Triggering and exacerbation of autoimmune arthritis by the Mycoplasma arthritidis superantigen MAM

Novel insights into the immune response to bacterial T cell superantigens

Bacterial T cell superantigens (SAgs) are a family of microbial exotoxins that function to activate large numbers of T cells simultaneously. SAgs activate T cells by direct binding and crosslinking of the lateral regions of MHC class II molecules on antigen-presenting cells with T cell receptors (TCRs) on T cells; these interactions alter the normal TCR-peptide-MHC class II architecture to activate T cells in a manner that is independent of the antigen specificity of the TCR. SAgs have well-recognized, central roles in human diseases such as toxic shock syndrome and scarlet fever through their quantitative effects on the T cell response; in addition, numerous other consequences of SAg-driven T cell activation are now being recognized, including direct roles in the pathogenesis of endocarditis, bloodstream infections, skin disease and pharyngitis. In this Review, we summarize the expanding family of bacterial SAgs and how these toxins can engage highly diverse adaptive immune receptors. We highlight recent findings regarding how SAg-driven manipulation of the adaptive immune response may operate in multiple human diseases, as well as contributing to the biology and life cycle of SAg-producing bacterial pathogens.

Mycoplasma pneumonia Infection Is Associated With an Increased Risk of Systemic Lupus Erythematosus: A Nationwide, Retrospective Cohort Study

Background

Infections may play a role in the development of systemic lupus erythematosus (SLE).

Objective

To assess the link between Mycoplasma pneumonia (M. pneumonia) infection and the incidence of SLE.

Method

We conducted a retrospective cohort study, which identified 116,043 hospitalized patients with M. pneumoniae between 2000 and 2012 from the Taiwan National Health Insurance Research Database and compared them with 447,839 matched inpatients who had never been diagnosed with M. pneumonia infection (at a 1:4 ratio, matched by age, gender, and index year). Their comparative risk of developing SLE was evaluated. The follow-up period was defined as the time from the initial diagnosis of M. pneumonia infection to the date of SLE diagnosis, or December 31, 2013. The incidence rates of SLE were assessed in people with and without M. pneumoniae infection. Cox proportional hazard models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs), with the uninfected group used as the reference.

Results

The adjusted HR of SLE for the M. pneumoniae group was 2.97 with 95% CI = 2.18–4.05 compared with the uninfected group. The risk was most significantly higher within 0.5 years after the M. pneumoniae infection with an adjusted HR of 6.18 (95% CI = 3.82–9.97, p < 0.01). The adjusted HR for SLE from 0.5 to 2 years and from 2 to 5 years after M. pneumoniae infection was 1.59 (95% CI = 0.70–3.59, p = 0.27) and 2.42 (95% CI = 1.22–4.81, p = 0.01), respectively.

Conclusion

The incidence of SLE was significantly higher in subjects infected with M. pneumoniae.

New Studies of Pathogenesis of Rheumatoid Arthritis with Collagen-Induced and Collagen Antibody-Induced Arthritis Models: New Insight Involving Bacteria Flora

Much public research suggests that autoimmune diseases such as rheumatoid arthritis (RA) are induced by aberrant “self” immune responses attacking autologous tissues and organ components. However, recent studies have reported that autoimmune diseases may be triggered by dysbiotic composition changes of the intestinal bacteria and an imbalance between these bacteria and intestinal immune systems. However, there are a few solid concepts or methods to study the putative involvement and relationship of these inner environmental factors in RA pathogenesis. Fortunately, Collagen-Induced Arthritis (CIA) and Collagen Antibody-Induced Arthritis (CAIA) models have been widely used as animal models for studying the pathogenesis of RA. In addition to RA, these models can be extensively used as animal models for studying complicated hypotheses in many diseases. In this review, we introduce some basic information about the CIA and CAIA models as well as how to apply these models effectively to investigate relationships between the pathogenesis of autoimmune diseases, especially RA, and the dysbiosis of intestinal bacterial flora.

Inflammatory arthritis disrupts gut resolution mechanisms, promoting barrier breakdown by Porphyromonas gingivalis

Rheumatoid arthritis is linked with altered host immune responses and severe joint destruction. Recent evidence suggests that loss of gut homeostasis and barrier breach by pathobionts, including Porphyromonas gingivalis, may influence disease severity. The mechanism(s) leading to altered gut homeostasis and barrier breakdown in inflammatory arthritis are poorly understood. In the present study, we found a significant reduction in intestinal concentrations of several proresolving mediators during inflammatory arthritis, including downregulation of the gut-protective mediator resolvin D5n-3 DPA (RvD5n-3 DPA). This was linked with increased metabolism of RvD5n-3 DPA to its inactive 17-oxo metabolite. We also found downregulation of IL-10 expression in the gut of arthritic mice that was coupled with a reduction in IL-10 and IL-10 receptor (IL-10R) in lamina propria macrophages. These changes were linked with a decrease in the number of mucus-producing goblet cells and tight junction molecule expression in the intestinal epithelium of arthritic mice when compared with naive mice. P. gingivalis inoculation further downregulated intestinal RvD5n-3 DPA and Il-10 levels and the expression of gut tight junction proteins. RvD5n-3 DPA, but not its metabolite 17-oxo-RvD5n-3 DPA, increased the expression of both IL-10 and IL-10R in macrophages via the upregulation of the aryl hydrocarbon receptor agonist l-kynurenine. Administration of RvD5n-3 DPA to arthritic P. gingivalis-inoculated mice increased intestinal Il-10 expression, restored gut barrier function, and reduced joint inflammation. Together, these findings uncover mechanisms in the pathogenesis of rheumatoid arthritis, where disruption of the gut RvD5n-3 DPA-IL-10 axis weakens the gut barrier, which becomes permissive to the pathogenic actions of the pathobiont P. gingivalis.

Increased risk of rheumatoid arthritis among patients with Mycoplasma pneumonia: A nationwide population-based cohort study in Taiwan

Objective

An association between Mycoplasma pneumonia (MP) and rheumatoid arthritis (RA) had been reported in animal studies for decades. However, clinical evidence for this association is lacking. Therefore, this study aimed to provide epidemiologic evidence to clarify the relationship between MP and development of RA.

Methods

This 13-year nationwide, population-based, retrospective cohort study analyzed the risk of RA in a cohort of MP patients. We cross linked and compared the database of those with catastrophic illnesses to make sure the diagnoses of RA are correctly labeled. We selected 116,053 hospitalized patients diagnosed with MP between 2000 and 2012 from the Taiwan National Health Insurance Research Database and 464,212 matched controls at a 1:4 ratio by age, gender, and index year, in relation to the risk of developing RA. The follow-up period referred to the initial diagnosis of MP until the date of RA diagnosis, censoring of RA, or 31^st December 2013. The Cox proportional hazard model was used to analyze the association between MP and incidence of RA among patients with different potential risks.

Results

The adjusted hazard ratio (HR) for incidental RA in the MP group was 1.37 (95% confidence interval CI = 0.87–2.16), compared to non-MP controls. Stratified analysis revealed that the adjusted HR was 3.05 (95% CI = 1.16–7.99, p = 0.02) in a subgroup of patients over the age of 65.The adjusted HR of RA for the MP group among aged ≦19 years and ≥ 65 years was 3.19 (95% CI = 1.04.9.76) and 4.14 (95% CI = 1.27,13.4) within the first 2 years of follow-up.

Conclusion

This cohort study demonstrated that patients with MP had a higher risk of developing RA, especially in the first 2 years, in those aged younger than 19 and over 65.

Streptococcal pharyngitis and rheumatic heart disease: the superantigen hypothesis revisited

Streptococcus pyogenes is a human-specific and globally prominent bacterial pathogen that despite causing numerous human infections, this bacterium is normally found in an asymptomatic carrier state. This review provides an overview of both bacterial and human factors that likely play an important role in nasopharyngeal colonization and pharyngitis, as well as the development of acute rheumatic fever and rheumatic heart disease. Here we highlight a recently described role for bacterial superantigens in promoting acute nasopharyngeal infection, and discuss how these immune system activating toxins could be crucial to initiate the autoimmune process in rheumatic heart disease.

Our Environment Shapes Us: The Importance of Environment and Sex Differences in Regulation of Autoantibody Production

Consequential differences exist between the male and female immune systems’ ability to respond to pathogens, environmental insults or self-antigens, and subsequent effects on immunoregulation. In general, females when compared with their male counterparts, respond to pathogenic stimuli and vaccines more robustly, with heightened production of antibodies, pro-inflammatory cytokines, and chemokines. While the precise reasons for sex differences in immune response to different stimuli are not yet well understood, females are more resistant to infectious diseases and much more likely to develop autoimmune diseases. Intrinsic (i.e., sex hormones, sex chromosomes, etc.) and extrinsic (microbiome composition, external triggers, and immune modulators) factors appear to impact the overall outcome of immune responses between sexes. Evidence suggests that interactions between environmental contaminants [e.g., endocrine disrupting chemicals (EDCs)] and host leukocytes affect the ability of the immune system to mount a response to exogenous and endogenous insults, and/or return to normal activity following clearance of the threat. Inherently, males and females have differential immune response to external triggers. In this review, we describe how environmental chemicals, including EDCs, may have sex differential influence on the outcome of immune responses through alterations in epigenetic status (such as modulation of microRNA expression, gene methylation, or histone modification status), direct and indirect activation of the estrogen receptors to drive hormonal effects, and differential modulation of microbial sensing and composition of host microbiota. Taken together, an intriguing question develops as to how an individual’s environment directly and indirectly contributes to an altered immune response, dysregulation of autoantibody production, and influence autoimmune disease development. Few studies exist utilizing well-controlled cohorts of both sexes to explore the sex differences in response to EDC exposure and the effects on autoimmune disease development. Translational studies incorporating multiple environmental factors in animal models of autoimmune disease are necessary to determine the interrelationships that occur between potential etiopathological factors. The presence or absence of autoantibodies is not a reliable predictor of disease. Therefore, future studies should incorporate all the susceptibility/influencing factors, coupled with individual genomics, epigenomics, and proteomics, to develop a model that better predicts, diagnoses, and treats autoimmune diseases in a personalized-medicine fashion.

Contribution of bacterial pathogens to evoking serological disease markers and aggravating disease activity in rheumatoid arthritis

Commensal bacteria and their pathogenic components in the gastrointestinal tract and oral cavity may play pathological roles in autoimmune diseases. To study the possible involvement of bacterial pathogens in autoimmune diseases, IgG and IgA antibodies against pathogenic components produced by three strains of commensal bacteria, Escherichia coli-lipopolysaccharide (E. coli-LPS), Porphyromonas gingivalis-LPS (Pg-LPS) and peptidoglycan polysaccharide (PG-PS) from Streptococcus pyogenes, were determined by an improved ELISA system for sera from two groups of patients with rheumatoid arthritis (RA), who met rapid radiographic progression (RRP) criteria and non-RRP, and compared to normal (NL) controls. Antibody responses to these bacterial pathogens are unique and consistent in individuals, and no fundamental difference was observed between RA and NL controls. Despite the similar antibody responses to pathogens, lower IgG or higher IgA and consequent higher IgA/IgG antibody ratio among the patients with RA related to disease marker levels and disease activity. Peculiarly, the IgA/IgG anti-Pg-LPS antibody ratio resulted from lower IgG and higher IgA antibody responses to Pg-LPS strongly correlated not only with rheumatoid factor (RF), but also correlated with erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) and disease activity score of 28 joints with ESR (DAS28-ESR) in the RRP group. In contrast, the IgA/IgG anti-E. coli-LPS and anti-PG-PS antibody ratio correlated or tended to correlate with RF, ESR, CRP, and DAS28-ESR in the non-RRP group, whereas either the IgG or IgA anti-Pg-LPS antibody levels and consequent IgA/IgG anti-Pg-LPS antibody ratio did not correlate with any clinical marker levels in this group. Notably, anti-circular-citrullinated peptide (CCP) antibody levels, which did not correlate with either IgG or IgA antibody levels to any pathogens, did not correlate with severity of arthritis in both RRP and non-RRP. Taken together, we propose that multiple environmental pathogens, which overwhelm the host antibody defense function, contribute independently or concomitantly to evoking disease makers and aggravating disease activity, and affect disease outcomes.

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Cellular and Molecular Mechanisms of Autoimmunity and Lupus Nephritis

Autoimmunity involves immune responses directed against self, which are a result of defective self/foreign distinction of the immune system, leading to proliferation of self-reactive lymphocytes, and is characterized by systemic, as well as tissue-specific, inflammation. Numerous mechanisms operate to ensure the immune tolerance to self-antigens. However, monogenetic defects or genetic variants that weaken immune tolerance render susceptibility to the loss of immune tolerance, which is further triggered by environmental factors. In this review, we discuss the phenomenon of immune tolerance, genetic and environmental factors that influence the immune tolerance, factors that induce autoimmunity such as epigenetic and transcription factors, neutrophil extracellular trap formation, extracellular vesicles, ion channels, and lipid mediators, as well as costimulatory or coinhibitory molecules that contribute to an autoimmune response. Further, we discuss the cellular and molecular mechanisms of autoimmune tissue injury and inflammation during systemic lupus erythematosus and lupus nephritis.

Superantigens: The Good, the Bad, and the Ugly

Increasing evidence suggests that superantigens play a role in Immune-mediated diseases. Superantigens are potent activators of CD4* T cells, causing rapid and massive proliferation of cells and cytokine production. This characteristic of superantigens can be exploited in diseases where strong immunologic responses are required, such as in the B16F10 animal model of melanoma. Superantigen administration is able to significantly enhance Ineffective anti-tumor Immune responses, resulting in potent and long-lived protective anti-tumor immunity. However, superantigens are more well-known for the role they play in diseases. Studies using an animal model for neurologic demy-elinatlng diseases such as multiple sclerosis show that superantigens can induce severe relapses and activate auto-reactive T cells not involved in the Initial bout of disease. This may also involve epitope spreading of disease. Superantigens have also been implicated in acute diseases such as food poisoning and TSS, and in chronic diseases such as psoriasis and rheumatoid arthritis. Viral superantigens are also involved in the disease process, including superantigens derived from human Immunodeficiency virus and mouse mammary tumor virus. Finally, immunotherapies that ameliorate the role played by superantigens in disease are discussed.

Bioinformatics evaluation of the possibility of heat shock proteins as autoantigens in multiple sclerosis based on molecular mimicry hypothesis

Molecular mimicry is the explanatory link between the heat shock proteins (HSPs) of infectious agents and triggering multiple sclerosis. Considering that there are many similarities between self- and bacterial-HSPs, the goal was to investigate a panel of 60- and 70kDa HSPs from a variety of bacteria in order to predict the role of each microorganism in triggering or progression of the disease under the molecular mimicry hypothesis. By clarifying the peptides meeting criteria for cross-reactivity and elucidating the role of each microorganism in MS pathogenesis, it would be easier to suggest more effective treatment and preventive strategies for this disease.

Slipping through the Cracks: Linking Low Immune Function and Intestinal Bacterial Imbalance to the Etiology of Rheumatoid Arthritis

Autoimmune diseases (ADs) are considered to be caused by the host immune system which attacks and destroys its own tissue by mistake. A widely accepted hypothesis to explain the pathogenic mechanism of ADs is “molecular mimicry,” which states that antibodies against an infectious agent cross-react with a self-antigen sharing an identical or similar antigenic epitope. However, this hypothesis was most likely established based on misleading antibody assay data largely influenced by intense false positive reactions involved in immunoassay systems. Thus reinvestigation of this hypothesis using an appropriate blocking agent capable of eliminating all types of nonspecific reactions and proper assay design is strongly encouraged. In this review, we discuss the possibility that low immune function may be the fundamental, common defect in ADs, which increases the susceptibility to potential disease causative pathogens located in the gastrointestinal tract (GI), such as bacteria and their components or dietary components. In addition to these exogenous agents, aberrations in the host's physical condition may disrupt the host defense system, which is tightly orchestrated by “immune function,” “mucosal barrier function,” and “intestinal bacterial balance.” These disturbances may initiate a downward spiral, which can lead to chronic health problems that will evolve to an autoimmune disorder.

Virus infection, antiviral immunity, and autoimmunity

As a group of disorders, autoimmunity ranks as the third most prevalent cause of morbidity and mortality in the Western World. However, the etiology of most autoimmune diseases remains unknown. Although genetic linkage studies support a critical underlying role for genetics, the geographic distribution of these disorders as well as the low concordance rates in monozygotic twins suggest that a combination of other factors including environmental ones are involved. Virus infection is a primary factor that has been implicated in the initiation of autoimmune disease. Infection triggers a robust and usually well-coordinated immune response that is critical for viral clearance. However, in some instances, immune regulatory mechanisms may falter, culminating in the breakdown of self-tolerance, resulting in immune-mediated attack directed against both viral and self-antigens. Traditionally, cross-reactive T-cell recognition, known as molecular mimicry, as well as bystander T-cell activation, culminating in epitope spreading, have been the predominant mechanisms elucidated through which infection may culminate in an T-cell-mediated autoimmune response. However, other hypotheses including virus-induced decoy of the immune system also warrant discussion in regard to their potential for triggering autoimmunity. In this review, we discuss the mechanisms by which virus infection and antiviral immunity contribute to the development of autoimmunity.

Microbial Infection and Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a complex autoimmune disease affecting 1–2% of general worldwide population. The etiopathogenesis of RA involves the interplay of multiple genetic risk factors and environmental triggers. Microbial infections are believed to play an important role in the initiation and perpetuation of RA. Recent clinical studies have shown the association of microbial infections with RA. Accumulated studies using animal models have also found that microbial infections can induce and/or exaggerate the symptoms of experimental arthritis. In this review, we have identified the most common microbial infections associated with RA in the literature and summarized the current evidence supporting their pathogenic role in RA. We also discussed the potential mechanisms whereby infection may promote the development of RA, such as generation of neo-autoantigens, induction of loss of tolerance by molecular mimicry, and bystander activation of the immune system.

Infection and autoimmunity: Lessons of animal models

While the key initiating processes that trigger human autoimmune diseases remain enigmatic, increasing evidences support the concept that microbial stimuli are among major environmental factors eliciting autoimmune diseases in genetically susceptible individuals. Here, we present an overview of evidences obtained through various experimental models of autoimmunity for the role of microbial stimuli in disease development. Disease onset and severity have been compared in numerous models under conventional, specific-pathogen-free and germ-free conditions. The results of these experiments suggest that there is no uniform scheme that could describe the role played by infectious agents in the experimental models of autoimmunity. While some models are dependent, others prove to be completely independent of microbial stimuli. In line with the threshold hypothesis of autoimmune diseases, highly relevant genetic factors or microbial stimuli induce autoimmunity on their own, without requiring further factors. Importantly, recent evidences show that colonization of germ-free animals with certain members of the commensal flora [such as segmented filamentous bacteria (SFB)] may lead to autoimmunity. These data drive attention to the importance of the complex composition of gut flora in maintaining immune homeostasis. The intriguing observation obtained in autoimmune animal models that parasites often confer protection against autoimmune disease development may suggest new therapeutic perspectives of infectious agents in autoimmunity.

Mycoplasma antigens as a possible trigger for the induction of antimitochondrial antibodies in primary biliary cirrhosis

BACKGROUND

In primary biliary cirrhosis (PBC), autoreactivity mainly targets members of the pyruvate dehydrogenase complex (PDC). Because PDC subunits are expressed on the surface of mycoplasma and molecular mimicry may be one aetiological factor, we analysed the presence of mammalian and mycoplasma PDC-specific antibodies in PBC patients.

METHODS

Antibodies to porcine PDC and Mycoplasma pneumoniae (mp) antigens mpPDH-C (to be designated mpPDC-E2 chain), mpPDH-B (to be designated mpPDC-E1beta chain), mpCARDS TX and mpP1 were investigated in sera from 43 PBC patients, 19 patients with autoimmune hepatitis and 11 healthy controls by an enzyme-linked immunosorbent assay and Western blotting. To study the rate of acute mycoplasma infection, an adhesin P1-specific polymerase chain reaction (PCR) was performed.

RESULTS

Immune reactivity to the mpPDC-E2 antigen was significantly enhanced in PBC patients (83.7%) as compared with controls (overall frequency of 36.7%), while antibodies to the porcine PDC-E2 chain were found only in PBC patients (88%) excluding a simple cross-reactivity of PDC-related antibodies. This observation was confirmed by inhibition studies demonstrating that porcine PDC did not inhibit mycoplasma PDC-specific antibodies and vice versa. The occurrence of antibodies to mpPDC seems to precede the occurrence of antibodies to porcine PDC. Infection with mycoplasma was equally distributed in the groups as evidenced by an antibody frequency comparable to CARDS TX and P1 and PCR reactivity.

CONCLUSION

Because PBC patients show a significantly enhanced frequency of mpPDC-E2-related antibodies, besides other factors, molecular mimicry between surface molecules of mycoplasma and epitopes of the autoantigen may play a central role in the aetiopathology of PBC.

Antiviral immune responses: triggers of or triggered by autoimmunity?

The predisposition of individuals to several common autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus and multiple sclerosis, is genetically linked to certain human MHC class II molecules and other immune modulators. However, genetic predisposition is only one risk factor for the development of these diseases, and low concordance rates in monozygotic twins, as well as the geographical distribution of disease risk, suggest the involvement of environmental factors in the development of these diseases. Among these environmental factors, infections have been implicated in the onset and/or promotion of autoimmunity. In this Review, we outline the mechanisms by which viral infection can trigger autoimmune disease and describe the pathways by which infection and immune control of infectious disease might be dysregulated during autoimmunity.

Superantigen-presentation by rat major histocompatibility complex class II molecules RT1.Bl and RT1.Dl

Rat major histocompatibility complex (MHC) class II molecules RT1.B(l) (DQ-like) and RT1.D(l) (DR-like) were cloned from the LEW strain using reverse transcription-polymerase chain reaction and expressed in mouse L929 cells. The transduced lines bound MHC class II-specific monoclonal antibodies in an MHC-isotype-specific manner and presented peptide antigens and superantigens to T-cell hybridomas. The T-cell-hybridomas responded well to all superantigens presented by human MHC class II, whereas the response varied considerably with rat MHC class II-transduced lines as presenters. The T-cell hybridomas responded to the pyrogenic superantigens Staphylococcus enterotoxin B (SEB), SEC1, SEC2 and SEC3 only at high concentrations with RT1.B(l)-transduced and RT1.D(l)-transduced cells as presenters. The same was true for streptococcal pyrogenic exotoxin A (SPEA), but this was presented only by RT1.B(l) and not by RT1.D(l). SPEC was recognized only if presented by human MHC class II. Presentation of Yersinia pseudotuberculosis superantigen (YPM) showed no MHC isotype preference, while Mycoplasma arthritidis superantigen (MAS or MAM) was presented by RT1.D(l) but not by RT1.B(l). Interestingly, and in contrast to RT1.B(l), the RT1.D(l) completely failed to present SEA and toxic shock syndrome toxin 1 even after transduction of invariant chain (CD74) or expression in other cell types such as the surface MHC class II-negative mouse B-cell lymphoma (M12.4.1.C3). We discuss the idea that a lack of SEA presentation may not be a general feature of RT1.D molecules but could be a consequence of RT1.D(l)beta-chain allele-specific substitutions (arginine 80 to lysine, asparagine 82 to aspartic acid) in the extremely conserved region flanking the Zn(2+)-binding histidine 81, which is crucial for high-affinity SEA-binding.

Crucial cytokine interactions in nitric oxide production induced by Mycoplasma arthritidis superantigen

Mycoplasma arthritidis causes autoimmune arthritis in rodents. It produces a superantigen (MAM) that simultaneously activates antigen presenting cells and T cells inducing nitric oxide and cytokine release. Nitric oxide is a key inducer and regulator of the immune system activation. Here, we investigated nitric oxide and cytokine production and interactions of these molecules in MAM-stimulated co-cultures of macrophages (J774A.1 cell line) with spleen lymphocytes. We found that: a) MAM-induced nitric oxide, interferon-gamma, membrane-associated tumor necrosis factor and interleukin-2 production in co-cultures of macrophages with lymphocytes from BALB/c and C3H/HePas but not from C57Bl/6 mice; b) production of nitric oxide was dependent on interferon-gamma whereas that of interferon-gamma was dependent on interleukin-2 and membrane-associated tumor necrosis factor; c) these cytokines up regulated MAM-induced nitric oxide production. Unraveling the mechanisms of cell activation induced by MAM might be helpful to design strategies to prevent immune system activation by superantigens and therefore in seeking amelioration of associated immunopathologies.

Association of Mycoplasma arthritidis mitogen with lethal toxicity but not with arthritis in mice

Mycoplasma arthritidis induces an acute to chronic arthritis in rodents. Arthritis induced in mice histologically resembles human rheumatoid arthritis and can be associated with lethal toxicity following systemic injection. The M. arthritidis mitogen (MAM) superantigen has long been implicated as having a role in pathogenesis, but its significance with respect to toxicity and arthritogenicity in mycoplasma-induced disease is unclear. To study the pathogenic significance of MAM, M. arthritidis mutants that overproduced or failed to produce MAM were developed. MAM overproduction and knockout mutants were more and less mitogenic, respectively, than the wild-type strain. The degree of mitogenic activity correlated with lethal toxicity in DBA/2J mice. In contrast, histopathological studies detected no correlation between MAM production and the severity of arthritis induced in DBA/2J and CBA/J mice.

Inflammatory lipoproteins purified from a toxigenic and arthritogenic strain of Mycoplasma arthritidis are dependent on Toll-like receptor 2 and CD14

Mycoplasma arthritidis is a naturally occurring murine pathogen, and the disease model has been used extensively to understand inflammatory mechanisms. Recently, Triton X-114 extracts of a virulent strain of M. arthritidis were found to be more potent in activating macrophages than were those from an avirulent strain, suggesting a role in disease. Here, octyl glucoside extraction of cells was used to identify four distinct bioactive moieties, with molecular masses of approximately 41, 37, 34, and 17 kDa. Their bioactivities were resistant to proteinase K but were destroyed by alkaline hydrolysis and oxidation. As for MALP-2, all were dependent upon Toll-like receptor 2, but unlike MALP-2, they were also dependent upon CD14. The M. arthritidis lipoproteins exhibited infrared absorbances at 2,900 cm(-1) and 1,662 cm(-1), similar to those seen in Pam(3)-Cys-Ser-(Lys)(4). Edman degradation failed to reveal N-terminal sequences, suggesting that they were blocked and therefore might be triacylated. However, mass spectrometry of fragments revealed that the 41-kDa moiety, which binds to serum apolipoprotein A-1, had similarity with the recently described MlpD lipoprotein of M. arthritidis.

Allergic fungal sinusitis

Many common chronic inflammatory rhinosinusitis conditions (hypertrophic sinus disease [HSD]) have the histopathological profile of allergic or asthmatic inflammation. Allergic fungal sinusitis (AFS) is both a type of noninvasive fungal rhinosinusitis and a type of HSD. AFS has clinicopathological features that make it similar, but not identical, to allergic bronchopulmonary aspergillosis (ABPA). Allergic mucin is a defined pathological entity occurring in ABPA, AFS, and in the HSD "eosinophilic mucin rhinosinusitis (EMRS)." Diagnosis of AFS requires a careful review of surgical reports, histopathology, and culture results. Treatment includes surgery and aggressive postoperative medical management of allergic inflammatory disease. Prognosis is good with integrated medical-surgical follow-up, but recurrence remains problematic. The association of ABPA, AFS, and HSD with class II genes of the major histocompatibility complex places the initiation of these inflammatory diseases within the context of antigen presentation and the acquired immune response. Pathological immunomanipulation of this response by local microbial superantigens may be a common mechanism for disease pathogenesis. Future research into the molecular biology of these related conditions may offer insight into the pathogenesis of other chronic inflammatory diseases.

Allergic fungal sinusitis

Many common chronic inflammatory rhinosinusitis conditions (hypertrophic sinus disease [HSD]) have the histopathological profile of allergic or asthmatic inflammation. Allergic fungal sinusitis (AFS) is both a type of noninvasive fungal rhinosinusitis and a type of HSD. AFS has clinicopathological features that make it similar, but not identical, to allergic bronchopulmonary aspergillosis (ABPA). Allergic mucin is a defined pathological entity occurring in ABPA, AFS, and in the HSD "eosinophilic mucin rhinosinusitis (EMRS)." Diagnosis of AFS requires a careful review of surgical reports, histopathology, and culture results. Treatment includes surgery and aggressive postoperative medical management of allergic inflammatory disease. Prognosis is good with integrated medical-surgical follow-up, but recurrence remains problematic. The association of ABPA, AFS, and HSD with class II genes of the major histocompatibility complex places the initiation of these inflammatory diseases within the context of antigen presentation and the acquired immune response. Pathological immunomanipulation of this response by local microbial superantigens may be a common mechanism for disease pathogenesis. Future research into the molecular biology of these related conditions may offer insight into the pathogenesis of other chronic inflammatory diseases.

A single point mutation changes the crystallization behavior of Mycoplasma arthritidis-derived mitogen

Mycoplasma arthritidis-derived mitogen (MAM) functions as a conventional superantigen (SAg). Although recombinant MAM has been crystallized by the hanging-drop vapour-diffusion method, the crystals diffracted poorly to only 5.0 A resolution, with large unit-cell parameters a = 163.8, b = 93.0, c = 210.9 A, beta = 93.7 degrees in the monoclinic space group P2(1). Unit-cell content analysis revealed that as many as 24 molecules could be present in the asymmetric unit. Systematic alanine mutagenesis was applied in order to search for mutants that give crystals of better quality. Two mutants, L50A and K201A, were crystallized under the same conditions as wild-type MAM (MAMwt). Crystals of the L50A mutant are isomorphous with those of MAMwt, while a new crystal form was obtained for the K201 mutant, belonging to the cubic space group P4(1)32 with unit-cell parameters a = b = c = 181.9 A. Diffraction data were collected to 3.6 and 2.8 A resolution from crystals of the MAM L50A and K201A mutants, respectively. Molecular-replacement calculations suggest the presence of two molecules in the asymmetric unit for the MAM K201A mutant crystal, resulting in a VM of 5.0 A Da(-1) and a solvent content of 75%. An interpretable electron-density map for the MAM K201A mutant crystal was produced using the molecular-replacement method.

Bone and joint disease associated with primary immune deficiencies

Primary immune deficiencies (PIDs) are characterized by functional and/or quantitative abnormalities of one or more immune system components. Several bone and joint abnormalities can occur in patients with PID, with arthritis being the most common. Joint manifestations, of which arthritis is the most common, occur chiefly in humoral PIDs (agammaglobulinemia, common variable immunodeficiency, hyper-IgM syndromes, and IgA deficiency) and occasionally in other PIDs (chronic granulomatous disease and Wiskott-Aldrich syndrome). Monoarthritis or oligoarthritis is the usual pattern, although polyarthritis may occur, occasionally with nodules suggesting rheumatoid arthritis. Arthritis in patients with PID is usually infectious in nature, the most common causative organism being Mycoplasma, followed by Staphylococcus, Streptococcus, and Haemophilus. These bacteria can induce not only synovial infections, but also aseptic arthritogenic inflammatory responses. Arthritis having no demonstrable relation to chronic infection has been reported also and ascribed to dysimmunity-driven mechanisms that exhibit a number of specific features. Bone lesions are far less common and usually due to infections complicating humoral PID. Distinctive bone manifestations occur in a number of rare PIDs (e.g., hyper-IgE syndrome and Di George syndrome) and in syndromes characterized by spondyloepiphyseal dysplasia. Familiarity with PID syndromes both enhances the diagnostic capabilities of physicians and provides insight into the pathophysiology of bone and joint abnormalities associated with immune dysfunction. In children and occasionally in adults, a combination of bone and/or joint manifestations and hypogammaglobulinemia may indicate PID. When there is no evidence of lymphoproliferative disease, infection, or iatrogenic complications, investigations for PID should be obtained. PID-related arthritis is a unique model for studying the pathogenesis of presumably postinfectious arthritis and of inflammatory joint diseases including rheumatoid arthritis.

Crystal structures of T cell receptor (beta) chains related to rheumatoid arthritis

The crystal structures of the Vbeta17+ beta chains of two human T cell receptors (TCRs), originally derived from the synovial fluid (SF4) and tissue (C5-1) of a patient with rheumatoid arthritis (RA), have been determined in native (SF4) and mutant (C5-1(F104-->Y/C187-->S)) forms, respectively. These TCR beta chains form homo-dimers in solution and in crystals. Structural comparison reveals that the main-chain conformations in the CDR regions of the C5-1 and SF4 Vbeta17 closely resemble those of a Vbeta17 JM22 in a bound form; however, the CDR3 region shows different conformations among these three Vbeta17 structures. At the side-chain level, conformational differences were observed at the CDR2 regions between our two ligand-free forms and the bound JM22 form. Other significant differences were observed at the Vbeta regions 8-12, 40-44, and 82-88 between C5-1/SF4 and JM22 Vbeta17, implying that there is considerable variability in the structures of very similar beta chains. Structural alignments also reveal a considerable variation in the Vbeta-Cbeta associations, and this may affect ligand recognition. The crystal structures also provide insights into the structure basis of T cell recognition of Mycoplasma arthritidis mitogen (MAM), a superantigen that may be implicated in the development of human RA. Structural comparisons of the Vbeta domains of known TCR structures indicate that there are significant similarities among Vbeta regions that are MAM-reactive, whereas there appear to be significant structural differences among those Vbeta regions that lack MAM-reactivity. It further reveals that CDR2 and framework region (FR) 3 are likely to account for the binding of TCR to MAM.

Relationship between rheumatoid arthritis and Mycoplasma pneumoniae: a case-control study

OBJECTIVE

Rheumatoid arthritis (RA) has a complex and multifactorial aetiology. Infectious agents could start this disease. The majority of the characteristics of this infirmity can be observed in chronic arthritis produced by mycoplasmas in animals. In this study the association between Mycoplasma pneumoniae and RA has been evaluated.

METHODS

A case-control study was performed. Sera taken from 78 RA patients and from 156 controls were analysed to ascertain the levels of immunoglobulin G (IgG) against M. pneumoniae. Other variables, like age, gender, work status, history of pneumonia, etc., were recorded in a questionnaire.

RESULTS

The presence of antibodies against M. pneumoniae was associated with RA (odds ratio=2.34, P<0.001).

CONCLUSIONS

The results suggest that M. pneumoniae could be a cofactor in the pathogenesis of RA; however, more studies need to be done.

Allergic fungal sinusitis

AFS is an increasingly recognized form of HSD, now reported throughout the world. It is probably the most frequently occurring fungal rhinosinusitis disorder. The term fungal sinusitis is no longer appropriate because the five categories of fungal rhinosinusitis can now be differentiated. Each category of fungal rhinosinusitis disorder carries different treatment approaches and prognosis. Diagnostic error can be minimized by adhering to strict diagnostic criteria. The analogy (but not identity) of AFS to ABPA has been supported by histopathology, immunopathology, and the clinical response to OCS treatment. AFS represents a true medical surgical disorder in which both surgery and postoperative medical treatment, if properly coordinated between medical and surgical specialists, leads to the best patient outcomes. Continued advances in the understanding of the immunogenetics and immunopathogenesis of AFS may provide fundamental insights into molecular mechanisms operant in other chronic inflammatory disorders, including other chronic eosinophilic-lymphocytic respiratory mucosal disorders such as common forms of HSD and chronic severe asthma.

Matrix metalloproteinases as targets for the immune system during experimental arthritis

Novel therapies for rheumatoid arthritis aiming at intervention in the inflammatory process by manipulation of autoreactive T and B lymphocytes receive major interest. However, the development of such therapies is largely hampered by the lack of knowledge of self-Ags recognized during the disease process. Recently, we predicted putative T cell self-epitopes based on a computer search profile. In the present study, the predicted self-epitopes were tested for T cell recognition in two experimental arthritis models, and their arthritogenic capacity was analyzed. Fourteen of n = 51 predicted self-epitopes were recognized during experimental arthritis of which six were able to actively induce arthritis. Interestingly, three of these six peptides were derived from matrix metalloproteinases (MMP), and only T cells responsive to MMP-derived epitopes were able to passively transfer arthritis to naive rats. Moreover, we demonstrate the presence of Abs to MMP-3 during the course of adjuvant arthritis. Together these data indicate that MMPs play a pivotal role as target for T and B cells during the development of inflammatory arthritis. This finding sheds new light on the pathophysiological role of MMPs during arthritis and opens novel possibilities for Ag-specific immunotherapy.

Chronic sinusitis: defective T-cells responding to superantigens, treated by reduction of fungi in the nose and air

In this study, the author used endoscopic sinus photography to study the effects of reduction of fungi in the nose, and in environmental air, on the sinus mucosa of 639 patients diagnosed with chronic rhinosinusitis. Sinus mucosal photographs were taken before and after reduction of fungal load in the nose and air, to determine if there was an optimum environmental air fungal load associated with sinus mucosal recovery to normal appearance. Systemic symptoms associated with fungal exposure, which resolved when fungus was removed from the patient and the environmental air and reappeared with recurrent environmental fungal exposure, are also discussed and are termed systemic fungal symptoms. Interventions consisted of nasal fungal load reduction with normal saline nasal irrigations and antimicrobial nasal sprays, and environmental air fungal load reduction with high-efficiency particulate air (HEPA) filtration in combination with ionizers or evaporation of a solution of botanical extract. Main outcome measures were obtained with environmental air 1-hr gravity-plate fungal colony counts, laser air particle counts, and endoscopic sinus photography. Blood levels of immunoglobulins IgG and IgE for 7 common molds were also determined. After intervention, 94% of patients who used antimicrobial nasal sprays and who reduced their environmental fungal air count to 0-4 colonies per 1-hr agar gravity-plate exposure (n = 365) exhibited normal sinus mucosa by endoscopic exam. Environmental air fungal counts that exceeded 4 colonies resulted in sinus mucosal abnormalities ranging from edema, to pus and/or nasal polyps at higher counts. Neutralization of allergy, and/or surgery, were used as appropriate following implementation of environmental measures. On the basis of these observations, as well as detailed clinical experience and a review of the current literature, the author hypothesizes that the pathogenesis of chronic rhinosinusitis, allergic fungal sinusitis, and systemic fungal symptoms is a genetic defect at the variable beta chain helper T-cell receptor (TCR Vbeta) site which requires the presence of an antigen (fungus). Chronic sinusitis patients who have recurring exposure to environmental air that contains fungal concentrations in excess of 4 colonies per 1-hr agar plate exposure appear to have an increased risk of persistent chronic sinusitis and/or systemic symptoms, regardless of the medical treatment provided.

Interplay Between Superantigens and Immunoreceptors

Superantigens (SAGs) cause a massive T-cell proliferation by simultaneously binding to major histocompatibility complex (MHC) class II on antigen-presenting cells and T-cell receptors (TCRs) on T cells. These T-cell mitogens can cause disease in host, such as food poisoning or toxic shock. The best characterized groups of SAGs are the bacterial SAGs secreted by Staphylococcus aureus and Streptococcus pyogenes. Despite a common overall three-dimensional fold of these SAGs, they have been shown to bind to MHC class II in different ways. Recently, it has also been shown that SAGs have individual preferences in their binding to the TCRs. They can interact with various regions of the variable beta-chain of TCRs and at least one SAG seems to bind to the alpha-chain of TCRs. In this review, different subclasses of SAGs are classified based upon their binding mode to MHC class II, and models of trimolecular complexes of MHC-SAG-TCR molecules are described in order to reveal and understand the complexity of SAG-mediated T-cell activation.

Crystallization and preliminary crystallographic analysis of Mycoplasma arthritidis-derived mitogen complexed with peptide/MHC class II antigen

Mycoplasma arthritidis-derived mitogen (MAM), a bacterial superantigen, has been crystallized in complex with its human receptor, major histocompatibility complex (MHC) class II antigen, by the hanging-drop vapor-diffusion method. Crystals were obtained under three conditions, with ammonium sulfate, phosphate salt and PEG 8000 as the precipitant. The crystals grown under these conditions all belong to space group I222, with the same unit-cell parameters: a = 137.4, b = 178.2, c = 179.6 A. Diffraction data were collected to 3.3 and 3.4 A resolution from crystals of native and selenomethionylated MAM-MHC complexes, respectively. Self- and cross-rotation function calculations suggest the presence of two complex molecules in the asymmetric unit, resulting in a V(M) of 4.0 and a solvent content of 69%. An interpretable electron-density map was produced using a combination of molecular replacement and SAD phasing.

Three-dimensional structural location and molecular functional effects of missense SNPs in the T cell receptor V? domain

The mechanisms by which human single nucleotide polymorphisms (SNPs) influence susceptibility to disease are not yet well understood. In a previous study, we developed a structure-based model that may be used to identify which missense SNPs are neutral and which are deleterious to protein function and so potentially involved in disease (Wang and Moult, Hum Mutat 2001;263-270). The model has now been applied to a set of 54 missense cSNPs in the 46 functional T-cell receptor Vbeta-genes. Most of these missense cSNPs are found to be neutral, but 10 are identified as likely deleterious to protein function. Only one was previously associated with disease. We suggest that the others may be disease related but that redundancy in the T-cell response prevents any simple, monogenic effect. Therefore, these SNPs are the most likely contributors to complex, polygenic disease traits. It has been noted that there is a surprisingly high (74%) fraction of nonsynonymous SNPs in these genes. Contrary to expectation, the analysis shows that these are not associated with an unusually high fraction of deleterious SNPs, nor do they significantly contribute to a larger range of antigen recognition or a reduced superantigen-binding repertoire.

Mycoplasma arthritidis superantigen (MAM)-induced macrophage nitric oxide release is MHC class II restricted, interferongamma dependent, and toll-like receptor 4 independent

Mycoplasma arthritidis causes arthritis in rodents that resembles human rheumatoid arthritis. It produces a superantigen (MAM) that stimulates production of cytokines by making a bridge between lymphocyte T-cell receptor with the appropriate Vbeta chain, and H-2 1-Ealpha MHC class II molecules. Here we studied MAM-induced nitric oxide (NO) production in mouse peritoneal macrophages and found that it was: (1) time and concentration dependent, (2) possibly derived from inducible NOS synthase since it was reduced significantly by amino guanidine pretreatment, (3) restricted to H-2(K) (C3H/HePas and C3H/HeJ) and H-2(d) strains (BALB/c), (4) independent of TLR4 signaling since the coisogenic strains C3H/HePas and C3H/HeJ (TLR4 deficient) produced similar levels of NO following MAM stimulation, (5) potentiated by lipopolysaccharide, and (6) dependent on the presence of nonadherent peritoneal cells. Neutralization of interferon-gamma (IFNgamma in the peritoneal cell cultures with monoclonal antibodies abolished MAM-induced NO production. Addition of rIFNgamma to the adherent cells substituted the nonadherent cells for MAM-induced NO production. A macrophage cell line, J774A.1 (H-2(d)), also produced NO upon MAM stimulation but only when BALB/c spleen lymphocytes were added. Thus, in murine macrophages, MAM induces NO production that is dependent on signaling through MHC class II molecules and IFNgamma but independent of TLR4 expression.

Therapeutic approaches to superantigen-based diseases: a review

Superantigens secreted by the bacterial pathogen Staphyloccocus aureus are extremely potent toxins that overstimulate the host immune system by binding to the MHC class II and T cell receptors and activating a large population of T cells. Superantigen infection has been shown to be the causative agents in acute diseases, food poisoning and toxic shock syndrome, and in more chronic conditions such as inflammatory skin diseases. In addition to the toll on public health, S. aureus superantigens also represent a potential biothreat to our national security. To address these risks, a number of different therapeutic strategies have been developed that target different aspects of the pathogenic mechanism of S. aureus and superantigen infection. These therapies, which encompass strategies as diverse as production of neutralizing antibodies, inhibitory peptide/receptor design and blockage of superantigen gene transcription, are being tested for treatment of established S. aureus infections in pre- and post-exposure scenarios. In this review, we will describe these different strategies and their efficacies in inhibition of superantigen-induced effects in the host, and present the future outlook for successfully producing therapies for superantigen-based disease.

Analysis of heat shock protein 60 encoding genes of mycoplasmas and investigations concerning their role in immunity and infection

Only little is known about the heat shock proteins (Hsp) and Hsp-encoding genes of mycoplasmas. The aim of this study was to identify and sequence the hsp60 gene of Mycoplasma agalactiae, Mycoplasma arthritidis, Mycoplasma bovis, and Mycoplasma hyopneumoniae, and to investigate the immune response to Hsp60. Fragments of the hsp60 genes of M. agalactiae, M. arthritidis, M. bovis and M. hyopneumoniae representing almost the entire coding region were amplified by PCR. Two fragments of a hsp60 gene were cloned in Escherichia coli and the antibody response of pigs infected with M. hyopneumoniae against the recombinant Hsp60 fusion proteins was analysed. Within the mycoplasmas, the hsp60 genes showed sequence identities of nearly 100%, with the exception of the hsp60 gene of Mycoplasma genitalium, which was determined to be only 76.5-77.7% identical. Identities to Clostridium perfringens, Bacillus subtilis and E. coli were determined between approximately 50 and 60%. The predicted amino acid sequences of Hsp60 showed an identity of 90 to nearly 100% among mycoplasmas and 50-60% to the other bacteria indicated above. Two Hsp60 derived glutathione-S-transferase fusion proteins containing mycoplasma peptides of 28 and 35kDa were isolated. M. hyopneumoniae-ELISA positive porcine convalescent sera reacted strongly with the recombinant Hsp60 fusion proteins in Western immunoblotting indicating for the first time that mycoplasmal Hsp60 is immunogenic in natural infection.

Involvement of zinc in the binding of Mycoplasma arthritidis-derived mitogen to the proximity of the HLA-DR binding groove regardless of histidine 81 of the beta chain

Although our recent studies have provided the first evidence demonstrating the direct binding of Mycoplasma arthritidis-derived mitogen (MAM) to MHC class II molecules, it is not yet established how MAM interacts with these molecules. Herein, we demonstrate that MAM binds preferentially and with high affinity to HLA-DR molecules in a zinc-dependent manner. MAM's affinity (25 nM) for HLA-DR molecules is comparable to that of staphylococcal superantigens, and is slightly higher than that for murine MHC class II molecules expressed on the A20 B cell line (111 nM). The amino acid residues located between 14 - 31 and 76 - 90 of the MAM N-terminus play a critical role in MAM / HLA-DR interactions. Histidine at position 81 of the HLA-DR beta-chain, known to be critical for binding of zinc-coordinated superantigens, is not necessary for MAM / HLA-DR interactions. The HLA-DR residues involved in MAM binding are located in the proximal binding groove of the HLA-DR molecule, where the nature of the peptide of the binding groove plays an important role in MAM / HLA-DR interaction. This is the first detailed characterization of MAM's interactions with MHC class II molecules showing a mode of interaction with HLA-DR distinct from that of other superantigens.

A superantigen hypothesis for the pathogenesis of chronic hypertrophic rhinosinusitis, allergic fungal sinusitis, and related disorders

BACKGROUND

Chronic eosinophilic-lymphocytic respiratory mucosal inflammatory disorders include hypertrophic sinus disease, allergic fungal sinusitis, allergic bronchopulmonary aspergillosis, and chronic severe asthma. They have many analogous or shared aspects of pathology at molecular, cellular, and clinical levels of analysis.

OBJECTIVE

To propose a theory, and supporting data through comprehensive literature review, that unifies these diseases' pathogenesis. METHODS AND DATA SOURCES: Current medical literature was used as supportive background information. Reinterpretation of existing studies and reasoned speculation were used when necessary and identified where used. English language MEDLINE articles that referenced sinusitis, rhinosinusitis, allergic fungal sinusitis, asthma, allergic bronchopulmonary aspergillosis, nasal polyp, superantigen, and T cell receptor from 1983 to present were potentially used as background or supportive information. Additional referenced articles, published abstracts, and National Center for Biotechnology Information Entrez protein database searches were used. Case reports, studies, review articles, and textbooks were included.

RESULTS

Multiple lines of evidence support the proposed hypothesis that microbial T cell superantigen production, persistence, and host-responsiveness are the fundamental components that unify the pathogenesis of all common chronic eosinophilic-lymphocytic respiratory mucosal inflammatory disorders. Superantigen amplification of preexisting immunopathology is the proposed mechanism for disease induction and maintenance. Preexisting immunopathology is created in the individual by a potential heterogeneity of immunopathologic signals that can include type I immediate hypersensitivity, other antigen-specific immune responses, cytokine dysregulation, eicosanoid dysregulation, various genetic mutations, and other molecular pathology. Although the ability to develop chronic severe inflammatory disease is dependent upon this immunopathology, host T cell receptor V beta genetics and persistent superantigen production/exposure at the respiratory mucosa by relevant superantigen-producing extra- or intracellular microbes are postulated to be required. This mechanism for disease pathogenesis may also apply to other disorders. Approaches to prove this theory and its predictions are presented.

CONCLUSIONS

The pathogenesis of all the disorders discussed can be unified through the superantigen hypothesis proposed. Multiple lines of evidence support this hypothesis. How we view these common conditions will change, and new research into pathogenesis and treatment will occur if this proves true.

Environmental modulation of autoimmune arthritis involves the spontaneous microbial induction of T cell responses to regulatory determinants within heat shock protein 65

Both genetic and environmental factors are believed to be involved in the induction of autoimmune diseases. Adjuvant arthritis (AA) is inducible in susceptible rat strains by injection of Mycobacterium tuberculosis, and arthritic rats raise T cell responses to the 65-kDa mycobacterial heat-shock protein (Bhsp65). We observed that Fischer 344 (F344) rats raised in a barrier facility (BF-F344) are susceptible to AA, whereas F344 rats maintained in a conventional facility (CV-F344) show significantly reduced incidence and severity of AA, despite responding well to the arthritogenic determinant within Bhsp65. The acquisition of protection from AA can be circumvented if rats are maintained on neomycin/acidified water. Strikingly, naive unimmunized CV-F344 rats but not BF-F344 rats raised T cell responses to Bhsp65 C-terminal determinants (BCTD) (we have previously shown that BCTD are involved in regulation of acute AA in the Lewis rat); however, T cells of naive CV-F344 and BF-F344 gave a comparable level of proliferative response to a mitogen, but no response at all to an irrelevant Ag. Furthermore, adoptive transfer into naive BF-F344 rats of splenic cells of naive CV-F344 rats (restimulated with BCTD in vitro) before induction of AA resulted in a considerably reduced severity of AA. These results suggest that spontaneous (inadvertent) priming of BCTD-reactive T cells, owing to determinant mimicry between Bhsp65 and its homologues in microbial agents in the conventional environment, is involved in modulating the severity of AA in CV-F344 rats. These results have important implications in broadening understanding of the host-microbe interaction in human autoimmune diseases.

Parasite-mediated down-regulation of collagen-induced arthritis (CIA) in DA rats

Microbial infection can impact on the course of autoimmune disease, both in disease-inducing and disease-protecting capacities. Here we investigated if infection with Trypanosoma brucei brucei (Tbb), the protozoan causative agent of African Sleeping Sickness, could ameliorate the course of CIA in the Dark Agouti rat, an experimental model which shares many features with human rheumatoid arthritis. Infection of animals with living, but not inoculation with dead Tbb resulted in complete or significant reduction of clinical arthritic symptoms. Infection prior to collagen immunization was more effective than a later treatment, and this effect was related to the level of parasitaemia. Using reverse transcriptase-polymerase chain reaction we detected an increase in interferon-gamma mRNA in the draining lymph nodes of Tbb-treated animals relative to controls at day 28 after disease induction. Transforming growth factor-beta could be detected in the lymph nodes in four out of six animals that had received Tbb. In the joints, immunohistochemistry revealed reduced production of tumour necrosis factor-alpha in Tbb-treated animals relative to controls. The most striking difference between Tbb-infected and control groups, as measured by ELISA, was the down-regulation of anti-collagen II IgG antibody responses in parasite-infected animals. We conclude that live parasites can exert an immunomodulatory and protective effect in CIA in which several mechanisms may work in parallel, although the almost complete down-regulation of the anti-collagen antibody response may alone explain the protective effect in CIA. The described model may be useful in further attempts to use the mechanisms involved in parasite immune defence to prevent and treat certain autoimmune conditions.

Unmethylated oligo-DNA containing CpG motifs aggravates collagen-induced arthritis in mice

OBJECTIVE

To investigate the effects of an intradermal injection of an unmethylated oligodeoxynucleotide (ODN) containing CpG motifs on the severity of collagen-induced arthritis (CIA).

METHODS

CIA was induced in DBA/1 LacJ mice by immunization with bovine type II collagen (CII) in Freund's complete adjuvant followed 3 weeks later by immunization with CII in Freund's incomplete adjuvant (yielding CIA mice). Unmethylated ODN containing a CpG motif was injected intradermally into DBA/1 LacJ mice at a dosage of 20 microg (yielding CpG-CIA mice) 1 week prior to the first immunization with CII. Unmethylated ODN containing a GpC motif instead of a CpG motif and ODN containing a methylated CpG motif were used to produce controls (GpC-CIA mice and mCpG-CIA mice, respectively). After the second immunization with CII, arthritis scores were measured weekly up to the eighth week. At the eighth week, the mice were killed, histopathologic changes in the ankle joints were examined, and titers of interferon-gamma (IFNgamma) in the supernatants of splenocytes (1 x 10(7)) stimulated in culture by CII for 3 days were determined by enzyme-linked immunosorbent assay.

RESULTS

CpG-CIA mice had significantly higher arthritis scores than CIA mice. CpG-CIA mice had more severe histopathologic changes than CIA mice and mCpG-CIA mice. Moreover, splenocytes in CpG-CIA mice produced higher IFNgamma titers in response to CII than did splenocytes in CIA mice and mCpG-CIA mice.

CONCLUSION

Injection of unmethylated oligo-DNA containing CpG motifs aggravated CIA through activation of the Th1-type immune response, suggesting that microbial infection could be one of the mechanisms for aggravation or exacerbation of arthritis or, alternatively, that such infection could be an adjuvant in the induction of arthritis in rheumatoid arthritis.