Dominant NZB contributions to lupus in the (SWR x NZB)F1 model

Genetic control of spontaneous arthritis in a four-way advanced intercross line

Identifying the genetic basis of complex diseases, such as rheumatoid arthritis, remains a challenge that requires experimental models to reduce the genetic and environmental variability. Numerous loci for arthritis have been identified in induced animal models; however, few spontaneous models have been genetically studied. Therefore, we generated a four-way advanced intercross line (AIL) from four inbred strains, including BXD2/TyJ which spontaneously develops autoimmune arthritis. A genome-wide scan for spontaneous arthritis was performed in a cohort of 366 mice of the fourth generation (G4) of this cross. Five loci contributing to clinical phenotypes were identified in chromosomes 3, 7, 13, 18, and X. Three of the loci found in this study, confirm previously identified loci; whereas two of them are novel loci. Interesting candidate genes for the loci are highlighted. This study provides a genetic overview of spontaneous arthritis in mice and aids to solve the genetic etiology of rheumatoid arthritis and to gain a better understanding of the disease.

Genetic contributions to the autoantibody profile in a rabbit model of Systemic Lupus Erythematosus (SLE)

For the development of rabbit models of Systemic Lupus Erythematosus (SLE), immunoglobulin allotype-defined pedigreed rabbits from the National Institute of Allergy and Infectious Diseases rabbit resource more closely approximate human populations due to their non-inbred pedigreed structure. In an initial study from this laboratory, peptides (SM and GR) from the spliceosomal Smith (Sm) and the NMDA glutamate receptor NR2b, on branched polylysine backbones (BB) elicited antinuclear and anti-dsDNA autoantibodies typical of SLE, as well as seizures and nystagmus sometimes observed as neurological manifestations in SLE patients. This suggested the feasibility of further selective breeding to develop a more reproducible rabbit model for investigations of SLE. Here we report the results of GR-MAP-8 and control BB immunization on autoantibody responses in a group of 24 rabbits specifically bred and developed from parents and ancestors tested for autoantibody responses. The changes in hematological profile and blood chemistry in the experimental rabbits were evaluated along with autoantibody responses. Elevations of total white blood cell (WBC), monocyte, eosinophil and basophil counts that developed following immunizations were moderately influenced by litter and presence of the antibody heavy chain allotype VH1a1. Autoantibody development followed a sequential pattern with anti-nuclear antibodies (ANA) followed by anti-dsDNA and subsequently anti-Sm and anti-RNP similar to SLE patients. High autoantibody levels to one autoantigen were not always associated with antibody response to another. Female rabbits had higher prevalence and levels of autoantibodies similar to human SLE. Higher autoantibody levels of anti-dsDNA and -ANA were observed among some full sibs and the presence of high responder ancestors in the pedigree was associated the augmented responses. We observed significant association between highest antibody responses to GR-MAP-8 and highest anti-dsDNA levels. Naturally occurring autoantibodies were found in some pre-immune sera and some unique ANA fluorescent staining patterns within the experimental group were observed. Background immunofluorescence in pre-immune sera, distinct patterns of programmed autoantibody responses unique among individual rabbits may have been modulated by genetic constitution, gender and environmental factors including exposure to antigens. The high incidence and intensity of autoantibody responses among descendants of high responders suggest that there may be an additive mode of inheritance with high heritability. It is conceivable that further rigorous pedigree selection for autoantibody responses could lead to development of rabbit models with spontaneous occurrence of SLE like serology and disease phenotypes.

Genetic basis of murine lupus nephritis

Systemic lupus erythematosus is a generalized autoimmune disease affecting multiple end-organs including the kidneys. Glomerulonephritis is a leading cause of death in lupus, both in patients and murine models that develop disease spontaneously. Genetic mapping studies have uncovered several genetic intervals that confer susceptibility to nephritis both in human beings and in mice. This review surveys the genomic positions of these nephritis susceptibility loci in murine lupus. Currently we know very little about the molecular identities of the culprit genes within these mapped loci and whether these genetic elements contribute to nephritis directly in a renal-intrinsic fashion or indirectly by augmenting the formation of pathogenic autoantibodies. The next decade is likely to witness a significant broadening of our understanding of how different genes and molecules might facilitate end-organ damage in lupus.

Overlapping BXSB congenic intervals, in combination with microarray gene expression, reveal novel lupus candidate genes

The BXSB mouse strain is an important model of glomerulonephritis observed in systemic lupus erythematosus (SLE). Linkage studies have successfully identified disease-susceptibility intervals; however, extracting the identity of the susceptibility gene(s) in such regions is the crucial next step. Congenic mouse strains present a defined genetic resource that is highly amenable to microarray analysis. We have performed microarray analysis using a series of chromosome 1 BXSB congenic mice with partially overlapping disease-susceptibility intervals. Simultaneous comparison of the four congenic lines allowed the identification of expression differences associated with both the initiation and progression of disease. Thus, we have identified a number of novel SLE disease gene candidates and have confirmed the identity of Ifi202 as a disease candidate in the BXSB strain. Sequencing of the promoter regions of Gas5 has revealed polymorphisms in the BXSB strain, which may account for the differential expression profile. Furthermore, the combination of the microarray results with the different phenotypes of these mice has allowed the identification of a number of expression differences that do not necessarily map to the congenic interval, but may be implicated in disease pathways.

Identification of chromosome intervals from 129 and C57BL/6 mouse strains linked to the development of systemic lupus erythematosus

Systemic lupus erythematosus is an autoimmune disease in which complex interactions between genes and environmental factors determine the disease phenotype. We have shown that genes from the non-autoimmune strains 129 and C57BL/6 (B6), commonly used for generating gene-targeted animals, can induce a lupus-like disease. Here, we conducted a genome-wide scan analysis of a cohort of (129 x B6)F2 C1q-deficient mice to identify loci outside the C1qa locus contributing to the autoimmune phenotype described in these mice. The results were then confirmed in a larger dataset obtained by combining the data from the C1q-deficient mice with data from previously reported wild-type mice. Both analyses showed that a 129-derived interval on distal chromosome 1 is strongly linked to autoantibody production. The B6 genome contributed to anti-nuclear autoantibody production with an interval on chromosome 3. Two regions were linked to glomerulonephritis: a 129 interval on proximal chromosome 7 and a B6 interval on chromosome 13. These findings demonstrate that interacting loci between 129 and B6 mice can cause the expression of an autoimmune phenotype in gene-targeted animals in the absence of any disrupted gene. They also indicate that some susceptibility genes can be inherited from the genome of non-autoimmune parental strains.

New insights from murine lupus: disassociation of autoimmunity and end organ damage and the role of T cells

PURPOSE OF REVIEW

This review summarizes current literature on genetic regulation of different phenotypes in systemic lupus erythematosus in context of end-organ disease. Recent findings conflicting with the current paradigm that loss of tolerance to chromatin is the critical step for end-organ injury are discussed.

RECENT FINDINGS

Systemic lupus erythematosus is a prototype immune complex disease with circulating autoantibodies to chromatin, histone proteins, Sm/La, and other nuclear and cytoplasmic proteins. Extensive studies have been carried out on the regulation of B-cell and autoantibody production in lupus mice. However, the hypothesis that autoantibodies are primary mediators of organ damage fails to explain the heterogenous presentation in patients. Studies in murine models of systemic lupus erythematosus clearly dissociate genetic control of autoantibody responses to classic lupus antigens and kidney disease. There is increasing evidence to support the role of autoreactive T cells and genetic control of end organ susceptibility. These studies suggest complex interactions between innate and adaptive immunity resulting in end-organ damage. This review focuses on autoimmune responses and renal involvement in spontaneous systemic lupus erythematosus using murine models of lupus nephritis.

SUMMARY

Studies in murine models demonstrate complex genetic interactions regulating spontaneous systemic lupus erythematosus. Although detection of serum autoantibodies is considered a hallmark for clinical diagnosis of systemic lupus erythematosus, recent evidence shows that autoantibodies to classic lupus antigens are neither required nor sufficient for end-organ damage. Thus, murine models provide new insights into the pathogenesis of systemic lupus erythematosus.

Genetic origin of lupus in NZB/SWR hybrids: Lessons from an intercross study

OBJECTIVE

(SWR x NZB)F(1) (or SNF(1)) hybrid mice succumb to lupus nephritis. A previous analysis of SNF(1) x NZB backcross mice revealed the existence of 4 SWR loci (H2 on chromosome 17, Swrl-1 on chromosome 1, Swrl-2 on chromosome 14, and Swrl-3 on chromosome 18) and 2 NZB loci (Nba1 and Lbw2/Sbw2, both on chromosome 4). A second study focusing on SNF(1) x SWR backcross offspring uncovered 5 suggestive loci for antinuclear antibody formation, consisting of 3 dominant NZB contributions (Nba4 on chromosome 5, Lbw4 on chromosome 6, and Nba5 on chromosome 7) and 2 recessive SWR contributions (Swrl-1 on chromosome 1 and Swrl-4 on chromosome 10). The present intercross study was executed to replicate the earlier findings, using an independent panel of (SWR x NZB)F(2) offspring.

METHODS

A panel of (NZB x SWR)F(2) hybrids were phenotyped (for renal disease, early mortality, and a variety of autoantibodies) and genotyped (using 95 microsatellite primers positioned across all 19 autosomes and the X chromosome). Linkage analysis was conducted using the derived phenotype and genotype data, with the interval-mapping program MapManager.

RESULTS

Four suggestive loci were mapped: Swrl-5 on chromosome 1 (peak at 106 cM), linked to hypergammaglobulinemia; an NZB locus on chromosome 5 (Nba4; peak at 15 cM), linked to IgG anti-single-stranded DNA (anti-ssDNA) antibodies, IgG anti-doubled-stranded DNA (anti-dsDNA) antibodies, and glomerulonephritis; an NZB locus on chromosome 13 (Nba6; peak at 28 cM), linked to IgG anti-dsDNA antibodies; and an SWR locus on chromosome 14 (Swrl-2; peak at 30 cM), linked to IgG anti-ssDNA antibodies. Eight additional loci revealed linkage at P < 0.01, of which 7 co-mapped with lupus susceptibility loci previously identified in other models.

CONCLUSION

Considering all 3 mapping studies together, lupus in SWR/NZB hybrids appears to be the epistatic end product of several distinct loci, of which 3 SWR-derived loci (Swrl-1, Swrl-2, and Swrl-3) and 5 NZB-derived loci (Nba1, Nba3, Nba4, Nba5, and Lbw4) have been independently confirmed. The immunologic functions and molecular identities of these loci await elucidation.

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.

Spontaneous autoimmunity in 129 and C57BL/6 mice-implications for autoimmunity described in gene-targeted mice

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disorder in which complex genetic factors play an important role. Several strains of gene-targeted mice have been reported to develop SLE, implicating the null genes in the causation of disease. However, hybrid strains between 129 and C57BL/6 mice, widely used in the generation of gene-targeted mice, develop spontaneous autoimmunity. Furthermore, the genetic background markedly influences the autoimmune phenotype of SLE in gene-targeted mice. This suggests an important role in the expression of autoimmunity of as-yet-uncharacterised background genes originating from these parental mouse strains. Using genome-wide linkage analysis, we identified several susceptibility loci, derived from 129 and C57BL/6 mice, mapped in the lupus-prone hybrid (129 × C57BL/6) model. By creating a C57BL/6 congenic strain carrying a 129-derived Chromosome 1 segment, we found that this 129 interval was sufficient to mediate the loss of tolerance to nuclear antigens, which had previously been attributed to a disrupted gene. These results demonstrate important epistatic modifiers of autoimmunity in 129 and C57BL/6 mouse strains, widely used in gene targeting. These background gene influences may account for some, or even all, of the autoimmune traits described in some gene-targeted models of SLE.

Several strains of gene-targeted mice develop systemic lupus erythematosus (SLE). Analysis of these strains demonstrates that the genetic background profoundly influences the development of autoimmunity

New loci from New Zealand Black and New Zealand White mice on chromosomes 4 and 12 contribute to lupus-like disease in the context of BALB/c

New Zealand Black (NZB) and New Zealand White (NZW) mice are genetically predisposed to a lupus-like autoimmune syndrome. To further define the loci linked to disease traits in NZB and NZW mice in the context of the BALB/c genetic background, linkage analyses were conducted in two crosses: (NZW x BALB/c.H2(z))F(1) x NZB and (NZB x BALB/c)F(2). Novel loci linked to autoantibody production and glomerulonephritis, present in both NZB and NZW mice, were identified on proximal chromosomes 12 and 4. The chromosome 12 locus showed the strongest linkage to anti-nuclear Ab production. Additionally, a number of other novel loci linked to lupus traits derived from both the New Zealand and non-autoimmune BALB/c genomes were identified. Furthermore, we confirm the linkage of disease to a number of previously described lupus-associated loci, demonstrating that they are relatively background independent. These data provide a number of additional candidate gene regions in murine lupus, and highlight the powerful effect the non-autoimmune background strain has in influencing the genetic loci linked to disease.