To B or not to B: role of B cells in pathogenesis of arthritis in HLA transgenic mice

Population studies have shown that amongst all the genetic factors linked with autoimmune disease development, MHC class II genes are the most significant. Experimental autoimmune arthritis resembling human rheumatoid arthritis (RA) can be induced in susceptible strains of mice following immunization with type II collagen (CIA). We generated transgenic mice lacking endogenous class II molecules and expressing various HLA genes including RA-associated, HLA-DRB1*0401 and HLA-DQ8, and RA-resistant, DRB1*0402, genes. The HLA molecules in these mice are expressed on the cell surface and can positively select CD4+ T cells expressing various Vβ T cell receptors. Endogenous class II invariant chain is required for proper functioning of the class II transgene. Arthritis development in transgenic mice is CD4+ and B cells dependent. Studies in humanized mice showed that B cells are required as antigen presenting cells in addition to antibody producing cells for the development of CIA. The transgenic mice expressing *0401 and *0401/DQ8 genes developed sex-biased arthritis with predominantly females being affected, similar to that of human RA. Further, the transgenic mice produced autoantibodies like rheumatoid factor and anti-cyclic antibodies. Antigen presentation by B cells leads to a sex-specific immune response in DRB1*0401 mice suggesting a role of B cells and HLA-DR in rendering susceptibility to develop arthritis in females.     

An HLA-DRB1*0402 derived peptide (HV3 65-79) prevents collagen-induced arthritis in HLA-DQ8 transgenic mice.

On the basis of our studies with HLA class II transgenic mice, we had proposed that complementation of HLA-DQ and HLA-DR alleles may determine both disease susceptibility and severity in rheumatoid arthritis (RA). According to our model, certain HLA-DQ alleles, such as HLA-DQ8, predispose individuals to RA, while a self-peptide derived from the third hypervariable region (HV3 65-79) of HLA-DR alleles, such as DRB 1*0402, can protect from disease if presented by the DQ molecule. To test this hypothesis, we examined the immunomodulatory effects of the DRB1*0402 derived peptide (HV3 65-79) on collagen-induced arthritis (CIA) in HLA-DQ8 mice. Co-immunization of the DRB 1*0402 peptide significantly reduced the severity of arthritis (mean score = 1.5+/-0.6 vs 5.2+/-1.4 in controls), whereas multiple doses of the peptide reduced the incidence of disease (3.5% vs 35-60% in controls). Subsequent analysis revealed that the DRB1*0402 peptide mediated protection may be due to the generation of a subset of regulatory cells, which down-regulate collagen-specific pro-inflammatory responses. These results provide additional insights towards understanding the role of MHC class II molecules in RA predisposition.     

Cross-Reactivity between the Rheumatoid Arthritis-Associated Motif EQKRAA and Structurally Related Sequences Found in Proteus mirabilis

Cross-reactivity or molecular mimicry may be one of the underlying mechanisms involved in the etiopathogenesis of rheumatoid arthritis (RA). Antiserum against the RA susceptibility sequence EQKRAA was shown to bind to a similar peptide ESRRAL present in the hemolysin of the gram-negative bacterium Proteus mirabilis, and an anti-ESRRAL serum reacted with EQKRAA. There was no reactivity with either anti-EQKRAA or anti-ESRRAL to a peptide containing the EDERAA sequence which is present in HLA-DRB1*0402, an allele not associated with RA. Furthermore, the EQKRAA and ESRRAL antisera bound to a mouse fibroblast transfectant cell line (Dap.3) expressing HLA-DRB1*0401 but not to DRB1*0402. However, peptide sequences structurally related to the RA susceptibility motif LEIEKDFTTYGEE (P. mirabilis urease), VEIRAEGNRFTY (collagen type II) and DELSPETSPYVKE (collagen type XI) did not bind significantly to cell lines expressing HLA-DRB1*0401 or HLA-DRB1*0402 compared to the control peptide YASGASGASGAS. It is suggested here that molecular mimicry between HLA alleles associated with RA and P. mirabilis may be relevant in the etiopathogenesis of the disease.     

Specificity of an HLA-DRB1*0401-restricted T cell response to type II collagen

A panel of HLA-DRB1*0401-restricted CD4⁺ mouse T cell hybridomas specific for bovine type II collagen were generated from transgenic mice expressing the human HLA-DRA1*0101/-DRB1*0401 and CD4 molecules. The vast majority recognized a single peptide determinant corresponding to residues 261–273 (CII 261–273). This determinant was rapidly defined by the use of a predictive algorithm for peptide binding to DRB1*0401. CII 261–273 is conserved in bovine and human type II collagen and overlaps with an important I-A^q-restricted T cell determinant in mice with collagen-induced arthritis. This study demonstrates how HLA-DR and human CD4-transgenic mice can be used to identify a T cell epitope in a potential or candidate autoantigen.     

HLA-DRB1*0401 IS ASSOCIATED WITH SUSCEPTIBILITY TO INSULIN-DEPENDENT DIABETES MELLITUS INDEPENDENTLY OF THE DQB1 LOCUS

The distribution of DRB1*04 alleles and DRB1/DQB1 haplotypes was analysed in 57 DR4⁺ caucasoid subjects with insulin-dependent diabetes mellitus (IDDM) and 96 DR4⁺ healthy controls selected on the basis of DR serology, and the findings were analysed in relation to age at diagnosis of IDDM. DNA samples were amplified using specific DR and DQ primers and hybridized with sequence-specific oligonucleotide probes. A significantly increased combined frequency of DRB 1*0401 and 0402 was observed in IDDM subjects aged ≤12 years at diagnosis (allele frequency 88.4% compared with 62.0% in controls, P < 0.025). There was a non-significant increase in DRB 1*0401 and 0402 in IDDM subjects ≤12 years when compared with IDDM subjects >12 years (P < 0.1). DRB 1 *0404 was decreased in the total IDDM subject group compared with controls (4.8% vs. 19.0%, P < 0.025) but did not reach statistical significance in the individual age at diagnosis groups. In contrast, the frequency of DQB1 *0302 was increased uniformly across both ages at diagnosis groups. In controls DRB 1*0401 occurred in haplotype association with DQB 1*0301 in a significantly greater frequency than with DQB 1*0302. However, 95.0% of DRB 1*0401 IDDM subjects were DQB 1*0302. DRB 1*0404, which was decreased in frequency in IDDM subjects, occurred in association significantly more frequently with DQB 1 *0302 in controls. These results imply that DRB 1 and DQB 1 have independent roles as HLA susceptibility genes in IDDM. DQB1 may have a permissive role whereas DRB1 could influence the rate at which underlying disease progresses to clinical IDDM.     

Increased autophagy in CD4+ T cells of rheumatoid arthritis patients results in T‐cell hyperactivation and apoptosis resistance

Rheumatoid arthritis (RA) is an autoimmune disease hallmarked by aberrant cellular homeostasis, resulting in hyperactive CD4⁺ T cells that are more resistant to apoptosis. Both hyperactivation and resistance to apoptosis may contribute to the pathogenicity of CD4⁺ T cells in the autoimmune process. A better knowledge of the mechanisms determining such impaired homeostasis could contribute significantly to both the understanding and the treatment of the disease. Here we investigated whether autophagy, is dysregulated in CD4⁺ T cells of RA patients, resulting in disturbed T‐cell homeostasis. We demonstrate that the rate of autophagy is significantly increased in CD4⁺ T cells from RA patients, and that increased autophagy is also a feature of in vitro activated CD4⁺ T cells. The increased apoptosis resistance observed in CD4⁺ T cells from RA patients was significantly reversed upon autophagy inhibition. These mechanisms may contribute to RA pathogenesis, as autophagy inhibition reduced both arthritis incidence and disease severity in a mouse collagen induced arthritis mouse model. Conversely, in Atg5^flox/flox‐CD4‐Cre⁺ mice, in which all T cells are autophagy deficient, T cells showed impaired activation and proliferation. These data provide novel insight into the pathogenesis of RA and underscore the relevance of autophagy as a promising therapeutic target.     

The influence of HLA-DR4 (0401) on the immune response to type II collagen and the development of collagen induced arthritis in mice

Rheumatoid arthritis (RA) is an autoimmune disease that is genetically associated with the MHC class II molecule HLA-DRbeta1*0401 (DR4). In order to determine if this MHC can influence the immune response to the candidate autoantigen type II collagen (CII), we have studied collagen induced arthritis (CIA) resistant C57BL/6 mice, made transgenic (Tg) for human DR4. These DR4 Tg mice exhibited a strong T cell proliferative response to CII and its DR4 restricted peptide p261-273 after immunization with these antigens that was not seen in the C57BL/6 wild type mice. DR4 Tg mice also exhibited an increase in IFN-gamma production in response to CII, indicating the activation of Th1 cells. While these Tg mice produced IgM anti-CII antibodies, they failed to produce a detectable level of IgG2a (Th1 type) anti-bCII antibody and did not develop CIA. This study shows that a Th1 type T cell response to CII can be established in CIA non-susceptible mice by introducing the human transgene, DR4. This T cell response, however, is not sufficient to induce an antibody isotype switch to IgG2a, nor is it sufficient for the induction of CIA. These results may help to explain why many individuals expressing HLA-DRbeta1*0401 do not develop RA.     

B cells as effectors and regulators of sex-biased arthritis

B cells have been implicated both with pathogenic as well as protective capabilities in induction and regulation of autoimmune diseases. Rheumatoid arthritis (RA) is an autoimmune disease that occurs more often in women than men. A significant role of B cells as antibody producing and antigen-presenting cells has been demonstrated in RA. Predisposition to RA is associated with the presence of certain HLA class II alleles that share sequences with DRB1*0401. To determine the role of HLA genes and B cells in vivo, we have generated transgenic mice carrying HLA genes, DRB1*0401 and DQ8, known to be associated with susceptibility to RA. Humanized mice can be induced to develop arthritis that mimics human disease in clinical, histopathological and sex bias. Effect of hormones on immune cells and their function has been described in humans and mice and has been suggested to be the major reason for female bias of autoimmune diseases. An immune response to an antigen requires presentation by HLA molecules thus suggesting a critical role of MHC in combination with sex hormones in susceptibility to develop rheumatoid arthritis. Based on our observations, we hypothesize that modulation of B cells by estrogen, presentation of modified antigens by DR4 and production of antigen-specific B cell modulating cytokines leads to autoreactivity in females. These data suggest that considering patient's sex may be crucial in selecting the optimal treatment strategy. Humanized mice expressing RA susceptible and resistant haplotype provide a means to investigate mechanism sex-bias of arthritis and future strategies for therapy.     

B cells as effectors and regulators of sex-biased arthritis

B cells have been implicated both with pathogenic as well as protective capabilities in induction and regulation of autoimmune diseases. Rheumatoid arthritis (RA) is an autoimmune disease that occurs more often in women than men. A significant role of B cells as antibody producing and antigen-presenting cells has been demonstrated in RA. Predisposition to RA is associated with the presence of certain HLA class II alleles that share sequences with DRB1*0401. To determine the role of HLA genes and B cells in vivo, we have generated transgenic mice carrying HLA genes, DRB1*0401 and DQ8, known to be associated with susceptibility to RA. Humanized mice can be induced to develop arthritis that mimics human disease in clinical, histopathological and sex bias. Effect of hormones on immune cells and their function has been described in humans and mice and has been suggested to be the major reason for female bias of autoimmune diseases. An immune response to an antigen requires presentation by HLA molecules thus suggesting a critical role of MHC in combination with sex hormones in susceptibility to develop rheumatoid arthritis. Based on our observations, we hypothesize that modulation of B cells by estrogen, presentation of modified antigens by DR4 and production of antigen-specific B cell modulating cytokines leads to autoreactivity in females. These data suggest that considering patient's sex may be crucial in selecting the optimal treatment strategy. Humanized mice expressing RA susceptible and resistant haplotype provide a means to investigate mechanism sex-bias of arthritis and future strategies for therapy.     

Antigen-Specific Expansion of TCR Vβ3+CD4+ T Cells in the Early Stage of Collagen-Induced Arthritis and its Arthritogenic Role in DBA/1J Mice

To investigate type II collagen (CII)-specific CD4⁺ T cell receptors involving in Collagen-induced arthritis (CIA) in DBA/1J mice as a model of rheumatoid arthritis in humans, TCRVβ usage in draining lymph nodes (dLNs) was assessed by flow cytometric analysis at 3, 5, and 8 weeks after bovine CII immunizations. In the early stage of CIA, the draining lymph node CD4⁺ T cells from CIA mice showed a higher proportion of CD4⁺ Vβ3⁺subsets compared with those from control mice. The CD4⁺ Vβ3⁺ T cells were specifically and primarily expanded by antigen-specific stimulation in in vitro culture of dLNs lymphocytes and splenocytes from CIA mice. In addition, CII-reactive response was observed when CD4⁺ Vβ3⁺ T cells were added to a non-responding T cell population. The adoptive transfer of CD4⁺ Vβ3⁺ T cells produced exaggerated arthritis compared with that in the control group. Our results indicate that CD4⁺Vβ3⁺ T cells, which were selectively expanded in dLN of CIA mice, play a pivotal role in CIA pathogenesis.     

DRB1 alleles in polymyalgia rheumatica and rheumatoid arthritis in southern France

To investigate the association of HLA‐DRB1 alleles with polymyalgia rheumatica (PMR) and rheumatoid arthritis (RA), 55 patients with PMR without giant cell arteritis, 203 patients with RA and 230 controls, all from the European population of Marseille, were HLA‐DRB1 genotyped by PCR‐SSO. HLA‐DRB1*01 was significantly increased in both the PMR and RA groups compared to controls (35% versus 17%, P_c < 0.05, and 41% versus 17%, P_c < 0.001, respectively). HLA‐DRB1*04 was significantly increased in the RA group compared to controls (48% versus 23%, P_c < 0.001) but not in the PMR group. HLA‐DRB1*04 subtype frequencies were significantly different between PMR patients and RA patients. Shared epitope‐positive HLA‐DRB1*04 alleles (DRB1*0401, 0404, 0405, 0408) were significantly overrepresented in RA patients compared to PMR patients and shared epitope‐negative HLA‐DRB1*04 alleles were overrepresented in PMR patients compared to RA patients. In conclusion, in the Mediterranean population studied, HLA‐DRB1*01 is associated with RA and PMR whereas HLA‐DRB1*04 is associated with RA only.     

IL-15 exacerbates collagen-induced arthritis with an enhanced CD4+ T cell response to produce IL-17

IL-15 is thought to be involved in the pathogenesis of rheumatoid arthritis (RA). We found that IL-15 plays an important role in the development of murine collagen-induced arthritis (CIA). The incidence and severity of CIA were slightly decreased in IL-15 KO mice but were increased in IL-15 Tg mice compared with wild-type (WT) mice. The levels of type II collagen (CII)-specific IL-17 production were significantly increased in IL-15 Tg mice compared with WT mice with CIA. Expression of IL-23R was up-regulated in CD4(+) T cells in IL-15 Tg mice but down-regulated in IL-15 KO mice compared with WT mice. In correlation with the expression levels of IL-23R, IL-17 production by CD4(+) T cells in response to exogenous IL-23 was increased in IL-15 Tg mice compared with WT mice. Furthermore, exogenous IL-15 synergized with IL-23 to induce CII-specific IL-17 production by CD4(+) T cells in vitro. Taken together, these results indicate that IL-15 plays an important role in the progression of CIA through increasing antigen-specific IL-17 production by CD4(+) T cells.     

Selection of Self-reactive Peptides Within Human Aggrecan by use of a HLA-DRB1*0401 Peptide Binding Motif

The pathogenesis of joint destruction in rheumatoid arthritis remains ill-defined. Joint destruction is thought to be the result of tissue damage mediated by T cells. The mere presence of articular cartilage appears responsible for sustaining chronic synovitis and thereby forwards a role for cartilage-responsive T cells in RA. Taking advantage of the positive DRB1*0401 association with RA susceptibility, we reasoned that T-cell recognition of autoantigens in RA would be restricted by DRB1*0401-encoded molecules. A DR4 (B1*0401) peptide binding motif was used for the identification of putative T-cell epitopes within human aggrecan, a candidate autoantigen. Thirteen peptides were synthesized and tested for binding DRB1*0401 or 0404-encoded molecules. Selected binders were tested for induction of pro-liferative responses in peripheral blood mononuclear cells from donors carrying the DR4 or DR1 specificity. Both healthy and RA donors responded to human aggrecan-derived peptides, thereby identifying these sequences as T-cell epitopes. Interestingly, responses to aggrecan-derived epitopes were significantly decreased in RA patients compared to controls. This was not due to an overall hyporesponsiveness of RA patients since responses to a recall antigen or mitogen did not differ from controls. The data suggest that in RA, aggrecan-specific T cells may exist in a different stage of activation or may have left the periphery to home to the joint.     

Alloreactive regulatory T cells generated with retinoic acid prevent skin allograft rejection

CD4⁺CD25⁺Foxp3⁺ regulatory T (Treg) cells mediate immunological self‐tolerance and suppress immune responses. Retinoic acid (RA), a natural metabolite of vitamin A, has been reported to enhance the differentiation of Treg cells in the presence of TGF‐β. In this study, we show that the co‐culture of naive T cells from C57BL/6 mice with allogeneic antigen‐presenting cells (APCs) from BALB/c mice in the presence of TGF‐β, RA, and IL‐2 resulted in a striking enrichment of Foxp3⁺ T cells. These RA in vitro‐induced regulatory T (RA‐iTreg) cells did not secrete Th1‐, Th2‐, or Th17‐related cytokines, showed a nonbiased homing potential, and expressed several cell surface molecules related to Treg‐cell suppressive potential. Accordingly, these RA‐iTreg cells suppressed T‐cell proliferation and inhibited cytokine production by T cells in in vitro assays. Moreover, following adoptive transfer, RA‐iTreg cells maintained Foxp3 expression and their suppressive capacity. Finally, RA‐iTreg cells showed alloantigen‐specific immunosuppressive capacity in a skin allograft model in immunodeficient mice. Altogether, these data indicate that functional and stable allogeneic‐specific Treg cells may be generated using TGF‐β, RA, and IL‐2. Thus, RA‐iTreg cells may have a potential use in the development of more effective cellular therapies in clinical transplantation.     

Allergen‐specific naïve and memory CD4+ T cells exhibit functional and phenotypic differences between individuals with or without allergy

Although allergen‐specific CD4⁺ T cells are detectable in the peripheral blood of both individuals with or without allergy, their frequencies and phenotypes within the memory as well as naïve repertoires are incompletely known. Here, we analyzed the DRB1*0401‐restricted responses of peripheral blood‐derived memory (CD4⁺CD45RO⁺) and naïve (CD4⁺CD45RA⁺) T cells from subjects with or without allergy against the immunodominant epitope of the major cow dander allergen Bos d 2 by HLA class II tetramers in vitro. The frequency of Bos d 2_127–142‐specific memory T cells in the peripheral blood‐derived cultures appeared to be higher in subjects with allergy than those without, whereas naïve Bos d 2_127–142‐specific T cells were detectable in the cultures of both groups at nearly the same frequency. Surprisingly, the TCR avidity of Bos d 2_127–142‐specific T cells of naïve origin, as assessed by the intensity of HLA class II tetramer staining, was found to be higher in individuals with allergy. Upon restimulation, long‐term Bos d 2_127–142‐specific T‐cell lines generated from both memory and naïve T‐cell pools from individuals with allergy proliferated more strongly, produced more IL‐4 and IL‐10, and expressed higher levels of CD25 but lower levels of CXCR3 than the T‐cell lines from individuals without allergy, demonstrating differences also at the functional level. Collectively, our current results suggest that not only the memory but also the naïve allergen‐specific T‐cell repertoires differ between individuals with or without allergy.     

CTLA4-Ig modifies dendritic cells from mice with collagen-induced arthritis to increase the CD4+CD25+Foxp3+ regulatory T cell population

Cytotoxic T lymphocyte antigen-4 (CTLA4) and IgG fusion protein, CTLA4-Ig, is a therapeutic agent used for rheumatoid arthritis. It binds B7 molecules on dendritic cells (DCs) and thereby blocks B7/CD28 costimulatory interaction and inhibits effective T cell proliferation. However, the effect of CTLA4-Ig on the regulatory T cell (Treg) is still not known. In this study, we investigated the influence of CTLA4-Ig on the CD4+CD25+Foxp3+ Treg population in collagen-induced arthritis (CIA) mouse model. CTLA4-Ig suppressed CIA and increased the CD4+CD25+Foxp3+ Treg population in joint and spleen. When CD11c + DCs and CD4+T cells from CIA mice were cultured with anti-CD3, CTLA4-Ig increased the CD4+CD25 + Foxp3+ Treg population in a TGF-β-dependent manner. When CD11c + DCs from CIA mice were treated with CTLA4-Ig and adoptively transferred into CIA-induced mice, arthritis did not develop in association with the increase in CD4+CD25+Foxp3+ Treg population. However, in CTLA4-Ig-untreated DC-transferred CIA mice, arthritis developed and then rapidly progressed. Our study demonstrated that CTLA4-Ig suppressed CIA by modifying DCs from CIA mice into tolerogenic DCs to increase the CD4+CD25+Foxp3+ Treg population and this seems to be the new immune regulatory mechanism of CTLA4-Ig.     

Autoimmunity versus tolerance: analysis using HLAtransgenic mice

On the basis of our extensive studies on collagen induced arthritis in HLA class II transgenic mice, we proposed a hypothesis to explain role of shared epitope in rheumatoid arthritis (RA) association. According to our hypothesis, complementation between both DQ and DR molecules is required for susceptibility or protection from disease. While certain DQ alleles predispose individuals to RA, DRB1 molecule can modulate disease by shaping T-cell repertoire in the thymus by providing self-peptides and presented by DQ molecules. Using Aβo.DQ8 transgenic mice, we tested ability of peptides derived from HV3 of DR molecules, implicated in RA positively or negatively, to activate T cells. While the peptides derived from RA susceptible DR molecule were poor binders and poor in activating T cells, the peptides derived from RA resistant DR molecules were high affinity binders and efficient T-cell activators. Our experiments suggest that high affinity DR peptides could induce tolerance to autoimmunity while the low affinity peptides could be permissive to autoimmunity. Using peptide from DRB1*0402 molecule, known to be associated with resistance to RA, prior to induction of collagen induced arthritis prevents the onset of disease. Thus, self-peptides derived from HLA molecules could potentially generate tolerance or autoimmunity depending on their binding affinity with HLA molecules.