Avridine-induced arthritis in rats; a T cell-dependent chronic disease influenced both by MHC genes and by non-MHC genes

Advancement in nanotechnology for treatment of rheumatoid arthritis: scope and potential applications

Rheumatoid arthritis is a hyperactive immune disorder that results in severe inflammation in synovial joints, cartilage, and bone deterioration, resulting in immobilization of joints. Traditional approaches for the treatment of rheumatoid arthritis are associated with some limiting factors such as suboptimal patient compliance, inability to control the progression of disorder, and safety concerns. Therefore, innovative drug delivery carriers for efficient therapeutic delivery at inflamed synovial sites with better safety assessment are urgently needed to address these issues. From this perspective, nanotechnology is an outstanding alternative to traditional drug delivery approaches, and it has shown great promise in developing novel carriers to treat rheumatoid arthritis. Considering the current research and future application of nanocarriers, it is believed that nanocarriers can be a crucial element in rheumatoid arthritis treatment. This paper covers all currently available pathophysiological aspects of rheumatoid arthritis and treatment options. Future research for the reduction of synovial inflammation should focus on developing multifunction nanoparticles capable of delivering therapeutic agents with improved safety, efficacy, and cost-effectiveness to be commercialized.

Adjuvants- and vaccines-induced autoimmunity: animal models

The emergence of autoimmunity after vaccination has been described in many case reports and series. Everyday there is more evidence that this relationship is more than casual. In humans, adjuvants can induce non-specific constitutional, musculoskeletal or neurological clinical manifestations and in certain cases can lead to the appearance or acceleration of an autoimmune disease in a subject with genetic susceptibility. The fact that vaccines and adjuvants can trigger a pathogenic autoimmune response is corroborated by animal models. The use of animal models has enabled the study of the effects of application of adjuvants in a homogeneous population with certain genetic backgrounds. In some cases, adjuvants may trigger generalized autoimmune response, resulting in multiple auto-antibodies, but sometimes they can reproduce human autoimmune diseases including rheumatoid arthritis, systemic lupus erythematosus, Sjögren syndrome, autoimmune thyroiditis and antiphospholipid syndrome and may provide insights about the potential adverse effects of adjuvants. Likewise, they give information about the clinical, immunological and histologic characteristics of autoimmune diseases in many organs, especially secondary lymphoid tissue. Through the description of the physiopathological characteristics of autoimmune diseases reproduced in animal models, new treatment targets can be described and maybe in the future, we will be able to recognize some high-risk population in whom the avoidance of certain adjuvants can reduce the incidence of autoimmune diseases, which typically results in high morbidity and mortality in young people. Herein, we describe the main animal models that can reproduce human autoimmune diseases with emphasis in how they are similar to human conditions.

Methods for Testing Immunological Factors

Hypersensitivity reactions can be elicited by various factors: either immunologically induced, i.e., allergic reactions to natural or synthetic compounds mediated by IgE, or non-immunologically induced, i.e., activation of mediator release from cells through direct contact, without the induction of, or the mediation through immune responses. Mediators responsible for hypersensitivity reactions are released from mast cells. An important preformed mediator of allergic reactions found in these cells is histamine. Specific allergens or the calcium ionophore 48/80 induce release of histamine from mast cells. The histamine concentration can be determined with the o-phthalaldehyde reaction.

Animal models of rheumatoid arthritis: How informative are they?

Animal models of arthritis are widely used to de-convolute disease pathways and to identify novel drug targets and therapeutic approaches. However, the high attrition rates of drugs in Phase II/III rates means that a relatively small number of drugs reach the market, despite showing efficacy in pre-clinical models. There is also increasing awareness of the ethical issues surrounding the use of animal models of disease and it is timely, therefore, to review the relevance and translatability of animal models of arthritis. In this paper we review the most commonly used animal models in terms of their pathological similarities to human rheumatoid arthritis as well as their response to drug therapy. In general, the ability of animal models to predict efficacy of biologics in man has been good. However, the predictive power of animal models for small molecules has been variable, probably because of differences in the levels of target knockdown achievable in vivo.

Amelioration of oxidative stress in the joint tissue may be the basis for the antiarthritic activity of Terminalia arjuna bark extract

AIM

In this study we have evaluated the antioxidant and antiarthritic activity of Terminalia arjuna bark extract (TABE) in collagen-induced arthritis (CIA) in rats.

METHODS

Arthritis was induced in rats by intradermal injection of the collagen-complete Freund's adjuvant emulsion. Right hind paw thickness was measured as a primary marker for severity of arthritis. Biochemical parameters such as tissue levels of superoxide dismutase (SOD), catalase, reduced glutathione (GSH), nitrites and thiobarbituric acid reactive substances (TBARS) were measured to determine the effect of treatment on antioxidant defenses. Articular elastase (ELA) level in the arthritic tissue was measured as a marker for neutrophil infiltration.

RESULT

Terminalia arjuna bark extract administration significantly inhibited the increase in paw thickness induced by immunization with collagen as compared to CIA-control animals. Further, it attenuated the fall in tissue SOD and GSH levels and mitigated the increase in tissue nitrites and TBARS levels as compared to CIA-control animals. Tissue ELA levels, which were significantly increased in the CIA-control animals as compared to normal animals were also significantly reduced by TABE administration.

CONCLUSION

Results of our study demonstrate the antioxidant and antiarthritic activity of TABE in CIA in rats. We believe that TABE could find clinical application in the management of rheumatoid arthritis and associated disorders.

Advances in research on animal models of rheumatoid arthritis

At present, rheumatoid arthritis (RA) is considered a type of autoimmune disease. Its pathology is not certain, and effective drugs with less toxicity have not been established. The establishment and application of animal models are effective methods for RA research, especially using animal models similar to humans. Arthritis is more heterogeneous, and this is an important starting point when discussing animal models for arthritis. Animal models are instrumental in understanding the etiology and pathogenetic mechanisms of RA. Appropriate animal models should be selected according to experiments because they have different traits. Various methods have been applied to induce arthritis in animal experimental models, which have provided important insights into the etiopathogenetic mechanisms of human RA. This review was written to give a broad introduction of the current stage of RA model and hope to offer beneficial help for RA-related research.

Gene expression profiling as a tool for positional cloning of genes-shortcut or the longest way round

The identification of quantitative trait loci, QTL, in arthritis animal models is a straight forward process. However, to identify the underlying genes is a great challenge. One strategy frequently used, is to combine QTL analysis with genomic/proteomic screens. This has resulted in a number of publications where carefully performed genomic analyses present likely candidate genes for their respective QTL s. However, seldom the findings are reconnected to the QTL controlled phenotypes. In this review, we use our own data as an illustrative example that "very likely candidate genes" identified by genomic/proteomics is not necessarily the same as true QTL underlying genes.

Predictivity and sensitivity of animal models of arthritis

Arthritis literally means joint inflammation. Arthritis is not a single disease. Arthritis refers to a group of rheumatic diseases and other conditions that can cause pain, stiffness and swelling in the joints. The forms range from those related to wear and tear of cartilage (such as osteoarthritis) to those associated with inflammation resulting from an overactive immune system (such as rheumatoid arthritis). Arthritis is more heterogeneous and this is an important starting point when discussing animal models for arthritis. Animal models are instrumental in understanding the etiology and pathogenetic mechanisms of rheumatoid arthritis. Several new mouse models have either been produced. Various methods have been applied to induce in animals experimental models of arthritis which would provide important insights into the aetiopathogenetic mechanisms of human RA.

Quantitative gait analysis as a method to assess mechanical hyperalgesia modulated by disease-modifying antirheumatoid drugs in the adjuvant-induced arthritic rat

In the present study, azothioprine, chloroquine, D-penicillamine, methotrexate and sodium aurothiomalate (gold salt) were evaluated for possible disease-modifying effects in the adjuvant-induced arthritis model of human rheumatoid arthritis in rats. Gait analysis was used to examine the role of disease-modifying antirheumatic drugs in the development of pain. Body weights were also measured to monitor the progression of disease and the systemic antiarthritic effects of the test compounds used in this study, as well as their systemic toxicity. Our results showed that azothioprine (5 mg/kg/day), chloroquine (12.5 mg/kg/day), sodium aurothiomalate (2.5 mg/kg/day) and methotrexate (1 mg/kg/week) not only inhibited the macroscopic changes such as erythema and swelling of limbs, but also exhibited significant reversal of gait deficits seen in the untreated or saline-treated arthritic rats. No reduction in the body weights were observed in the arthritic rats treated with azothioprine, chloroquine, sodium aurothiomalate and methotrexate. D-Penicillamine (12.5 mg/kg/day), however, showed a significant reduction (P < 0.03) in the body weights of the arthritic rats over a period of 22 days; furthermore, it was unable to show any reduction in arthritic score (P < 0.1). In earlier experiments, chloroquine and methotrexate failed to suppress carageenan-induced edema, suggesting that the mode of antiarthritic action may be different from those of nonsteroidal anti-inflammatory agents. Since these disease-modifying antirheumatic drugs are reported to have an immunomodulatory role, especially the gold salt, which influences the monocyte–macrophage system, it is suggested that the observed antiarthritic effects of disease-modifying antirheumatic drugs may be partly attributed to their immunomodulatory activity.

A new arthritis therapy with oxidative burst inducers

BACKGROUND

Despite recent successes with biological agents as therapy for autoimmune inflammatory diseases such as rheumatoid arthritis (RA), many patients fail to respond adequately to these treatments, making a continued search for new therapies extremely important. Recently, the prevailing hypothesis that reactive oxygen species (ROS) promote inflammation was challenged when polymorphisms in Ncf1, that decrease oxidative burst, were shown to increase disease severity in mouse and rat arthritis models. Based on these findings we developed a new therapy for arthritis using oxidative burst-inducing substances.

METHODS AND FINDINGS

Treatment of rats with phytol (3,7,11,15-tetramethyl-2-hexadecene-1-ol) increased oxidative burst in vivo and thereby corrected the effect of the genetic polymorphism in arthritis-prone Ncf1(DA) rats. Importantly, phytol treatment also decreased the autoimmune response and ameliorated both the acute and chronic phases of arthritis. When compared to standard therapies for RA, anti-tumour necrosis factor-alpha and methotrexate, phytol showed equally good or better therapeutic properties. Finally, phytol mediated its effect within hours of administration and involved modulation of T cell activation, as injection prevented adoptive transfer of disease with arthritogenic T cells.

CONCLUSIONS

Treatment of arthritis with ROS-promoting substances such as phytol targets a newly discovered pathway leading to autoimmune inflammatory disease and introduces a novel class of therapeutics for treatment of RA and possibly other chronic inflammatory diseases.

Adjuvant oil induces waves of arthritogenic lymph node cells prior to arthritis onset

A single intradermal injection of the adjuvant-oil squalene induces T cell mediated arthritis in DA rats. The chain of events leading from nonspecific provocation of the immune system to arthritis is largely unknown. Previous studies have demonstrated that lymph node (LN) cells are of pathogenic importance, i.e. cells from LNs draining the injection site can transfer arthritis to naïve DA rats. Recently we have demonstrated cellular uptake of adjuvant oil in draining lymph nodes but also that nondraining LNs become hyperplastic and harbour arthritogenic cells. Here, we aimed to determine from which time-point prior to arthritis onset arthritogenic cells appear in draining inguinal and nondraining axillary/brachial LNs, respectively. We demonstrated that the ability to transfer arthritis was strongly dependent on the time-point after adjuvant-injection with clear-cut differences between draining and nondraining LN cells. Cells harvested at day 5 postinjection (p.i) were not able to transfer arthritis, while at day 8 p.i, a first wave of arthritogenic cells appeared in draining LNs. The ability to transfer arthritis was associated with a pro-inflammatory cytokine profile as indicated by the IL-1beta and IFNgamma expression in cells from draining LNs. Subsequently, at day 11 p.i., just before arthritis onset, arthritogenic cells appeared also in nondraining LNs. These results shed new light on the induction of arthritic diseases, implicating a two step mechanism for the development of pathogenic cells. Firstly, a pro-inflammatory burst in responding lymphoid organs leading to a local pool of arthritogenic cells and, secondly, a transmission of arthritogenecity to other LNs and precipitation of disease in peripheral joints.

Neural immune pathways and their connection to inflammatory diseases

Inflammation and inflammatory responses are modulated by a bidirectional communication between the neuroendocrine and immune system. Many lines of research have established the numerous routes by which the immune system and the central nervous system (CNS) communicate. The CNS signals the immune system through hormonal pathways, including the hypothalamic-pituitary-adrenal axis and the hormones of the neuroendocrine stress response, and through neuronal pathways, including the autonomic nervous system. The hypothalamic-pituitary-gonadal axis and sex hormones also have an important immunoregulatory role. The immune system signals the CNS through immune mediators and cytokines that can cross the blood-brain barrier, or signal indirectly through the vagus nerve or second messengers. Neuroendocrine regulation of immune function is essential for survival during stress or infection and to modulate immune responses in inflammatory disease. This review discusses neuroimmune interactions and evidence for the role of such neural immune regulation of inflammation, rather than a discussion of the individual inflammatory mediators, in rheumatoid arthritis.

Both common and unique susceptibility genes in different rat strains with pristane-induced arthritis

Pristane-induced arthritis (PIA) in rats is an animal model for rheumatoid arthritis (RA). We have previously identified seven quantitative trait loci (QTLs), which regulate arthritis development using a cross between the susceptible DA strain and the resistant E3 strain of rats (Pia2-8). In the present study the inbred rat strain LEW.1F was used as the susceptible strain in a cross with the E3 strain. The results confirmed the locus Pia4 on chromosome 12, which previously was shown to be associated with PIA, and also with experimental allergic encephalomyelitis, in crosses between the rat strains E3 and DA. On chromosome 1, linked to the albino locus, we identified a novel QTL, Pia9 in the LEW.F1 cross. This locus was associated with arthritis severity in the early phase of disease. A locus on chromosome 16, denoted Pia11, was also associated with arthritis severity in the early phase of the disease. A suggestive locus was detected on chromosome 14, which was associated with arthritis severity at the time when PIA progresses into a chronic phase. Using a congenic LEW.1F strain, which carries E3 alleles at the Pia9 locus, we confirmed that the E3 allele significantly suppresses arthritis severity during the early phase of the disease. The results revealed synergistic effects between different susceptibility loci using ANOVA analysis. These interactions were influenced by gender. Rats with Pia9 alleles from LEW.1F and Pia11 alleles from E3, were shown to suffer from much more severe arthritis in the early stage of the disease. On the other hand, the Pia9 and the suggestive locus on chromosome 14 affected only males during the chronic phase of the disease. These findings provide clues to how genetic factors by themselves, and in interaction with each other, regulate the development of a disease, which displays many similarities to RA.

Immune regulation in adjuvant disease and other arthritis models: relevance to pathogenesis of chronic arthritis

Experimental models of arthritis and their human counterparts fall into three distinct classes: (a) responses of T cells to disseminated microbial antigens (Ags) as such; (b) responses of T cells to cartilage autoAgs; and (c) responses of T cells to major histocompatibility complex (HLA-B27, DRB1) or other membrane components (LFA-1) expressed on bone marrow-derived cells. The primary immune response is driven, in naturally occurring disease, by microbial infection, e.g. with streptococci, enteric gram-negative rods or spirochetes, or is experimentally induced with mycobacterial and other adjuvants. The response to cartilage components, such as collagen type-II and various proteoglycans, may be driven by cross-reactive microbial Ags, heat shock proteins (HSPs) in particular, or the adjuvant effect of intense primary joint inflammation, as in rheumatoid arthritis and the spondyloarthropathies. Adjuvant disease appears to be purely T-cell-mediated, whereas both T cells and antibody play a role in collagen and many other forms of arthritis. Experimental evidence suggests a pathogenetic role for T-cell receptor gammadelta T cells in some lesions. Arthritis may be regulated by microbial and tissue HSPs, when these are administered by a nonimmunizing route or as altered peptide ligands, by anti-idiotypic responses that block the action of effector T cells, and by competing Ags. Immune regulation involving natural killer (NK), NK T and certain subsets of gammadelta and alphabeta T cells, which may affect the occurrence, localization and character of this group of diseases, presents a challenge for further investigation.

Immunization of rats with homologous type XI collagen leads to chronic and relapsing arthritis with different genetics and joint pathology than arthritis induced with homologous type II collagen

The most commonly used animal model for rheumatoid arthritis (RA) is collagen-induced arthritis (CIA), induced by immunization with type II collagen (CII), a cartilage restricted protein. In this work we show that type XI collagen (CXI), which is a minor component in cartilage, induces a different form of erosive and chronic relapsing polyarthritis in rats. Using a series of inbred rat strains involving various genetic backgrounds (DA, LEW, E3), and congenic MHC regions (a, u, f, n, c, d), we found that CXI induced arthritis (C(XI)IA) is associated with the RT1f haplotype in contrast to CII induced arthritis (C(II)IA), which is associated with the RT1a and RT1u haplotypes. The C(XI)IA follows a chronic disease course affecting peripheral joints with both progression and relapses, which appear not to cease (occurring >800 days). Susceptible strains showed a sustained antibody response to CXI with time indicating that the autoimmune response was self-perpetuated. Microscopic analysis of the joints at different stages demonstrated the severe destruction of bone and cartilage by pannus tissue consisting of activated macrophages and T cells. The main difference to joints from rats with C(II)IA was larger numbers of infiltrating lymphocytes and these tended to form follicle-like aggregates. Surprisingly, males were more susceptible to C(XI)IA than females whereas the opposite has been observed in other rat arthritis models, including C(II)IA. Taken together, C(XI)IA is a chronic relapsing and erosive polyarthritis that is MHC associated, which in fact fulfills the criteria for diagnosis of RA. Thus the C(XI)IA model will be useful as a novel and relevant animal model for RA.

The arthritogenic adjuvant squalene does not accumulate in joints, but gives rise to pathogenic cells in both draining and non-draining lymph nodes

A single intradermal injection of the adjuvant-oil squalene induces T cell-mediated arthritis in DA rats. The chain of events leading from non-specific provocation of the immune system to arthritis, with clinical similarities to rheumatoid arthritis, is largely undetermined. Here, we combined in vivo tracking of tritium-labelled squalene with lymph node (LN) cell transfer experiments to determine where critical activation events may take place. The majority of squalene remained at the injection site (79%). The amounts recovered in peripheral joints (<1%) were equal to that recovered in other organs that can be targets in autoimmune diseases. This argues that arthritis does not develop as a consequence of adjuvant accumulation in joints. In contrast, substantial amounts of squalene were recovered in hyperplastic LN draining the injection site (1-13%). The adjuvant was deposited to a larger extent in cells than in extracellular matrix. The draining LN cells could transfer arthritis to naïve irradiated DA rats following in vitro stimulation with conA. Interestingly, non-draining LN were also hyperplastic and harboured arthritogenic cells, although they contained low amounts of squalene (<1%). Consequently, the amount of arthritogenic adjuvant in a particular LN is not closely linked to the development of pathogenic cells. The distribution pattern of squalene was similar in MHC-identical but arthritis-resistant PVG.1AV1 and LEW.1AV1 rats, and it was unaffected by T cell depletion with a monoclonal antibody (R73). Thus, T cells and non-MHC genes do not regulate dissemination of squalene, but rather determine arthritis development at the level of adjuvant response.

Cartilage-specific autoimmunity in animal models and clinical aspects in patients - focus on relapsing polychondritis

Relapsing polychondritis is an autoimmune disease in which an inappropriate immune response destroys cartilage. Cartilage of the ears, larynx and nose rather than spine and joint cartilage is affected by a chronic relapsing and erosive inflammation. Several animal models for relapsing polychondritis have been published in which immunization with various cartilage proteins induces a variety of chondritis symptoms that mimic those seen in patients. In this review we describe the collagens, matrilin-1 and cartilage oligomeric matrix protein as potential autoantigens able to trigger the tissue-specific immune response seen both in patients and in animal models for relapsing polychondritis and related autoimmune diseases.

Susceptibility to autoimmune disease and drug addiction in inbred rats. Are there mechanistic factors in common related to abnormalities in hypothalamic-pituitary-adrenal axis and stress response function?

DA and LEW inbred rats are extraordinarily susceptible to a wide range of experimental autoimmune diseases. These diseases include rheumatoid arthritis models such as collagen-induced arthritis (CIA) and adjuvant-induced arthritis (AIA), multiple sclerosis models such as myelin-basic-protein (MBP)-induced experimental autoimmune encephalomyelitis (MBP-EAE), and autoimmune uveitis models such as retinal S antigen (SAG) and interphotoreceptor-retinoid-binding-protein (IRBP)-induced experimental autoimmune uveitis (SAG-EAU and IRBP-EAU, respectively). DA and LEW rats are also addiction-prone to various drugs of abuse, such as cocaine. Moreover, they exhibit a variety of behavioral and biochemical characteristics that appear to be related to their susceptibility to addiction. By contrast, F344 and BN rats show quite different phenotypes. They are relatively resistant to CIA, AIA, MBP-EAE, SAG-EAU, and IRBP-EAU, and they are relatively resistant to addiction. Interestingly, both DA and LEW rats, in contrast to F344 and BN rats, have abnormalities in hypothalamic-pituitary-adrenal (HPA) axis function. For example, circadian production of corticosteroids is very abnormal in DA and LEW rats; that is, they exhibit minimal circadian variation in corticosterone levels. Since corticosteroids potentially have significant influences on immune function and autoimmune disease susceptibility and may also influence sensitivity to drugs of abuse, we have begun to dissect genetic control of these various phenotypic differences, focusing initially on the regulation of autoimmune disease expression. Using genomewide scanning techniques involving F2 crosses of DA x F344 (CIA and AIA), DA x BN (CIA), and LEW x F344 [IRBP-EAU and streptococcal-cell-wall arthritis (SCWA)], we have identified, to date, 14 genomic regions [quantitative trait loci (QTL)] that regulate disease expression in these crosses. Development and analysis of QTL-congenic rats involving these loci are in progress and should permit us to address the relationships among autoimmune disease susceptibility, drug addiction, and HPA axis and stress response function. These initial data, however, indicate that the genetic control of the autoimmune disease traits is highly complex.

The genetics of rheumatoid arthritis and the need for animal models to find and understand the underlying genes

The causes of rheumatoid arthritis (RA) are largely unknown. However, RA is most probably a multifactorial disease with contributions from genetic and environmental factors. Searches for genes that influence RA have been conducted in both human and experimental model materials. Both types of study have confirmed the polygenic inheritance of the disease. It has become clear that the features of RA complicate the human genetic studies. Animal models are therefore valuable tools for identifying genes and determining their pathogenic role in the disease. This is probably the fastest route towards unravelling the pathogenesisis of RA and developing new therapies.

A new animal model for relapsing polychondritis, induced by cartilage matrix protein (matrilin-1)

Relapsing polychondritis (RP) differs from rheumatoid arthritis (RA) in that primarily cartilage outside diarthrodial joints is affected. The disease usually involves trachea, nose, and outer ears. To investigate whether the tissue distribution of RP may be explained by a specific immune response, we immunized rats with cartilage matrix protein (matrilin-1), a protein predominantly expressed in tracheal cartilage. After 2-3 weeks, some rats developed a severe inspiratory stridor. They had swollen noses and/or epistaxis, but showed neither joint nor outer ear affection. The inflammatory lesions involved chronic active erosions of cartilage. Female rats were more susceptible than males. The disease susceptibility was controlled by both MHC genes (f, l, d, and a haplotypes are high responders, and u, n, and c are resistant) and non-MHC genes (the LEW strain is susceptible; the DA strain is resistant). However, all strains mounted a pronounced IgG response to cartilage matrix protein. The initiation and effector phase of the laryngotracheal involvement causing the clinical symptoms were shown to depend on alphabeta T cells. Taken together, these results represent a novel model for RP: matrilin-1-induced RP. Our findings also suggest that different cartilage proteins are involved in pathogenic models of RP and RA.

Transgenic mouse models of rheumatoid arthritis

A combined analysis of data available in the literature has demonstrated that the strongest association in rheumatoid arthritis (RA) is with DR genes rather than DQ or DP genes. Functional and structural data of RA-associated DR molecules suggest that selective binding of peptides is the molecular basis for this association. The establishment of functional transgenic mice expressing RA-associated HLA class II molecules has proven to be useful in the delineation of the role of these molecules in immune responses possibly related to RA and in the development of humanized models for this disease. Such humanized mice develop arthritis upon immunization with type II collagen (CII), which shows similarities with RA. Interestingly, the immunodominant T-cell determinant in CII is derived from positions 261-273, which overlap with a previously identified CII T-cell epitope restricted by the mouse Aq molecule, which is associated with collagen-induced arthritis. Studies in collagen transgenic mice have shown that recognition of this peptide may lead either to T-cell tolerance or to an arthritogenic response. It is therefore proposed that the T-cell recognition of the CII peptide bound by DR molecules is one of the molecular interactions of critical importance in the development of RA and accordingly also an important target for prevention and treatment of this disease.

Identification of arthritogenic adjuvants of self and foreign origin

The lack of defined triggers for human inflammatory joint diseases warrants efforts to identify candidate molecules. For this task, it may be an important lead that nonspecific activation of the immune system can precipitate arthritis in rats. Consequently, arthritis-prone rat strains were used to search for disease-triggering factors among molecules which initially induce innate defence reactions rather than specific immune responses. A variety of immunological adjuvants were investigated by intradermal injection into DA and LEW.1AV1 rats and monitoring of clinical signs for 30 days. Several arthritogenic cell-wall structures from yeast and bacteria were identified, such as beta-glucan, lipopolysaccharide and trehalosedimycolate. The test procedures also revealed arthritogens of chemical origin, such as dioctadecyldiammoniumbromide (DDA = C38H80NBr) and heptadecane (C17H36). Furthermore, it allowed the precise definition of arthritogenic determinants of lipids, since C16H34 induced arthritis, whereas the closely related linear hydrocarbons C16H32, C16H33Br and C15H32 did not. The observed pathogenicity of organic lipids raised the question of whether endogenous lipids can also precipitate arthritis. Indeed, this was true for the cholesterol precursor squalene (C30H50). In conclusion, this article describes the rational use of arthritis-prone rat strains to identify arthritogenic factors of both foreign and self origin. Although structurally unrelated, the pathogenic molecules defined here share the feature of being nonspecific triggers of the immune system. This consolidates a general principle for the induction of adjuvant arthritis which may provide clues to the aetiology of human arthritides, including rheumatoid arthritis.

Cartilage oligomeric matrix protein (COMP)-induced arthritis in rats

In rheumatoid arthritis peripheral cartilaginous joints are inflamed and eroded. One driving factor may be an immune response towards proteins in the cartilage. Here it is shown that cartilage oligomeric matrix protein (COMP), expressed specifically in cartilage, is arthritogenic in the rat. Both native and denatured rat COMP induced severe arthritis in selected rat strains. The arthritis occurred only in peripheral joints which were attacked by an erosive inflammatory process similar to that seen in the human disease. The disease was self-limited and no permanent destruction of joints was seen macroscopically. Disease development appeared to be dependent on an immune response to autologous (rat) COMP and not on cross-reactivity to other cartilage rat collagens (types II, IX and XI). The disease and the immune response to COMP were genetically controlled by the MHC; the RT1u and RT1l haplotypes were more susceptible than the a, c, d, f and n haplotypes. Both LEW and E3 gene backgrounds were highly permissive for disease induction. These findings suggest that the induction of arthritis with rat COMP represents a unique pathogenesis which is controlled by different genes compared with collagen-induced arthritis or adjuvant-induced arthritis.

A dominant role for non-MHC gene effects in susceptibility to cyclosporin A (CsA)-induced autoimmunity

Lethally irradiated LEW rats reconstituted with syngeneic bone marrow and given CsA for a 4-week period develop a graft-versus-host-like disease upon withdrawal of CsA. This T cell-mediated autoimmune disease is referred to as CsA-induced autoimmunity (CsA-AI). CsA-AI-susceptible LEW rats and resistant BN rats differ greatly in the composition of their peripheral T cell compartment. To dissect the role of MHC and non-MHC genes in the development of peripheral T cell subsets in combination with susceptibility to CsA-AI the respective MHC congenic strains (LEW-1N and BN-1L) were examined for their T cell subsets and for their ability to develop CsA-AI. In this study we show that the Th1/Th2-like cell ratio as well as susceptibility to CsA-AI are under control of the non-MHC genes. This suggests that the Th1/Th2-like cell ratio is a critical determinant for development of CsA-AI. Alternatively, resistance can be attributed to lack of target organ susceptibility due to the absence of the target autoantigen in resistant rat strains. This interpretation is rejected, since both BN as well as BN-1L rats consistently develop the characteristic macroscopic and microscopic signs of CsA-AI upon adoptive transfer with autoreactive LEW-1N and LEW T cells, respectively. Therefore, it can be concluded that the non-MHC genes encode for immune deviation and thereby determine susceptibility or resistance to CsA-AI.

Effects of a novel non-steroidal anti-inflammatory drug (M-5011) on bone metabolism in rats with collagen-induced arthritis

The effects of a novel non-steroidal anti-inflammatory drug (NSAID), d-2-[4-(3-methyl-2-thienyl)phenyl]propionic acid: M-5011, and other NSAIDs (indomethacin, zaltoprofen and tiaprofenic acid) on bone metabolism in Dark Agouti (DA) strain rats with collagen-induced arthritis were evaluated. M-5011 (1.5 and 4.5 mg/kg) and other NSAIDs (1.5 mg/kg) were administered orally once a day from day 14 to day 35 after collagen immunization. In arthritic rats, paw volume and serum levels of anti-type II collagen antibody were increased on day 21 compared to those in non-immunized rats. M-5011 (4.5 mg/kg), indomethacin and zaltoprofen tended to prevent this increase in paw volume. Elevated urinary pyridinoline and deoxypyridinoline levels were found on days 28 and 35 in arthritic rats. M-5011 (4.5 mg/kg) also tended to prevent the increase in urinary pyridinoline level on day 28, but none of the other NSAIDs affected urinary deoxypyridinoline levels. Bone mineral densities in the hindpaw and vertebrae were also decreased in arthritic rats. M-5011 and tiaprofenic acid prevented this decrease in vertebral bone mineral density. These findings indicate that M-5011 partially inhibits the generalized bone loss accompanying the development of collagen-induced arthritis in rats.

Identification of rat susceptibility loci for adjuvant-oil-induced arthritis

One intradermal injection of incomplete Freund's adjuvant-oil induces a T cell-mediated inflammatory joint disease in DA rats. Susceptibility genes for oil-induced arthritis (OIA) are located both within and outside the major histocompatibility complex (MHC, Oia1). We have searched for disease-linked non-MHC loci in an F2 intercross between DA rats and MHC-identical but arthritis-resistant LEW.1AV1 rats. A genome-wide scan with microsatellite markers revealed two major chromosome regions that control disease incidence and severity: Oia2 on chromosome 4 (P = 4 x 10(-13)) and Oia3 on chromosome 10 (P = 1 x 10(-6)). All animals homozygous for DA alleles at both loci developed severe arthritis, whereas all those homozygous for LEW.1AV1 alleles were resistant. These results have general implications for situations where nonspecific activation of the immune system (e.g., incomplete Freund's adjuvant-oil) causes inflammation and disease, either alone or in conjunction with specific antigens. They may also provide clues to the etiology of inflammatory diseases in humans, including rheumatoid arthritis.

Peptide-induced nasal tolerance for a mycobacterial heat shock protein 60 T cell epitope in rats suppresses both adjuvant arthritis and nonmicrobially induced experimental arthritis

Adjuvant arthritis (AA) can be induced in Lewis rats by immunization with mycobacterial antigens. Passive transfer of a T cell clone recognizing the 180-188 amino acid sequence in mycobacterial heat shock protein 60 (hsp60) was found to induce AA. In the present study, we investigated whether tolerance was obtained for this AA-associated T cell epitope after intranasal or s.c. administration of a peptide containing this epitope. Two 15-mer peptides containing the mycobacterial hsp60 sequences 176-190 and 211-225 were used; 176-190 contained the T cell epitope 180-188, which was recognized by the arthritogenic T cell clone A2b and was the immunodominant hsp60 T cell epitope after induction of AA, and 211-225 contained a T cell epitope that was recognized both after induction of arthritis with whole Mycobacterium tuberculosis and after immunization with mycobacterial hsp60. In rats treated intranasally or subcutaneously with 176-190 and immunized with mycobacterial hsp60, proliferative responses to 176-190 were reduced. Proliferative responses to 211-225 and to whole mycobacterial hsp60 were not affected. AA was inhibited intranasally in the 176-190-treated rats but not in the 211-225-treated rats. Moreover, intranasal 176-190 led to similar arthritis-protective effects in a nonmicrobially induced experimental arthritis (avridine-induced arthritis). Therefore, tolerance for a disease-triggering, microbial cartilage-mimicking epitope may cause resistance to arthritis irrespective of the actual trigger leading to development of the disease.

Pristane-induced arthritis in rats: a new model for rheumatoid arthritis with a chronic disease course influenced by both major histocompatibility complex and non-major histocompatibility complex genes

We present a novel animal model for rheumatoid arthritis induced with a well defined synthetic adjuvant oil, pristane. Two weeks after a single intradermal injection of 150 microliters of pristane, the rats developed severe and chronic arthritis. The inflammation was restricted to the joints and involved pannus formation, major histocompatibility complex (MHC) class II expression, and T lymphocyte infiltration. The initial development as well as the chronic stage of pristane-induced arthritis was ameliorated by treatment with antibodies to the alpha beta-T-cell receptor showing that the disease is T cell dependent. Increased levels of interleukin in serum was seen after pristane injection but not during the chronic stage of arthritis. Joint erosions were accompanied by elevated serum levels of cartilage oligomeric matrix protein. Comparison of MHC congenic LEW strains showed that the severity and chronicity of arthritis varied among the different MHC haplotypes. Rats with RT1f haplotype showed a significantly higher susceptibility to pristane-induced arthritis. A strong influence of non-MHC genes was also suggested by the variability of arthritis susceptibility among different strains with the same MHC haplotype; the most susceptible background was the DA and the least susceptible was the E3. Arthritis induced with a well defined nonimmunogenic adjuvant, with a disease course that closely resembles that of rheumatoid arthritis, makes a suitable animal model for future studies of the pathology and genetics of rheumatoid arthritis.

Regulation by non-major histocompatibility complex genes of the allo-4-hydroxy-phenylpyruvate dioxygenase (F liver protein) response

Although rapid progress is being made in the quantitative genetics of multifactorial disease, no response to a simple antigen has yet been subjected to full genomic analysis. The well-characterized antigen allo-HPPD (4-hydroxy-phenylpyruvate dioxygenase, previously known as F liver antigen) is a good candidate for such treatment. Old and new data bearing on this possibility are here assembled. In respect of antibody production and an early burst of interleukin-4 (IL-4) transcription, introduction of the non-major histocompatibility complex (MHC) background from A/J strain mice into F1 hybrids with C57BL10 strains up-regulates the response. These findings can be aligned with previous quantitative genetics carried out on airway hyper-responsiveness in related strains, and to a lesser extent with the genetics of autoimmune diabetes in the mouse. Taken together, the findings suggest that regulation of the pro-inflammatory cytokines are largely responsible for the variation. Additional data indicate that these non-MHC genes are are to a variable extent (depending on the response parameter) epistatic to the down-regulatory MHC allele H-2Ab.

Female preponderance for development of arthritis in rats is influenced by both sex chromosomes and sex steroids

Autoimmune arthritis was induced after a single injection of the non-immunogenic adjuvant (avridine) or with autologous rat type II collagen. Females of two different rat strains, DA and LEW, were found to be more susceptible than males. To investigate further the mechanisms behind the female preponderance, we selected the avridine induced arthritis model. This is known to be a chronic joint-specific disease which is T-cell dependent and associated with MHC genes and, therefore, is an appropriate model for rheumatoid arthritis. To address the possibility of sex chromosome involvement, reciprocal F1 hybrids were produced. Female (DAxLEW)F1 rats were found to be more prone to arthritis than their male counterparts. This difference could be explained, at least partly, by the influence of sex chromosomes since reciprocal (LEWxDA)F1 rats showed no sex linkage. However, the sex linkage was more pronounced in normal rats when compared to castrated (DAxLEW)F1 rats indicating a role for sex hormones in conjunction with the sex chromosome-linked effect. Both oestrogen and testosterone had a suppressive effect on the development of arthritis. The findings presented here suggest the presence of a sex chromosome gene, which mediates its function only in the presence of sex hormones and is associated with a female preponderance for development of arthritis.