The genetic control of rheumatoid factor production in a rat model of rheumatoid arthritis

Tripterygium hypoglaucum extract ameliorates adjuvant-induced arthritis in mice through the gut microbiota

Traditionally, Tripterygium hypoglaucum (Levl.) Hutch (THH) are widely used in Chinese folk to treat rheumatoid arthritis (RA). This study aimed to investigate whether the anti-RA effect of THH is related with the gut microbiota. The main components of prepared THH extract were identified by HPLC-MS. C57BL/6 mice with adjuvant-induced arthritis (AIA) were treated with THH extract by gavage for one month. THH extract significantly alleviated swollen ankle, joint cavity exudation, and articular cartilage destruction in AIA mice. The mRNA and protein levels of inflammatory mediators in muscles and plasma indicated that THH extract attenuated inflammatory responses in the joint by blocking TLR4/MyD88/MAPK signaling pathways. THH extract remarkably restored the dysbiosis of the gut microbiota in AIA mice, featuring the increases of Bifidobacterium, Akkermansia, and Lactobacillus and the decreases of Butyricimonas, Parabacteroides, and Anaeroplasma. Furthermore, the altered bacteria were closely correlated with physiological indices and drove metabolic changes of the intestinal microbiota. In addition, antibiotic-induced pseudo germ-free mice were employed to verify the role of the intestinal flora. Strikingly, THH treatment failed to ameliorate the arthritis symptoms and signaling pathways in pseudo germ-free mice, which validates the indispensable role of the intestinal flora. For the first time, we demonstrated that THH extract protects joint inflammation by manipulating the intestinal flora and regulating the TLR4/MyD88/MAPK signaling pathway. Therefore, THH extract may serve as a microbial modulator to recover RA in clincial practice.ver RA in clincial practice.

"Cerastes snake venom as a promising approach in the management of complete Freund's adjuvant-induced rheumatoid arthritis in rats: Involvement of RANKL and JAK/STAT pathway"

ETHNOPHARMACOLOGICAL RELEVANCE

Cerastes cerastes is a snake found mainly in the Egyptian desert. Many studies were performed to explain the possible snake venom's pharmacological therapeutic effect in different autoimmune diseases. One of the most common auto-immune diseases is rheumatoid arthritis. Rheumatoid arthritis is characterized by a high release of pro-inflammatory and immune-modulatory cytokines. The reduction of these markers can indicate how effective is the administered drug.

AIM OF THE STUDY

This study aims to explore the potential pharmacological effects of cerastes venom in experimentally-induced RA in rats using Complete Freund's adjuvant - via different mechanisms - by assessing various tissue and serum parameters.

MATERIALS AND METHODS

The rats were assigned to negative control group, cerastes control group, positive control group, dexamethasone-treated group, infliximab-treated group, and cerastes-treated group. The study ended on the 20^th day when serum and tissue samples were prepared for further evaluation of reduced glutathione, malondialdehyde, rheumatoid factor, tumor necrosis factor-α, interleukin-6, and nuclear factor kappa-light-chain-enhancer of activated B cells as well as relative expression of phosphorylated Janus-kinase, phosphorylated signal transducers and activators of transcription, nuclear factor erythroid 2-related factor 2, and receptor activator of nuclear factor Kappa-B ligand. In addition, a histopathological examination of different groups' knees joints, and spleen was done.

RESULTS

The results showed a significant improvement of arthritis induced in the cerastes-treated group in contrast to the positive control group in all assessed parameters. In addition, significant improvement of arthritis was observed in the histopathological examination of different groups' knees joints, and spleen.

CONCLUSION

These results revealed that cerastes snake venom has potent anti-inflammatory and immunomodulatory effects and can be used in the management of arthritis.

Leurieus quinquestriatus scorpion venom ameliorates adjuvant-induced arthritis in rats: Modulating JAK/STAT/RANKL signal transduction pathway

Leurieus quinquestriatus (LQ) is a type of Egyptian scorpions. Prior studies have established the potential use of scorpion venoms in treating several autoimmune diseases. Therefore, the current study investigates the possible pharmacological effect of LQ venom in CFA-induced arthritis - through different mechanisms - by assessing different serum and tissue parameters. This study was divided into two phases: phase I was conducted to determine the lowest therapeutic dose of LQ scorpion venom, whereas phase II investigated the potential therapeutic effect of the chosen dose of LQ venom on induced arthritis through different mechanisms. The Wistar albino rats were divided equally and randomly into normal control group, LQ control group, arthritis control group, infliximab-treated group, and LQ-treated group. On day 20, blood and tissue samples were collected for further analysis of serum and tissue biomarkers as well as histopathological examination. The results revealed a potential therapeutic effect of LQ venom on arthritic-induced rats through a significant decrease in Rheumatoid Factor, Janus Kinase, Signal transducers and activators of transcription, Receptor activator of nuclear factor Kappa-B ligand, Tumor Necrosis Factor-alpha, Interleukin-6, Nuclear factor kappa-light-chain-enhancer of activated B cells and Malondialdehyde by 57%, 66%, 64%, 62%, 75%, 59%, 38%, and 69%, respectively as well as a significant increase in reduced glutathione, and Nuclear factor erythroid 2-related factor 2 by 102% and 360%, respectively. Histopathological examination of knee joint and spleen also revealed a substantial improvement, indicating the possible utilization of LQ venom in the treatment of rheumatoid arthritis.

14-3-3ζ: A suppressor of inflammatory arthritis

Inflammatory arthritis (IA) is a common disease that affects millions of individuals worldwide. Proinflammatory events during IA pathogenesis are well studied; however, loss of protective immunity remains underexplored. Earlier, we reported that 14-3-3zeta (ζ) has a role in T-cell polarization and interleukin (IL)-17A signal transduction. Here, we demonstrate that 14-3-3ζ knockout (KO) rats develop early-onset severe arthritis in two independent models of IA, pristane-induced arthritis and collagen-induced arthritis. Arthritic 14-3-3ζ KO animals showed an increase in bone loss and immune cell infiltration in synovial joints. Induction of arthritis coincided with the loss of anti-14-3-3ζ antibodies; however, rescue experiments to supplement the 14-3-3ζ antibody by passive immunization did not suppress arthritis. Instead, 14-3-3ζ immunization during the presymptomatic phase resulted in significant suppression of arthritis in both wild-type and 14-3-3ζ KO animals. Mechanistically, 14-3-3ζ KO rats exhibited elevated inflammatory gene signatures at the messenger RNA and protein levels, particularly for IL-1β. Furthermore, the immunization with recombinant 14-3-3ζ protein suppressed IL-1β levels, significantly increased anti-14-3-3ζ antibody levels and collagen production, and preserved bone quality. The 14-3-3ζ protein increased collagen expression in primary rat mesenchymal cells. Together, our findings indicate that 14-3-3ζ causes immune suppression and extracellular remodeling, which lead to a previously unrecognized IA-suppressive function.

Activation of formyl peptide receptor 1 elicits therapeutic effects against collagen-induced arthritis

Rheumatoid arthritis (RA) is an autoimmune disorder which shows production of autoantibodies, inflammation, bone erosion, swelling and pain in joints. In this study, we examined the effects of an immune-modulating peptide, WKYMVm, that is an agonist for formyl peptide receptors (FPRs). Administration of WKYMVm into collagen-induced arthritis (CIA) mice, an animal model for RA, attenuated paw thickness, clinical scores, production of type II collagen-specific antibodies and inflammatory cytokines. WKYMVm treatment also decreased the numbers of T_H 1 and T_H 17 cells in the spleens of CIA mice. WKYMVm attenuated T_H 1 and T_H 17 differentiation in a dendritic cell (DC)-dependent manner. WKYMVm-induced beneficial effects against CIA and WKYMVm-attenuated T_H 1 and T_H 17 differentiation were reversed by cyclosporin H but not by WRW4, indicating a crucial role of FPR1. We also found that WKYMVm augmented IL-10 production from lipopolysaccharide-stimulated DCs and WKYMVm failed to suppress T_H 1 and T_H 17 differentiation in the presence of anti-IL-10 antibody. The therapeutic administration of WKYMVm also elicited beneficial outcome against CIA. Collectively, we demonstrate that WKYMVm stimulation of FPR1 in DCs suppresses the generation of T_H 1 and T_H 17 cells via IL-10 production, providing novel insight into the function of FPR1 in regulating CIA pathogenesis.

The involvement of Toll-like receptor 9 in the pathogenesis of erosive autoimmune arthritis

Endogenous nucleic acids and their receptors may be involved in the initiation of systemic autoimmune diseases including rheumatoid arthritis (RA). As the role of the DNA sensing Toll-like receptor (TLR) 9 in RA is unclear, we aimed to investigate its involvement in the pathogenesis of autoimmune arthritis using three different experimental models of RA. The data obtained revealed involvement of TLR9 in the T cell-dependent phase of inflammatory arthritis. In rats with pristane-induced arthritis (PIA), TLR9 inhibition before disease onset reduced arthritis significantly and almost completely abolished bone erosion. Accordingly, serum levels of IL-6, α-1-acid-glycoprotein and rheumatoid factor were reduced. Moreover, in TLR9-/- mice, streptococcal cell wall (SCW)-induced arthritis was reduced in the T cell-dependent phase, whereas T cell-independent serum-transfer arthritis was not affected. Remarkably, while TLR7 expression did not change during in vitro osteoclastogenesis, TLR9 expression was higher in precursor cells than in mature osteoclasts and partial inhibition of osteoclastogenesis was achieved only by the TLR9 antagonist. These results demonstrate a pivotal role for TLR9 in the T cell-dependent phases of inflammatory arthritis and additionally suggest some role during osteoclastogenesis. Hence, endogenous DNA seems to be crucially involved in the pathophysiology of inflammatory autoimmune arthritis.

Rheumatoid arthritis: identifying and characterising polymorphisms using rat models

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.

Immunization of BALB/c mice with pigeon IgY induces the production of anti-IgG autoantibodies

The breakdown of immunological tolerance due to the activation of autoreactive B and T cells triggers physiopathological processes. An example of such conditions is the production of IgG autoantibodies specific for the Fc portion of IgG (anti-Fcγ IgG). Previous reports have shown that patients with pigeon-related hypersensitivity pneumonitis exhibit an increase in the serum levels of anti-Fcγ IgG. There is no in vivo model for the study of this condition and the immunological mechanisms of tolerance breakdown associated with sensitization by pigeon antigens are still unknown. In this work, we show that the repeated immunization of BALB/c mice with pigeon IgY during 16-weeks induces the production of anti-Fcγ IgG and keeps their high levels for seven weeks. The late appearance of anti-Fcγ IgG autoantibodies in the plasma is similar to what has been reported in other experimental autoimmune models. With the occurrence of anti-Fcγ IgG, there is a reduction in the proportion of Foxp3 + cells (regulatory T cells, Tregs) within the population of splenic CD4 + CD25 + T cells. Thus, our data showed that the immunization of BALB/c mice with IgY promotes the production of anti-Fcγ IgG along with a decrease in Tregs in the spleen. We propose that immunization of mice with pigeon antigens, like IgY can provide a model to study the immunological mechanisms involved in the development of pigeon-related hypersensitivity pneumonitis.

Effect of dietary pristane and other saturated mineral oils (MOSH) on autoimmune arthritis in rats

Pristane and other adjuvants based on mineral oil saturated hydrocarbons (MOSH) may induce autoimmunity in rodents after intradermal injection; however there is a lack of information on immune effects after oral MOSH exposure. The aim of our study was to determine the impact of dietary exposure to pristane and other MOSH on the development of autoimmune arthritis.

Dark Agouti (DA) rats were given feed containing 4000 mg/kg pristane or a broad MOSH mixture in various concentrations (0–4000 mg/kg) for 90 days, or a single intradermal injection of 200 μl pristane (positive control). Arthritis scores, and serum and splenocyte markers previously associated with arthritis development, were determined.

All rats injected with pristane displayed arthritis symptoms and higher levels of certain serum markers. None of the rats fed pristane or MOSH developed arthritis symptoms or demonstrated clear changes in any measured arthritis-associated biological markers in serum or splenocytes.

The absence of clinical arthritis symptoms or any increase in common arthritis-associated biological markers in sera and spleen following dietary exposure to pristane or a broad MOSH mixture in a sub-chronic rat model of arthritis suggest that dietary MOSH have low capacity to promote development of autoimmunity.

VAV1 regulates experimental autoimmune arthritis and is associated with anti-CCP negative rheumatoid arthritis

Rheumatoid arthritis (RA) patients can be stratified into two subgroups defined by the presence or absence of antibodies against citrullinated circular peptides (anti-CCP) with most of the genetic association found in anti-CCP positive RA. Here we addressed the role of VAV1, previously associated to multiple sclerosis (MS), in the pathogenesis of RA in experimental models and in a genetic association study. Experimental arthritis triggered by pristane or collagen type II was induced in DA rats and in the DA.BN-R25 congenic line that carries a polymorphism in Vav1. Difference in arthritis severity was observed only after immunization with pristane. In a case-control study, 34 SNPs from VAV1 locus were analyzed by Immunochip genotyping in 11475 RA patients (7573 anti-CCP positive and 3902 negative) and 15,870 controls in six cohorts of European Caucasians. A combination of the previous MS-associated haplotype and two additional SNPs was associated with anti-CCP negative RA (alleles G-G-A-A of rs682626-rs2546133-rs2617822-rs12979659, OR=1.13, P=1.27 × 10^-5). The same markers also contributed to activity of RA at baseline with the strongest association in the anti-CCP negative group for the rs682626-rs12979659 G-A haplotype (β=-0.283, P=0.0048). Our study suggests a role for VAV1 and T-cell signaling in the pathology of anti-CCP-negative RA.

Effects of Libby amphibole asbestos exposure on two models of arthritis in the Lewis rat

Epidemiological data suggest that occupational exposure to the amphibole-containing vermiculite in Libby, MT, was associated with increased risk for developing autoimmune diseases and had an odds ratio of 3.23 for developing rheumatoid arthritis (RA). The collagen-induced arthritis (CIA) and the peptidoglycan-polysaccharide (PG-PS) models of RA were employed to determine whether exposure to Libby amphibole (LA) induced a more rapid onset, increased expression, or prolonged course of RA. Female Lewis rats were intratracheally instilled with total doses of 0.15, 0.5, 1.5, or 5 mg LA or 0.5 or 1.5 mg amosite asbestos, and arthritis was induced with either the PG-PS or CIA model. Neither LA nor amosite exposure affected the disease course in the CIA model, or the production of rheumatoid factor (RF) or anti-cyclic citrullinated peptide (CCP) antibodies. LA exposure reduced swelling in the PG-PS model and decreased anti-PG-PS and total immunoglobulin M (IgM) antibody titers. Both amosite and LA exposure increased the number of rats with circulating anti-nuclear antibodies (ANA), the majority of which presented a speckled staining pattern. However, this ANA enhancement was not dose responsive. These results failed to show a positive correlation between LA exposure and RA disease in two animal models, although upregulated ANA suggest an altered immunological profile consistent with other systemic autoimmune diseases.

Investigation of the role of tumour necrosis factor-α, interleukin-1β, interleukin-10, nitric oxide and rheumatoid factor-immunoglobulin M in a rat model of arthritis

Collagen-induced arthritis (CIA) in rats is a widely used preclinical animal model of rheumatoid arthritis (RA). However, CIA development in Sprague-Dawley (SD) rats is less severe in terms of inflammatory response compared with other strains. Therefore, a modified CIA model called MCIA, using N-acetylmuramyl dipeptide (MDP), has been developed in the less sensitive SD rat strains. This work was conducted to better understand the immunopathological role and contributions of the pro-inflammatory T-helper type 1 (Th-1) cytokines and inflammatory mediators, interleukin-1 (IL-1 β), tumour necrosis factor-alpha (TNF- α) and nitric oxide (NO); the anti-inflammatory T-helper type 2 (Th-2) cytokine, IL-10 and autoantibodies such as rheumatoid factor (RF)-immunoglobulin M (IgM) in this newly developed RA model. TNF-α, NO and RF-IgM levels were significantly increased, while IL-1 β levels were not affected in this MCIA rat model. The levels of IL-10 were lower than the baseline when compared with controls. In conclusion: (1) the immunological features represented in the MCIA rat model favour the Th-1 cytokine profile over Th-2 and (2) RF-IgM can be used as a diagnostic test in preclinical RA models.

The value of animal models in predicting genetic susceptibility to complex diseases such as rheumatoid arthritis

For a long time, genetic studies of complex diseases were most successfully conducted in animal models. However, the field of genetics is now rapidly evolving, and human genetics has also started to produce strong candidate genes for complex diseases. This raises the question of how to continue gene-finding attempts in animals and how to use animal models to enhance our understanding of gene function. In this review we summarize the uses and advantages of animal studies in identification of disease susceptibility genes, focusing on rheumatoid arthritis. We are convinced that animal genetics will remain a valuable tool for the identification and investigation of pathways that lead to disease, well into the future.

Positional cloning of the Igl genes controlling rheumatoid factor production and allergic bronchitis in rats

Rheumatoid factors (RF), autoantibodies that bind the Fc region of IgG, are one of the major diagnostic marker in rheumatoid arthritis (RA) but occur with lower frequency also in other infectious and inflammatory conditions. Through positional cloning of the previously described quantitative trait locus (QTL) Rf1 in congenic and advanced intercrossed rats, we identified the Ig lambda light chain locus as a locus that regulates the production of RF in rats. The congenic rats produce RF-Ig lambda and have significant higher levels of RF-IgG and RF-IgM in serum, while the DA rat has an impaired RF production and does not produces RF-Ig lambda. Thus, we could investigate the role of RF in pristane-induced arthritis (PIA) as well as ovalbumin-induced airway inflammation. We show that there was no difference in the development and severity of PIA between congenic and parental DA rats, suggesting that RF using lambda light chains have no impact on PIA. However, the RF producing congenic rats developed a more severe airway inflammation as indicated in the significantly increased number of eosinophils in bronchoalveolar lavage fluid as well as total IgE in serum. In addition, RF congenic rats had a significantly enhanced immune response toward OVA due to increased OVA-Igk but not OVA-Igl antibodies, suggesting a possible involvement of RF in the regulation of the humoral immune response.

Abnormal immune responses in fa/fa Zucker rats and effects of feeding conjugated linoleic acid

OBJECTIVE

The objective of this study was to characterize immune function in the fa/fa Zucker rat, and to determine the effects of feeding conjugated linoleic acid (CLA) isomers on immune function.

METHODS AND PROCEDURES

Lean and fa/fa Zucker rats were fed for 8 weeks nutritionally complete diets with different CLA isomers (%wt/wt): control (0%), c9t11 (0.4%), t10c12 (0.4%), or MIX (0.4% c9t11 + 0.4% t10c12). Isolated splenocytes were used to determine phospholipid (PL) fatty acid composition and cell phenotypes, or stimulated with mitogen to determine their ability to produce cytokines, immunoglobulins (Ig), and nitric oxide (NO).

RESULTS

Splenocyte PL of fa/fa rats had a higher proportion of total monounsaturated fatty acids and n -3 polyunsaturated fatty acids (PUFA), and lower n -6 PUFA and n -6-to-n -3 PUFA ratio (P < 0.05). Feeding CLA increased the content of CLA isomers into PL, but there were lower proportions of each CLA isomer in fa/fa rats. Splenocytes of fa/fa rats produced more amounts of IgA, IgG, and IgM, NO, and interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha) (P < 0.05). Obese rats fed the t10c12 diet produced less TNF-alpha and IL-1beta (lippopolysaccharide (LPS), P < 0.05). Splenocytes of fa/fa rats produced less concanavalin A (ConA)-stimulated IL-2 (P < 0.0001) than lean rats, except fa/fa rats fed the c9t11 diet (P < 0.05).

DISCUSSION

The c9t11 and t10c12 CLA isomers were incorporated into the membrane PL of the fa/fa Zucker rat, but to a lesser extent than lean rats. Splenocytes of obese rats responded in a proinflammatory manner and had reduced T-cell function and feeding the t10c12 and c9t11 CLA isomers may improve some of these abnormalities by distinct methods.

Cia25 on rat chromosome 12 regulates severity of autoimmune arthritis induced with pristane and with collagen

BACKGROUND

A genomewide scan in a DA x ACI F2 intercross studied for collagen-induced arthritis (CIA) identified the severity quantitative trait locus Cia25 on rat chromosome 12. Cia25 co-localises with loci regulating several forms of autoimmune diseases in rats, mice and humans, suggesting a common gene.

OBJECTIVE

To characterise the effects of Cia25 on severity of arthritis in congenic rats.

METHODS

DA.ACI(Cia25) congenic rats were constructed according to a genotype-guided strategy, and tested for pristane-induced arthritis (PIA) and CIA, induced with rat type II collagen (CII). A well-established scoring system previously shown to correlate with histological damage, including cartilage and bone erosions, synovial hyperplasia and synovial inflammation, was used.

RESULTS

The introgression of ACI alleles at Cia25 into DA background, as in DA.ACI(Cia25) rats, was enough to significantly reduce arthritis severity by 60% in PIA and by 40% in CIA, both in males and females compared with DA rats of the same sex. Levels of IgG anti-CII in male DA.ACI(Cia25) rats were 83% lower than in male DA. Levels of anti-CII in females were not affected by the congenic interval.

CONCLUSIONS

Cia25 contains a gene that regulates disease severity in two distinct models of autoimmune arthritis. Although both genders were protected in arthritis studies, only male congenic rats had a dramatic reduction in levels of anti-CII, suggesting the possibility of a second arthritis gene in this interval that operates via the regulation of autoantibodies in a sex-specific manner. The identification of the gene(s) accounting for Cia25 is expected to generate novel prognostic biomarkers and targets for therapy.

Cia27 is a novel non-MHC arthritis severity locus on rat chromosome 10 syntenic to the rheumatoid arthritis 17q22–q25 locus

Cia27 on rat chromosome 10 is a collagen-induced arthritis (CIA) severity quantitative trait locus originally identified in a study of (DA x ACI) F2. As an initial step towards the positional cloning of the Cia27 gene, a 17 cM (21 Mb) interval from the DA strain (arthritis-susceptible) containing the two-logarithm of odds support interval comprising Cia27 was introgressed into the ACI (arthritis-resistant) background through genotype-guided congenic breeding. ACI.DA(Cia27) congenics developed a significantly more severe form of arthritis (CIA), with a 5.9-fold increase in median arthritis severity index, a parameter known to correlate with synovial inflammation, and cartilage and bone erosions, compared with ACI (P< or =0.001). The arthritis severity enhancing effect could be detected from day 21 onwards. Rats heterozygous at the congenic interval developed a disease similar to ACI rats, suggesting that DA alleles operate in a recessive manner. Levels of autoantibodies anti-rat type II collagen did not correlate with arthritis severity. Synovial tissue mRNA levels of interleukin-1beta (IL-1beta) were significantly increased in ACI.DA(Cia27) congenics compared with ACI. These results demonstrate that Cia27 harbors a novel arthritis severity regulatory gene. The identification of this gene should facilitate the identification of the rheumatoid arthritis gene mapped to the human syntenic region on chromosome 17q22-q25.

The Non-MHC Quantitative Trait Locus Cia5 Contains Three Major Arthritis Genes That Differentially Regulate Disease Severity, Pannus Formation, and Joint Damage in Collagen- and Pristane-Induced Arthritis

Cia5 is a locus on rat chromosome 10 which regulates the severity of collagen- and pristane-induced arthritis (CIA and PIA). To refine the region toward positional identification, Cia5 subcongenic strains were generated and studied in PIA and CIA. The protective effect of the telomeric locus Cia5a was confirmed in both models. A second arthritis severity locus (Cia5d) was identified within the most centromeric portion of Cia5. DA.F344(Cia5d) rats had a significantly lower median arthritis severity index in PIA, but not in CIA, compared with DA. On histologic analyses DA.F344(Cia5a) and DA.F344(Cia5d) congenics with PIA preserved a nearly normal joint architecture compared with DA, including significant reduction in synovial hyperplasia, pannus, angiogenesis, inflammatory infiltration, bone and cartilage erosions. Cia5 and Cia5a synovial levels of IL-1beta mRNA were reduced. Although both DA.F344(Cia5) and DA.F344(Cia5a) rats were protected in CIA, the arthritis scores of DA.F344(Cia5) were significantly higher than those of DA.F344(Cia5a), suggesting the existence of a third locus where F344-derived alleles centromeric from Cia5a contribute to increased arthritis severity. The existence of the third locus was further supported by higher levels of autoantibodies against rat type II collagen in DA.F344(Cia5) congenics compared with DA.F344(Cia5a). Our results determined that Cia5 contains three major arthritis severity regulatory loci regulating central events in the pathogenesis of arthritis, and differentially influencing CIA and PIA. These loci are syntenic to regions on human chromosomes 17q and 5q implicated in the susceptibility to rheumatoid arthritis, suggesting that the identification of these genes will be relevant to human disease.

The non-major histocompatibility complex quantitative trait locus Cia10 contains a major arthritis gene and regulates disease severity, pannus formation, and joint damage

OBJECTIVE

To construct rats congenic for the chromosome 2 arthritis-regulatory quantitative trait locus Cia10, originally identified in a (DA x ACI)F(2) intercross rat strain that had been assessed for collagen-induced arthritis (CIA), and to determine the effect of this congenic interval on arthritis severity, joint histologic structure, and cytokine transcription in rats with pristane-induced arthritis (PIA).

METHODS

A 52.6-MB interval derived from the ACI (CIA- and PIA-resistant) strain and containing the Cia10 interval was introgressed into the DA (arthritis-susceptible) background through genotype-guided congenic breeding. Homozygous male and female DA.ACI(Cia10) congenic rats were studied for their susceptibility to and severity of PIA, and were compared with same-sex DA rats. Histologic analyses were done on hind paws collected on day 32 following the pristane injection. Levels of interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha) messenger RNA (mRNA) were measured with real-time polymerase chain reaction on synovial tissues from day-32 ankles.

RESULTS

Both male and female DA.ACI(Cia10) congenic rats developed a significantly milder form of arthritis, with a 95% and 92% reduction in the arthritis severity index compared with DA male and female controls, respectively (males P < or = 0.001 and females P = 0.003). DA.ACI(Cia10) congenic rat synovial tissue was more likely to preserve its normal histologic architecture, including minimal to no cartilage and bone erosions, synovial hyperplasia, and pannus formation, and reduced numbers of vessels (angiogenesis), when compared with DA synovial tissue. There was a 2.7- and 2.4-fold reduction in the amount of IL-1beta and TNFalpha mRNA, respectively, in the synovial tissue of DA.ACI(Cia10) congenic rats compared with DA rats. Sequencing analyses of complementary DNA for the Cia10-predicted candidate gene Ptpn8, the rat homolog of the rheumatoid arthritis (RA)-susceptibility gene PTPN22, revealed no polymorphisms between the DA and ACI strains.

CONCLUSION

This study determined that Cia10 harbors a major autoimmune arthritis-regulatory gene. This gene regulates clinical disease severity, histologic damage, and the levels of at least two central proinflammatory cytokines. We are in the process of narrowing down the critical region for positional cloning of the Cia10 gene. The identification of this gene will provide novel targets or pathways for focused candidate-gene studies in RA.

Identification of two novel female-specific non-major histocompatibility complex loci regulating collagen-induced arthritis severity and chronicity, and evidence of epistasis

OBJECTIVE

To identify additional sex-specific and epistatic quantitative trait loci (QTL) regulating collagen-induced arthritis (CIA) severity overall, as well as within different stages during the disease course, in an intercross between major histocompatibility complex-identical inbred rat strains DA/Bkl (susceptible) and ACI/Hsd (resistant).

METHODS

Arthritic male (DA x ACI)F2 intercross offspring (n = 143) were analyzed separately from the females (n = 184). Phenotypic extremes (maximum arthritis scores [MAS]) were genotyped and used for QTL analysis. All 327 rats were genotyped with the simple sequence-length polymorphism (SSLP) markers closest to the peak of Cia7 and Cia10, the major loci previously identified in this intercross, and with SSLPs covering chromosomes 12 and 18. Phenotypes studied were disease onset, arthritis severity scores on days 14-39, MAS, mean and cumulative arthritis scores, delayed-type hypersensitivity, and antibody responses to rat type II collagen.

RESULTS

A new female-specific arthritis-severity recessive locus was identified on rat chromosome 12 (Cia25), with a maximum effect observed on day 28 (logarithm of odds [LOD] 4.7). The homozygous DA genotype at Cia25 was associated with a 45% higher median arthritis score in females. Sequencing analyses of the Cia25 candidate gene Ncf1 revealed polymorphisms between DA and ACI. The previously identified locus, Cia10, was found to be male-specific. A 2-locus interaction model analysis identified a novel recessive chromosome 18 QTL, Cia26, which was dependent on Cia7, with its maximum effect observed at later stages during the disease course (peak LOD score of 3.6 for arthritis scores on day 39).

CONCLUSION

This study identified 2 novel female-specific loci, and 1 male-specific locus. Cia25 regulates MAS and disease severity during the mid-to-late stages of the disease course and may be accounted for by Ncf1 polymorphisms. Cia26 is in epistasis with Cia7 and regulates later stages of disease, suggesting an involvement in disease perpetuation and/or chronicity.

A combination of autoantibodies to cyclic citrullinated peptide (CCP) and HLA-DRB1 locus antigens is strongly associated with future onset of rheumatoid arthritis

Antibodies against cyclic citrullinated peptide (CCP) and rheumatoid factors (RFs) have been demonstrated to predate the onset of rheumatoid arthritis (RA) by years. A nested case–control study was performed within the Northern Sweden Health and Disease study cohort to analyse the presence of shared epitope (SE) genes, defined as HLA-DRB1*0404 or DRB1*0401, and of anti-CCP antibodies and RFs in individuals who subsequently developed RA. Patients with RA were identified from among blood donors whose samples had been collected years before the onset of symptoms. Controls matched for age, sex, and date of sampling were selected randomly from the same cohort. The SE genes were identified by polymerase chain reaction sequence-specific primers. Anti-CCP2 antibodies and RFs were determined using enzyme immunoassays. Fifty-nine individuals with RA were identified as blood donors, with a median antedating time of 2.0 years (interquartile range 0.9–3.9 years) before presenting with symptoms of RA. The sensitivity for SE as a diagnostic indicator for RA was 60% and the specificity was 64%. The corresponding figures for anti-CCP antibodies were 37% and 98%, and for RFs, 17–42% and 94%, respectively. In a logistic regression analysis, SE (odds ratio [OR] = 2.35), anti-CCP antibodies (OR = 15.9), and IgA-RF (OR = 6.8) significantly predicted RA. In a combination model analysis, anti-CCP antibodies combined with SE had the highest OR (66.8, 95% confidence interval 8.3–539.4) in predicting RA, compared with anti-CCP antibodies without SE (OR = 25.01, 95% confidence interval 2.8–222.2) or SE without anti-CCP antibodies (OR = 1.9, 95% confidence interval 0.9–4.2). This study showed that the presence of anti-CCP antibodies together with SE gene carriage is associated with a very high relative risk for future development of RA.

Experimental arthritis in CC chemokine receptor 2-null mice closely mimics severe human rheumatoid arthritis

The prevailing paradigm is that in human rheumatoid arthritis (RA), the accumulation of monocytes and T cells in the joint, mediated in part by such CC chemokine receptors (CCRs) as CCR2 and CCR5, respectively, plays a central role in disease pathogenesis. To further validate this paradigm, we conducted proof-of-principle studies and tested the hypothesis that gene inactivation of Ccr2 or Ccr5 will ameliorate experimental RA. Contrary to our expectations, we found that in two well-established murine models of experimental RA, CCR2 expression in the hematopoietic cell compartment served as a negative regulator of autoantibody production as well as arthritic disease onset, severity, and resolution. In contrast, the RA phenotype in Ccr5-null mice was similar to that of WT mice. Remarkably, the collagen-induced arthritis phenotype of Ccr2-/- mice mimicked closely that of severe human RA, including production of rheumatoid factor, enhanced T cell production, and monocyte/macrophage accumulation in the joints. Our findings demonstrate an essential protective role of CCR2 expression in RA, indicate the existence of alternative receptors responsible for monocyte/macrophage accumulation to inflamed joints, and emphasize the need to clarify carefully the complex effects of the chemokine system in RA before they can be considered as therapeutic targets.