Anthony C. Y. Yau

Animal Models of Rheumatoid Arthritis (I): Pristane-Induced Arthritis in the Rat

Background To facilitate the development of therapies for rheumatoid arthritis (RA), the Innovative Medicines Initiative BTCure has combined the experience from several laboratories worldwide to establish a series of protocols for different animal models of arthritis that reflect the pathogenesis of RA. Here, we describe chronic pristane-induced arthritis (PIA) model in DA rats, and provide detailed instructions to set up and evaluate the model and for reporting data. Methods We optimized dose of pristane and immunization procedures and determined the effect of age, gender, and housing conditions. We further assessed cage-effects, reproducibility, and frequency of chronic arthritis, disease markers, and efficacy of standard and novel therapies. Results Out of 271 rats, 99.6% developed arthritis after pristane-administration. Mean values for day of onset, day of maximum arthritis severity and maximum clinical scores were 11.8±2.0 days, 20.3±5.1 days and 34.2±11 points on a 60-point scale, respectively. The mean frequency of chronic arthritis was 86% but approached 100% in long-term experiments over 110 days. Pristane was arthritogenic even at 5 microliters dose but needed to be administrated intradermally to induce robust disease with minimal variation. The development of arthritis was age-dependent but independent of gender and whether the rats were housed in conventional or barrier facilities. PIA correlated well with weight loss and acute phase reactants, and was ameliorated by etanercept, dexamethasone, cyclosporine A and fingolimod treatment. Conclusions PIA has high incidence and excellent reproducibility. The chronic relapsing-remitting disease and limited systemic manifestations make it more suitable than adjuvant arthritis for long-term studies of joint-inflammation and screening and validation of new therapeutics.

Positional Identification of RT1-B (HLA-DQ) as Susceptibility Locus for Autoimmune Arthritis

Rheumatoid arthritis (RA) is associated with amino acid variants in multiple MHC molecules. The association to MHC class II (MHC-II) has been studied in several animal models of RA. In most cases these models depend on T cells restricted to a single immunodominant peptide of the immunizing Ag, which does not resemble the autoreactive T cells in RA. An exception is pristane-induced arthritis (PIA) in the rat where polyclonal T cells induce chronic arthritis after being primed against endogenous Ags. In this study, we used a mixed genetic and functional approach to show that RT1-Ba and RT1-Bb (RT1-B locus), the rat orthologs of HLA-DQA and HLA-DQB, determine the onset and severity of PIA. We isolated a 0.2-Mb interval within the MHC-II locus of three MHC-congenic strains, of which two were protected from severe PIA. Comparison of sequence and expression variation, as well as in vivo blocking of RT1-B and RT1-D (HLA-DR), showed that arthritis in these strains is regulated by coding polymorphisms in the RT1-B genes. Motif prediction based on MHC-II eluted peptides and structural homology modeling suggested that variants in the RT1-B P1 pocket, which likely affect the editing capacity by RT1-DM, are important for the development of PIA.

Class II major histocompatibility complex–associated response to type XI collagen regulates the development of chronic arthritis in rats

OBJECTIVE Chronic inflammation of the peripheral joints is a hallmark of rheumatoid arthritis (RA). The autoantibody response in RA has been shown to be directed mainly to ubiquitous antigens, whereas the response to cartilage proteins has been less extensively investigated. This study was undertaken to characterize the immune response in pristane-induced arthritis (PIA) in the rat to the cartilage-specific proteins type II collagen (CII) and type XI collagen (CXI) and to genetically fine-map their underlying major histocompatibility complex (MHC) associations. METHODS The genetic control of CII and CXI immunity was mapped using intra-MHC-recombinant inbred strains immunized with the respective collagens. Reactivity with CII and CXI was tested in acute and chronic PIA and in 356 HLA-typed patients with recently diagnosed RA. RESULTS Mapping of arthritis susceptibility within the MHC region revealed a 144-223-kb locus containing <12 genes, including paralogs for HLA-DQ and HLA-DR. Susceptibility to CII and CXI was linked to haplotypes RT1(av1) (DA) and RT1(f) (DA.1F), respectively. After injection of pristane, rats of both strains developed weak T cell and IgG responses to CII, but not to CXI. In chronic arthritis, however, collagen reactivity was stronger, specific for CXI, and restricted to rats with RT1(f) MHC. Among RA patients, 12% exhibited a specific IgG response to CXI, 6% to CII, and 6% to both collagens. CONCLUSION These findings demonstrate a shift in cartilage recognition in early and chronic arthritis in the rat, suggesting that CXI autoreactivity contributes to the perpetuation of chronic disease. The results provide evidence of the importance of joint antigens in arthritis development.

Rheumatoid arthritis: identifying and characterising polymorphisms using rat models.

ABSTRACT Rheumatoid arthritis is a chronic inflammatory joint disorder characterised by erosive inflammation of the articular cartilage and by destruction of the synovial joints. It is regulated by both genetic and environmental factors, and, currently, there is no preventative treatment or cure for this disease. Genome-wide association studies have identified ∼100 new loci associated with rheumatoid arthritis, in addition to the already known locus within the major histocompatibility complex II region. However, together, these loci account for only a modest fraction of the genetic variance associated with this disease and very little is known about the pathogenic roles of most of the risk loci identified. Here, we discuss how rat models of rheumatoid arthritis are being used to detect quantitative trait loci that regulate different arthritic traits by genetic linkage analysis and to positionally clone the underlying causative genes using congenic strains. By isolating specific loci on a fixed genetic background, congenic strains overcome the challenges of genetic heterogeneity and environmental interactions associated with human studies. Most importantly, congenic strains allow functional experimental studies be performed to investigate the pathological consequences of natural genetic polymorphisms, as illustrated by the discovery of several major disease genes that contribute to arthritis in rats. We discuss how these advances have provided new biological insights into arthritis in humans. Summary: Using experimental models of rheumatoid arthritis, natural genetic polymorphisms associated with arthritis are identified and characterised in rats, bringing in new biological insights into arthritis in humans.

Natural Polymorphisms in Tap2 Influence Negative Selection and CD4:CD8 Lineage Commitment in the Rat

Genetic variation in the major histocompatibility complex (MHC) affects CD4∶CD8 lineage commitment and MHC expression. However, the contribution of specific genes in this gene-dense region has not yet been resolved. Nor has it been established whether the same genes regulate MHC expression and T cell selection. Here, we assessed the impact of natural genetic variation on MHC expression and CD4∶CD8 lineage commitment using two genetic models in the rat. First, we mapped Quantitative Trait Loci (QTLs) associated with variation in MHC class I and II protein expression and the CD4∶CD8 T cell ratio in outbred Heterogeneous Stock rats. We identified 10 QTLs across the genome and found that QTLs for the individual traits colocalized within a region spanning the MHC. To identify the genes underlying these overlapping QTLs, we generated a large panel of MHC-recombinant congenic strains, and refined the QTLs to two adjacent intervals of ∼0.25 Mb in the MHC-I and II regions, respectively. An interaction between these intervals affected MHC class I expression as well as negative selection and lineage commitment of CD8 single-positive (SP) thymocytes. We mapped this effect to the transporter associated with antigen processing 2 (Tap2) in the MHC-II region and the classical MHC class I gene(s) (RT1-A) in the MHC-I region. This interaction was revealed by a recombination between RT1-A and Tap2, which occurred in 0.2% of the rats. Variants of Tap2 have previously been shown to influence the antigenicity of MHC class I molecules by altering the MHC class I ligandome. Our results show that a restricted peptide repertoire on MHC class I molecules leads to reduced negative selection of CD8SP cells. To our knowledge, this is the first study showing how a recombination between natural alleles of genes in the MHC influences lineage commitment of T cells.

Conserved 33-kb haplotype in the MHC class III region regulates chronic arthritis

Significance The role of the MHC region has been a long-standing issue in chronic inflammatory diseases, such as rheumatoid arthritis, and it has not been possible to identify the underlying specific polymorphism. Here, we provide evidence that some of the MHC association must be explained by how closely linked genes operate together as haplotype blocks. We identified a conserved haplotype, Ltab-Ncr3, comprising five genes (lymphotoxin α and β, Tnf, leukocyte-specific transcript 1, and natural cytotoxicity-triggering receptor 3) within MHC class III, regulating arthritis. We found significant coexpression of the Ltab-Ncr3 genes, indicating how these genes may work together as a haplotype. Furthermore, haplotype-specific differences in Ltab-Ncr3 gene expression and alternative splicing correlate remarkably to susceptibility to arthritis. Our data show that a conserved haplotype within MHC class III regulates arthritis development. Genome-wide association studies have revealed many genetic loci associated with complex autoimmune diseases. In rheumatoid arthritis (RA), the MHC gene HLA-DRB1 is the strongest candidate predicting disease development. It has been suggested that other immune-regulating genes in the MHC contribute to the disease risk, but this contribution has been difficult to show because of the strong linkage disequilibrium within the MHC. We isolated genomic regions in the form of congenic fragments in rats to test whether there are additional susceptibility loci in the MHC. By both congenic mapping in inbred strains and SNP typing in wild rats, we identified a conserved, 33-kb large haplotype Ltab-Ncr3 in the MHC-III region, which regulates the onset, severity, and chronicity of arthritis. The Ltab-Ncr3 haplotype consists of five polymorphic immunoregulatory genes: Lta (lymphotoxin-α), Tnf, Ltb (lymphotoxin-β), Lst1 (leukocyte-specific transcript 1), and Ncr3 (natural cytotoxicity-triggering receptor 3). Significant correlation in the expression of the Ltab-Ncr3 genes suggests that interaction of these genes may be important in keeping these genes clustered together as a conserved haplotype. We studied the arthritis association and the spliceo-transcriptome of four different Ltab-Ncr3 haplotypes and showed that higher Ltb and Ncr3 expression, lower Lst1 expression, and the expression of a shorter splice variant of Lst1 correlate with reduced arthritis severity in rats. Interestingly, patients with mild RA also showed higher NCR3 expression and lower LST1 expression than patients with severe RA. These data demonstrate the importance of a conserved haplotype in the regulation of complex diseases such as arthritis.

Influence of hydrocarbon oil structure on adjuvanticity and autoimmunity

Mineral oils are extensively used in our daily life, in food, cosmetics, biomedicine, vaccines and in different industrial applications. However, exposure to these mineral oils has been associated with immune adjuvant effects and the development of autoimmune diseases. Here we investigate the structural impacts of the hydrocarbon oil molecules on their adjuvanticity and autoimmunity. First, we showed that hydrocarbon oil molecules with small atomic differences could result in experimental arthritis in DA rats differing in disease severity, incidence, weight change and serum levels of acute phase proteins. Injection of these hydrocarbon oils resulted in the activation, proliferation and elevated expression of Th1 and especially Th17 cytokines by the T cells, which correlate with the arthritogenicity of the T cells. Furthermore, the more arthritogenic hydrocarbon oils resulted in an increased production of autoantibodies against cartilage joint specific, triple-helical type II collagen epitopes. When injected together with ovalbumin, the more arthritogenic hydrocarbon oils resulted in an increased production of αβ T cell-dependent anti-ovalbumin antibodies. This study shows the arthritogenicity of hydrocarbon oils is associated with their adjuvant properties with implications to not only arthritis research but also other diseases and medical applications such as vaccines in which oil adjuvants are involved.

Effects of C2ta genetic polymorphisms on MHC class II expression and autoimmune diseases

Antigen presentation by the MHC‐II to CD4+ T cells is important in adaptive immune responses. The class II transactivator (CIITA in human and C2TA in mouse) is the master regulator of MHC‐II gene expression. It coordinates the transcription factors necessary for the transcription of MHC‐II molecules. In humans, genetic variations in CIITA have been associated with differential expression of MHC‐II and susceptibility to autoimmune diseases. Here we made use of a C2ta congenic mouse strain (expressing MHC‐II haplotype H‐2q) to investigate the effect of the natural genetic polymorphisms in type I promoter of C2ta on MHC‐II expression and function. We demonstrate that an allelic variant in the type I promoter of C2ta resulted in an increased expression of MHC‐II on macrophages (72–151% higher mean florescence intensity) and conventional dendritic cells (13–65% higher mean florescence intensity) in both spleen and peripheral blood. The increase in MHC‐II expression resulted in an increase in antigen presentation to T cells in vitro and increased T‐cell activation. The differential MHC‐II expression in B6Q.C2ta, however, did not alter the disease development in models of rheumatoid arthritis (collagen‐induced arthritis and human glucose‐6‐phosphate‐isomerase325–339‐peptide‐induced arthritis), or multiple sclerosis (MOG1–125 protein‐induced and MOG79–96 peptide‐induced experimental autoimmune encephalomyelitis). This is the first study to address the role of an allelic variant in type I promoter of C2ta in MHC‐II expression and autoimmune diseases; and shows that C2ta polymorphisms regulate MHC‐II expression and T‐cell responses but do not necessarily have a strong impact on autoimmune diseases.

The Major Histocompatibility Complex Class III Haplotype Ltab-Ncr3 Regulates Adjuvant-Induced but Not Antigen-Induced Autoimmunity

Rheumatoid arthritis is a complex disease associated with >100 risk loci, with the strongest association from the major histocompatibility complex (MHC) region. Here, we analyzed a new genetic association in the MHC class-III region (MHC-III) using adjuvant- and antigen-induced arthritis models. In addition, we used models for multiple sclerosis for comparison and dissected the MHC-III-mediated mechanisms of importance for antibody and T-cell responses to antigens. With the use of a panel of MHC-III recombinant inbred strains, we found that the 33-kb Ltab-Ncr3 haplotype in MHC-III was linked to the induction of arthritis with incomplete Freunds adjuvant, with similar effects in arthritis induced by several oil adjuvants (hexadecane, heptadecane, squalene, arlacel). Adoptive T-cell transfer experiment showed that this arthritis-protective effect operated during the priming of T cells by controlling their arthritogenicity. Interestingly, Ltab-Ncr3 did not regulate autoimmune diseases induced with tissue-specific antigens emulsified in adjuvant oils, such as collagen-induced arthritis or experimental autoimmune encephalomyelitis. No effect on antibody or T-cell response to tissue antigens in the Ltab-Ncr3 could be demonstrated. The finding that Ltab-Ncr3 is specific in regulating adjuvant-induced arthritis but not antigen-induced autoimmunity, and with unique effects on priming of autoreactive and arthritogenic T cells, provides new insight for understanding the regulation of autoimmune diseases.

Reply to Liu et al.: Translation of rat congenic data to humans on a conserved MHC-III haplotype associated with rheumatoid arthritis

Major histocompatibility complex (MHC)-related phenotype/genotype correlations are important in study of autoimmune disorders. We previously identified a conserved 33-kb haplotype comprising five genes, lymphotoxin-α (Lta), Tnf, lymphotoxin-β (Ltb), leukocyte-specific transcript 1 (Lst1), and natural cytotoxicity-triggering receptor 3 (Ncr3), in the MHC class-III region regulating arthritis in rats (1). In our study, higher Ltb and Ncr3 expression and lower Lst1 expression correlate with reduced arthritis severity in rats (1). Following these findings, we compared expression of these genes in a cohort of patients with rheumatoid arthritis (RA) and healthy controls and found that the expression of LTB, LST1, and NCR3 was higher in RA cases, but patients with mild RA showed higher NCR3 expression and …