Genetic analysis of the NZB contribution to lupus-like autoimmune disease in (NZB x NZW)F1 mice

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.

Genetic contributions of nonautoimmune SWR mice toward lupus nephritis

(SWR x New Zealand Black (NZB))F(1) (or SNF(1)) mice succumb to lupus nephritis. Although several NZB lupus susceptibility loci have been identified in other crosses, the potential genetic contributions of SWR to lupus remain unknown. To ascertain this, a panel of 86 NZB x F(1) backcross mice was immunophenotyped and genome scanned. Linkage analysis revealed four dominant SWR susceptibility loci (H2, Swrl-1, Swrl-2, and Swrl-3) and a recessive NZB locus, Nba1. Early mortality was most strongly linked to the H2 locus on chromosome (Chr) 17 (log likelihood of the odds (LOD) = 4.59 - 5.38). Susceptibility to glomerulonephritis was linked to H2 (Chr 17, LOD = 2.37 - 2.70), Swrl-2 (Chr 14, 36 cM, LOD = 2.48 - 2.71), and Nba1 (Chr 4, 75 cM, LOD = 2.15 - 2.23). IgG antinuclear autoantibody development was linked to H2 (Chr 17, LOD = 4.92 - 5.48), Swrl-1 (Chr 1, 86 cM, colocalizing with Sle1 and Nba2, LOD = 2.89 - 2.91), and Swrl-3 (Chr 18, 14 cM, LOD = 2.07 - 2.13). For each phenotype, epistatic interaction of two to three susceptibility loci was required to attain the high penetrance levels seen in the SNF(1) strain. Although the SWR contributions H2, Swrl-1, and Swrl-2 map to loci previously mapped in other strains, often linked to very similar phenotypes, Swrl-3 appears to be a novel locus. In conclusion, lupus in the SNF(1) strain is truly polygenic, with at least four dominant contributions from the SWR strain. The immunological functions and molecular identities of these loci await elucidation.

Tumor necrosis factor receptor 2 polymorphism in systemic lupus erythematosus: no association with disease

Genetic factors and immune dysregulation play important roles in the development of systemic lupus erythematosus (SLE). Tumor necrosis factor receptor 2 (TNFR2) is suggested to be involved in the development of SLE because its genetic locus (1p36) encompasses one of the susceptible loci for SLE and its ligand (TNF) is associated with SLE. To investigate the role of TNFR2 in the pathogenesis of SLE, 139 Korean patients were genotyped with SLE, 137 healthy control subjects were genotyped for TNFR2 196 R/M polymorphism in exon 6 with PCR-SSCP, and the clinical characteristics of SLE were analyzed according to the genotypes. The genotype frequencies of 196 R/R, 196 R/M, and 196 M/M were 3.6%, 30.9%, and 65.5% in SLE patients and 4.4%, 26.3%, and 69.3% in healthy controls (p = 0.676). The allelic frequency of 196 R was 19.1% in SLE patients and 17.5% in healthy controls (p = 0.638, odds ratio = 1.109, and the 95% confidence interval = 0.720-1.708). The clinical characteristics were not different according to the genotypes. In conclusion, no skewed distribution of TNFR2 196 R/M polymorphism was found in Korean patients with SLE compared with healthy controls. Further studies in other populations will be needed to elucidate the role of the TNFR2 polymorphism in the development of SLE.

Deficiency in beta(2)-microglobulin, but not CD1, accelerates spontaneous lupus skin disease while inhibiting nephritis in MRL-Fas(lpr) nice: an example of disease regulation at the organ level

When mutations that inactivate molecules that function in the immune system have been crossed to murine lupus strains, the result has generally been a uniform up-regulation or down-regulation of autoimmune disease in the end organs. In the current work we report an interesting dissociation of target organ disease in beta(2)-microglobulin (beta(2)m)-deficient MRL-Fas(lpr) (MRL/lpr) mice: lupus skin lesions are accelerated, whereas nephritis is ameliorated. beta(2)m deficiency affects the expression of classical and nonclassical MHC molecules and thus prevents the normal development of CD8- as well as CD1-dependent NK1(+) T cells. To further define the mechanism by which beta(2)m deficiency accelerates skin disease, we studied CD1-deficient MRL/lpr mice. These mice do not have accelerated skin disease, excluding a CD1 or NK1(+) T cell-dependent mechanism of beta(2)m deficiency. The data indicate that the regulation of systemic disease is not solely governed by regulation of initial activation of autoreactive lymphocytes in secondary lymphoid tissue, as this is equally relevant to renal and skin diseases. Rather, regulation of autoimmunity can also occur at the target organ level, explaining the divergence of disease in skin and kidney in beta(2)m-deficient mice.

Delineating the genetic basis of systemic lupus erythematosus

Genetic predisposition plays a crucial role in susceptibility to systemic lupus erythematosus (SLE) in both human patients and animal models. Recent progress in experimental systems and human linkage analysis is providing key insights into the genetic basis for susceptibility and elucidating the manner in which genetic interactions mediate severe disease pathogenesis. Genes in multiple pathways appear to participate in specific elements of the disease, and epistatic interactions among these genes play an important role in both aggravating and suppressing disease development.

Resistance to xenobiotic-induced autoimmunity maps to chromosome 1

Although evidence indicates that environmental factors play a major role in precipitating systemic autoimmunity in genetically susceptible individuals, little is known about the mechanisms involved. Certain heavy metals, such as mercury, are potent environmental immunostimulants that produce a number of immunopathologic sequelae, including lymphoproliferation, hypergammaglobulinemia, and overt systemic autoimmunity. Predisposition to such metal-induced immunopathology has been shown to be influenced by both MHC and non-MHC genes, as well as susceptibility to spontaneous lupus, in mice and other experimental animals. Among the various mouse strains examined to date, the DBA/2 appears to uniquely lack susceptibility to mercury-induced autoimmunity (HgIA), despite expressing a susceptible H-2 haplotype (H-2d). To define the genetic basis for this trait, two genome-wide scans were conducted using F2 intercrosses of the DBA/2 strain with either the SJL or NZB strains, both of which are highly susceptible to HgIA. A single major quantitative trait locus on chromosome 1, designated Hmr1, was shown to be common to both crosses and encompassed a region containing several lupus susceptibility loci. Hmr1 was linked to glomerular immune complex deposits and not autoantibody production, suggesting that DBA/2 resistance to HgIA may primarily involve the later stages of disease pathogenesis. Identification and characterization of susceptibility/resistance genes and mechanisms relevant to the immunopathogenesis of mercury-induced autoimmunity should provide important insights into the pathogenesis of autoimmunity and may reveal novel targets for intervention.

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.

Lessons from the NZM2410 model and related strains

SLE susceptibility requires the interplay of an unknown number of genes and equally unidentified triggering events. The past few years have seen significant advances in our understanding of SLE susceptibility through the genetic analysis of murine models. The NZM2410 strain, which is derived from the NZB/WF1 model has played a significant role in these advances. The main advantages presented by this strain over other models are the genetic homozygozity at all loci and an highly penetrant early onset lupus nephritis in both males and females, indicating that the strongest BWF1 susceptibility loci were retained in NZM2410. After identification of NZM2410 susceptibility loci via linkage analyses, congenic strains have been derived in order to convert a polygenic system into a series of monogenic traits. These congenic strains have been analyzed in an integrated process which has provided simultaneously 1) novel functional characterization of the Sle susceptibility loci, 2) high resolution genetic maps that will lead to the identification of the corresponding susceptibility genes by either candidate locus or positional cloning, and 3) insights into the mechanisms by which these loci interact to produce systemic autoimmunity with fatal end-organ damage.

Genetics of systemic autoimmunity in mouse models of lupus

Systemic lupus erythematosus (SLE) is inherited as a complex polygenic trait, involving genetic, environmental and stochastic factors. Although definition of these etiologic processes has been elusive, solid progress has been made toward elucidating the genetic basis for susceptibility. Herein, we summarize our genome wide mapping effort that has defined loci for component phenotypes for lupus-prone NZB, NZW, MRL-Fas(lpr) and BXSB strains. With this framework in place, identification of the specific genetic alterations and mechanisms is now proceeding through the generation of interval congenic lines, precise mapping and screening of candidate genes. In addition to this approach, transgenic and gene knockout studies have begun to identify genes that can induce or modify autoimmunity in nonautoimmune and lupus-prone background mice, including studies by us and others on Th1 and Th2 cytokine genes in lupus. It is apparent that a diversity of genes and mechanisms can independently or in combination promote systemic autoimmunity in mice. This complexity, which is also observed in human lupus, emphasizes the importance of using experimental and less complex mouse models to define these processes, a tactic that has already yielded new insights. With current technologies and the anticipated definition of mammalian genomes, identification of genes predisposing to lupus and elucidation of processes critical for disease pathogenesis appear within grasp.

Lupus susceptibility genes on human chromosome 1

During the past five years, there has been an intense interest in studying candidate susceptibility genes for systemic lupus erythematosus (SLE). Many such studies have been focused on candidates located on chromosome 1, demonstrating association of certain genetic variants with SLE. Some of the tested candidate genes were chosen because they encode molecules with relevant immunological functions that may play a role in the pathogenesis of SLE. More recently, the identification of genomic segments linked to SLE has suggested novel positional candidate genes. Thus far, there is considerable evidence supporting that multiple genes on this chromosome contribute to the development and expression of SLE. This review highlights the genetic loci located on chromosome 1 that have recently been associated with SLE. These include loci encoding the tumor necrosis factor receptor 2 (TNFR2), complement component C1q, Fcgamma receptors, T cell receptor zeta chain, interleukin-10 (IL-10), poly (ADP-ribose) polymerase (PARP), and HRES-1.

Suggestive evidence for association of human chromosome 18q12-q21 and its orthologue on rat and mouse chromosome 18 with several autoimmune diseases

Some immune system disorders, such as type 1 diabetes, multiple sclerosis (MS), and rheumatoid arthritis (RA), share common features: the presence of autoantibodies and self-reactive T-cells, and a genetic association with the major histocompatibility complex. We have previously published evidence, from 1,708 families, for linkage and association of a haplotype of three markers in the D18S487 region of chromosome 18q21 with type 1 diabetes. Here, the three markers were typed in an independent set of 627 families and, although there was evidence for linkage (maximum logarithm of odds score [MLS] = 1.2; P = 0.02), no association was detected. Further linkage analysis revealed suggestive evidence for linkage of chromosome 18q21 to type 1 diabetes in 882 multiplex families (MLS = 2.2; lambdas = 1.2; P = 0.001), and by meta-analysis the orthologous region (also on chromosome 18) is linked to diabetes in rodents (P = 9 x 10(-4)). By meta-analysis, both human chromosome 18q12-q21 and the rodent orthologous region show positive evidence for linkage to an autoimmune phenotype (P = 0.004 and 2 x 10(-8), respectively, empirical P = 0.01 and 2 x 10(-4), respectively). In the diabetes-linked region of chromosome 18q12-q21, a candidate gene, deleted in colorectal carcinoma (DCC), was tested for association with human autoimmunity in 3,380 families with type 1 diabetes, MS, and RA. A haplotype ("2-10") of two newly characterized microsatellite markers within DCC showed evidence for association with autoimmunity (P = 5 x 10(-6)). Collectively, these data suggest that a locus (or loci) exists on human chromosome 18q12-q21 that influences multiple autoimmune diseases and that this association might be conserved between species.

Fine mapping of the SLEB2 locus involved in susceptibility to systemic lupus erythematosus

We have previously reported linkage of systemic lupus erythematosus to chromosome 2q37 in multicase families from Iceland and Sweden. This locus (SLEB2) was identified by linkage to the markers D2S125 and D2S140. In the present study we have analyzed additional microsatellite markers and SNPs covering a region of 30 cM around D2S125 in an extended set of Nordic families (Icelandic, Swedish, and Norwegian). Two-point linkage analysis in these families gave a maximum lod score at the position of markers D2S2585 and D2S2985 (Z = 4.51, PIC = 0.65), by applying a "model-free" pseudo-marker linkage analysis. Based on multipoint linkage analysis in the Nordic families, the most likely location of the SLEB2 locus is estimated to be in the interval between D2S125 and the position of markers D2S2585 and D2S2985, with a peak multipoint lod score of Z = 6.03, assuming a dominant pseudo-marker model. Linkage disequilibrium (LD) analysis was performed using the data from the multicase families and 89 single-case families of Swedish origin, using the same set of markers. The LD analysis showed evidence for association in the single-case and multicase families with locus GAAT3C11 (P < 0.0003), and weak evidence for association was obtained for several markers located telomeric to D2S125 in the multicase families. Thirteen Mexican families were analyzed separately and found not to have linkage to this region. Our results support the presence of the SLEB2 locus at 2q37.

Genetic studies in systemic autoimmunity and aging

The etiopathogenesis of systemic lupus erythematosus remains an enigma that will probably not be solved until the genetic basis for susceptibility is defined. Through genomewide searches, we have provided a foundation for this by identifying and characterizing loci predisposing to specific disease traits in four major lupus-susceptible mouse strains. Further ongoing work that includes the study of interval-specific congenic lines and precise mapping of loci should lead to identification of the corresponding genes and elucidation of processes critical for disease pathogenesis. Another important area of investigation is the study of cell-cycle and apoptosis genes in systemic autoimmunity and aging. Based on earlier work, we proposed that the characteristic overexpansion of memory phenotype cells in these conditions may be owing to replicative senescence. Understanding the molecular mechanisms that regulate the generation of these cells may permit selective manipulations to control this process. Other areas of investigation that we are actively engaged in are the role of T cell receptor repertoire in disease and the definition of cellular genes affected by infection with human immunodeficiency virus.

Calorie restriction decreases proinflammatory cytokines and polymeric Ig receptor expression in the submandibular glands of autoimmune prone (NZB x NZW)F1 mice

Calorie restriction or fish oil (enriched in n-3 fatty acids) supplementation ameliorates glomerulonephritis and Sjögren's syndrome lesions in (NZB x NZW)F1(B/W) mice. Enhanced proinflammatory cytokine expression and deposition of immune complexes are the important pathological events in the development of Sjögren's syndrome. In the present study, we have examined the effect of calorie restriction and fish oil supplementation on the expression of key inflammatory cytokines [gamma interferon (INF-gamma), interleukin-10 (IL-10), and IL-12] and polymeric immunoglobulin (Ig) receptor (pIgR) (receptor for IgA and IgM) and the secretion of Ig in the submandibular glands (SMG) of B/W mice. Weanling B/W mice were fed either ad libitum (AL) or calorie restricted (CR) (40% less calories than AL) diet supplemented with 5% corn oil (CO) or 5% fish oil (FO) until 4 or 9 months of age. The SMGs were removed and a portion of the tissue used for semiquantitive determinations of IFN-gamma, IL-10, IL-12 (p40), and pIgR mRNA. The remaining SMG tissue was fragmented and cultured for 7 days and the culture supernatants assayed for IgA, IgM, and IgG2a levels by enzyme-linked immunosorbent assay. Results revealed a significant increase in the expression of IFN-gamma, IL-10, and IL-12 mRNA with age in AL fed mice, whereas CR fed mice maintained their levels to near those seen in young animals regardless of the dietary fat. PIgR mRNA expression also remained unaltered in CR animals irrespective of age and dietary fat, while it was found significantly increased in AL fed mice. CR significantly inhibited the elevated levels of IgA and IgG2a seen in aged mice. Interestingly, CR also influenced the Ig level in young animals. In summary, these results indicate that amelioration of autoimmune disease by CR in B/W mice is possibly mediated by the lowered mRNA expression of IFN-gamma, IL-10, IL-12, and pIgR and the reduced Ig secretion.

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.

Genetic control of glycoprotein 70 autoantigen production and its influence on immune complex levels and nephritis in murine lupus

The F1 hybrids of New Zealand Black (NZB) and New Zealand White (NZW) mice spontaneously develop an autoimmune disease that serves as a model for human systemic lupus erythematosus. Autoimmunity in (NZB x NZW)F1 mice includes the production of autoantibodies to the endogenous retroviral envelope glycoprotein, gp70, and gp70-anti-gp70 immune complexes (gp70 IC) have been implicated in the development of lupus nephritis in these animals. We used backcross and intercross combinations of C57BL/6 (B6; low gp70 levels) and NZB mice (high gp70 levels) to examine the contribution of serum gp70 Ag levels to the development of gp70 IC and nephritis. Analysis of (B6.H2z x NZB)F1 x NZB backcross mice and (NZB x B6)F2 mice showed a much stronger association of gp70 IC with kidney disease compared with IgG anti-chromatin autoantibodies in both populations of mice. Serum levels of gp70 correlated with production of gp70 IC in mice producing autoantibodies, although the overall effect on nephritis appeared to be small. Genetic mapping revealed three NZB-derived regions on chromosomes 2, 4, and 13 that were strongly linked with increased gp70 levels, and together, accounted for over 80% of the variance for this trait. However, additional linkage analyses of these crosses showed that loci controlling autoantibody production rather than gp70 levels were most important in the development of nephritogenic immune complexes. Together, these studies characterize a set of lupus-susceptibility loci distinct from those that control autoantibody production and provide new insight into the components involved in the strong association of gp70 IC with murine lupus nephritis.

The NOD Idd9 genetic interval influences the pathogenicity of insulitis and contains molecular variants of Cd30, Tnfr2, and Cd137

Previous analyses of NOD mice have shown that some genes control the development of both insulitis and diabetes, while other loci influence diabetes without reducing insulitis. Evidence for the existence of a gene only influencing diabetes, Idd9 on mouse chromosome 4, is provided here by the development of a novel congenic mouse strain, NOD.B10 Idd9. NOD.B10 Idd9 mice display profound resistance to diabetes even though nearly all develop insulitis. Subcongenic analysis has demonstrated that alleles of at least three B10 genes, Idd9.1, Idd9.2, and Idd9.3 are required to produce Idd9-mediated diabetes resistance. Candidate genes with amino acid differences between the NOD and B10 strains have been localized to the 5.6 cM Idd9.2 interval (Tnfr2, Cd30) and to the 2.0 cM Idd9.3 interval (Cd137).

Involvement of Sp1 and microsatellite repressor sequences in the transcriptional control of the human CD30 gene

CD30, as a member of the tumor necrosis factor (TNF) receptor family, is expressed on the surface of activated lymphoid cells. CD30 overexpression is a characteristic of lymphoproliferative diseases such as Hodgkin's/non-Hodgkin's lymphomas, embryonal carcinoma, and a number of Th2-associated diseases. The CD30 gene has been mapped to a region of the murine genome that is involved in susceptibility to systemic lupus erythematosus. Functionally, CD30 may play a role in the deletion of autoreactive T cells. We were interested in determining the molecular nature of CD30 overexpression. Sequence comparison has revealed significant identity between the TATA-less human and murine CD30 promoters; they share a number of common consensus binding motifs. Transfection assays identified three regions of transcriptional importance; the region between position -1.2 kb and -336 bp, containing a CCAT microsatellite sequence, a conserved Sp1 site at positions -43 to -38, and a downstream promoter element (DPE) at positions +24 to +29. EMSA and DNase I footprinting showed specific DNA-protein interactions of the CD30 promoter with the Sp1 site and the CCAT repeat region. The DPE element was shown to be essential for start site selection. We conclude that the conserved Sp1 site at -43 to -38 is associated with maximum reporter gene activity, the DPE element is required for start site selection, and the CCAT tetranucleotide repeats act to repress transcription. We also have shown that the microsatellite is multiallelic, when we screened a random healthy population. Further studies are required to determine whether microsatellite instability in the repressor predisposes susceptible individuals to CD30 overexpression.

A susceptibility locus for human systemic lupus erythematosus (hSLE1) on chromosome 2q

To identify chromosomal regions containing susceptibility loci for systemic lupus erythematosus (SLE), we performed genome scans in families with multiple SLE patients from Iceland, a geographical and genetic isolate, and from Sweden. A number of chromosomal regions showed maximum lod scores (Z) indicating possible linkage to SLE in both the Icelandic and Swedish families. In the Icelandic families, five regions showed lod scores greater than 2.0, three of which (4p15-13, Z=3.20; 9p22, Z=2.27; 19q13, Z=2.06) are homologous to the murine regions containing the lmb2, sle2 and sle3 loci, respectively. The fourth region is located on 19p13 (D19S247, Z=2.58) and the fifth on 2q37 (D2S125, Z=2.06). Only two regions showed lod scores above 2.0 in the Swedish families: on chromosome 2q11 (D2S436, Z=2. 13) and 2q37 (D2S125, Z=2.18). The combination of both family sets gave a highly significant lod score at D2S125 of Z=4.24 in favor of linkage for 2q37. This region represents a new locus for SLE. Our results underscore the importance of studying well-defined populations for genetic analysis of complex diseases such as SLE.

Structure and localization of mouse Pmscl1 and Pmscl2 genes

Sera from some patients with polymyositis-scleoderma overlap syndrome (PM-SCL) recognize two antigenically unrelated proteins, PMSCL1 and PMSCL2. Complete mouse Pmscl1 and Pmscl2 cDNA sequences, chromosomal localizations, exon/intron structure, and promoter region sequences of the mouse Pmscl2 gene are presented. The PMSCL1 gene was found to overlap significantly with cyclin A2 in both human and mouse. As such, it may be deduced that PMSCL1 sequences map to human chromosome 4q27 and the proximal portion of mouse chromosome (Chr) 3 where human and mouse cyclin A2 genes reside. Analysis of human and mouse PMSCL1 cDNA sequences provides evidence that the PMSCL1 protein is 68 amino acids longer than previously thought. A BAC containing mouse Pmscl2 was localized to distal mouse Chr 4 by FISH. This BAC contains the microsatellite D4Mit310. D4Mit310 colocalizes with a number of genes that map to human 1p36. In fact, a STS (G25404) located 54.6 cR from the top of human chromosome 1 was found to contain PMSCL2 sequence upon BLAST search.

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.

Genetic basis of autoimmune sialadenitis in MRL/lpr lupus-prone mice: additive and hierarchical properties of polygenic inheritance

OBJECTIVE

To clarify the mode of inheritance of autoimmune sialadenitis in MRL/MpJ-lpr/lpr (MRL/lpr) lupus-prone mice and identify the susceptibility loci.

METHODS

MRL/lpr, C3H/HeJ-lpr/lpr (C3H/lpr), (MRL/lpr x C3H/lpr)F1 intercross, and MRL/lpr x (MRL/lpr x C3H/lpr)F1 backcross mice were prepared, and sialadenitis in individual mice was analyzed by histopathologic grading. The genomic DNA of the backcross mice was examined by simple sequence-length polymorphism analysis, and the highly associated polymorphic microsatellite markers with sialadenitis were determined as sialadenitis susceptibility loci.

RESULTS

Four susceptible gene loci recessively associated with sialadenitis were mapped on chromosomes 10, 18, 4, and 1, respectively. These loci manifested additive and hierarchical properties in the development of sialadenitis.

CONCLUSION

The results indicate that sialadenitis in MRL/lpr mice is under the control of polygenic inheritance, possibly involving allelic polymorphism.

Genetic dissection of systemic lupus erythematosus

Recent progress towards elucidating the genetic basis for susceptibility to systemic lupus erythematosus (SLE) has provided insights into the manner in which individual susceptibility genes contribute to disease pathogenesis. Studies in animal models of systemic autoimmunity suggest that genes in three separate pathways contribute to the initiation and progression of systemic autoimmunity. Linkage studies in humans suggest that at least some susceptibility genes mediating disease in lupus-prone mice may also contribute to susceptibility in humans.

Epistatic modifiers of autoimmunity in a murine model of lupus nephritis

Sle1 and Sle3 are NZW-derived loci that mediate lupus nephritis on a C57BL/6 background. The absence of severe autoimmunity in NZW suggests that the NZW genome suppresses these genes. (B6.NZMc1[Sle1] x NZW)F1 hybrids develop severe humoral autoimmunity and fatal lupus nephritis, indicating that suppression of Sle1 from NZW is recessive. Linkage analysis identified four epistatic modifiers, Sles1-4, whose cumulative effect accounted for the benign autoimmunity in NZW. The specific suppression of Sle1 but not Sle2 or Sle3 by Sles1 was directly demonstrated via the production and analysis of bicongenic strains. Moreover, Sles1 was sufficient to completely suppress autoimmunity initiated by Sle1 in B6.NZMc1 x NZW hybrids. These results demonstrate the complex epistatic interactions of loci augmenting and suppressing systemic autoimmunity.

Anti-DNA autoantibodies and systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that affects most of the organs and tissues of the body, causing glomerulonephritis, arthritis, and cerebritis. SLE can be fatal with nephritis, in particular, predicting a poor outcome for patients. In this review, we highlight what has been learned about SLE from the study of mouse models, and pay particular attention to anti-DNA autoantibodies, both as pathological agents of lupus nephritis and as DNA-binding proteins. We summarize the current approaches used to treat SLE and discuss the targeting of anti-DNA autoantibodies as a new treatment for lupus nephritis.

Control of separate pathogenic autoantibody responses marks MHC gene contributions to murine lupus

Previous studies have suggested that MHC and non-MHC genes contribute to the development of autoimmune disease in F1 hybrids of New Zealand black (NZB) and white (NZW) mice. We conducted a genome-wide screen of 148 female (NZB x NZW)F1 x NZB backcross mice to map dominant NZW genetic loci linked with lupus disease traits. In this backcross analysis, inheritance of the NZW MHC (H2(d/z) vs. H2(d/d)) was strongly linked with the development of lupus nephritis (P approximately 1 x 10(-16)), increasing the risk of disease by over 30-fold. H2(d/z) was also linked with elevated serum levels of IgG autoantibodies to single-stranded DNA, double-stranded DNA, histones, and chromatin but not with anti-gp70 autoantibodies, measured as circulating gp70-anti-gp70 immune complexes. Non-MHC contributions from NZW seemed weak in comparison to MHC, although NZW loci on chromosomes 7 and 16 were noted to be suggestively linked with autoantibody production. Strikingly, H2(d/z) (compared with H2(d/d)) enhanced antinuclear antibodies in a coordinate fashion but did not affect anti-gp70 production in the current backcross. However, the opposite influence was noted for H2(d/z) (compared with H2(z/z)) when (NZB x NZW)F1 x NZW backcross mice were analyzed. These results suggest that H2(z) and H2(d) haplotypes differentially regulate two different sets of nephritogenic autoantibody responses. This study confirms a critical role for H2(z) compared with other dominant NZW loci in (NZB x NZW)F1 mice and provides an explanation as to why H2(d/z) heterozygosity is required for full expression of disease in this model.

A Major Linkage Region on Distal Chromosome 4 Confers Susceptibility to Mouse Autoimmune Gastritis

Although much is known about the pathology of human chronic atrophic (type A, autoimmune) gastritis, its cause is poorly understood. Mouse experimental autoimmune gastritis (EAG) is a CD4+ T cell-mediated organ-specific autoimmune disease of the stomach that is induced by neonatal thymectomy of BALB/c mice. It has many features similar to human autoimmune gastritis. To obtain a greater understanding of the genetic components predisposing to autoimmune gastritis, a linkage analysis study was performed on (BALB/cCrSlc × C57BL/6)F2 intercross mice using 126 microsatellite markers covering 95% of the autosomal genome. Two regions with linkage to EAG were identified on distal chromosome 4 and were designated Gasa1 and Gasa2. The Gasa1 gene maps within the same chromosomal segment as the type 1 diabetes and systemic lupus erythematosus susceptibility genes Idd11 and Nba1, respectively. Gasa2 is the more telomeric of the two genes and was mapped within the same chromosomal segment as the type 1 diabetes susceptibility gene Idd9. In addition, there was evidence of quantitative trait locus controlling autoantibody titer within the telomeric segment of chromosome 4. The clustering of genes conferring susceptibility to EAG with those conferring susceptibility to type 1 diabetes is consistent with the coinheritance of gastritis and diabetes within human families. This is the first linkage analysis study of autoimmune gastritis in any organism and as such makes an important and novel contribution to our understanding of the etiology of this disease.

The genes of systemic autoimmunity

Autoimmune diseases include a wide spectrum of disorders, which have been divided into systemic and organ-specific disorders. Lupus, the prototypic systemic autoimmune disease, is characterized by female predominance, multiorgan pathology, and autoantibodies, primarily directed against nuclear antigens. The disease is heterogeneous, with variable organ involvement, serology, and clinical course. Susceptibility to lupus is inherited as a polygenic trait with added contributions from environmental and stochastic variance. Concerted efforts have recently been made by several laboratories to define the genetic basis of this disease in predisposed mice and humans. The identification of the Fas/FasL defects in lpr and gld lupus mice was the first example of spontaneous mutations of apoptosis-promoting genes being associated with systemic autoimmunity. This research was instrumental in clarifying the roles of these genes in tolerance and immunoregulation, and in extrapolating these results to other autoimmune diseases, as well as cancer and transplantation. To these findings have been added those from transgenic and gene knockout mouse studies that have helped to define the systemic autoimmunity-inducing or -modifying effects of specific genes in normal background and lupus-congenic mice. In addition, the findings from genome-wide searches have begun to identify predisposing loci (and ultimately genes) for the spontaneous lupus-like diseases in various mouse strains and in humans. The emerging picture is that multiple genetic contributions can independently lead to systemic autoimmunity in mice, which reinforces the view that human lupus may be similarly composed of diverse genotypes. This complexity underscores the importance of defining the predisposing alleles and mechanisms of action, an undertaking that is certainly feasible given current technologies and future advances in the definition of mammalian genomes.

Deficiency in CD22, a B cell-specific inhibitory receptor, is sufficient to predispose to development of high affinity autoantibodies

CD22 is a B cell-specific transmembrane glycoprotein that acts to dampen signals generated through the B cell antigen receptor (BCR): B cells from CD22-deficient mice give increased Ca2+ fluxes on BCR ligation. Here we show that this B cell hyperresponsiveness correlates with the development of autoantibodies. After the age of eight months, CD22-deficient mice developed high titers of serum IgG directed against double-stranded DNA; these antibodies were of multiclonal origin, somatically mutated, and high affinity. Increased titers of antibodies to cardiolipin and myeloperoxidase were also noted. The results demonstrate that a single gene defect exclusive to B lymphocytes is, without additional contrivance, sufficient to trigger autoantibody development in a large proportion of aging animals. Thus, CD22 might have evolved specifically to regulate B cell triggering thresholds for the avoidance of autoimmunity.

Production of High Affinity Autoantibodies in Autoimmune New Zealand Black/New Zealand White F1 Mice Targeted with an Anti-DNA Heavy Chain

Lupus-prone, anti-DNA, heavy (H) chain “knock-in” mice were obtained by backcrossing C57BL/6 mice, targeted with a rearranged H chain from a VH11(S107)-encoded anti-DNA hybridoma (D42), onto the autoimmune genetic background of New Zealand Black/New Zealand White (NZB/NZW) F1 mice. The targeted female mice developed typical lupus serologic manifestations, with the appearance of transgenic IgM anti-DNA autoantibodies at a young age (2–3 mo) and high affinity, somatically mutated IgM and IgG anti-DNA Abs at a later age (6–7 mo). However, they did not develop clinical, lupus-associated glomerulonephritis and survived to at least 18 mo of age. L chain analysis of transgenic anti-DNA Abs derived from diseased NZB/NZW mouse hybridomas showed a very restricted repertoire of Vκ utilization, different from that of nonautoimmune (C57BL/6 × BALB/c)F1 transgenic anti-DNA Abs. Strikingly, a single L chain was repetitively selected by most anti-DNA, transgenic NZB/NZW B cells to pair with the targeted H chain. This L chain had the same Vκ-Jκ rearrangement as that expressed by the original anti-DNA D42 hybridoma. These findings indicate that the kinetics of the autoimmune serologic manifestations are similar in wild-type and transgenic lupus-prone NZB/NZW F1 mice and suggest that the breakdown of immunologic tolerance in these mice is associated with the preferential expansion and activation of B cell clones expressing high affinity anti-DNA H/L receptor combinations.

Genome-wide screen for systemic lupus erythematosus susceptibility genes in multiplex families

Systemic lupus erythematosus (SLE) is the prototype of human autoimmune diseases. Its genetic component has been suggested by familial aggregation (lambdas = 20) and twin studies. We have screened the human genome to localize genetic intervals that may contain lupus susceptibility loci in a sample of 188 lupus patients belonging to 80 lupus families with two or more affected relatives per family using the ABI Prism linkage mapping set which includes 350 polymorphic markers with an average spacing of 12 cM. Non-parametric multipoint linkage analysis suggests evidence for predisposing loci on chromosomes 1 and 18. However, no single locus with overwhelming evidence for linkage was found, suggesting that there are no 'major' susceptibility genes segregating in families with SLE, and that the genetic etiology is more likely to result from the action of several genes of moderate effect. Furthermore, the support for a gene in the 1q44 region as well as in the 1p36 region is clearly found only in the Mexican American families with SLE but not in families of Caucasian ethnicity, suggesting that consideration of each ethnic group separately is crucial.

Analysis of MHC Class II Genes in the Susceptibility to Lupus in New Zealand Mice

Hybrids of New Zealand Black (NZB) and New Zealand White (NZW) mice spontaneously develop a disease similar to human systemic lupus erythematosus. MHC and non-MHC genes contribute to disease susceptibility in this murine model. Multiple studies have shown that the NZW H2z locus is strongly associated with the development of lupus-like disease in these mice. The susceptibility gene(s) within H2z is not known, but different lines of evidence have pointed to class II MHC genes, either H2-E or H2-A (Ez or Az in NZW). Recent studies from our laboratory showed that Ez does not supplant H2z in the contribution to lupus-like disease. In the present work we generated C57BL/10 (B10) mice transgenic for Aaz and Abz genes (designated B10.Az mice) and used a (B10.Az × NZB)F1 × NZB backcross to assess the contributions of Az genes to disease. A subset of backcross mice produced high levels of IgG autoantibodies and developed severe nephritis. However, no autoimmune phenotype was linked to the Az transgenes. Surprisingly, in the same backcross mice, inheritance of H2b from the nonautoimmune B10 strain was strongly linked with both autoantibody production and nephritis. Taken together with our previous Ez studies, the present work calls into question the importance of class II MHC genes for lupus susceptibility in this model and provides new insight into the role of MHC in lupus-like autoimmunity.

Immune cell signaling defects in lupus: activation, anergy and death

Recent studies have identified novel aberrations in antigen receptor-mediated signaling events in lymphocytes from patients with systemic lupus erythematosus. Here, we propose that in lupus lymphocytes, the receptor-mediated increase in protein tyrosine phosphorylation and cytoplasmic free Ca2+ responses, along with T-cell receptor zeta chain deficiency, might explain the previously described diverse and conflicting immunoregulatory defects in human lupus.

Thymic microenvironment and NZB mice: the abnormal thymic microenvironment of New Zealand mice correlates with immunopathology

There are distinct microenvironmental abnormalities of thymic architecture in several murine models of SLE defined using immunohistochemistry and a panel of mAb dissected at thymic epithelial markers. To address the issue of the relationship between the thymic microenvironment and autoimmunity, we studied backcross (NZB x NZW) F1 x NZW mice in which 50% of offspring develop nephritis associated with proteinuria and anti-DNA antibodies. We reasoned that if thymic abnormalities are associated with development of disease, the correlation of abnormalities with lupus-like disease in individual backcross mice will form the foundation for identification of the mechanisms involved. In parallel, we directed a genetic linkage analysis, using markers previously shown to be linked to nephritis and IgG autoantibody production, to determine if such loci were similarly associated with microenvironmental changes. Our data demonstrate that all (NZB x NZW) F1 x NZW backcross mice with disease have microenvironmental defects. Although the microenvironmental defects are not sufficient for development of autoimmune disease, the severity of thymic abnormalities correlates with titers of IgG autoantibodies to DNA and with proteinuria. Consistent with past studies of (NZB x NZW) F1 x NZW mice, genetic markers on proximal chromosome 17 (near MHC) and distal chromosome 4 showed trends for linkage with nephritis. Although the markers chosen only covered about 10-15% of the genome, the results demonstrated trends for linkage with thymic medullary abnormalities for loci on distal chromosome 4 and distal chromosome 1. We believe it will be important to define the biochemical nature of the molecules recognized by these mAbs to understand the relationships between thymic architecture and immunopathology.

Effector and predisposing genes in murine lupus

This Publication is No. 11789-IMM from the Department of Immunology, The Scripps Research Institute, 10550 North Torrey Pines Road/IMM3, La Jolla, CA 92037. The work of the author reported herein was supported, in part, by NIH grants AR39555, AR31203, and AG15061.

Terminal Deoxynucleotidyl Transferase Deficiency Reduces the Incidence of Autoimmune Nephritis in (New Zealand Black × New Zealand White)F1 Mice

Terminal deoxynucleotidyl transferase (TdT) enzyme activity in lymphocytes generates diversity in the Ag receptor repertoires by adding template-independent N nucleotides and disrupting homology-directed rearrangements. The importance of this diversity in vivo and the significance of the suppression of TdT during fetal life remain uncertain. Previous studies have shown that in TdT knockout mice (TdT°) 1) the T cell repertoire is less peptide oriented; and 2) natural autoantibody, particularly anti-DNA autoantibodies, are less polyreactive, and their mean affinities are reduced. Consequently, the suppression of TdT during early T/B cell ontogeny may participate in controlling autoimmunity. To study the impact of TdT suppression in autoimmune-prone mice, we introduced the TdT null mutation into the (NZB × NZW)F1 (B/W) mouse strain. We show that TdT deficiency significantly reduces the incidence of autoimmune nephritis and prolongs survival compared with those in control mice. Surprisingly, the long-term survivor TdT° mice produced amounts of anti-ADN and anti-histone autoantibodies similar to those of their TdT+ littermates. However, these TdT° mice showed no evidence of renal inflammation, and the immune deposits were restricted to the mesangium, whereas basal membrane deposits were clearly correlated with overt renal disease. The present study supports the idea that the absence of TdT enzyme activity in lymphocytes protects mice against autoimmunity and could offer a therapeutic approach to autoimmune diseases. Moreover, our results may help to unravel the mechanisms of lupus nephritis.

Genetic Determinants of Autoimmune Disease and Coronary Vasculitis in the MRL-lpr/lpr Mouse Model of Systemic Lupus Erythematosus

MRL-lpr/lpr (MRL/lpr) mice are a model of human autoimmune disease. They exhibit a number of characteristics of systemic lupus erythematosus, including anti-DNA Abs, anti-cardiolipin Abs, immune complex-mediated vasculitis, lymphadenopathy, and severe glomerulonephritis. Although the autoimmune disorder is mediated primarily by mutation of the Fas gene (lpr), which interferes with lymphocyte apoptosis, MRL/lpr mice also have other predisposing genetic factors. In an effort to identify these additional factors, we have applied quantitative trait locus (QTL) mapping using an intercross between MRL/lpr mice and the nonautoimmune inbred strain BALB/cJ. A complete linkage map spanning the entire genome was constructed for 189 intercross progeny, and genetic loci contributing to features of the autoimmunity were identified using statistical analytic procedures. As expected, the primary genetic determinant of autoimmune disease in this cross was the Fas gene on mouse chromosome 19, exhibiting a lod score of 60. In addition, two novel loci, one on chromosome 2 (lod score, 4.3) and one on chromosome 11 (lod score, 3.1), were found to contribute to levels of anti-DNA Abs. Interestingly, the chromosome 19 and chromosome 11 QTLs, but not the chromosome 2 QTL, also exhibited associations with anti-cardiolipin Abs (lod scores, 38.4 and 2.6). We further examined the effects of these QTLs on the development of coronary vasculitis in the F2 mice. Our results indicate that the QTLs on chromosomes 11 and 19 also control the development of vasculitis, demonstrating common genetic determinants of autoantibody levels and vasculitis.

A genome-wide search for susceptibility genes in human systemic lupus erythematosus sib-pair families

Systemic lupus erythematosus (SLE) is an autoimmune multisystem inflammatory disease characterized by the production of pathogenic autoantibodies. Previous genetic studies have suggested associations with HLA Class II alleles, complement gene deficiencies, and Fc receptor polymorphisms; however, it is likely that other genes contribute to SLE susceptibility and pathogenesis. Here, we report the results of a genome-wide microsatellite marker screen in 105 SLE sib-pair families. By using multipoint nonparametric methods, the strongest evidence for linkage was found near the HLA locus (6p11-p21) [D6S257, logarithm of odds (lod) = 3.90, P = 0.000011] and at three additional regions: 16q13 (D16S415, lod = 3.64, P = 0.000022), 14q21-23 (D14S276, lod = 2.81, P = 0.00016), and 20p12 (D20S186, lod = 2.62, P = 0.00025). Another nine regions (1p36, 1p13, 1q42, 2p15, 2q21-33, 3cent-q11, 4q28, 11p15, and 15q26) were identified with lod scores >/=1.00. These data support the hypothesis that multiple genes, including one in the HLA region, influence susceptibility to human SLE.

Linkage of a major quantitative trait locus to Yaa gene-induced lupus-like nephritis in (NZW x C57BL/6)F1 mice

In the present study, we mapped the major quantitative trait loci (QTL) differing between the NZW and C57BL/6 inbred strains of mice by making use of (NZW x C57BL/6.Yaa)F1 mice, a model in which the lupus-like autoimmune syndrome observed in male mice is associated with the presence of an as yet unidentified Y chromosome-linked autoimmune acceleration gene, Yaa. Linkage analysis of 126 C57BL/6 x (NZW x C57BL/6.Yaa)F1 backcross males provided evidence for a major QTL on chromosome 7 controlling both the severity of glomerulonephritis and the production of IgG anti-DNA autoantibody and retroviral gp70-anti-gp70 immune complexes. Two additional QTL of C57BL/6 origin on chromosome 17 had no apparent individual effects, but showed strong epistatic interaction with chromosome 7 QTL for disease severity and anti-DNA autoantibody production. Our data also identified on chromosome 13 a QTL of NZW origin with a major effect on the level of gp70, and showing an additive effect with the chromosome 7 QTL on the level of gp70 immune complexes. Our study thus provides a model to dissect the complex genetic interactions that result in manifestations of murine lupus-like disease.

Susceptibility to lupus nephritis in the NZB/W model system

Advances in genetic mapping have resulted in the identification of multiple lupus susceptibility loci in the NZB/W mouse model. The analysis of congenic strains carrying these loci is now providing functional data on their role in lupus pathogenesis and is paving the way to the identification of the susceptibility genes and their molecular characterization.

Identification of a new non-major histocompatibility complex genetic locus on chromosome 2 that controls disease severity in collagen-induced arthritis in rats

OBJECTIVE

To identify novel non-major histocompatibility complex (non-MHC) genetic loci controlling the severity of homologous rat type II collagen-induced arthritis (CIA).

METHODS

We conducted a genome-wide scan to identify CIA regulatory quantitative trait loci (QTL) in an F2 cross between DA (CIA highly susceptible) and ACI (CIA resistant) inbred rats immunized with homologous rat type II collagen (RII). These strains share the MHC/RT1av1 haplotype required for susceptibility to RII-induced CIA.

RESULTS

F2 females had higher median arthritis scores than did males. Relative resistance in the males was determined by inheriting either a DA or an ACI Y chromosome and was independent of the source of the X chromosome. In addition, a major QTL was localized on chromosome 2 (Cia7, logarithm of odds score 4.6). Cia7 is in a region that shows linkage conservation with chromosomal regions that regulate autoimmune diabetes and experimental autoimmune encephalomyelitis in mice and multiple sclerosis in humans.

CONCLUSION

Sex chromosomes and Cia7 play an important role in regulating CIA in response to RII. This rat model should facilitate positional cloning and functional characterization of regulatory genes that may play a role in several forms of autoimmune disease, including rheumatoid arthritis.

Susceptibility Alleles for Aberrant B-1 Cell Proliferation Involved in Spontaneously Occurring B-Cell Chronic Lymphocytic Leukemia in a Model of New Zealand White Mice

B-cell chronic lymphocytic leukemia (B-CLL) and autoimmune disease are a related event, and genetic factors are linked to both diseases. As B-CLL is mainly of B-1 cell type that participates in autoantibody production, genetically-determined regulatory abnormalities in proliferation and/or differentiation of B-1 cells may determine their fate. We earlier found that, in H-2–congenic (NZB × NZW) F1 mice, while H-2d/z heterozygosity predisposes to autoimmune disease, H-2z/z homozygosity predisposes to B-CLL. Studies also suggested the involvement of non–H-2-linked NZW allele(s) in leukemogenesis. Using H-2–congenic NZW and B10 mouse strains, their F1 and backcross progeny, we have now identified three major NZW susceptibility loci for abnormal proliferation of B-1 cells, which form the basis of leukemogenesis; one H-2–linked locus on chromosome 17 and the other two non–H-2-linked loci, each on chromosome 13 and chromosome 17. Each susceptibility allele functioned independently, in an incomplete dominant fashion, the sum of effects determining the extent of aberrant B-1 cell frequencies. The development of leukemia was associated with age-related increase in B-1 cell frequencies in the blood. Thus, these alleles probably predispose B-1 cells to accumulate genetic alterations, giving rise to B-CLL. Potentially important candidate genes and correlation of the findings with autoimmune disease are discussed.

Susceptibility Alleles for Aberrant B-1 Cell Proliferation Involved in Spontaneously Occurring B-Cell Chronic Lymphocytic Leukemia in a Model of New Zealand White Mice

B-cell chronic lymphocytic leukemia (B-CLL) and autoimmune disease are a related event, and genetic factors are linked to both diseases. As B-CLL is mainly of B-1 cell type that participates in autoantibody production, genetically-determined regulatory abnormalities in proliferation and/or differentiation of B-1 cells may determine their fate. We earlier found that, in H-2–congenic (NZB × NZW) F1 mice, while H-2d/z heterozygosity predisposes to autoimmune disease, H-2z/z homozygosity predisposes to B-CLL. Studies also suggested the involvement of non–H-2-linked NZW allele(s) in leukemogenesis. Using H-2–congenic NZW and B10 mouse strains, their F1 and backcross progeny, we have now identified three major NZW susceptibility loci for abnormal proliferation of B-1 cells, which form the basis of leukemogenesis; one H-2–linked locus on chromosome 17 and the other two non–H-2-linked loci, each on chromosome 13 and chromosome 17. Each susceptibility allele functioned independently, in an incomplete dominant fashion, the sum of effects determining the extent of aberrant B-1 cell frequencies. The development of leukemia was associated with age-related increase in B-1 cell frequencies in the blood. Thus, these alleles probably predispose B-1 cells to accumulate genetic alterations, giving rise to B-CLL. Potentially important candidate genes and correlation of the findings with autoimmune disease are discussed.

Multiple Lupus Susceptibility Loci Map to Chromosome 1 in BXSB Mice

BXSB mice spontaneously develop a lupus-like syndrome that is accelerated by the Yaa gene (Y-linked autoimmune accelerator). We studied the phenotype of disease in (B10 × BXSB)F1 and (BXSB × (B10 × BXSB)F1) backcross mice and genotyped 224 backcross animals to allow a microsatellite-based genome-wide linkage analysis to be conducted. In the backcross population, three intervals on chromosome 1 showed significant linkage to disease, suggesting that multiple loci contribute to the production of autoimmune disease. D1Mit5 at 32.8 cM was linked to development of nephritis (χ2 = 15.68, p = 7.5 × 10−5), as was D1Mit12 at 63.1 cM (χ2 = 20.17, p = 7.1 × 10−6). D1Mit403 at 100 cM was linked to anti-dsDNA Ab production (χ2 = 17.28, p = 3.2 × 10−5). Suggestive linkages to antinuclear Abs and nephritis were identified on chromosome 3, to splenomegaly on chromosome 4, and to anti-ssDNA Ab production on chromosome 10. Chromosome 4 and the telomeric region of chromosome 1 have previously been linked to disease in other mouse models of systemic lupus erythematosus; however, the centromeric regions of chromosome 1 and chromosomes 3 and 10 are unique to BXSB. This implies that, though some loci may be common to a number of mouse models of lupus, different clusters of disease genes confer disease susceptibility in different strains of mice.

Multigenic control of lupus-associated antiphospholipid syndrome in a model of (NZW x BXSB) F1 mice

In a subset of systemic lupus erythematosus (SLE) patients, antiphospholipid syndrome, characterized by occurrence of anti-cardiolipin (CL) antibodies, thrombocytopenia, thrombosis and recurrent intrauterine fetal death occurs. Male (NZW x BXSB)F1 mice, carrying the BXSB Yaa gene, serve as a model for SLE-associated antiphospholipid syndrome. Using microsatellite markers in the NZW x (NZW x BXSB)F1 backcross male progeny, we mapped BXSB alleles contributing to the generation of anti-CL antibodies, platelet-binding antibodies, thrombocytopenia and myocardial infarction. Generation of each disease character was controlled by two major independently segregating dominant alleles, i.e. those on chromosomes (Chr.) 4 and 17 for anti-CL antibodies, Chr. 8 and 17 for both anti-platelet antibodies and thrombocytopenia and, to our surprise, Chr. 7 and 14 for myocardial infarction, and that a combination of the two alleles appeared to produce full expression of each character, as a complementary gene action. The alleles on Chr. 17 linked to the above three characters were all mapped in close proximity to the H-2 complex. Therefore, no single factor such as anti-CL antibodies can explain the pathogenesis of SLE-associated antiphospholipid syndrome. Rather, a combination of susceptibility alleles such as described here, along with additional modifying loci, i.e. BXSB Yaa and some from NZW, characterizes unique SLE features in male (NZW x BXSB) F1 mice. There are potentially important candidate genes which may be linked to the syndrome.

The mouse tumor necrosis factor receptor 2 gene: genomic structure and characterization of the two transcripts

The mouse TNFR2 gene has been cloned, sequenced, and characterized as a gene spanning >44 kb of the genome. By alignment of five genomic clones we have established that TNFR2 consists of 10 exons and 9 introns with exons ranging in size from 35 bp to 2.6 kb and introns ranging from 322 bp to >16 kb. All splice acceptor and donor sites conform to the canonical AG/GT rule. The translation initiation and termination sites are located in exon 1 and 10, respectively. Although TNFR2 lacks a canonical TATA box, the gene is transcribed from a unique start site located 70 bp upstream of the ATG initiation codon that conforms to the consensus Inr motif. Several cis-elements for transcription factors were identified in the 5' flanking region, including NF-1, Sp-1, AP2, gamma-IRE, and NF-kappaBeta motifs. Functional analysis indicates that the region -705/-412 contains a negative cis-acting element and that the minimal promoter contains motifs that confer LPS inducibility. Two mouse TNFR2 mRNAs of 3.2 and 4.1 kb are detected by Northern blot analysis, but until now their origin has not been explained. No evidence of alternative splicing of the coding exons was found. However, hybridization studies and amplification of cDNA ends suggest the use of a noncanonical polyadenylation signal in the untranslated region of exon 10. A comparative analysis of the 3' untranslated regions of the human and mouse TNFR2 genes shows highly divergent 3' ends. The possibility of an ancestral mouse TNFR2 mRNA similar to the short transcript is discussed.