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

Autoimmune Hemolysis: A Journey through Time

The existence of autoimmune diseases in humans has been known for almost 100 years. Currently, autoimmune pathogenesis has been attributed to more than 40 human diseases; yet it is still not clear what immune abnormalities conclusively prove underlying autoimmune pathogenesis. Hence, although much has been learned, research is still needed for complete elucidation of the mechanisms of the immune dysregulation in AIHA. Better understanding of the underlying mechanism(s) may allow for development of more specific therapies of these not uncommon and often difficult-to-treat disorders.

Genome-wide genetic study in autoimmune disease-prone mice

Mouse models of autoimmune diseases provide invaluable insights into the cellular and molecular bases of autoimmunity. Genetic linkage studies focusing on their abnormal quantitative phenotypes in relation to the loss of self-tolerance will lead to the identification of polymorphic genes that play pivotal roles in the genetic predisposition to autoimmunity. In this chapter, we first overview the basic concepts in the statistical genetics and then provide guides to genotyping microsatellite DNA markers and to quantitative trait loci mapping using a MAPMAKER program.

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.

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.

Quantitative trait locus analysis of ovarian cysts derived from rete ovarii in MRL/MpJ mice

MRL/MpJ (MRL) is a model mouse for autoimmune diseases such as dermatitis, vasculitis, arthritis, and glomerulonephritis. In addition to these immune-associated disorders, we found that older MRL mice develop ovarian cysts originating from the rete ovarii, which is lined by ciliated or nonciliated epithelium and considered remnants of mesonephric tubules. Ovarian cysts, which are reported to have several sources, are associated with female infertility, but information regarding the genetic etiology of ovarian cysts originating from the rete ovarii is rare. In this study, to elucidate the genetic background of development of ovarian cysts, we performed quantitative trait locus (QTL) analysis using 120 microsatellite markers, which cover the whole genome of murine chromosomes, and 213 backcross progenies between female MRL and male C57BL/6N mice. The quantitative trait measured was the circumferences of rete ovarii or ovarian cysts. As a result, suggestive linkages were detected on Chrs 3, 4, 6, and 11, but significant linkages were located on Chr 14 by interval mapping. We thereby designated the 27.5-cM region of Chr 14 "MRL Rete Ovarian Cysts (mroc)." The peak regions of Chrs 4 and 14 in particular showed a close additive interaction (p < 0.00001). From these results we concluded that multiple loci on Chrs 3, 4, 6, 11, and 14 interact to result in development of ovarian cysts in MRL mice.

CD19 hyperexpression augments Sle1-induced humoral autoimmunity but not clinical nephritis

OBJECTIVE

B cell hyperactivity is a common denominator in murine and human systemic lupus erythematosus. Some susceptibility genes in lupus are associated with B cell hyperactivity, but others are clearly not. While the Sle1 lupus susceptibility locus of NZM2410/NZW origin leads to chromatin-focused autoimmunity, genetically engineered overexpression of CD19 leads to "generalized" B cell hyperactivity. We undertook this study to determine the degree to which generalized B cell hyperactivity can amplify lupus pathogenesis.

METHODS

To elucidate the impact of generalized B cell hyperactivity on Sle1-triggered autoimmunity, B6 mice bearing the human CD19 transgene were rendered congenic for the Sle1(z) genetic locus and phenotyped for serologic, cellular, and pathologic evidence of lupus.

RESULTS

As expected, B6.Sle1.hCD19(Tg/Tg) mice, homozygous at Sle1 and bearing the hCD19 transgene, exhibited high levels of IgM and IgG anti-DNA/antiglomerular autoantibodies, skewed B cell subsets, and profoundly activated B and T cells. Despite exhibiting glomerular IgM, IgG, and complement deposits, these mice did not exhibit accelerated mortality or any clinical evidence of renal dysfunction.

CONCLUSION

Generalized B cell hyperactivity may augment humoral autoimmunity, but this may not suffice to engender end-organ disease in lupus. These findings allude to the presence of an additional distal checkpoint that dissociates pathogenic autoantibody formation and renal immunoglobulin deposition from the progression to clinical nephritis in lupus.

Mouse bone marrow and peripheral blood erythroid cell counts are regulated by different autosomal genetic loci

Erythropoiesis is under fine control and genetic loci that affect it are likely to be important in a range of conditions. To assess the relative contributions of different genetic loci to parameters of erythropoiesis, we have measured RBC counts in the peripheral circulation and committed erythroid cells (RBC and small normoblasts) in the bone marrow in a cohort of (CBA/H x C57BL/6) F2 mice to map quantitative trait loci (QTL). Candidate genes were assessed using bioinformatics and DNA sequencing. Different autosomal loci affect bone marrow (chromosomes 5, 11 and 19) and peripheral blood (chromosome 4) erythroid cell counts but there may be a common chromosome X locus. Spleen weight QTL were found on chromosomes 3, 15 and 17. Surprisingly, erythropoietin (Epo) is the best candidate quantitative trait gene (QTG) in the chromosome 5 locus that affects bone marrow but not peripheral blood erythroid cell counts. Epo gene expression is known to be genetically regulated in mice, but our data suggest a tissue-specific role for epo in mouse erythropoiesis that is also genetically determined. The identity of the other QTG will be important both to further knowledge of the control of erythropoiesis and as potential modifier genes for haematological disorders.

Polymorphism discovery and association analyses of the interferon genes in type 1 diabetes

Background

The aetiology of the autoimmune disease type 1 diabetes (T1D) involves many genetic and environmental factors. Evidence suggests that innate immune responses, including the action of interferons, may also play a role in the initiation and/or pathogenic process of autoimmunity. In the present report, we have adopted a linkage disequilibrium (LD) mapping approach to test for an association between T1D and three regions encompassing 13 interferon alpha (IFNA) genes, interferon omega-1 (IFNW1), interferon beta-1 (IFNB1), interferon gamma (IFNG) and the interferon consensus-sequence binding protein 1 (ICSBP1).

Results

We identified 238 variants, most, single nucleotide polymorphisms (SNPs), by sequencing IFNA, IFNB1, IFNW1 and ICSBP1, 98 of which where novel when compared to dbSNP build 124. We used polymorphisms identified in the SeattleSNP database for INFG. A set of tag SNPs was selected for each of the interferon and interferon-related genes to test for an association between T1D and this complex gene family. A total of 45 tag SNPs were selected and genotyped in a collection of 472 multiplex families.

Conclusion

We have developed informative sets of SNPs for the interferon and interferon related genes. No statistical evidence of a major association between T1D and any of the interferon and interferon related genes tested was found.

Autoimmune Pathogenesis and Autoimmune Hemolytic Anemia

Autoimmune hemolytic anemia (AIHA) is an autoimmune disorder in which autoantibodies are directed against an individual's own red blood cells (RBCs), leading to enhanced clearance through Fc receptor (FcR)-mediated phagocytosis. Although there is a large literature relating to clinical aspects of AIHA, relatively little work addresses how IgG autoantibodies are actually produced against RBC autoantigens. This review will first discuss the current understanding of autoimmunity in general and then focus on the knowledge of the immunopathogenic mechanisms responsible for autoantibody production in AIHA. Both human and animal studies will be discussed. Understanding theses mechanism is vital for developing antigen-specific immunotherapies to treat the disease.

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.

Genetic segregation of spontaneous erosive arthritis and generalized autoimmune disease in the BXD2 recombinant inbred strain of mice

The BXD2 strain of mice is one of approximately 80 BXD recombinant inbred (RI) mouse strains derived from an intercross between C57BL/6J (B6) and DBA/2J (D2) strains. We have discovered that adult BXD2 mice spontaneously develop generalized autoimmune disease, including glomerulonephritis (GN), increased serum titres of rheumatoid factor (RF) and anti-DNA antibody, and a spontaneous erosive arthritis characterized by mononuclear cell infiltration, synovial hyperplasia, and bone and cartilage erosion. The features of lupus and arthritis developed by the BXD2 mice segregate in F2 mice generated by crossing BXD2 mice with the parental B6 and D2 strains. Genetic linkage analysis of the serum levels of anti-DNA and RF by using the BXD RI strains shows that the serum titers of anti-DNA and RF were influenced by a genetic locus on mouse chromosome (Chr) 2 near the marker D2Mit412 (78 cm, 163 Mb) and on Chr 4 near D4Mit146 (53.6 cm, 109 Mb), respectively. Both loci are close to the B-cell hyperactivity, lupus or GN susceptibility loci that have been identified previously. The results of our study suggest that the BXD2 strain of mice is a novel model for complex autoimmune disease that will be useful in identifying the mechanisms critical for the immunopathogenesis and genetic segregation of lupus and erosive arthritis.

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.

Genome screening for susceptibility loci in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex, multigenic autoimmune disease with a wide spectrum of clinical manifestations. Much of the pathology is attributed to deposition to various tissues of immune complexes continuously formed with autoantibodies; thus, the pathogenesis is related to dysregulation of self-reactive B cells. Recent family linkage studies and allele-sharing linkage analyses of affected sibling pairs have advanced genome screening for susceptibility loci in SLE, and a considerable number of chromosomal intervals with significant or suggestive linkage to SLE have been identified. However, there are still several inherent difficulties in precisely identifying loci and genes, as the complexity of polygenic inheritance of SLE phenotypes is considerable. One must note that each specific aspect of diverse SLE phenotypes (clinical manifestations and immunological abnormalities) is mostly controlled separately by a different set of susceptibility loci. Involvement of positive and negative epistatic gene interactions often puzzles genetic analyses. Studies on SLE using murine lupus models are ongoing to solve some of these difficulties. Comparative studies have identified several syntenic chromosomal intervals with susceptibility loci in both mouse models and humans. Thus, combining knowledge derived from both human and murine studies is vital. The ultimate identification of susceptibility genes and their functions will probably depend largely on studies using genetically manipulated mutant mice, including those with homologous recombination of potent polymorphic target genes. The up-coming completion of genomic sequences in mice and humans is predicted to limit the numbers of potent candidate genes in particular genomic intervals and accelerates this line of studies. Such knowledge will lead to elucidation of genetic and cellular mechanisms involved in the dysregulation of self-reactive lymphocytes in the pathogenesis of SLE. Prophylactic and therapeutic clinical approaches can then be better designed.

The NOD mouse as a model of SLE

In addition to developing a high incidence of type 1 diabetes caused by a specific autoimmune response against pancreatic beta cells in the islets of Langerhans, NOD mice also demonstrate spontaneous autoimmunity to other targets including the thymus, adrenal gland, salivary glands, thyroid, testis, nuclear components and red blood cells. Moreover, treatment of pre-diabetic NOD mice with an intravenous dose of heat killed Mycobacterium bovis (M. bovis; bacillus Calmette-Guèrin (BCG)) protects them from developing type 1 diabetes, but instead precipitates an autoimmune rheumatic disease similar to systemic lupus erythematosus (SLE), characterised by accelerated and increased incidence of haemolytic anaemia (HA), anti-nuclear autoantibody (ANA) production, exacerbation of sialadenitis, and the appearance of immune complex-mediated glomerulonephritis (GN). The reciprocal switching between the two phenotypes by a single environmental trigger (mycobacterial exposure) raised the possibility that genetic susceptibility for type 1 diabetes and SLE may be conferred by a single collection of genes in the NOD mouse. This review will focus on the genetic components predisposing NOD mice to SLE induced by BCG treatment and compare them to previously determined diabetes susceptibility genes in this strain and SLE susceptibility genes in the BXSB, MRL and the New Zealand mouse strains.

The genetic control of sialadenitis versus arthritis in a NOD.QxB10.Q F2 cross

The non-obese diabetic (NOD) mouse spontaneously develops diabetes and sialadenitis. The sialadenitis is characterized by histopathological changes in salivary glands and functional deficit similar to Sjögren's syndrome. In humans, Sjögren's syndrome could be associated with other connective tissue disorders, such as rheumatoid arthritis. In the present study the genetic control of sialadenitis in mice was compared to that of arthritis. We have previously reported a NOD locus, identified in an F2 cross with the H2(q) congenic NOD (NOD.Q) and C57BL/10.Q (B10.Q) strains, that promoted susceptibility to collagen-induced arthritis. The sialadenitis in NOD.Q showed a similar histological phenotype as in NOD, whereas no submandibular gland infiltration was found in B10.Q. The development of sialadenitis was independent of immunization with type II collagen and established arthritis. To identify the genetic control of sialadenitis, a gene segregation experiment was performed on an (NOD.QxB10.Q)F2 cross and genetic mapping of 353 F2 mice revealed one significant locus associated with sialadenitis on chromosome 4, LOD score 4.7. The NOD.Q allele-mediated susceptibility under a recessive inheritance pattern. The genetic control of sialadenitis seemed to be unique in comparison to diabetes and arthritis, as no loci associated with these diseases have been identified at the same location.

Murine lupus genetics: lessons learned

Recent reverse genetic studies in murine lupus have taught us the following lessons: (1) Lupus is extremely polygenic; (2) A single locus may be associated with many different phenotypes; (3) What appears to be a single locus may turn out to be a cluster of loci; (4) Different loci facilitate different immunologic steps leading to lupus; (5) Epistatic interactions between loci may engender novel autoimmune phenotypes; (6) Whereas some loci may be pathogenic, others may confer disease resistance; (7) Whereas the expression of some loci is sex-dependent, the expression of others clearly is not; (8) Two or more loci may have an impact on the same phenotype; (9) Lupus susceptibility loci appear to co-cluster with other autoimmunity susceptibility loci; (10) Lupus genes are likely to be polymorphic alleles with subtle impacts, rather than outright mutations with extreme functions. In contrast, forward genetic studies have revealed that molecules that impact apoptosis, the clearance of apoptotic cells, B-cell or T-cell function, and end-organ pathology can all potentially contribute to lupus. Collectively, the loci and genes identified by these two different approaches factorize into a few distinct pathways leading to lupus. Delineating the molecular mediators of these distinct checkpoints is the challenge that lies ahead.

Practical approaches to determining disease-susceptible loci in multigenic autoimmune models

Linkage analysis using polymorphic DNA markers has paved the way toward the identification of genes responsible for rare recessive traits and for the susceptibility to certain tumors in humans. However, genetic susceptibility to common diseases, including systemic autoimmune diseases, is difficult to determine, hence has remained a challenging problem in the field of molecular genetics. Elucidation of multiple quantitative trait loci that predispose individuals to multi-phenotypic systemic autoimmune disease requires formidable research efforts, and there is a growing consensus that mouse models are required. This review provides a guide to methods that can be used in linkage studies of autoimmune mice. Mouse studies in relation to recent advances in bio-informatics are also discussed.

Genetic aspects of inherent B-cell abnormalities associated with SLE and B-cell malignancy: lessons from New Zealand mouse models

Genes that predispose to SLE are closely related to key events in pathogenesis of this disease. As much of the pathology can be attributed to high affinity autoantibodies and/or their immune complexes, some of the genes may exert effects in the process of emergence, escape from tolerance mechanisms, activation, clonal expansion, differentiation, class switching and affinity maturation of self-reactive B cells. A number of growth and differentiation factors and signaling molecules, including positive and negative regulators, are involved in this process. Genetic variations associated with functional deficits in some of such molecules can be involved in the susceptibility for SLE. As is the case with SLE, hereditary factors play significant roles in the pathogenesis of B cell chronic lymphocytic leukemia (B-CLL). Patients with B-CLL or their family members frequently have immunological abnormalities, including those associated with SLE. It is suggested that certain genetically determined regulatory abnormalities of B cells may be a crossroad between B-CLL and SLE. A thorough understanding of the genetic pathways in B cell abnormalities leading to either SLE or B-CLL is expected to shed light on their association. New Zealand mouse strains are pertinent laboratory models for these studies. Chromosomal locations of several major genetic loci for abnormal proliferation, differentiation and maturation of B cells and relevant candidate genes, located in close proximity to these intervals and potentially related to the SLE pathogenesis, have been identified in these mice. Further studies make for a wider knowledge and understanding of the pathogenesis of SLE and related B-cell malignancy.

Linkage analysis of systemic lupus erythematosus induced in diabetes-prone nonobese diabetic mice by Mycobacterium bovis

Systemic lupus erythematosus induced by Mycobacterium bovis in diabetes-prone nonobese diabetic mice was mapped in a backcross to the BALB/c strain. The subphenotypes-hemolytic anemia, antinuclear autoantibodies, and glomerular immune complex deposition-did not cosegregate, and linkage analysis for each trait was performed independently. Hemolytic anemia mapped to two loci: Bah1 at the MHC on chromosome 17 and Bah2 on distal chromosome 16. Antinuclear autoantibodies mapped to three loci: Bana1 at the MHC on chromosome 17, Bana2 on chromosome 10, and Bana3 on distal chromosome 1. Glomerular immune complex deposition did not show significant linkage to any genomic region. Mapping of autoantibodies (Coombs' or antinuclear autoantibodies) identified two loci: Babs1 at the MHC and Babs2 on distal chromosome 1. It has previously been reported that genes conferring susceptibility to different autoimmune diseases map nonrandomly to defined regions of the genome. One possible explanation for this clustering is that some alleles at loci within these regions confer susceptibility to multiple autoimmune diseases-the "common gene" hypothesis. With the exception of the H2, this study failed to provide direct support for the common gene hypothesis, because the loci identified as conferring susceptibility to systemic lupus erythematosus did not colocalize with those previously implicated in diabetes. However, three of the four regions identified had been previously implicated in other autoimmune diseases.