Severity Of Arthritis In Mice Research Articles

A Matrix Metalloproteinase 1–Cleavable Composite Peptide Derived From Transforming Growth Factor β–Inducible Gene h3 Potently Inhibits Collagen‐Induced Arthritis

Transforming growth factor β-inducible gene h3 (βIG-H3), which is abundantly expressed in rheumatoid synovium, and matrix metalloproteinases (MMP) play important roles in the pathogenesis of rheumatoid arthritis (RA). The aim of this study was to determine the therapeutic efficacy of βIG-H3-derived peptides using MMP-1-dependent target tissue delivery in chronic inflammatory arthritis. Peptides developed from βIG-H3 derivatives, including the second and fourth YH peptides, the fourth fas-1 domain, the fourth fas-1 domain truncated for H1 and H2 sequences (dhfas-1), and an MMP-1- cleavable composite peptide (MFK24), were cloned. We confirmed the specificity of MFK24 cleavage by immunoblot analysis after treatment with different proteases. The YH18 peptide in the fourth fas-1 domain of βIG-H3 was weakly effective in suppressing arthritis severity in mice with collagen-induced arthritis (CIA). Treatment with higher-dose dhfas-1 (30 mg/kg) showed remarkable efficacy, whereas treatment with a lower dose (10 mg/kg) resulted in only partial improvement. MFK24, a composite peptide consisting of dhfas-1 and RGD peptide linked by MMP-1 substrate, was cleaved specifically by MMP-1. The adhesion and migration of NIH3T3 cells mediated by βIG-H3 were inhibited by MFK24 at a low concentration. MFK24 suppressed the adhesion of NIH3T3 cells more efficiently compared with murine dhfas-1 (MFK00) or RGD, either alone or in combination. The therapeutic efficacy of MFK24 in mice with CIA was remarkably enhanced, with consistently reduced expression of inflammatory mediators within joint tissue. This proof-of-concept study showed that an MMP-cleavable composite peptide, based on βIG-H3 derivatives, had markedly improved therapeutic efficacy in chronic inflammatory arthritis, implicating a new expandable strategy for enhancement of the efficacy of 2 different active molecules in RA.

Polymerized-Type I Collagen Induces Upregulation of Foxp3-Expressing CD4 Regulatory T Cells and Downregulation of IL-17-Producing CD4+T Cells (Th17) Cells in Collagen-Induced Arthritis

Previous studies showed that polymerized-type I collagen (polymerized collagen) exhibits potent immunoregulatory properties. This work evaluated the effect of intramuscular administration of polymerized collagen in early and established collagen-induced arthritis (CIA) in mice and analyzed changes in Th subsets following therapy. Incidence of CIA was of 100% in mice challenged with type II collagen. Clinimorphometric analysis showed a downregulation of inflammation after administration of all treatments (P < 0.05). Histological analysis showed that the CIA-mice group had extensive bone erosion, pannus and severe focal inflammatory infiltrates. In contrast, there was a remarkable reduction in the severity of arthritis in mice under polymerized collagen, methotrexate or methotrexate/polymerized collagen treatment. Polymerized Collagen but not methotrexate induced tissue joint regeneration. Polymerized Collagen and methotrexate/polymerized collagen but not methotrexate alone induces downregulation of CD4+/IL17A+ T cells and upregulation of Tregs and CD4+/IFN-γ + T cells. Thus, Polymerized Collagen could be an effective therapeutic agent in early and established rheumatoid arthritis by exerting downregulation of autoimmune inflammation.

Rabeximod reduces arthritis severity in mice by decreasing activation of inflammatory cells

ObjectivesThe novel small molecule 9-chloro-2,3-dimethyl-6-(N,N-dimethylaminoethylamino-2-oxoethyl)-6H-indolo[2,3-b] quinoxaline (Rabeximod) reduces severity of arthritis in rodent models of rheumatoid arthritis (RA) and multiple sclerosis (MS). This study aimed to investigate the cellular target...

Enhanced Th1 and Th17 responses and arthritis severity in mice with a deficiency of myeloid cell–specific interleukin‐1 receptor antagonist

The balance between interleukin-1 (IL-1) and its specific inhibitor, the IL-1 receptor antagonist (IL-1Ra), plays a major role in the development of arthritis. The purpose of this study was to investigate the role of IL-1Ra produced specifically by myeloid cells in the control of collagen-induced arthritis (CIA) by using myeloid cell-specific IL-1Ra-deficient mice (IL-1Ra(DeltaM)). IL-1Ra(DeltaM) mice were generated by using the loxP/Cre recombinase system. CIA was induced in IL-1Ra(DeltaM) mice and littermate control mice by a single immunization with bovine type II collagen (CII) in Freund's complete adjuvant. Arthritis severity was assessed by clinical and histologic scoring. Draining lymph node (DLN) cell responses were examined ex vivo, and ankle extracts were used in the quantification of cytokines and chemokines. Clinical and histopathologic evaluations revealed an early disease onset and a severe form of CIA in IL-1Ra(DeltaM) mice. This was characterized by increased production of interferon-gamma (IFNgamma) and IL-17 by CII-stimulated DLN cells. We also observed that the CII-specific CD4+ T cell response shifted in vivo, from a dominant Th1 response early in the course of the arthritis to the presence of both Th1 and Th17 cytokines later in the disease course. Interestingly, IL-1Ra levels were higher in the arthritic joints of IL-1Ra(DeltaM) mice as compared with the controls, indicating that nonmyeloid cells strongly contribute to the local production of IL-1Ra. However, this enhanced IL-1Ra production was not sufficient to limit joint inflammation and tissue damage. Our results suggest that myeloid cell-derived IL-1Ra plays a critical role in the control of the development and the severity of CIA by modulating Th1 and Th17 responses in lymphoid organs.

Therapeutic effects of antibodies to tumor necrosis factor-α, interleukin-6 and cytotoxic T-lymphocyte antigen 4 immunoglobulin in mice with glucose-6-phosphate isomerase induced arthritis

IntroductionImmunization with glucose-6-phosphate isomerase (GPI) induces severe arthritis in DBA/1 mice. The present study was designed to identify the cytokines and co-stimulatory molecules involved in the development of GPI-induced arthritis.MethodsArthritis was induced in DBA/1 mice with 300 μg human recombinant GPI. CD4+ T cells and antigen-presenting cells from splenocytes of arthritic mice were cultured in the presence of GPI. Tumor necrosis factor (TNF)-α, IFN-γ, IL-2, IL-4, IL-5, IL-6, IL-10, and IL-12 levels were assessed using cytometric bead array. Monoclonal antibodies to TNF-α, IFN-γ, IL-12, CD40L, inducible co-stimulator (ICOS), and cytotoxic T-lymphocyte antigen 4 immunoglobulin (CTLA-4Ig) were used to block TNF-α and IFN-γ production, examine clinical index in mice with GPI-induced arthritis, and determine anti-GPI antibody production.ResultsLarge amounts of TNF-α and IFN-γ and small amounts of IL-2 and IL-6 were produced by splenocytes from mice with GPI-induced arthritis. Anti-TNF-α mAbs and CTLA-4Ig suppressed TNF-α production, whereas anti-IFN-γ mAbs, anti-IL-12 mAbs, and CTLA-4 Ig inhibited IFN-γ production. A single injection of anti-TNF-α and anti-IL-6 mAbs and two injections of CTLA-4Ig reduced the severity of arthritis in mice, whereas injections of anti-IFN-γ and anti-IL-12 mAbs tended to exacerbate arthritis. Therapeutic efficacy tended to correlate with reduction in anti-GPI antibodies.ConclusionTNF-α and IL-6 play an important role in GPI-induced arthritis, whereas IFN-γ appears to function as a regulator of arthritis. Because the therapeutic effects of the tested molecules used in this study are similar to those in patients with rheumatoid arthritis, GPI-induced arthritis appears to be a suitable tool with which to examine the effect of various therapies on rheumatoid arthritis.

Adiponectin mitigates the severity of arthritis in mice with collagen‐induced arthritis

Objective: Adiponectin (AD) is considered an inflammation modulator. In this study, we investigated the effect of AD on rheumatoid arthritis (RA) using a collagen‐induced arthritis (CIA) mouse model and RA synovial fibroblasts (RASF).Methods: Fifteen DBA/1 mice were divided into three groups. All mice, except the control group, were injected with type II collagen. AD was intra‐articularly injected in the left hind legs after arthritis development (the AD‐treated group). The severity of the arthritis was measured using an arthritis score and paw thickness. A histopathological assessment of joint sections was performed by haematoxylin/eosin (H&E) staining. Tumour necrosis factor (TNF)‐α, interleukin (IL)‐1β, IL‐6, and matrix metalloproteinase (MMP)‐3 expression was evaluated by immunohistochemical staining in the CIA mice. Synovial tissue was obtained from four RA patients during total joint replacement. RASF cultures were established from this tissue. RASF were pretreated with AD and stimulated by TNFα or IL‐1β. TNFα, IL‐1β, IL‐6, and MMP‐3 production was measured by enzyme‐linked immunosorbent assay (ELISA) and reverse transcription polymerase chain reaction (RT‐PCR). RASF proliferation was evaluated using the MTT assay.Results: AD significantly mitigated the severity of the arthritis and histopathological findings indicative of RA in CIA mice. TNFα, IL‐1β, and MMP‐3 expression decreased, but IL‐6 expression in AD‐treated joint tissues increased. Moreover, AD reduced TNFα, IL‐1β, and MMP‐3 expression in stimulated RASF and increased IL‐6 expression in IL‐1β‐stimulated RASF. AD significantly inhibited IL‐1β‐induced RASF proliferation, despite increased IL‐6 expression.Conclusion: These data suggest that AD may play an anti‐inflammatory role in the pathophysiology of RA.

Arthritis suppression by NADPH activation operates through an interferon-β pathway

BackgroundA polymorphism in the activating component of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex, neutrophil cytosolic factor 1 (NCF1), has previously been identified as a regulator of arthritis severity in mice and rats. This discovery resulted in a search for NADPH oxidase-activating substances as a potential new approach to treat autoimmune disorders such as rheumatoid arthritis (RA). We have recently shown that compounds inducing NCF1-dependent oxidative burst, e.g. phytol, have a strong ameliorating effect on arthritis in rats. However, the underlying molecular mechanism is still not clearly understood. The aim of this study was to use gene-expression profiling to understand the protective effect against arthritis of activation of NADPH oxidase in the immune system.ResultsSubcutaneous administration of phytol leads to an accumulation of the compound in the inguinal lymph nodes, with peak levels being reached approximately 10 days after administration. Hence, global gene-expression profiling on inguinal lymph nodes was performed 10 days after the induction of pristane-induced arthritis (PIA) and phytol administration. The differentially expressed genes could be divided into two pathways, consisting of genes regulated by different interferons. IFN-γ regulated the pathway associated with arthritis development, whereas IFN-β regulated the pathway associated with disease protection through phytol. Importantly, these two molecular pathways were also confirmed to differentiate between the arthritis-susceptible dark agouti (DA) rat, (with an Ncf-1DA allele that allows only low oxidative burst), and the arthritis-protected DA.Ncf-1E3 rat (with an Ncf1E3 allele that allows a stronger oxidative burst).ConclusionNaturally occurring genetic polymorphisms in the Ncf-1 gene modulate the activity of the NADPH oxidase complex, which strongly regulates the severity of arthritis. We now show that the Ncf-1 allele that enhances oxidative burst and protects against arthritis is operating through an IFN-β-associated pathway, whereas the arthritis-driving allele operates through an IFN-γ-associated pathway. Treatment of arthritis-susceptible rats with an NADPH oxidase-activating substance, phytol, protects against arthritis. Interestingly, the treatment led to a restoration of the oxidative-burst effect and induction of a strikingly similar IFN-β-dependent pathway, as seen with the disease-protective Ncf1 polymorphism.

Part II: Beneficial Effects of the Peroxynitrite Decomposition Catalyst FP15 in Murine Models of Arthritis and Colitis

Peroxynitrite is a reactive oxidant species produced from nitric oxide and superoxide, which has been indirectly implicated in the pathogenesis of many inflammatory conditions including arthritis and colitis. Here, using a novel peroxynitrite decomposition catalyst, FP15, we directly investigate the role of peroxynitrite in the pathogenesis of arthritis and colitis in rodent models. Arthritis was induced in mice by intradermal collagen injection; incidence and severity of arthritis was monitored using a macroscopic scoring system. At the end of the experiment paws were taken for determination of neutrophil infiltration (myeloperoxidase [MPO] activity), oxidative stress (malondialdehyde [MDA] level), and cytokine/chemokine levels. Colitis was induced in mice by 5% dextran sodium sulfate (DSS) in their drinking water. Colitis symptoms were assessed 10 days later, the parameters determined included body weight, rectal bleeding, colon length, colonic MPO and MDA levels, and colon histologic damage. Treatment with FP15 significantly reduced the inflammation and oxidative stress in arthritis and colitis. FP15 reduced both the incidence and severity of arthritis in mice and this was associated with reduced paw MPO and MDA levels. Similarly, in colitis, FP15 reduced colon damage, and this was associated with reduced colon neutrophil infiltration and oxidative stress. The protective effect of FP15 suggests that peroxynitrite plays a significant pathogenetic role in arthritis and colitis in the currently employed rodent models. Further work is needed to determine whether neutralization of peroxynitrite also represents a promising strategy to treat human inflammatory diseases such as arthritis and colitis.

Addition of an IL-15 mutant/FCγ2A antagonist protein protects islet allografts from rejection overriding costimulation blockade

IL-15, a powerful chemoattractant and growth factor for antigen-activated T cells and NK cells, contributes to lymphocyte homeostasis and selectively induces the activation and proliferation of memory CD8+ T cells.1,2 Analysis of the phenotype of IL-15−/− mice3 and IL-15Rα−/− mice4 demonstrate that IL-15 is a critical factor for innate and adaptive immune responses. IL-15 is produced by the monocyte/macrophage lineage, by epithelial and endothelial cells but not by T-cells. The IL-15 receptor (IL-15R) expressed upon T cells is composed of three chains. Two are constitutively expressed and shared with the IL-2 receptor (IL-2R), the IL-2Rβ and IL-2Rγc chains, and a unique IL-15Rα chain is expressed upon activation of, but not during resting of mononuclear leukocytes.5,6 Because IL-15 and IL-2 share two receptor signaling components (IL-2/IL-15Rβγc), they display similar biological properties in vitro. Nevertheless, there are differential patterns of IL-15/IL-15Rα expression and in vivo studies have revealed major nonredundant roles for these two T-cell growth factors (TCGFs). In organ transplantation, T cells play a critical role in initiating the immune response leading ultimately to the effector mechanisms mediating allograft rejection. An analysis of biopsies taken from rejecting human renal allografts has revealed that intragraft gene expression of IL-15 is a far more consistent marker of rejection than IL-2 gene expression.7 Moreover, IL-2 expression is not a prerequisite for allograft rejection as IL-2 knockout (KO) mice promptly reject islet and cardiac allografts.7,8 Immunohistology in the IL-2 KO recipients reveals infiltration of rejecting grafts by CD4 and CD8 T cells as well as robust intragraft expression of the IL-4, IL-7, and IL-15 as well as granzyme B genes.8 Since costimulation blockade drastically decreases post-transplant expression of IL-2,9 the clonal proliferation of alloreactive T cells in hosts treated with costimulation blockade may be explained by the action of a non-T-cell-derived cytokine, such as IL-15. Although costimulatory blockade of CD28/CTLA4/B7 or CD40/CD40L interactions reduces immune activation and provides a powerful inhibition of alloimmune responses in both rodents and primates,9–11 in some circumstances it failed to induce permanent engraftment. Several reports suggest that CD8+ T cells are responsible for costimulation blockade-resistant rejection in various models, such as intestinal and skin allograft models.12,13 For example, adjunctive treatment with anti-CD8 mAb or other agents to deplete CD8+ T cells, are required to induce tolerance in these models.14 The resistance of CD8+ T cells to costimulation blockade may be explained by a poor effect of CTLA4Ig and αCD154 Abs to regulate activation and proliferation of CD8+ compared to CD4+ T cells.14,15 Recently, Smith et al16 have reported the prolonged survival of heart allografts in a treatment protocol consisting of soluble IL-15 receptor- α chain proteins and nondepleting anti-CD4 mAb. Thus the expression of IL-15 may be linked to CD8-dependent costimulation-resistant rejection. As costimulation blockade resistant rejection is mediated by CD8+ T cells and as IL-15 is essential for the activation and proliferation of CD8+ T cells, we hypothesized that targeting the IL-15/IL-15R system in conjunction with costimulation blockade would provide a new perspective for inducing allograft tolerance. The development of agents targeting the receptor and signaling elements of IL-15 may provide new perspectives for treatment of diseases associated with the IL-15/IL-15R pathway. The idea of creating an IL-15 antagonist was based on the homology of glutamine residues within the C-terminus of the four helix structures shared by IL-2 and IL-15, and on the report that a C-terminal glutamine in IL-2 is crucial for IL-2 binding to IL-2Rγ chain.17 In our laboratory a novel IL-15 mutant/Fcγ2a protein was genetically constructed, linked to murine Fcγ2a and expressed in mammalian cells. The IL-15 mutant was constructed by replacing the codons for the C-terminal glutamine amino acid residues with codons for aspartic acid (ie, Q101 and Q108).18 The mutant IL-15 moiety is a high-affinity IL-15R site-specific antagonist. The Fc portion of this fusion protein confers longevity and is designed to support cytocidal activities against IL-15R α+ cells insofar as the Fc-related sequences of mouse IgG2a isotype that support complement activation and activation of FcR+ phagocytes are present.18 Moreover, this IL-15 mutant/Fcγ2a protein competitively inhibits IL-15-triggered cell proliferation and does not activate the STAT-signaling pathway. Because the receptor site-specific antagonist IL-15 mutant/Fcγ2a protein had a prolonged half-life in vivo and the potential for destruction of IL-15R + leukocytes, the immunosuppressive effects of this agent were examined in mice with induced delayed-type hypersensitivity (DTH) and collagen-induced arthritis (CIA), a murine model for RA. In the DTH model, treatment with IL-15 mutant/Fcγ2a protein attenuated DTH responses and mononuclear leukocyte infiltration within the DTH sites.18 In the CIA model, treatment with IL-15 mutant/Fcγ2a protein markedly decreased the incidence and severity of arthritis in mice (S. Ferrari-Lacraz, inpreparation). As this unique IL-15 mutant/Fcγ2a protein displays promising effects on T-cell-derived pathogenesis, we wanted to determine its role and relative merits as a new therapeutic strategy in transplantation.

Gamma interferon is not required for arthritis resistance in the murine Lyme disease model.

Lyme arthritis is the most common complication following infection of human individuals with Borrelia burgdorferi sensu stricto. In mice, B. burgdorferi infection leads to arthritis of the tibiotarsal joints. Arthritis severity in mice is under host genetic control, as BALB/c mice developed mild arthritis but C3H/He mice developed severe disease following B. burgdorferi infection. To study the role of gamma interferon (IFN-gamma) in arthritogenesis, targeted mutant mice lacking the IFN-gamma receptor (IFN-gammaR) were infected by inoculation with B. burgdorferi. IFN-gammaR(-/-) and parental 129/SvEv mice developed mild arthritis of similar severity, as determined both by weekly tibiotarsal joint measurements and histopathology at 2 and 5 weeks postinfection. Both strains of mice had the same spirochetal burden in the joints, suggesting that the IFN-gammaR(-/-) mice were not impaired in controlling spirochetal expansion in vivo. The wild-type mice mounted a Th1 response, with a predominance of CD4(+) IFN-gamma(+) T cells observed by flow cytometry. In contrast, the IFN-gammaR(-/-) mice mounted a Th2 response, with a predominance of CD4(+) IL-4(+) T cells. As expected given their cytokine profile, the IFN-gammaR(-/-) mice produced fewer CD8(+) IFN-gamma(+) and MAC-1(+) IL-12(+) cells and less immunoglobulin G2a (IgG2a) than their wild-type counterparts. These results strongly suggest that IFN-gamma is not required for arthritis resistance or as part of an effective immune response against B. burgdorferi.

Effect of a CC chemokine receptor antagonist on collagen induced arthritis in DBA/1 mice

Chemokines are small proteins that selectively activate and recruit leukocytes to sites of inflammation. Several of them, including the CC chemokines RANTES, MIP-1 α, MIP-1 β, MCP-1, and the CXC chemokines IL-8, GRO- α, ENA-78 have been identified in rheumatoid synovium, implicating a potential role for these molecules in rheumatoid arthritis. We have investigated the expression patterns of CC chemokine receptors in the joints of mice with collagen-induced arthritis, a model for human rheumatoid arthritis. In addition, we have investigated the incidence and severity of arthritis in mice receiving administration of MetRANTES, a modified chemokine which is a nanomolar antagonist of certain CC chemokine receptors. The mRNA expression pattern of the chemokines and their receptors in the joints of arthritic mice was investigated using reverse transcriptase-PCR and in situ hybridization. An upregulation of the CC chemokine receptors mCCR1, mCCR2, mCCR3 and mCCR5 was found in the joints from arthritic mice, compared to control animals. In addition, injections of MetRANTES reduced the incidence of disease in a dose dependent manner. Furthermore, in MetRANTES-treated mice that did develop arthritis a significantly lower severity of disease was observed compared with control animals. Our data clearly demonstrate a role for CC chemokines and their receptors in inflammatory joint destruction and support the use of chemokine receptor antagonists as potential tools to control inflammatory diseases such as rheumatoid arthritis.

Effect of IL-10 on collagen-induced arthritis in mice.

In the present study we investigated the effect of a potent anti-inflammatory cytokine, interleukin (IL)-10, on the development of collagen-induced arthritis (CIA) in mice. Each DBA1/J mouse was immunized with 200 micrograms of native collagen and followed by booster injections at 3 weeks. rmIL-10 was injected i.p. daily at a dose of 100 ng/mouse. Mice were divided into four groups according to the administration period of rmIL-10. As a result, a 48-day course of IL-10 treatment significantly suppressed the severity of arthritis. Among the 4 groups, the most pronounced suppression was observed in the group in which IL-10 was given from day 0 to 21. On the other hand, there were no significant differences in the serum IgG anti-type II collagen (CII) titers between the four groups. Moreover, the production of cytokines (IL-6 and tumor necrosis factor-alpha (TNF-alpha)) and other mediators (prostaglandin E2 (PGE2) and nitric oxide (NO)) by peritoneal macrophages seemed to show no clear correlation with the severity of arthritis in mice. These results raise the possibility that IL-10 might be a useful agent for suppressing the progression and the development of CIA in mice.

Induction of T helper cell hyporesponsiveness in an experimental model of autoimmunity by using nonmitogenic anti-CD3 monoclonal antibody.

Autoimmune diseases can be characterized by increases in Th cell activities, suggesting that inhibition of Th cell function might ameliorate autoimmunity. We have recently reported that administration of nonmitogenic anti-CD3 mAb (nmCD3) to nonautoimmune mice can induce long-term Th cell hyporesponsiveness, reflected by reduced IL-2 secretion upon re-exposure to Ag. This study was designed to determine the effects of nmCD3 on autoimmunity by using the murine collagen-induced arthritis model. Treatment of DBA/1 mice with nmCD3 delayed the onset and reduced the severity of arthritis in mice immunized with type II collagen (CII). This effect was not caused by depletion of T cells or modulation of TCR. The observed inhibition of arthritis was not caused by decreased Ab production, as anti-CII titers were not affected. Rather, lymph node cells from CII-immunized mice treated with nmCD3 were hyporesponsive to in vitro stimulation with CII. This hyporesponsiveness was reflected by a marked decrease in secretion of IL-2 and IFN-gamma, but not of IL-4, which suggests that nmCD3 had its principal effect on Th1 cells. The hyporesponsiveness was not Ag-specific, because IL-2 and IFN-gamma production in response to a pan-T cell mitogen was also reduced. These results demonstrate that induction of Th1 cell hyporesponsiveness with nmCD3 can significantly alter the course of CIA and suggest that IL-2 and/or IFN-gamma play a crucial role in disease pathogenesis.

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

It has been postulated that superantigens might play a role in the human rheumatic diseases, by activation of self-reactive T cells or by induction of autoantibodies. The Mycoplasma arthritidis superantigen MAM, which is derived from a naturally occurring murine arthitogenic mycoplasma, uses certain V beta chains of the murine T cell receptor (TCR) that have been proposed to be involved in murine collagen-induced arthritis (CIA). The present study was designed to determine whether MAM influences the course of arthritis mediated by immunization with porcine type II collagen (PII). MAM or phosphate buffered saline (PBS) was injected locally or systemically into mice convalescing from CIA or mice suboptimally immunized with collagen. In contrast to PBS, MAM caused an exacerbation of arthritis in mice that were recovering from CIA. MAM also triggered arthritis onset in mice that had been suboptimally immunized with PII up to 160 days previously. Injection of MAM during the onset phase of CIA also triggered and enhanced the severity of arthritis in mice given low doses of PII. MAM can both trigger and exacerbate murine autoimmune arthritis induced by immunization with type II collagen. Since T cells bearing the same V beta TCRs as are used by MAM have been found to comprise a major portion of the activated cells in the synovial tissue of patients with rheumatoid arthritis, it is possible that superantigens similar to MAM may play a role in this human disease.