. The combination of these techniques established the correct diagnosis in a case of haemolytic anaemia of unknown cause.

B-cell receptor configuration and adverse cytogenetics are associated with autoimmune hemolytic anemia in chronic lymphocytic leukemia

The development of autoimmune hemolytic anemia (AIHA) in patients with chronic lymphocytic leukemia (CLL) is associated with specific biological features. The occurrence of AIHA was hereby investigated in a retrospective series of 585 CLL patients with available immunoglobulin heavy chain variable (IGHV) gene status. AIHA occurred in 73 patients and was significantly associated with an IGHV unmutated (UM) status (P < 0.0001) and unfavorable [del(17)(p13) and del(11)(q23)] cytogenetic lesions (P < 0.0001). Stereotyped HCDR3 sequences were identified in 29.6% of cases and were similarly represented among patients developing or not AIHA; notably, subset #3 was associated with a significantly higher risk of AIHA than the other patients (P = 0.004). Multivariate analysis showed that UM IGHV, del(17)(p13) and del(11)(q23), but not stereotyped subset #3, were the strongest independent variables associated with AIHA. Based on these findings, we generated a biological risk score for AIHA development according to the presence of none (low risk), one (intermediated risk), or two (high risk) of the independent risk factors. Overall, our data indicate that UM IGHV status and/or unfavorable cytogenetic lesions are associated with the risk of developing secondary AIHA in CLL patients and suggest a possible role of specific stereotyped B-cell receptor subsets in a proportion of cases.

Exome sequencing and unrelated findings in the context of complex disease research: ethical and clinical implications

Exome sequencing has identified the causes of several Mendelian diseases, although it has rarely been used in a clinical setting to diagnose the genetic cause of an idiopathic disorder in a single patient. We performed exome sequencing on a pedigree with several members affected with attention deficit/hyperactivity disorder (ADHD), in an effort to identify candidate variants predisposing to this complex disease. While we did identify some rare variants that might predispose to ADHD, we have not yet proven the causality for any of them. However, over the course of the study, one subject was discovered to have idiopathic hemolytic anemia (IHA), which was suspected to be genetic in origin. Analysis of this subject's exome readily identified two rare non-synonymous mutations in PKLR gene as the most likely cause of the IHA, although these two mutations had not been documented before in a single individual. We further confirmed the deficiency by functional biochemical testing, consistent with a diagnosis of red blood cell pyruvate kinase deficiency. Our study implies that exome and genome sequencing will certainly reveal additional rare variation causative for even well-studied classical Mendelian diseases, while also revealing variants that might play a role in complex diseases. Furthermore, our study has clinical and ethical implications for exome and genome sequencing in a research setting; how to handle unrelated findings of clinical significance, in the context of originally planned complex disease research, remains a largely uncharted area for clinicians and researchers.

STIM1 mutation associated with a syndrome of immunodeficiency and autoimmunity

A mutation in ORAI1, the gene encoding the pore-forming subunit of the Ca(2+)-release-activated Ca(2+) (CRAC) channel, abrogates the store-operated entry of Ca(2+) into cells and impairs lymphocyte activation. Stromal interaction molecule 1 (STIM1) in the endoplasmic reticulum activates ORAI1-CRAC channels. We report on three siblings from one kindred with a clinical syndrome of immunodeficiency, hepatosplenomegaly, autoimmune hemolytic anemia, thrombocytopenia, muscular hypotonia, and defective enamel dentition. Two of these patients have a homozygous nonsense mutation in STIM1 that abrogates expression of STIM1 and Ca(2+) influx.

A high rate of CLL phenotype lymphocytes in autoimmune hemolytic anemia and immune thrombocytopenic purpura

Minor CLL-like clones are found in approximately 3% of healthy individuals. AIHA and ITP are common in CLL and may be causally linked. We investigated the presence of CLL phenotype lymphocytes in 11 cases of primary AIHA, 18 of ITP and 2 of Evans' Syndrome, compared with 26 age-matched healthy controls. A population of 'CLL phenotype' was seen in 6/31 patients compared to 1/26 healthy controls (chi(2)=3.9; p=0.05). Such clones may be important in the pathogenesis of autoimmune blood disorders.

Association of a common dog leucocyte antigen class II haplotype with canine primary immune-mediated haemolytic anaemia

Immune-mediated haemolytic anaemia (IMHA) is the commonest immune-mediated disease of the dog, representing a major health concern to this species. The aim of this investigation was to determine whether genetic susceptibility to IMHA is associated with genes of the canine major histocompatibility complex (MHC; dog leucocyte antigen system, DLA). Samples were collected from 108 dogs with primary idiopathic, Coombs' positive IMHA. This diseased population was subdivided on the basis of Coombs' test results into two groups: 1) dogs with dominant warm-reactive immunoglobulin (Ig) G haemagglutinins and (2) dogs with an additional or dominant cold-reactive IgM haemagglutinin. The DLA class II alleles and haplotypes of the diseased population were characterised, and these data were compared with those derived from a breed-matched control cohort and a much larger group of DLA-typed dogs. Two haplotypes were increased in the patient group: DLA-DRB1*00601/DQA1*005011/DQB1*00701 (in the group with warm-reactive IgG haemagglutinins only) and DLA-DRB1*015/DQA1*00601/DQB1*00301 (in both groups, but more so in the group with cold-reactive IgM haemagglutinins). One haplotype, DLA-DRB1*001/DQA1*00101/DQB1*00201, was decreased in the total patient group, but this decrease was limited to the warm-reactive IgG haemagglutinins group, and it was actually increased in the cold-reactive IgM haemagglutinins group. A second haplotype, DLA-DRB1*015/DQA1*00601/DQB1*02301, was also decreased in the total patient group, and this decrease was found in both subgroups. In addition, all haplotypes carrying DLA-DRB1*001 were significantly increased in the cold-reactive IgM haemagglutinins group. When the overall patient group was divided on the basis of individual breeds with more than six animals represented, each of the haplotypes could be shown to be implicated in one of the breeds. Thus, it was apparent that different breeds had different MHC associations with canine IMHA, which is similar to the observation that different human ethnic groups can have different HLA associations with the same immune-mediated disease.

[Molecular approaches to the Rh blood group system]

The Rh system clinically is one of the important blood groups. The major Rh antigens are RhD, RhC/c, and RhE/e, which are carried by two integral membrane polypeptides consisted of 416 amino acids. These polypeptides are encoded by two closely related genes, RHD and RHCE. Both RH genes are composed of ten exons. It is thought that multiple recombinations, nucleotide substitutions, large nucleotide gaps (due to Alu sequence), and high level of the homology between the RHD and RHCE genes are the important factors in the formation and evolution of these genes. The RHD gene is deleted in most white individuals who lack the RhD antigen, while 12% of Japanese individuals have an RHD gene. Molecular analyses have elucidated the background of various Rh-related variants; D--, partial D, weak D, and Rhnull. The Rhnull phenotype is divided into the most common type by the Rhnull regulator gene and second type by the amorph gene that arose by homozygosity of a silent allele at the RH locus. The RhAG glycoprotein has been regarded as a most critical Rhnull gene of the reglurator type and a critical co-expressing factor of the Rh polypetides on red blood cells. Studies on the autoantibodies against red blood cells in aoutoimmune hemolytic anemia have suggested that the public epitopes of autoantigens exist on the Rh polypeptides.

Cutting Edge: Allogeneic CD4+CD25+Foxp3+ T Regulatory Cells Suppress Autoimmunity while Establishing Transplantation Tolerance

An important unresolved question with regard to T regulatory (Treg) cell specificity and suppressive activity is whether allogeneic Treg cells inhibit self-reactive T cells. In the present study, this issue was addressed using IL-2Rbeta-deficient mice that develop rapid lethal autoimmunity due to impaired production of Treg cells. We show that adoptive transfer of completely MHC-mismatched Treg cells into IL-2Rbeta(-/-) mice resulted in life-long engraftment of the donor cells, which exhibited skewed reactivity toward host alloantigens, and prevented autoimmunity. Thus, Treg cells that underwent thymic selection by peptide/MHC class II complexes distinct from those recognized by autoreactive T cells, still effectively suppress autoimmunity. Remarkably, when such animals were skin grafted, they exhibited dominant tolerance to those grafts bearing MHC molecules that were shared with donor Treg cells. Collectively, these data demonstrate that effective engraftment by allogeneic Treg cells controls autoimmunity and results in permissive conditions for long-term acceptance of allografts.

Anémie hémolytique auto-immune et dysérythropoïèse révélatrices d'un déficit de l'apoptose Fas chez 3 enfants

Defective apoptosis caused by mutations of the Fas gene can lead to an autoimmune lymphoproliferative syndrome (ALPS). The main autoimmune manifestations are haematological: hemolytic anemia, thrombocytopenia and neutropenia. We described 3 patients with ALPS presenting as a lymphoproliferative syndrome associated with a Coomb's negative autoimmune hemolytic anemia and dyserythropoiesis predominating on the more mature erythroblasts. Fas apoptosis deficiency was evidenced in the 3 patients by the demonstration of an increased number of CD4(-)CD8(-)TCRalphabeta(+) T cells, a decreased apoptotic response of activated T lymphocytes to anti-Apo 1-3 monoclonal antibody and the presence of a heterozygous mutation of the Fas receptor gene.

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.

Syndrome d'Evans : étude rétrospective de la société d'hématologie et d'immunologie pédiatrique (36 cas)

Evans' Syndrome (ES) is defined as the combination of immune thrombocytopenia (ITP) and autoimmune haemolytic anemia (AIHA), in the absence of any known underlying etiology. Pathophysiology, epidemiology and outcome remain unclear.

POPULATION

Thirty-six children (20 male, 16 female), who were diagnosed in the SHIP french centres (Société d'hématologie et d'immunologie pédiatrique) between 1990 and 2002 with ES, were included in this retrospective study.

RESULTS

Median age at diagnosis was 4 years. In 21 children, ES occurred in the setting of consanguinity, family history of autoimmune/inflammatory disease, associated autoimmune disorder or immunoregulatory abnormalities (serum imunoglobulins, peripheral blood lymphocytes subsets, low level of the C3-C4 complement components, nuclear antibodies). Several successive treatments were used in this serie (median: 3, range: 0-10) including corticosteroid therapy (35/36), intravenous immunoglobulins (32/36), immunosuppressive agents (14/36), splenectomy (9/36) and anti CD 20 monoclonal antibodies (6/36). Patients with a low level of serum immunoglobulins were more often non-responders to corticosteroidtherapy/intravenous immunoglobulins and required more frequently further therapy (P=0.03). Three patients died (intracranial bleeding, N=2, Guillain-Barre syndrome; N=1).

CONCLUSION

ES was a severe, life-threatening disease, requiring aggressive immunosuppressive therapy in as many as half the patients. Our forthcoming study aims to (i) describe homogeneously-studied and prospectively-analysed cohort of childhood ES, (ii) separate ES from specific immune deficiency (especially fas gene mutations), generalised autoimmune/inflammatory disorders and genetic diseases, (iii) identify well-defined ES subsets, (iv) establish prognostic factors and optimal treatment within these subsets.

A novel human CD32 mAb blocks experimental immune haemolytic anaemia in FcgammaRIIA transgenic mice

A fully human IgG1 kappa antibody (MDE-8) was generated, which recognised Fc-gamma receptor IIa (FcgammaRIIa) molecules on CD32 transfectants, peripheral blood monocytes, polymorphonuclear cells and platelets. This antibody blocked FcgammaRIIa ligand-binding via its F(ab')(2) fragment. Overnight incubation of monocytes with F(ab')(2) fragments of MDE-8 leads to a c. 60% decrease in cell surface expression of FcgammaRIIa. MDE-8 whole antibody induced a concomitant c. 30% decrease of FcgammaRI on THP-1 cells and monocytes. In humans FcgammaRIIa plays an important role in the clearance of antibody-coated red blood cells in vivo. As an equivalent of FcgammaRIIa does not exist in mice, the in vivo effect of MDE-8 was studied in an FcgammaRIIa transgenic mouse model. In these mice, antibody-induced anaemia could readily be blocked by MDE-8. These data document a new human antibody that effectively blocks FcgammaRIIa, induces modulation of both FcgammaRIIa and FcgammaRI from phagocytic cells, and ameliorates antibody-induced anaemia in vivo.

Identification of 2 major loci linked to autoimmune hemolytic anemia in NZB mice

Using a cohort of C57BL/6 (B6) x (NZB x B6)F1 backcross male mice bearing the Yaa (Y-linked autoimmune acceleration) mutation, we mapped and characterized the NZB-derived susceptibility loci predisposing to the development of autoimmune hemolytic anemia (AHA). Our analysis identified 2 major loci on NZB chromosome 7 and chromosome 1 linked with Coombs antierythrocyte autoantibody production, and their contributions were confirmed by the analysis of B6.Yaa mice (B6 mice bearing the Yaa mutation) congenic for each NZB-derived susceptibility interval. A newly identified Aia3 (autoimmune anemia 3) locus present on NZB chromosome 7 selectively regulated Coombs antibody responses, while the second locus, directly overlapping with Nba2 (NZB autoimmunity 2) on chromosome 1, promoted the development of AHA, likely as part of its effect on overall production of lupus autoantibodies. A higher incidence of Coombs antibody production in B6.Aia3 congenic mice (B6 mice bearing the NZB-Aia3 locus) than B6.Nba2 mice (B6 mice bearing the NZB-Nba2 locus) indicated a major role for Aia3 in AHA. Notably, lack of expansion of B1 cells in B6.Aia3 congenic mice argued against the involvement of this subset in AHA. Finally, our analysis of BC mice also demonstrated the presence of a B6-derived H2-linked locus on chromosome 17 that apparently regulated the production of Coombs antibodies as a result of its overall autoimmune promoting effect.

Differential activation of anti-erythrocyte and anti-DNA autoreactive B lymphocytes by the Yaa mutation

An as-yet-unidentified mutation, Y-linked autoimmune acceleration (Yaa), is responsible for the accelerated development of lupus-like autoimmune syndrome in mice. In view of a possible role for Yaa as a positive regulator of BCR signaling, we have explored whether the expression of the Yaa mutation affects the development and activation of transgenic autoreactive B cells expressing either 4C8 IgM anti-RBC or Sp6 IgM anti-DNA. In this study, we show that the expression of the Yaa mutation induced a lethal form of autoimmune hemolytic anemia in 4C8 transgenic C57BL/6 mice, likely as a result of activation of 4C8 anti-RBC autoreactive B cells early in life. This was further supported, although indirectly, by increased T cell-independent IgM production in spleens of nontransgenic C57BL/6 mice bearing the Yaa mutation. In contrast, Yaa failed to induce activation of Sp6 anti-DNA autoreactive B cells, consistent with a lack of increased IgM anti-DNA production in nontransgenic C57BL/6 Yaa mice. Our results suggest that Yaa can activate autoreactive B cells in a BCR-dependent manner, related to differences in the form and nature of autoantigens.

Review: complement receptor 1 therapeutics for prevention of immune hemolysis

The complement system plays a crucial role in fighting infections and is an important link between the innate and adaptive immune responses. However, inappropriate complement activation can cause tissue damage, and it underlies the pathology of many diseases. In the transfusion medicine setting, complement sensitization of RBCs can lead to both intravascular and extravascular destruction. Moreover, complement deficiencies are associated with autoimmune disorders, including autoimmune hemolytic anemia (AIHA). Complement receptor 1 (CR1) is a large single-pass glycoprotein that is expressed on a variety of cell types in blood, including RBCs and immune cells. Among its multiple functions is its ability to inhibit complement activation. Furthermore, gene knockout studies in mice implicate a role for CR1 (along with the alternatively spliced gene product CR2) in prevention of autoimmunity. This review discusses the possibility that the CR1 protein may be manipulated to prevent and treat AIHA. In addition, it will be shown in an in vivo mouse model of transfusion reaction that recombinant soluble forms of CR1 can reduce complement-mediated RBC destruction, thereby prolonging survival of transfused RBCs. It is proposed that CR1-based therapeutics have potential for effective and safe prophylactic short-term use and for treatment of hemolytic transfusion reactions.

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.

Transgenic Expression of CTLA-4 Controls Lymphoproliferation in IL-2-Deficient Mice

IL-2-deficient mice develop a lymphoproliferative and autoimmune disease characterized by autoimmune hemolytic anemia (AHA) and inflammatory bowel disease. We have previously reported that IL-2 is necessary for optimal up-regulation of CTLA-4, an inducible negative regulator of T cell activation. In this study, we have tested the hypothesis that reduced expression of CTLA-4 in IL-2-deficient T cells contributes to the pathogenesis of disease in IL-2-deficient mice. Expression of CTLA-4 as a transgene completely prevented lymphoaccumulation and AHA in IL-2-deficient mice. The normalization of T cell numbers was due to inhibition of expansion of conventional CD4+CD25- T cells rather than to rescue of the numbers or function of CD4+CD25+ regulatory T cells, suggesting that CTLA-4 expression on conventional T cells plays a role in maintaining normal T cell homeostasis. In addition, the inhibitory effect of the CTLA-4 transgene on T cell expansion was at least in part independent of CD28 expression. Our results suggest that deficient CTLA-4 expression on conventional T cells contributes to the pathophysiology of the lymphoproliferative disease and AHA in IL-2-deficient mice. Thus, restoring CTLA-4 expression in T cells may be an attractive strategy to control clinical autoimmune diseases in which CTLA-4 expression is reduced.

Translocation (8;22) in cold agglutinin disease associatedwith B-cell lymphoma

Cold agglutinin disease (CAD) is a hemolytic anemia due to anti-red cell autoantibodies that are reactive at cold temperatures. In the elderly, it may be associated with underlying B-cell lymphoma, usually a lympho-plasmacytic lymphoma variant. We report a case of CAD in an elderly Indonesian female, which was associated with a B-cell lymphoma that showed a histologic appearance consistent with large-cell lymphoma. Cytogenetic analysis revealed the presence of trisomies 3 and 12, which have been reported previously in B-cell lymphoma associated with CAD. In addition, a t(8;22) was found in 24 out of 28 metaphases. Translocation (8;22) is associated with Burkitt lymphoma or acute lymphoblastic lymphoma, French-American-British subtype L3. It has not been previously reported in B-cell lymphoma asssociated with CAD, and could represent a blastic transformation of the underlying B-cell lymphoma.

Targeted disruption of Nrf2 causes regenerative immune-mediated hemolytic anemia

A basic leucine zipper transcription factor, NF-E2-related factor 2 (Nrf2), plays a critical role in the cellular defense mechanism by mediating a coordinate up-regulation of antioxidant responsive element-driven detoxification and antioxidant genes. Here, we report that targeted disruption of Nrf2 causes regenerative immune-mediated hemolytic anemia due to increased sequestration of damaged erythrocytes. Splenomegaly and spleen toxicity in Nrf2(-/-) mice raised a possibility of hemolytic anemia and splenic extramedullary hematopoiesis in Nrf2(-/-) mice. In support of this, hematology analysis revealed that Nrf2(-/-) mice suffer from anemia with abnormal red cell morphologies (i.e., Howell-Jolly bodies, acantocytes, and schistocytes). In addition, Nrf2(-/-) erythrocytes were more sensitive to H(2)O(2)-induced hemolysis, and erythrocyte-bound IgG levels were markedly increased in Nrf2(-/-) mice compared with Nrf2(+/+) mice. Because IgG bound to erythrocytes in the presence of oxidative damage in erythrocytes (regardless of Nrf2 genotype), these data support that Nrf2(-/-) erythrocytes have higher levels of damage compared with Nrf2(+/+) cells. Finally, Nrf2(-/-) mice showed increased levels of erythrocyte-bound IgG compared with Nrf2(+/+) mice after H(2)O(2) injection in vivo, suggesting that the decreased glutathione and increased H(2)O(2) render the Nrf2(-/-) mice more susceptible to toxicity. Taken together, these observations indicate that a chronic increase in oxidative stress due to decreased antioxidant capacity sensitizes erythrocytes and causes hemolytic anemia in Nrf2(-/-) mice, suggesting a pivotal role of Nrf2-antioxidant responsive element pathway in the cellular antioxidant defense system.

Autoimmune cytopenias in the 22q11.2 deletion syndrome

We describe two cases of recurrent autoimmune cytopenias, which were subsequently diagnosed with a 22q11.2 deletion/DiGeorge syndrome. The cases are of particular interest as both possessed limited clinical features of this syndrome, and the investigation of haematological abnormalities led to the establishment of a definitive genetic diagnosis.

Evans syndrome in a patient with chromosome 22q11.2 deletion syndrome: a case report

One patient with a chromosome 22q11.2 deletion and Evans syndrome is reported in this paper. Microdeletions of 22q11.2 are the main etiology for DiGeorge syndrome, a disorder characterized by heart defects, immune deficiencies due to aplasia or hypoplasia of the thymus, and hypocalcemia. Evans syndrome refers to a hematological autoimmune disorder with autoimmune hemolytic anemia accompanied by immune thrombocytopenia. A wide range of autoimmune disorders have been described in DiGeorge syndrome and velocardiofacial syndrome, including one prior report of autoimmune hemolytic anemia and immune thrombocytopenia. The patient reported herein strengthens the association between the 22q11.2 deletion spectrum and Evans syndrome.

CTLA-4 exon 1 polymorphism in patients with autoimmune blood disorders

CTLA-4 is a CD28 homologue that plays an important role in negative regulation of T-cell responses. Its transient expression on the surface of activated T cells antagonizes the activating signals and terminates the T-cell response. An A to G polymorphism at position 49 of the CTLA-4 first exon has recently been associated with several autoimmune disorders. In the present study we have examined the prevalence of the A and G alleles of the CTLA-4 gene in 50 patients with autoimmune hemolytic anemia (AIHA), of which 20 had idiopathic AIHA and 30 had AIHA and chronic lymphocytic leukemia (CLL), and in 60 patients with immune thrombocytopenic purpura (ITP). Control subjects were 100 healthy individuals and 100 CLL patients without clinical evidence for an autoimmune disease. The G allele was present at a significantly higher frequency among the patients with AIHA (P = 0.003), whereas no difference was observed between patients with ITP and controls. The G allele frequency was highest among CLL patients who had developed AIHA. The obtained data indicate that the G allele of CTLA-4 predisposes to the development of AIHA, particularly among patients with CLL.

Chronic lymphocytic leukemia preceded by cold agglutinin disease: intraclonal immunoglobulin light-chain diversity in V(H)4-34 expressing single leukemic B cells

Autoimmune phenomena may precede or accompany lymphoid malignancies, especially B-chronic lymphocytic leukemia (B-CLL). We report a patient with a 7-year history of primary (idiopathic) cold agglutinin (CA) disease in whom B-CLL subsequently developed. Immunophenotyping and single-cell reverse transcription-polymerase chain reaction (RT-PCR) were applied to investigate the origin and diversification of leukemic B cells. The obtained data indicate a memory cell-type origin of the B-CLL cells. Remarkably, the IgV(kappa) genes of the B-CLL cells showed intraclonal diversity, whereas the mutational pattern of their paired IgV(H) genes were invariant. Thus, the light-chain-restricted intraclonal diversity in individual leukemic B cells in this patient strongly indicates a differential regulation or selection of the ongoing mutational process. Of note, our findings suggest that this B-CLL had developed from the patient's CA-producing B-cell population.

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.

Defective apoptosis in lymphocytes and the role of IL-2 in autoimmune hematologic cytopenias

Fas-mediated signaling is important for lymphocyte elimination. We investigated lymphocytes for Fas-signaling defects in 20 pediatric patients with chronic hematologic autoimmunity. In 5 of 20 (25%), there was profound resistance to exogenous FasL-mediated lysis, Fas mAb, and anti-CD3. FasL function, though variable, was not significantly different from that of simultaneously evaluated controls. Only 1 patient had a Fas mutation and manifestations of autoimmune lymphoproliferative syndrome. In contrast, lymphocytes from his clinically normal mother with the same mutation were normally sensitive to FasL. In 3 patients, normal Fas-mediated lysis was restored with rhIL-2. IL-2 had no effect in the other 2 patients. Activation and proliferation functions of IL-2 were normal in all 5. We conclude that altered Fas signaling, independent of Fas mutations, can precipitate hematologic autoimmunity. IL-2 can rescue some lymphocytes from this defect. In IL-2 refractory cases, a persistently defective response to IL-2 continues to confer a lymphocyte survival advantage. Hence, altered Fas pathway signaling with or without defective IL-2 responses should be considered in the etiology of hematologic autoimmunity.

Anemia, splenomegaly, and increased osmotic fragility of erythrocytes in Abyssinian and Somali cats

OBJECTIVE

To determine clinical and clinicopathologic features of a chronic intermittent severe hemolytic anemia characterized by erythrocyte osmotic fragility in Abyssinian and Somali cats.

DESIGN

Case series.

ANIMALS

13 Abyssinian and 5 Somali cats.

PROCEDURES

History, pedigree information, and results of routine laboratory tests, special erythrocyte studies, and histologic evaluation of splenic and hepatic specimens were analyzed.

RESULTS

Age at which clinical signs of anemia were first apparent ranged from 6 months to 5 years. Ten cats had splenomegaly. Most often, the PCV was between 15 and 25%, but it was as low as 5% at some times. The anemia was characterized by macrocytosis and mild to moderate reticulocytosis, but no poikilocytosis. Hyperglobulinemia, lymphocytosis, mild hyperbilirubinemia, and high hepatic enzyme activities were common findings. Results of Coombs tests and tests for infectious diseases were negative. The erythrocytic osmotic fragility was high in affected cats (mean osmotic fragility, 0.66 to 0.78%), compared with healthy cats (0.48 to 0.58). No specific membrane protein abnormality, erythrocyte enzyme deficiency, or hemoglobinopathy was identified. Histologic evaluation of splenic and hepatic specimens revealed extramedullary hematopoiesis and hemosiderosis. Four of the 5 Somali cats were closely related.

CONCLUSIONS AND CLINICAL RELEVANCE

On the basis of results of pedigree analyses, the apparent breed predilection, and the exclusion of other known causes of anemia in cats, we believe that the hemolytic anemia in these cats was likely a result of a novel hereditary erythrocyte defect. A genetic predisposition to immune-mediated destruction of erythrocytes could not be ruled out.

Quantitative deficiency of monocyte-specific esterase (MSE) mRNA in monocyte esterase deficiency (MED)

Cytochemical staining of monocyte-specific esterase (MSE) is widely used for identification of the monocytic lineage in leukaemias. Deficiency of this enzymatic activity occurs as a familial trait and the deficiency has been shown to occur with greater frequency in patients with lymphoproliferative or gastrointestinal malignant neoplastic diseases than in normal blood donors. Reverse transcriptase polymerase chain reaction (RT-PCR), sequencing and quantification by Northern blot analysis was conducted on the MSE mRNA of 12 subjects with monocyte esterase deficiency (MED) and seven MSE-positive subjects to examine whether mutations were present or whether the defect was quantitative. Mutations were not found in the mRNA sequences. However, MED subjects had significantly less MSE mRNA than MSE-positive subjects (P = 0.001). These findings show that deficiency of monocyte esterase activity in MED is not as a result of the presence of inactive isoenzymes and may be owing to an abnormality in the regulation of mRNA production.

Generation, expansion, migration and activation of mouse B1 cells

We have studied the expansion, activation, homing and antibody production of B1 cells in two different mouse models. One is the HL transgenic mouse, which carries Ig genes encoding the anti-red blood cell autoantibody (4C8) and develops autoimmune hemolytic anemia by the activation of autoreactive B1 cells that escape from clonal deletion and expand in the peritoneal cavity (PEC). The other model is represented by alymphoplasia (aly) mice, which carry a point mutation in the gene encoding NF-kappaB-inducing kinase (NIK) and have drastically reduced immunoglobulin serum levels, in spite of their peritoneal cavity containing a large number of B1 cells. We have found that a) expression levels of the B-cell antigen receptor (BCR) influence the size of the B1 -cell compartment and efficiency of allelic exclusion and B2-cell deletion; b) antibody production of B1 cells is closely related with their migration from PEC to other lymphoid organs and is dependent on NIK; and c) infection, lipopolysaccharide stimulation, cytokine administration or T-cell activation by noncanonical antigens induces migration and differentiation of peritoneal B1 cells into antibody-producing cells. We describe a scenario where most of B1 and B2 differences are due to a distinct activation threshold of BCR and antigen repertoire.

Markedly different pathogenicity of four immunoglobulin G isotype-switch variants of an antierythrocyte autoantibody is based on their capacity to interact in vivo with the low-affinity Fcgamma receptor III

Using three different Fcgamma receptor (FcgammaR)-deficient mouse strains, we examined the induction of autoimmune hemolytic anemia by each of the four immunoglobulin (Ig)G isotype-switch variants of a 4C8 IgM antierythrocyte autoantibody and its relation to the contributions of the two FcgammaR, FcgammaRI, and FcgammaRIII, operative in the phagocytosis of opsonized particles. We found that the four IgG isotypes of this antibody displayed striking differences in pathogenicity, which were related to their respective capacity to interact in vivo with the two phagocytic FcgammaRs, defined as follows: IgG2a > IgG2b > IgG3/IgG1 for FcgammaRI, and IgG2a > IgG1 > IgG2b > IgG3 for FcgammaRIII. Accordingly, the IgG2a autoantibody exhibited the highest pathogenicity, approximately 20-100-fold more potent than its IgG1 and IgG2b variants, respectively, while the IgG3 variant, which displays little interaction with these FcgammaRs, was not pathogenic at all. An unexpected critical role of the low-affinity FcgammaRIII was revealed by the use of two different IgG2a anti-red blood cell autoantibodies, which displayed a striking preferential utilization of FcgammaRIII, compared with the high-affinity FcgammaRI. This demonstration of the respective roles in vivo of four different IgG isotypes, and of two phagocytic FcgammaRs, in autoimmune hemolytic anemia highlights the major importance of the regulation of IgG isotype responses in autoantibody-mediated pathology and humoral immunity.

Molecular characterization of cold agglutinins

An unusual bias involving the exclusive usage of the V4-34 gene segment by pathogenic antibodies with I/i antigen specificity has been documented in the literature. In addition, all unmutated and several mutated V4-34 encoded antibodies have been shown to be reactive with the anti-idiotypic monoclonal antibody 9G4. The 9G4 Id, therefore, is a marker for V4-34 gene segment expression. Based on these two correlations, it became vital to localize and characterize the nature of the 9G4 Id and to determine the relationship between the Id and I binding. Mutational analysis indicated that the 9G4 Id is located in framework region 1 (FR1) of V4-34 encoded antibodies. Two distinct sections of FR1, encompassing amino acid residues 6-12 and 23-25, form the 9G4 Id. Mutational analysis demonstrated that both FR1 and CDRH3 were required for I binding. When either one was disrupted, the mutant antibody could not bind I. This indicates that I binds through a framework region, and not exclusively through CDRH3. This renders the I interaction with the V4-34 encoded portion of immunoglobulins unconventional, with characteristics similar to superantigen binding to immunoglobulin through FR. When the FR1 DNA sequence of V4-34 was exchanged for FR1 sequences from other VH families I binding was lost, providing a structural explanation for this restricted VH usage. An understanding of the localization and structure of the 9G4 Id and the requirements of V4-34 encoded antibodies for I binding provide insights into the structure of pathogenic antibodies and their requirements for binding antigen. This information should be useful in analyzing new interactions such as the lytic activity of some V4-34 encoded antibodies for B cells.

Genetic regulation of anti-erythrocyte autoantibodies and splenomegaly in autoimmune hemolytic anemia-prone new zealand black mice

New Zealand Black (NZB) mice spontaneously produce anti-erythrocyte autoantibodies (AEA) in association with splenomegaly, thus serving as a model for autoimmune hemolytic anemia. Although these autoimmune traits are inherited as a dominant fashion, expression in F(1) hybrids of NZB and most non-New Zealand strains is suppressed due to the contribution of wild-type modifying genes present in the latter strains. Using chromosomal microsatellite markers in the (C57BL/6 x NZB)F(1) x NZB backcross progeny, we mapped C57BL/6 modifying loci for AEA production and splenomegaly. Generation of AEA was found to be down-regulated by a combined effect of two major independently segregating dominant alleles-one linked to D7MIT30 on chromosome 7 and the other linked to D10MIT42 on chromosome 10. Splenomegaly was modified mainly by a single C57BL/6 allele linked to D4MIT58 on chromosome 4. Thus, the autoimmune hemolytic anemia in the NZB strain is under multigenic control and a combined action of not only susceptibility but also modifying alleles with suppressive activities affects the outcome of disease features in the progeny. There are potentially important candidate genes which may be linked to the regulation of AEA and splenomegaly.

Requirement of IL-5 for induction of autoimmune hemolytic anemia in anti-red blood cell autoantibody transgenic mice

IL-5, IL-10 and lipopolysaccharide (LPS) are known to activate B-1 cells in vivo in normal mice and anti-red blood cell autoantibody transgenic mice (HL mice). To assess the exact role of IL-5 in proliferation and activation of peritoneal B-1 cells, we analyzed IL-5 receptor alpha chain-deficient HL (IL-5Ralpha-/- x HL) mice generated by the cross between IL-5Ralpha-/- and HL mice. In IL-5Ralpha-/- x HL mice, Ig-producing B-1 cells in the peritoneal cavity were negligible, although the total number of B-1 cells in the peritoneal cavity were as many as 30% of that in HL mice. Moreover, LPS- or IL-10-induced differentiation of B-1 cells into antibody-producing cells was severely impaired in IL-5Ralpha-/- x HL mice. We also used in vivo 5-bromo-2'-deoxyuridine labeling to estimate the proliferation of B-1 cells in IL-5Ralpha-/- mice. The absence of IL-5Ralpha did not affect spontaneous proliferation of peritoneal B-1 cells. However, induced proliferation of peritoreal B-1 cells by oral administration of LPS was markedly impaired in IL-5Ralpha-/- mice. These results suggest that IL-5 is required for activation-associated proliferation of B-1 cells but not for their spontaneous proliferation and support the idea that IL-5 plays an important role on the induction of autoantibody production from B-1 cells.