Susceptibility to pristane-induced arthritis is altered with changes in bowel flora

Environmental Exposures and Autoimmune Diseases: Contribution of Gut Microbiome

Environmental agents have been gaining more attention in recent years for their role in the pathogenesis of autoimmune diseases (ADs). Increasing evidence has linked environmental exposures, including trichloroethene (TCE), silica, mercury, pristane, pesticides, and smoking to higher risk for ADs. However, potential mechanisms by which these environmental agents contribute to the disease pathogenesis remains largely unknown. Dysbiosis of the gut microbiome is another important environmental factor that has been linked to the onset of different ADs. Altered microbiota composition is associated with impaired intestinal barrier function and dysregulation of mucosal immune system, but it is unclear if gut dysbiosis is a causal factor or an outcome of ADs. In this review article, we first describe the recent epidemiological and mechanistic evidences linking environmental/occupational exposures with various ADs (especially SLE). Secondly, we discuss how changes in the gut microbiome composition (dysbiosis) could contribute to the disease pathogenesis, especially in response to exposure to environmental chemicals.

Modulation of autoimmune arthritis by environmental 'hygiene' and commensal microbiota

Observations in patients with autoimmune diseases and studies in animal models of autoimmunity have revealed that external environmental factors including exposure to microbes and the state of the host gut microbiota can influence susceptibility to autoimmunity and subsequent disease development. Mechanisms underlying these outcomes continue to be elucidated. These include deviation of the cytokine response and imbalance between pathogenic versus regulatory T cell subsets. Furthermore, specific commensal organisms are associated with enhanced severity of arthritis in susceptible individuals, while exposure to certain microbes or helminths can afford protection against this disease. In addition, the role of metabolites (e.g., short-chain fatty acids, tryptophan catabolites), produced either by the microbes themselves or from their action on dietary products, in modulation of arthritis is increasingly being realized. In this context, re-setting of the microbial dysbiosis in RA using prebiotics, probiotics, or fecal microbial transplant is emerging as a promising approach for the prevention and treatment of arthritis. It is hoped that advances in defining the interplay between gut microbiota, dietary products, and bioactive metabolites would help in the development of therapeutic regimen customized for the needs of individual patients in the near future.

Early Peritoneal CC Chemokine Production Correlates with Divergent Inflammatory Phenotypes and Susceptibility to Experimental Arthritis in Mice

The inflammatory and autoimmune events preceding clinical symptoms in rheumatoid arthritis (RA) and other autoimmune diseases are difficult to study in human patients. Therefore, animal models that share immunologic and clinical features with human RA, such as pristane-induced arthritis (PIA), are valuable tools for assessing the primordial events related to arthritis susceptibility. PIA-resistant HIII and susceptible LIII mice were injected i.p. with pristane, and peritoneal lavage fluid was harvested in the early (7 days) and late (35 days) preclinical phases of PIA. Chemokine and cytokine levels were measured in lavage supernatant with ELISA, peritoneal inflammatory leukocytes were immunophenotyped by flow cytometry, and gene expression was determined by qRT-PCR. Leukocyte recruitment was quantitatively and qualitatively divergent in the peritoneum of HIII and LIII mice, with an early increase of CC chemokines (CCL2/CCL3/CCL5/CCL12/CCL22) in the susceptible LIII strain. Also, cytokines such as IL-12p40, IL-23, and IL-18 were elevated in LIII mice while IL-6 was increased in HIII animals. The results show that an early peritoneal CC chemokine response is an important feature of arthritis susceptibility and defines potential biomarkers in this model.

Pristane-induced arthritis loci interact with the Slc11a1 gene to determine susceptibility in mice selected for high inflammation

AIRmax (maximal inflammation) and AIRmin (minimal inflammation) mice show distinct susceptibilities to pristane-induced arthritis (PIA). The Slc11a1 gene, which regulates macrophage and neutrophil activity, is involved in this infirmity. AIRmax^SS mice homozygous for the non-functional Slc11a1 S (gly169asp) allele obtained by genotype-assisted crosses from AIRmax and AIRmin mice are more susceptible than mice homozygous for the Slc11a1 resistant (R) allele. The present work sought to identify the quantitative trait loci (QTL) regulating PIA and to examine the interactions of these QTL with Slc11a1 alleles in modulating PIA. Mice were given two ip injections of 0.5 mL pristane at 60 day intervals, and the incidence and severity of PIA was scored up to 160 days. Genome-wide linkage studies were performed to search for arthritis QTL in an F2 (AIRmax × AIRmin, n = 290) population. Significant arthritis QTL (LODscore>4) were detected on chromosomes 5 and 8, and suggestive QTL on chromosomes 7, 17 and 19. Global gene expression analyses performed on Affymetrix mouse 1.0 ST bioarrays (27k genes) using RNA from arthritic or control mice paws showed 419 differentially expressed genes between AIRmax and AIRmin mice and demonstrated significantly (P<0.001) over-represented genes related to inflammatory responses and chemotaxis. Up-regulation of the chemokine genes Cxcl1, Cxcl9, Cxcl5, Cxcl13 on chromosome 5 was higher in AIRmax^SS than in the other lines. Macrophage scavenger receptor 1 and hemeoxigenase (decycling) 1 genes on chromosome 8 were also expressed at higher levels in AIRmax^SS mice. Our results show that the gene expression profiles of the two arthritis QTL (on chromosomes 5 and 8) correlate with Slc11a1 alleles, resulting in enhanced AIRmax^SS mice susceptibility to PIA.

Heat shock proteins induce T cell regulation of chronic inflammation

The significance of immune responses to certain heat shock proteins (HSPs) that develop in virtually all inflammatory diseases is only now becoming clear. In experimental models, HSPs prevent or arrest inflammatory damage, and initial clinical trials in chronic inflammatory disease have shown HSP peptides to promote production of anti-inflammatory cytokines-indicating immunoregulatory potential. HSPs are ubiquitous self-antigens that are highly expressed in inflamed tissues. The prokaryotic homologous proteins, present in every bacterial species, are dominantly immunogenic. This is striking, especially as these proteins have large areas of sequence homologies with the host (mammalian) counterparts. In several experimental models of autoimmune diseases, immunisation with bacterial HSPs inhibited disease development, as did oral/nasal administration. Based on the experimental evidence so far, it is tempting to speculate that: firstly, exposure to homologues of these self-antigens, as present in, for instance, the bacterial intestinal flora, has a decisive impact on the regulation of self-tolerance at the level of T cells; and secondly, such proteins or their derivative peptides may have a role in an antigen specific immunotherapy approach involving modulation of relevant T cells, without the immediate necessity of defining disease specific autoantigens. Recent findings in experimental asthma and atherosclerosis have indicated that the field of application of such immunotherapy can be broader than just autoimmunity.

Slc11a1 (formerly NRAMP1) gene modulates both acute inflammatory reactions and pristane-induced arthritis in mice

Mice selected for the maximum acute inflammatory reaction (AIRmax) are highly susceptible to pristane-induced arthritis (PIA), whereas mice selected for the minimum response (AIRmin) are resistant. These lines show distinct patterns of leukocyte infiltration and R and S allele frequency disequilibrium of the solute carrier family 11a member 1 (Slc11a1) gene. In order to study the interactions of the Slc11a1 R and S alleles with the inflammation modulating Quantitative Trait Loci (QTL) during PIA development, homozygous AIRmax(RR), AIRmax(SS), AIRmin(RR) and AIRmin(SS) lines were produced by genotype-assisted breedings. These mice received two intraperitoneal injections of 0.5 ml pristane at 60-day intervals, and the subsequent development of arthritis was assessed for 210 days. Cytokine-secreting cell profiles were investigated using enzyme-linked immunospot. Arthritis incidence in AIRmax(RR) mice reached 29%, whereas PIA incidence in AIRmax(SS) mice was 70% by day 180. AIRmin(RR) mice were resistant, whereas 13.3% of AIRmin(SS) mice became arthritic. The presence of the defective S allele also increased arthritis severity, although acute inflammation was higher in mice bearing the R allele. A predominant Th0/Th2-type response in Slc11a1(SS) mice was observed. These results indicate that Slc11a1 is a strong candidate for the QTL modulating acute inflammation and for PIA.

Immunomodulation and protection induced by DNA-hsp65 vaccination in an animal model of arthritis

We described a prophylactic and therapeutic effect of a DNA vaccine encoding the Mycobacterium leprae 65-kDa heat shock protein (DNA-hsp65) in experimental murine tuberculosis. However, high homology of the vaccine to the corresponding mammalian hsp60, together with the CpG motifs in the plasmidial vector, could trigger or exacerbate an autoimmune disease. In the present study, we evaluate the potential of DNA-hsp65 vaccination to induce or modulate arthritis in mice genetically selected for acute inflammatory reaction (AIR), either maximal (AIRmax) or minimal (AIRmin). Mice immunized with DNA-hsp65 or injected with the corresponding DNA vector (DNAv) developed no arthritis, whereas pristane injection resulted in arthritis in 62% of AIRmax mice and 7.3% of AIRmin mice. Administered after pristane, DNA-hsp65 downregulated arthritis induction in AIRmax animals. Levels of interleukin (IL)-12 were significantly lower in mice receiving pristane plus DNA-hsp65 or DNAv than in mice receiving pristane alone. However, when mice previously injected with pristane were inoculated with DNA-hsp65 or DNAv, the protective effect was significantly correlated with lower IL-6 and IL-12 levels and higher IL-10 levels. Our results strongly suggest that DNA-hsp65 has no arthritogenic potential and is actually protective against experimentally induced arthritis in mice.

Involvement of antibody production quantitative trait loci in the susceptibility to pristane-induced arthritis in the mouse

Mice obtained by bidirectional selective breeding for high (HIII) or low (LIII) antibody (Ab) production are resistant or extremely susceptible to pristane-induced arthritis (PIA), respectively. Several quantitative trait loci regulating Ab production (Ab QTL) have been mapped in these lines, which were used to investigate the influence of these Ab QTL in PIA. Parental HIII and LIII mice and their F1 and F2 intercrosses were injected twice with pristane, and arthritis was observed for 200 days. In LIII mice PIA was more severe and incidence was 100% at day 105, while F1 and F2 mice showed intermediate values. HIII mice were totally resistant. Microsatellite polymorphisms of Ab QTL were analysed and D3Mit100 alleles cosegregated significantly with PIA incidence, severity and onset in F2 intercross mice, while the other four markers showed suggestive values. Results indicate colocalization of QTL for Ab production and PIA susceptibility. Moreover, the different cytokine and IgG isotype profiles observed in HIII and LIII lines after PIA induction are useful to candidate genes endowed with the regulation of the Ab production and arthritis phenotypes.

Pristane-induced autoimmunity in germ-free mice

Hypergammaglobulinemia and autoantibodies are reduced in pristane-treated specific pathogen-free mice vs. conventionally housed controls, consistent with the role of microbial stimulation in this model. To determine whether microbial stimulation is required, BALB/c mice housed under germ-free conditions were treated i.p. with sterile PBS or pristane and examined 6 months later. As in conventional mice, pristane-treated germ-free mice developed peritoneal granulomas and hypergammaglobulinemia with increased IgG2a/IgG1 ratios. LPS stimulation induced more IL-6, IL-12, and TNF-alpha, and anti-CD3 induced more IFN-gamma and IL-4 by peritoneal cells from pristane-treated mice vs. control. Anti-nRNP/Sm and -Su autoantibodies were found in 40% and 43%, respectively, of pristane-treated germ-free mice by immunoprecipitation. Thus, bacterial stimulation was not required for lupus autoantibodies, peritoneal granuloma formation, hypergammaglobulinemia, or cytokine overproduction. Although microbial stimulation acts synergistically with pristane, these results clearly indicate that pristane does not act merely by increasing exposure to microbial products such as LPS.

Inflammation induced by inoculation of the joint with Candida albicans

In humans Candida albicans is the most frequently isolated opportunistic fungal pathogen. In immunocompromized host the balance with the commensal fungus easily turns to life-threatening disseminated infection. The asymptomatic Candida persistence in organs and the recurrent infections suggest continuous circulation of yeast cells and their degradation products. Under certain conditions, joints might become one of the infectious sites. More easily a reactivation and destructive process can be provoked in individuals with established arthritis. We have investigated the joint inflammation caused by inoculation of the paw with live C. albicans, in intact mice and mice with collagen-induced arthritis (CIA). The results demonstrate that C. albicans infection when localized into the joints caused rapidly progressing septic arthritis. The effect was associated with a strong swelling, a rapid influx of polymorphonuclear (PMN) cells, and an elevated secretion of TNF-alpha and IFN-gamma by lymph node cells. Joint infection exacerbated the established CIA which correlated with an increased level of anti-collagen antibodies.

Characterization of pristane-induced arthritis, a murine model of chronic disease: Response to antirheumatic agents, expression of joint cytokines, and immunopathology

OBJECTIVE

To characterize chronic murine pristane-induced arthritis (PIA) with regard to the response to antirheumatic agents, expression levels of proinflammatory cytokines, and immunopathologic features.

METHODS

Male DBA/1 mice were injected intraperitoneally with pristane oil to induce a chronic polyarthritis, which was monitored by visual scoring. Serum antibody and splenocyte responses to a panel of putative joint-derived autoantigens were measured. Whole paws were evaluated postmortem for changes in the levels of proinflammatory cytokines tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and IL-6 by enzyme-linked immunosorbent assay, and standard histopathology techniques were used to determine joint structural changes. Therapeutic studies were performed for up to 8 weeks of dosing with prednisolone, methotrexate, 3 nonsteroidal antiinflammatory drugs (celecoxib, diclofenac, and indomethacin), a p38 MAPK inhibitor, SB242235, and human soluble TNF receptor (sTNFR; etanercept) and murine sTNFR fusion proteins.

RESULTS

Antibody and cellular responses to the putative joint autoantigens revealed a broad extent of autoimmunity in PIA. TNFalpha, IL-1beta, and IL-6 were all persistently up-regulated in PIA joints. Prednisolone, methotrexate, celecoxib, indomethacin, and SB242235 all significantly reduced the arthritis scores. Etanercept was ineffective in reducing the arthritis scores, whereas murine sTNFR produced a significant, but nonsustained, benefit. Only prednisolone significantly reduced the expression of TNFalpha, IL-1beta, and IL-6 in the joints. Prednisolone and methotrexate demonstrated the most effective joint protection.

CONCLUSION

We have markedly extended the characterization of PIA as a murine model of chronic inflammatory arthritis by demonstrating cellular and humoral autoantigenicity, elevation of clinically precedented joint cytokines, and variation in the response to several antirheumatic therapies. PIA offers significant potential for the long-term study of immunopathologic mechanisms and novel therapies in rheumatoid arthritis.

Streptococcus sanguis modulates type II collagen-induced arthritis in DBA/1J mice

Native type II collagen is tolerogenic when given orally or i.p. to DBA/1J mice and induces autoimmune arthritis when given s.c. in CFA. The tolerogenic epitope is contained in cyanogen bromide fragment 11 (CB11) and is structurally mimicked by PGEQGPK within the platelet aggregation-associated protein (PAAP) on Streptococcus sanguis. To learn whether S. sanguis modulates transmucosally the Ag-specific development of autoimmune arthritis, DBA/1J pups were given live S. sanguis, CB11, or type II collagen intragastrically. Feeding S. sanguis at 6 days postpartum delayed the onset of arthritis, and reduced the rate, final severity, and percentage of affected limbs. Next, PAAP(+) S. sanguis and type II collagen were tested for T cell cross-reactivity. T cells primed with the tolerogenic epitope of type II collagen proliferated more when incubated with PAAP(+) S. sanguis than with PAAP(-) Streptococcus gordonii or type II collagen, suggesting an Ag-specific transmucosal tolerogenic effect. In neonatal mice, therefore, bacterial surface Ags that mimic self can transmucosally stimulate Ag-specific inhibitory T cells. In adult mice immunized with type II collagen, these Ag-specific inhibitory T cells manifest later as attenuated arthritis. The PAAP(+) S. sanguis appear to activate adult memory, rather than naive, type II collagen-specific T cells, suggesting that systemic challenge with commensal self-mimicking microorganisms may perpetuate existing autoimmunity, but not initiate autorecognition.

Chondrocyte antigen expression, immune response and susceptibility to arthritis

The association of HLA-B27 with certain forms of arthritis implies a role for MHC class I-restricted T cells in the arthritic process. Our aim was to study CD8(+) T cell responses towards specific antigens localized in joint tissue. Known determinants were introduced into chondrocytes of transgenic (TG) mice, under the control of the cis-regulatory sequences of the human type II collagen gene (COL2A1). Two Escherichia coli beta-galactosidase (beta-gal)-expressing lines were derived (CIIL73 and CIIL64) as well as two lines (CIINP) expressing influenza A virus nucleoprotein (NP). Expression of the antigens could be demonstrated in cartilaginous tissues. The TG lines showed variable degrees of responsiveness towards the transgene-introduced antigens; whilst 75% of CIIL73 mice had an impaired cytotoxic T lymphocyte (CTL) response towards beta-gal, the response in CIIL64 mice was essentially normal. However, both lines displayed normal proliferative and antibody responses to beta-gal. A reduced CTL response was seen to NP in the CIINP lines in approximately 65% of the animals. In spite of the persistence of T cell responses to the transgene antigens in these lines, induction of CTL responses alone has so far failed to induce clinical signs of arthritis. Interestingly, some animals expressing beta-gal were susceptible to arthritis following challenge with type II collagen alone, whilst their non-TG littermates and TG mice from other lines remained unaffected. As beta-gal is expressed by E. coli, a component of the normal gut flora, this suggests a possible role for gut-derived immune responses. We believe these lines could form the basis of a model for studying links between intestinal inflammation and arthritis.

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.

Immunity to heat shock proteins and arthritic disorders

Adjuvant arthritis (AA) is a frequently used model of experimental arthritis. Because of its histopathology, which is reminiscent of rheumatoid arthritis in humans, AA is used as a model for the development of novel anti-inflammatory drugs. Recently, it has become evident that AA is a typical T-cell-mediated autoimmune condition. Therefore, novel immunotherapies targeted to T cells can be developed in this model. Analysis of responding T cells in AA have now led to the definition of various antigens with potential relevance to arthritis, including human arthritic conditions. One such antigen defined in AA is the 60kD heat shock protein. Both T-cell vaccination approaches and active antigen immunizations and antigen toleration approaches have turned out to be effective in suppressing AA.

Diversification of response to hsp65 during the course of autoimmune arthritis is regulatory rather than pathogenic

Determinant spreading has been implicated in the pathogenesis of certain autoimmune diseases in animal models. We have observed that during the course of adjuvant arthritis (AA) in the Lewis rat, there is 'diversification' of response to the bacterial 65-kDa heat shock protein (Bhsp65) towards its carboxy-terminal determinants (BCTD). Strikingly, pretreatment of naive Lewis rats with BCTD affords significant protection from AA. Our preliminary studies indicate that the diversification of response to BCTD in the Lewis rat is probably triggered in vivo by the induction and enhanced processing of self(rat) hsp65. Thus, the self hsp65-directed T-cell responses appear to be involved in mediating natural remission from acute inflammatory arthritis induced by a foreign antigen, Mycobacterium tuberculosis. This the first report describing that the new T-cell specificities arising during the course of an autoimmune disease are regulatory/protective rather than pathogenic. Moreover, our results suggest that a final common mechanism involving BCTD might be recruited by other rat strains which either are resistant to AA (WKY rats) or whose susceptibility to AA is modulated significantly by microbial flora (Fisher rats). The results of this study would contribute significantly to understanding of the pathogenesis of human rheumatoid arthritis, and in devising new therapeutic strategies for this disease.

An Immunodominant Epitope from Mycobacterial 65-kDa Heat Shock Protein Protects Against Pristane-Induced Arthritis

Previous studies showed that mice with pristane-induced arthritis (PIA) and those protected from the disease by preimmunization with mycobacterial 65-kDa heat shock protein (hsp65) possess raised immune responses to hsp65. Additionally, T cells from hsp65-protected mice, but not from pristane-injected or normal mice, produced the Th2-associated cytokines IL-4, IL-5, and IL-10 in response to stimulation with hsp65. Here we demonstrate that the specificity of the immune response to hsp65 and related heat shock protein (hsps) differs between protected and PIA mice. T cells from hsp65-protected mice respond to the bacterial hsps tested but not to the mammalian homologue, hsp58. Similarly, they exhibit high serum titers of anti-hsp65 Abs, yet they have virtually undetectable levels of anti-hsp58 IgG. By contrast, both cellular and humoral immune responses are detectable to bacterial and mammalian hsps in mice with PIA. An immunodominant T cell epitope has been identified in hsp65-protected mice corresponding to amino acids 261–271 from hsp65. Immunization of mice, either before or after the induction of arthritis, with this bacterial peptide, but not its mammalian homologue, protects mice from the development of PIA, and protection is associated with the production of Th2-type cytokines. Other experiments revealed that T cells primed with bacterial 261–271 or the mammalian homologue do not cross-react at the proliferative or cytokine level. These results demonstrate that an hsp65 peptide-specific Th2 response confers protection from PIA but do not support the idea that protection is mediated by a cross-reaction with self hsp58 in the joints.

Heat shock proteins as potential targets in the therapy of inflammatory arthritis

Whether heat shock proteins (hsp) will be therapeutic targets in arthritis depends on their role in pathogenesis. In this article, three possibilities are considered. Firstly, an excessive immune response to bacterial hsp could be arthritogenic - as may occur in reactive arthritis. In these circumstances therapy would be directed to down-regulating this immune response, or altering the nature of the immune response e.g. by changing cytokine production from interferon-g to IL-4. However this approach depends on the immune response to bacterial hsp not being critical for control of the bacterial infection. Secondly, an immune response to bacterial hsp may induce autoimmunity by cross-reactivity, e.g. with the homologous human. This could also be modulated in the same way with a lower likelihood of interfering with control of the infectious agent, since only a component of the immune response against the bacterial hsp will be cross-reactive with self. Thirdly, recent experiments raise the possibility that joint inflammation might be controlled by T cells which recognizes self hsp, particularly hsp60. Therapies might enhance this response; protection from experimental arthritis by prior immunization with hsp60 is well established. Whether similar approaches will be viable after arthritis is established remains to be seen.

Heat shock proteins and arthritis--new readers start here

The possible roles of heat shock proteins in the pathogenesis of inflammatory arthritis have been discussed for a number of years, and investigated intensively in both animal models and human disease. This review surveys evidence which has pointed, on the one hand, to hsp as targets of a pathogenic immune response, and on the other, to an immunoregulatory role for T cell recognition of self hsp. The extent to which findings in experimental animals have led to further insights applicable to human disease is also emphasised.

Influence of microbial stimulation on hypergammaglobulinemia and autoantibody production in pristane-induced lupus

Pristane induces a lupus-like syndrome characterized by autoantibody production and glomerulonephritis in nonautoimmune strains of mice. Although it has been suggested that this syndrome results from nonspecific immune activation, there is little evidence so far that B cells are activated nonspecifically by pristane or that this promotes autoimmunity. In this study, we examined whether polyclonal hypergammaglobulinemia occurs in pristane-induced lupus, and its relationship to the production of anti-DNA, nRNP/Sm, and Su autoantibodies. In conventionally housed mice, there was a marked increase in total IgM and IgG3 2 weeks after i.p. pristane injection, followed by increased IgG1, IgG2a, and IgG2b levels. IgM levels were higher in pristane-treated specific pathogen-free (SPF) mice than in conventionally housed mice, whereas IgG and IgA levels were reduced. Pristane induced anti-nRNP/Sm and Su autoantibodies in SPF mice, but their onset was delayed and levels were lower than those in conventionally housed mice. There was no consistent relationship between total IgG1, 2a, and 2b hypergammaglobulinemia and production of anti-nRNP/Sm and Su autoantibodies. Moreover, the total Ig levels were similar in the anti-nRNP/Sm-positive and -negative groups. In contrast, production of IgM anti-ssDNA antibodies paralleled IgM hypergammaglobulinemia in some, but not all, mice. These studies indicate that pristane-induced lupus is associated with marked hypergammaglobulinemia, the magnitude of which is influenced by the microbial environment. However, anti-nRNP/Sm and Su autoantibody production is at least partly independent of polyclonal B cell activation. The data strongly suggest that pristane-induced lupus is not exclusively the consequence of nonspecific immune stimulation. They also point to the importance of microbial stimulation in the development of hypergammaglobulinemia in this inducible lupus model.

Pristane-induced arthritis is CD4+ T-cell dependent

The development of arthritis induced in mice by intraperitoneal injection of the non-antigenic mineral oil pristane (2,6,10,14-tetramethylpentadecane) was shown to depend on the presence of CD4+ T cells. Initial experiments assessed the influx of lymphoid cells into the peritoneal cavity of CBA/Igb mice after pristane injection. Both CD4+ and CD8+ cell numbers were maximal around 50 days. Other experiments confirmed our original observation that irradiated pristane-treated mice failed to develop arthritis unless they were reconstituted with spleen cells from normal donors. This finding has been extended by showing that the population of transferred splenic lymphoid cells must contain CD4+ T cells, while CD8+ T cells and B cells were not required for reconstitution. Conventionally housed and hsp 65-immunized animals are known to harbour T cells reactive with hsp 65. In addition, hsp 65-immunized mice are resistant to the development of pristane-induced arthritis (PIA). Thus, additional experiments assessed the population of splenic T cells activated and proliferating against mycobacterial 65,000 MW heat shock protein (hsp 65). In cultures of purified splenic T cells derived from both conventional and hsp 65-immunized mice, removal of CD4+ T cells significantly reduced the proliferative response to hsp 65, while removal of CD8+ T cells often enhanced the response. These proliferative responses were also shown to be major histocompatibility complex (MHC) class II restricted. The present findings demonstrate that PIA is CD4+ T-cell mediated, and immunodominant environmental antigens such as hsp 65 activate this population of lymphocytes. The CD4+ hsp 65-reactive population may be pathogenic or protective in PIA, depending upon the route of sensitization.

Heat shock proteins and experimental autoimmune encephalomyelitis (EAE): I. Immunization with a peptide of the myelin protein 2',3' cyclic nucleotide 3' phosphodiesterase that is cross-reactive with a heat shock protein alters the course of EAE

We describe sequence similarity and immunologic cross-reactivity between a peptide of the mycobacterial hsp, HSP65, and the myelin protein 2',3' cyclic nucleotide 3' phosphodiesterase (CNP). We demonstrate that immunization with the homologous cross-reactive CNP peptide (hsp-CNP peptide) has significant biological consequences. Rats immunized with hsp-CNP peptide in either complete Freund's adjuvant (CFA) or incomplete Freund's adjuvant (IFA) produce large amounts of peptide-specific antibody. Isotypes of antibodies in animals immunized with peptide in CFA are IgG1 and IgG2a. Isotypes of antibodies in rats immunized with peptide in IFA are predominantly IgG1, with low titers of IgG2a. T cell proliferative responses to HSP65 are present in rats immunized with peptide in CFA. T cell responses to HSP65 initially are absent in rats immunized with peptide in IFA but develop over time. T cell proliferative responses to hsp-CNP peptide were not detected. None of the groups of rats developed clinical or histologic evidence of experimental autoimmune encephalomyelitis (EAE). To induce EAE, rats preimmunized with hsp-CNP peptide were challenged with guinea pig spinal cord (GPSC) emulsified in CFA. Rats preimmunized with peptide in CFA developed severe EAE. Rats preimmunized with hsp-CNP peptide in IFA were protected from EAE, with both a lower incidence and severity of disease. Injecting the murine monoclonal antibody recognizing the shared HSP65 and CNP epitope did not protect against EAE. Our data suggest that a Th2 pattern of immune response to a CNP peptide that itself is non-encephalitogenic protects against EAE. Immune responses to either hsp or myelin proteins cross-reactive with hsp may play an important role in the development of EAE.

Infection, autoimmunity and autoimmune disease

Studies of the immune response of mammals to infectious agents have revealed that members of the hsp60 and hsp 70 family are highly immunodominant. Given their high conservation during evolution this was surprising, because of the apparent risk of triggering of autoimmunity and autoimmune disease during the defense of a mammal against infection. However, detailed studies of the immune responses to HSP in models of autoimmune diseases in animals resulted in a change of the view that autoimmunity necessarily leads to autoimmune disease. It has been found that modulation of autoimmunity to HSP is one way to prevent autoimmune disease. At least in some cases even treatment of autoimmune diseases by immunization with heat shock protein appears feasible. This was shown in adjuvant arthritis in Lewis rats and insulin dependent diabetes in NOD mice. Hsp60 and hsp70 are ubiquitous proteins. Their involvement in regulatory loops of autoimmunity may serve as basis for the development of strategies, to prevent and/or treat autoimmune diseases even without knowledge of the causative (auto-)antigen.

Immunologically ignorant autoreactive T cells, epitope spreading and repertoire limitation

The factors that may cause antigen-presenting cells to alter the pattern of protein processing and presentation to autoreactive T cells, and thereby stimulate autoimmune disease, are currently under debate. In this article, Chris Elson and colleagues suggest that cytokines associated with T helper 1 (Th1) cells alter the processing of proteins and that this effect can be counteracted by Th2-associated cytokines.

Immunotoxicity of silicone: implications of oxidant balance towards adjuvant activity

A variety of mechanisms can be proposed to explain the potential effects of silicone and silicone by-products on the immune response. In this paper, we discuss information on the chemistry of silicon and silicone gels/elastomers, and the manufacture of silicone breast implants as they pertain to the bioreactivity of silicone. Moreover, with reference to silicone-mediated human adjuvant disease, an overview of experimental adjuvant-induced arthritis is presented; comparisons with graft-versus-host disease and chemically induced autoimmunity then follow. Particular attention is paid to similarities in the characteristics of silicone and classic lipid adjuvants. For example, macrophage activation is presumed to be a central event in silicone-induced autoimmunity. Since those genes uniquely expressed in macrophages activated by plastic adherence are similar to those induced by lipopolysaccharide, adherence to silicone rubber may initiate an inflammatory response by the same mechanism. Macrophage effects would also include the erosion of implants through the generation of oxidants and localized pH changes. The degradation products of silicone are also implicated in the adjuvant effects of silicone implants. There is evidence to suggest that oxidants produced by inflammatory cells preferentially inactivate CD8+ suppressor T cells. This could then lead to an inflammatory state, perhaps through oxidant-induced transcription factors such as NF-kB, resulting in a long-term pro-oxidant imbalance that manifests itself as a breakdown in immunological self-tolerance. The authors hypothesize that autoreactivity following oxidant stress evolved to enhance inflammatory repair mechanisms after tissue, cell or molecular damage by oxidants.