Multifunctional T cell reactivity with native and glycosylated type II collagen in rheumatoid arthritis

A pathological joint-liver axis mediated by matrikine-activated CD4+ T cells

The knee joint has long been considered a closed system. The pathological effects of joint diseases on distant organs have not been investigated. Herein, our clinical data showed that post-traumatic joint damage, combined with joint bleeding (hemarthrosis), exhibits a worse liver function compared with healthy control. With mouse model, hemarthrosis induces both cartilage degeneration and remote liver damage. Next, we found that hemarthrosis induces the upregulation in ratio and differentiation towards Th17 cells of CD4+ T cells in peripheral blood and spleen. Deletion of CD4+ T cells reverses hemarthrosis-induced liver damage. Degeneration of cartilage matrix induced by hemarthrosis upregulates serological type II collagen (COL II), which activates CD4+ T cells. Systemic application of a COL II antibody blocks the activation. Furthermore, bulk RNAseq and single-cell qPCR analysis revealed that the cartilage Akt pathway is inhibited by blood treatment. Intra-articular application of Akt activator blocks the cartilage degeneration and thus protects against the liver impairment in mouse and pig models. Taken together, our study revealed a pathological joint-liver axis mediated by matrikine-activated CD4+ T cells, which refreshes the organ-crosstalk axis and provides a new treatment target for hemarthrosis-related disease. Intra-articular bleeding induces cartilage degradation through down-reulation of cartilage Akt pathway. During this process, the soluble COL II released from the damaged cartilage can activate peripheral CD4+ T cells, differention into Th17 cells and secretion of IL-17, which consequently induces liver impairment. Intra-articular application of sc79 (inhibitor of Akt pathway) can prevent the cartilage damage as well as its peripheral influences.

Overdose with the anesthetic propofol causes hematological cytotoxicity and immune cell alteration in an experimental ex vivo whole blood culture model

Propofol, an anesthetic characterized by its benefits of rapid induction, maintenance, and recovery times, may cause cytotoxic effects, resulting in propofol infusion syndrome (PRIS). In addition to causing dyslipidemia in PRIS, our previous works showed that propofol overdose induced phagocyte apoptosis. This study, using an experimental ex vivo model of propofol treatment, investigated the possible cytopathology in the blood. A complete blood count examination showed the deregulating effects of propofol overdose 24 h postinoculation, characterized by mononuclear cell increase (lymphocyte and monocyte subsets) and granulocyte decrease. Advanced marker-based flow cytometric analysis confirmed these findings, although there was no change in CD14+ monocytes. Blood smear staining showed the deregulating effects of propofol overdose 24 h postinoculation, characterized by cytosolic vacuolization and cytotoxicity, particularly in neutrophils. Immune cell profiling of caspase-3 activation demonstrated the induction of cell apoptosis following propofol overdose treatment, particularly in granulocytes. Using multiparameter flow cytometry, this study further analyzed the changes in the profile of immune cells, showing a notable increase in CD4 + HLA-DR-CD62L- helper T cells. These studies explored an ex vivo model of cytopathogenic propofol overdose and its special immune-deregulating effects on peripheral blood cells.

Anticitrullinated antibodies recognize rheumatoid arthritis associated T-cell epitopes modified by bacterial L-asparaginase

Citrullinated proteins and anti-citrullinated protein antibodies (ACPAs) play an important role in the pathogenesis of rheumatoid arthritis (RA). It has been suggested that during inflammation or dysbiosis, bacteria could initiate production of ACPAs. Most patients with RA are seropositive for ACPAs, but these antibodies have overlapping reactivity to different posttranslational modifications (PTMs). For initiation and development of RA, T lymphocytes and T cell epitopes are still required. In this study, we evaluated the ability of bacterial L-asparaginase to modify RA-related T cell epitopes within type II collagen (CII259-273 and CII311-325), as well as whether these modified epitopes are recognized by ACPAs from RA patients. We included 12 patients with early RA and 11 healthy subjects selected according to predefined specific criteria. LC-MS/MS analyses revealed that the bacterial L-asparaginase can modify investigated T cell epitopes. ELISA tests showed cross-reactivity of ACPA positive sera from early RA patients towards the enzymatically modified immunodominant T cell epitopes within type II collagen (CII), but not to the modified irrelevant peptides. These data suggest that the cross-reactive ACPAs recognize the "carbonyl-Gly-Pro" motif in CII. Moreover, the T cell recognition of the modified major immunodominant T cell epitope Gal264-CII259-273 was not affected. This epitope was still able to activate autoreactive T cells from early RA patients. It is likely that such modifications are the missing link between the T cell priming and the development of anti-modified protein antibodies (AMPAs). Our results provide additional information on the etiology and pathogenesis of RA.

NIH/3T3 Fibroblasts Selectively Activate T Cells Specific for Posttranslationally Modified Collagen Type II

It has been shown that synovial fibroblasts (SF) play a key role in the initiation of inflammation and joint destruction, leading to arthritis progression. Fibroblasts may express major histocompatibility complex class II region (MHCII) molecules, and thus, they could be able to process and present antigens to immunocompetent cells. Here we examine whether different types of fibroblasts (synovial, dermal, and thymic murine fibroblasts, destructive LS48 fibroblasts, and noninvasive NIH/3T3 fibroblasts) may be involved in the initiation of rheumatoid arthritis (RA) pathogenesis and can process and present type II collagen (COL2)-an autoantigen associated with RA. Using a panel of MHCII/Aq-restricted T-cell hybridoma lines that specifically recognize an immunodominant COL2 epitope (COL2_259-273), we found that NIH/3T3 fibroblasts activate several T-cell clones that recognize the posttranslationally glycosylated or hydroxylated COL2_259-273 epitope. The HCQ.3 hybridoma, which is specific for the glycosylated immunodominant COL2 epitope 259-273 (Gal264), showed the strongest response. Interestingly, NIH/3T3 cells, but not destructive LS48 fibroblasts, synovial, dermal, or thymic fibroblasts, were able to stimulate the HCQ.3 hybridoma and other COL2-specific T-cell hybridomas. Our experiments revealed that NIH/3T3 fibroblasts are able to activate COL2-specific T-cell hybridomas even in the absence of COL2 or a posttranslationally modified COL2 peptide. The mechanism of this unusual activation is contact-dependent and involves the T-cell receptor (TCR) complex.

Significance of Type II Collagen Posttranslational Modifications: From Autoantigenesis to Improved Diagnosis and Treatment of Rheumatoid Arthritis

Collagen type II (COL2), the main structural protein of hyaline cartilage, is considerably affected by autoimmune responses associated with the pathogenesis of rheumatoid arthritis (RA). Posttranslational modifications (PTMs) play a significant role in the formation of the COL2 molecule and supramolecular fibril organization, and thus, support COL2 function, which is crucial for normal cartilage structure and physiology. Conversely, the specific PTMs of the protein (carbamylation, glycosylation, citrullination, oxidative modifications and others) have been implicated in RA autoimmunity. The discovery of the anti-citrullinated protein response in RA, which includes anti-citrullinated COL2 reactivity, has led to the development of improved diagnostic assays and classification criteria for the disease. The induction of immunological tolerance using modified COL2 peptides has been highlighted as a potentially effective strategy for RA therapy. Therefore, the aim of this review is to summarize the recent knowledge on COL2 posttranslational modifications with relevance to RA pathophysiology, diagnosis and treatment. The significance of COL2 PTMs as a source of neo-antigens that activate immunity leading to or sustaining RA autoimmunity is discussed.

Autoimmune susceptible HLA class II motifs facilitate the presentation of modified neoepitopes to potentially autoreactive T cells

Rheumatoid arthritis (RA), multiple sclerosis (MS), type 1 diabetes (T1D), and celiac disease (CD), are strongly associated with susceptible HLA class II haplotypes. The peptide-binding pockets of these molecules are polymorphic, thus each HLA class II protein presents a distinct set of peptides to CD4⁺ T cells. Peptide diversity is increased through post-translational modifications, generating non-templated sequences that enhance HLA binding and/or T cell recognition. The high-risk HLA-DR alleles that confer susceptibility to RA are notable for their ability to accommodate citrulline, promoting responses to citrullinated self-antigens. Likewise, HLA-DQ alleles associated with T1D and CD favor the binding of deamidated peptides. In this review, we discuss structural features that promote modified self-epitope presentation, provide evidence supporting the relevance of T cell recognition of such antigens in disease processes, and make a case that interrupting the pathways that generate such epitopes and reprogramming neoepitope-specific T cells are key strategies for effective therapeutic intervention.

Characteristics of the (Auto)Reactive T Cells in Rheumatoid Arthritis According to the Immune Epitope Database

T cells are known to be involved in the pathogenesis of rheumatoid arthritis (RA). Accordingly, and to better understand T cells' contribution to RA, a comprehensive review based on an analysis of the Immune Epitope Database (IEDB) was conducted. An immune CD8+ T cell senescence response is reported in RA and inflammatory diseases, which is driven by active viral antigens from latent viruses and cryptic self-apoptotic peptides. RA-associated pro-inflammatory CD4+ T cells are selected by MHC class II and immunodominant peptides, which are derived from molecular chaperones, host extra-cellular and cellular peptides that could be post-translationally modified (PTM), and bacterial cross-reactive peptides. A large panel of techniques have been used to characterize (auto)reactive T cells and RA-associated peptides with regards to their interaction with the MHC and TCR, capacity to enter the docking site of the shared epitope (DRB1-SE), capacity to induce T cell proliferation, capacity to select T cell subsets (Th1/Th17, Treg), and clinical contribution. Among docking DRB1-SE peptides, those with PTM expand autoreactive and high-affinity CD4+ memory T cells in RA patients with an active disease. Considering original therapeutic options in RA, mutated, or altered peptide ligands (APL) have been developed and are tested in clinical trials.

Tolerogenic nanoparticles induce type II collagen-specific regulatory T cells and ameliorate osteoarthritis

Local inflammation in the joint is considered to contribute to osteoarthritis (OA) progression. Here, we describe an immunomodulating nanoparticle for OA treatment. Intradermal injection of lipid nanoparticles (LNPs) loaded with type II collagen (Col II) and rapamycin (LNP-Col II-R) into OA mice effectively induced Col II-specific anti-inflammatory regulatory T cells, substantially increased anti-inflammatory cytokine expression, and reduced inflammatory immune cells and proinflammatory cytokine expression in the joints. Consequently, LNP-Col II-R injection inhibited chondrocyte apoptosis and cartilage matrix degradation and relieved pain, while injection of LNPs loaded with a control peptide and rapamycin did not induce these events. Adoptive transfer of CD4⁺CD25⁺ T cells isolated from LNP-Col II-R-injected mice suggested that T_regs induced by LNP-Col II-R injection were likely responsible for the therapeutic effects. Collectively, this study suggests nanoparticle-mediated immunomodulation in the joint as a simple and effective treatment for OA.

Randomized phase I trial of antigen-specific tolerizing immunotherapy with peptide/calcitriol liposomes in ACPA+ rheumatoid arthritis

BACKGROUNDAntigen-specific regulation of autoimmune disease is a major goal. In seropositive rheumatoid arthritis (RA), T cell help to autoreactive B cells matures the citrullinated (Cit) antigen-specific immune response, generating RA-specific V domain glycosylated anti-Cit protein antibodies (ACPA VDG) before arthritis onset. Low or escalating antigen administration under "sub-immunogenic" conditions favors tolerance. We explored safety, pharmacokinetics, and immunological and clinical effects of s.c. DEN-181, comprising liposomes encapsulating self-peptide collagen II259-273 (CII) and NF-κB inhibitor 1,25-dihydroxycholecalciferol.METHODSA double-blind, placebo-controlled, exploratory, single-ascending-dose, phase I trial assessed the impact of low, medium, and high DEN-181 doses on peripheral blood CII-specific and bystander Cit64vimentin59-71-specific (Cit-Vim-specific) autoreactive T cell responses, cytokines, and ACPA in 17 HLA-DRB1*04:01+ or *01:01+ ACPA+ RA patients on methotrexate.RESULTSDEN-181 was well tolerated. Relative to placebo and normalized to baseline values, Cit-Vim-specific T cells decreased in patients administered medium and high doses of DEN-181. Relative to placebo, percentage of CII-specific programmed cell death 1+ T cells increased within 28 days of DEN-181. Exploratory analysis in DEN-181-treated patients suggested improved RA disease activity was associated with expansion of CII-specific and Cit-Vim-specific T cells; reduction in ACPA VDG, memory B cells, and inflammatory myeloid populations; and enrichment in CCR7+ and naive T cells. Single-cell sequencing identified T cell transcripts associated with tolerogenic TCR signaling and exhaustion after low or medium doses of DEN-181.CONCLUSIONThe safety and immunomodulatory activity of low/medium DEN-181 doses provide rationale to further assess antigen-specific immunomodulatory therapy in ACPA+ RA.TRIAL REGISTRATIONAnzctr.org.au identifier ACTRN12617001482358, updated September 8, 2022.FUNDINGInnovative Medicines Initiative 2 Joint Undertaking (grant agreement 777357), supported by European Union's Horizon 2020 research and innovation programme and European Federation of Pharmaceutical Industries and Associations; Arthritis Queensland; National Health and Medical Research Council (NHMRC) Senior Research Fellowship; and NHMRC grant 2008287.

Molecular Mimicry of the Rheumatoid Arthritis-Related Immunodominant T-Cell Epitope within Type II Collagen (CII260-270) by the Bacterial L-Asparaginase

The etiology of most autoimmune diseases, including rheumatoid arthritis (RA), remains unclear. Both genetic and environmental factors are believed to be involved in pathogenesis. Molecular mimicry is considered one of the mechanisms for the occurrence of autoimmune diseases. The aim of the study was to determine whether the bacterial peptide L-ASNase67-81, which mimics the immunodominant T-cell epitope CII259-273, can induce T-cell reactivity in blood samples from RA patients and healthy subjects through molecular mimicry. Using bioinformatic molecular modeling methods, we first determined whether the L-ASNase67-81 peptide binds to the HLA-DRB1*04:01 molecule and whether the formed MHCII–peptide complex interacts with the corresponding T-cell receptor. To validate the obtained results, leukocytes isolated from early RA patients and healthy individuals were stimulated in vitro with L-ASNase67-81 and CII259-273 peptides as well as with bacterial L-asparaginase or human type II collagen (huCII). The activated T cells (CD4+CD154+) were analyzed by flow cytometry (FACS), and the levels of cytokines produced (IL-2, IL-17A/F, and IFN-γ) were measured by ELISA. Our in silico analyses showed that the bacterial peptide L-ASNase67-81 binds better to HLA-DRB1*04:01 compared to the immunodominant T-cell epitope CII259-273, mimicking its structure and localization in the binding groove of MHCII. Six contact points were involved in the molecular interaction of the peptide with the TCR. FACS data showed that after in vitro stimulation with the L-ASNase67-81 peptide, the percentage of activated T cells (CD154⁺CD4⁺) was significantly increased in both cell cultures isolated from ERA patients and those isolated from healthy individuals, as higher values were observed for the ERA group (9.92 ± 0.23 vs. 4.82 ± 0.22). Furthermore, the ELISA assays revealed that after stimulation with L-ASNase67-81, a significant increase in the production of the cytokines IL-2, IL-17A/F, and IFN-γ was detected in the group of ERA patients. Our data showed that the bacterial L-ASNase67-81 peptide can mimic the immunodominant T-cell epitope CII259-273 and activate HLA-DRB1*04:01-restricted T cells as well as induce cytokine production in cells isolated from ERA patients. These results are the first to demonstrate that a specific bacterial antigen could play a role in the pathogenesis of RA, mimicking the immunodominant T-cell epitope from type II collagen.

Key interactions in the trimolecular complex consisting of the rheumatoid arthritis-associated DRB1*04:01 molecule, the major glycosylated collagen II peptide and the T-cell receptor

Objectives

Rheumatoid arthritis (RA) is an autoimmune disease strongly associated with the major histocompatibility complex (MHC) class II allele DRB1*04:01, which encodes a protein that binds self-peptides for presentation to T cells. This study characterises the autoantigen-presenting function of DRB1*04:01 (HLA-DRA*01:01/HLA-DRB1*04:01) at a molecular level for prototypic T-cell determinants, focusing on a post-translationally modified collagen type II (Col2)-derived peptide.

Methods

The crystal structures of DRB1*04:01 molecules in complex with the peptides HSP70_289-306, citrullinated CILP_982-996 and galactosylated Col2_259-273 were determined on cocrystallisation. T cells specific for Col2_259-273 were investigated in peripheral blood mononuclear cells from patients with DRB1*04:01-positive RA by cytofluorometric detection of the activation marker CD154 on peptide stimulation and binding of fluorescent DRB1*0401/Col2_259-273 tetramer complexes. The cDNAs encoding the T-cell receptor (TCR) α-chains and β-chains were cloned from single-cell sorted tetramer-positive T cells and transferred via a lentiviral vector into TCR-deficient Jurkat 76 cells.

Results

The crystal structures identified peptide binding to DRB1*04:01 and potential side chain exposure to T cells. The main TCR recognition sites in Col2_259-273 were lysine residues that can be galactosylated. RA T-cell responses to DRB1*04:01-presented Col2_259-273 were dependent on peptide galactosylation at lysine 264. Dynamic molecular modelling of a functionally characterised Col2_259-273-specific TCR complexed with DRB1*04:01/Col2_259-273 provided evidence for differential allosteric T-cell recognition of glycosylated lysine 264.

Conclusions

The MHC-peptide-TCR interactions elucidated in our study provide new molecular insights into recognition of a post-translationally modified RA T-cell determinant with a known dominant role in arthritogenic and tolerogenic responses in murine Col2-induced arthritis.

The shared susceptibility epitope of HLA-DR4 binds citrullinated self-antigens and the TCR

Individuals expressing HLA-DR4 bearing the shared susceptibility epitope (SE) have an increased risk of developing rheumatoid arthritis (RA). Posttranslational modification of self-proteins via citrullination leads to the formation of neoantigens that can be presented by HLA-DR4 SE allomorphs. However, in T cell-mediated autoimmunity, the interplay between the HLA molecule, posttranslationally modified epitope(s), and the responding T cell repertoire remains unclear. In HLA-DR4 transgenic mice, we show that immunization with a Fibβ-74cit_69-81 peptide led to a population of HLA-DR4^{Fibβ-74cit69-81} tetramer⁺ T cells that exhibited biased T cell receptor (TCR) β chain usage, which was attributable to selective clonal expansion from the preimmune repertoire. Crystal structures of pre- and postimmune TCRs showed that the SE of HLA-DR4 represented a main TCR contact zone. Immunization with a double citrullinated epitope (Fibβ-72,74cit_69-81) altered the responding HLA-DR4 tetramer⁺ T cell repertoire, which was due to the P2-citrulline residue interacting with the TCR itself. We show that the SE of HLA-DR4 has dual functionality, namely, presentation and a direct TCR recognition determinant. Analogous biased TCR β chain usage toward the Fibβ-74cit_69-81 peptide was observed in healthy HLA-DR4⁺ individuals and patients with HLA-DR4⁺ RA, thereby suggesting a link to human RA.

Inhibition of acid ceramidase regulates MHC class II antigen presentation and suppression of autoimmune arthritis

The bioactive sphingolipid ceramide affects immune responses although its effect on antigen (Ag) processing and delivery by HLA class II to CD4+T-cells remains unclear. Therefore, we examined the actions of a novel cell-permeable acid ceramidase (AC) inhibitor [(1R,2R) N myristoylamino-(4'-nitrophenyl)-propandiol-1,3] on antigen presentation and inflammatory cytokine production by Ag-presenting cells (APCs) such as B-cells, macrophages, and dendritic cells. We found that AC inhibition in APCs perturbed Ag-processing and presentation via HLA-DR4 (MHC class II) proteins as measured by coculture assay and T-cell production of IL-2. Mass spectral analyses showed that B13 treatment significantly raised levels of four types of ceramides in human B-cells. B13 treatment did not alter Ag internalization and class II protein expression, but significantly inhibited lysosomal cysteinyl cathepsins (B, S and L) and thiol-reductase (GILT), HLA class II Ag-processing, and generation of functional class II-peptide complexes. Ex vivo Ag presentation assays showed that inhibition of AC impaired primary and recall CD4+T-cell responses and cytokine production in response against type II collagen. Further, B13 delayed onset and reduced severity of inflamed joints and cytokine production in the collagen-induced arthritis mouse model in vivo. These findings suggest that inhibition of AC in APCs may dysregulate endolysosomal proteases and HLA class II-associated self-antigen presentation to CD4+T-cells, attenuating inflammatory cytokine production and suppressing host autoimmune responses.

Modulation of receptor binding to collagen by glycosylated 5-hydroxylysine: Chemical biology approaches made feasible by Carpino's Fmoc group

The creation of the 9-fluorenylmethoxycarbonyl (Fmoc) group by the Carpino laboratory facilitated the synthesis of peptides containing acid-sensitive groups, such as O-linked glycosides. To fully investigative collagen biochemistry, one needs to assemble peptides that possess glycosylated 5-hydroxylysine (Hyl). A convenient method for the synthesis of Fmoc-Hyl(ε-tert-butyloxycarbonyl (Boc),O-tert-butyldimethylsilyl (TBDMS)) and efficient methods for the synthesis of Fmoc-Hyl[ε-Boc,O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)] have been developed. Glycosylated Fmoc-Hyl derivatives were used to construct a series of types I-IV collagen-model triple-helical peptides (THPs) that incorporated known or proposed receptor binding sites. Glycosylation of Hyl was found to strongly down-regulate the binding of CD44 and the α3β1 integrin to collagen, while the impact on α2β1 integrin binding was more modest. Molecular modeling of integrin binding indicated that Hyl glycosylation directly impacted the association between the α3β1 integrin metal ion-dependent adhesion site (MIDAS) and the receptor binding site within type IV collagen. The Fmoc solid-phase strategy ultimately allowed for chemical biology approaches to be utilized to study tumor cell interactions with glycosylated collagen sequences and document the modulation of receptor interactions by Hyl posttranslational modification.

Memory CD4+ T Cells in Immunity and Autoimmune Diseases

CD4⁺ T helper (Th) cells play central roles in immunity in health and disease. While much is known about the effector function of Th cells in combating pathogens and promoting autoimmune diseases, the roles and biology of memory CD4⁺ Th cells are complex and less well understood. In human autoimmune diseases such as multiple sclerosis (MS), there is a critical need to better understand the function and biology of memory T cells. In this review article we summarize current concepts in the field of CD4⁺ T cell memory, including natural history, developmental pathways, subsets, and functions. Furthermore, we discuss advancements in the field of the newly-described CD4⁺ tissue-resident memory T cells and of CD4⁺ memory T cells in autoimmune diseases, two major areas of important unresolved questions in need of answering to advance new vaccine design and development of novel treatments for CD4⁺ T cell-mediated autoimmune diseases.

Autophagy enhances mesenchymal stem cell-mediated CD4+ T cell migration and differentiation through CXCL8 and TGF-β1

BACKGROUND

Mesenchymal stem cells (MSCs) have been recognized as a promising tool for the treatment of various inflammatory disorders and autoimmune diseases. Stress conditions affect immune-mediated treatment and activate autophagy in MSCs. However, whether autophagy affects the MSC-mediated recruitment and differentiation of CD4⁺ T cells remains elusive.

METHODS

MSCs were pretreated with 3-methyladenine (3-MA) and rapamycin to regulate autophagy, and then co-cultured with CD4⁺ T cells. CD4⁺ T cell migration and differentiation were detected by flow cytometry. Further, gene expression levels of well-known chemokines were analyzed by quantitative real-time PCR. Enzyme-linked immunosorbent assays and western blot analysis were performed to detect C-X-C motif chemokine ligand 8 (CXCL8) and transforming growth factor (TGF)-β1 protein levels. An exogenous antibody and short hairpin RNA were used to regulate CXCL8 and TGF-β1 levels, which enabled us to evaluate how autophagy affected MSC-mediated CD4⁺ T cell migration and differentiation.

RESULTS

3-MA inhibited autophagy in MSCs, which was activated by rapamycin. Rapamycin increased the migration of CD4⁺ T cells, whereas 3-MA decreased their migration. Mechanistically, we found that autophagy strengthened CXCL8 secretion, and the addition of exogenous CXCL8 and an anti-CXCL8 antibody eliminated the difference of CD4⁺ T cell migration among groups. Further, the ratio of regulatory T (Treg) cells was increased in rapamycin-pretreated MSCs, but the ratio of T helper 1 (Th1) cells was decreased, while pretreatment of MSCs with 3-MA induced the opposite effect compared with the control group. TGF-β1 overexpression and knockdown using lentiviruses rectified the differences in the ratios of Treg and Th1 cells among the groups.

CONCLUSION

This study demonstrates that autophagy of mesenchymal stem cells mediates CD4⁺ T cell migration and differentiation through CXCL8 and TGF-β1, respectively. These results provide a potential new strategy for improving MSC-mediated therapy.

T cells specific for post-translational modifications escape intrathymic tolerance induction

Establishing effective central tolerance requires the promiscuous expression of tissue-restricted antigens by medullary thymic epithelial cells. However, whether central tolerance also extends to post-translationally modified proteins is not clear. Here we show a mouse model of autoimmunity in which disease development is dependent on post-translational modification (PTM) of the tissue-restricted self-antigen collagen type II. T cells specific for the non-modified antigen undergo efficient central tolerance. By contrast, PTM-reactive T cells escape thymic selection, though the PTM variant constitutes the dominant form in the periphery. This finding implies that the PTM protein is absent in the thymus, or present at concentrations insufficient to induce negative selection of developing thymocytes and explains the lower level of tolerance induction against the PTM antigen. As the majority of self-antigens are post-translationally modified, these data raise the possibility that T cells specific for other self-antigens naturally subjected to PTM may escape central tolerance induction by a similar mechanism.

Post-translational modifications are associated with autoimmune diseases but definitive evidence of their contribution to escape from central tolerance mechanisms is needed. Here, the authors show that T cells specific for post-translational modifications of type II collagen escape intrathymic tolerance induction in a mouse model of rheumatoid arthritis.

Flow Cytometric Clinical Immunomonitoring Using Peptide-MHC Class II Tetramers: Optimization of Methods and Protocol Development

With the advent of novel strategies to induce tolerance in autoimmune and autoimmune-like conditions, clinical trials of antigen-specific tolerizing immunotherapy have become a reality. Besides safety, it will be essential to gather mechanistic data on responding CD4⁺ T cells to assess the effects of various immunomodulatory approaches in early-phase trials. Peptide–MHC class II (pMHCII) multimers are an ideal tool for monitoring antigen-specific CD4⁺ T cell responses in unmanipulated cells directly ex vivo. Various protocols have been published but there are reagent and assay limitations across laboratories that could hinder their global application to immune monitoring. In this methodological analysis, we compare protocols and test available reagents to identify sources of variability and to determine the limitations of the tetramer binding assay. We describe a robust pMHCII flow cytometry-based assay to quantify and phenotype antigen-specific CD4⁺ T cells directly ex vivo from frozen peripheral blood mononuclear cell samples, which we suggest should be tested across various laboratories to standardize immune-monitoring results.

Inflammatory Cell Migration in Rheumatoid Arthritis: A Comprehensive Review

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease that primarily affects the joints. Self-reactive B and T lymphocytes cooperate to promote antibody responses against self proteins and are major drivers of disease. T lymphocytes also promote RA independently of B lymphocytes mainly through the production of key inflammatory cytokines, such as IL-17, that promote pathology. While the innate signals that initiate self-reactive adaptive immune responses are poorly understood, the disease is predominantly caused by inflammatory cellular infiltration and accumulation in articular tissues, and by bone erosions driven by bone-resorbing osteoclasts. Osteoclasts are giant multinucleated cells formed by the fusion of multiple myeloid cells that require short-range signals, such as the cytokines MCSF and RANKL, for undergoing differentiation. The recruitment and positioning of osteoclast precursors to sites of osteoclast differentiation by chemoattractants is an important point of control for osteoclastogenesis and bone resorption. Recently, the GPCR EBI2 and its oxysterol ligand 7a, 25 dihydroxycholesterol, were identified as important regulators of osteoclast precursor positioning in proximity to bone surfaces and of osteoclast differentiation under homeostasis. In chronic inflammatory diseases like RA, osteoclast differentiation is also driven by inflammatory cytokines such as TNFa and IL-1, and can occur independently of RANKL. Finally, there is growing evidence that the chemotactic signals guiding osteoclast precursors to inflamed articular sites contribute to disease and are of great interest. Furthering our understanding of the complex osteoimmune cell interactions should provide new avenues of therapeutic intervention for RA.

Mechanisms involved in triggering rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory syndrome with a strong autoimmune component. The autoantigens in RA are neither tissue nor organ-specific, but comprise a broad collection of post-translational modified proteins, such as citrullinated proteins. These modifications are likely to be triggered by innate stimuli. In genetically susceptible hosts, they can lead to a more substantiated secondary autoimmune reaction targeting the joints and precipitating the clinical onset of RA. Both innate and adaptive mechanisms will then closely interplay to promote chronic joint inflammation in the several absence of appropriate treatment. This scenario, is shared with other autoimmune diseases where potentially pathogenic immune responses are present already before disease onset. Better understanding of these processes will allow both earlier diagnosis of RA and identification of those healthy individuals that are at risk of developing disease, opening possibilities for disease prevention. In this review, we discuss the iterative processes of innate and adaptive immunity responsible for the (longitudinal) development of immune reactions that may contribute to the development of RA.

Xianfanghuomingyin, a Chinese Compound Medicine, Modulates the Proliferation and Differentiation of T Lymphocyte in a Collagen-Induced Arthritis Mouse Model

In traditional Chinese medicine (TCM), xianfanghuomingyin (XFHM) is used to treat autoimmune diseases, including rheumatoid arthritis (RA). Here, we studied the mechanisms underlying its treatment effects, especially its anti-inflammatory effects in a collagen-induced arthritis (CIA) mouse model. We found that cartilage destruction and pannus formation were alleviated by treatment with XFHM. The abnormal differentiation of Th1 and Th17 cells was downregulated significantly by XFHM, and Th2 and Treg cells were upregulated. Moreover, the expression levels of specific cytokines and transcription factors related to Th1 cells (interferon γ [IFNγ], T-bet) and Th17 cells (interleukin- [IL-] 17) and the nuclear receptor retinoic acid receptor-related orphan receptor-gamma (RORγ) were downregulated. Serum IL-4 and GATA-3, which contribute to Th2 cells differentiation, increased significantly after XFHM administration. These results indicate that XFHM can restore the balance of T lymphocytes and reestablish the immunological tolerance to inhibit autoinflammatory disorder of RA. Taken together, XFHM can be used as a complementary or alternative traditional medicine to treat RA.

Schistosoma japonicum cystatin attenuates murine collagen-induced arthritis

Recombinant SjCystatin (rSjCystatin), a recombinant protein of Schistosoma japonicum cystatin, has been reported to have an effect on immunoregulation mediated by IL-10 induction. Rheumatoid arthritis (RA) is a common autoimmune inflammatory arthropathy, and recombinant immune-modulating drugs for RA treatment are under development. We aimed to study the putative immune regulation of rSjCystatin and its prophylactic/therapeutic effects on murine collagen-induced arthritis (CIA). CIA was induced in DBA/1 mice by inoculation with bovine collagen II (CII). rSjCystatin was administered prior or post development of CIA. The severity of CIA was assessed using established clinical and histopathological scoring systems. The incidence was also determined. The CII-specific antibodies in sera and cytokines in splenocyte culture supernatants were measured by ELISA. Th1/Th2/Th17 cells and Tregs development in splenocytes were monitored by flow cytometry. The inflammatory mediators in the diseased joint were semiquantitated by qPCR. Prophylactic injection of rSjCystatin attenuated paw clinical scores, incidence, and histopathology scores of joints in CIA mice. The arthritis-alleviative effects were closely associated with the augmentation of IL-4, IL-10, and collagen-specific IgG1, and with the distinct reduction of IFN-γ, collagen-specific IgG2a, and the marked decrease of proinflammatory cytokines IL-6, IL-17, and TNF-α and RANKL. The data indicate that rSjCystatin may prevent cartilage destruction and inflammation of joints in CIA mice. The effects are related to the inhibitory modulation of Th1 and Th17 and upregulation of Tregs and Th2 via a shift of cytokines profiling from Th1 to Th2 response.

TCR repertoire sequencing identifies synovial Treg cell clonotypes in the bloodstream during active inflammation in human arthritis

OBJECTIVES

The imbalance between effector and regulatory T (Treg) cells is crucial in the pathogenesis of autoimmune arthritis. Immune responses are often investigated in the blood because of its accessibility, but circulating lymphocytes are not representative of those found in inflamed tissues. This disconnect hinders our understanding of the mechanisms underlying disease. Our goal was to identify Treg cells implicated in autoimmunity at the inflamed joints, and also readily detectable in the blood upon recirculation.

METHODS

We compared Treg cells of patients with juvenile idiopathic arthritis responding or not to therapy by using: (i) T cell receptor (TCR) sequencing, to identify clonotypes shared between blood and synovial fluid; (ii) FOXP3 Treg cell-specific demethylated region DNA methylation assays, to investigate their stability and (iii) flow cytometry and suppression assays to probe their tolerogenic functions.

RESULTS

We found a subset of synovial Treg cells that recirculated into the bloodstream of patients with juvenile idiopathic and adult rheumatoid arthritis. These inflammation-associated (ia)Treg cells, but not other blood Treg cells, expanded during active disease and proliferated in response to their cognate antigens. Despite the typical inflammatory-skewed balance of immune mechanisms in arthritis, iaTreg cells were stably committed to the regulatory lineage and fully suppressive. A fraction of iaTreg clonotypes were in common with pathogenic effector T cells.

CONCLUSIONS

Using an innovative antigen-agnostic approach, we uncovered a population of bona fide synovial Treg cells readily accessible from the blood and selectively expanding during active disease, paving the way to non-invasive diagnostics and better understanding of the pathogenesis of autoimmunity.

Feeding transgenic plants that express a tolerogenic fusion protein effectively protects against arthritis

Although much explored, oral tolerance for treatment of autoimmune diseases still awaits the establishment of novel and effective vectors. We investigated whether the tolerogenic CTA1(R7K)-COL-DD fusion protein can be expressed in edible plants, to induce oral tolerance and protect against arthritis. The fusion protein was recombinantly expressed in Arabidopsis thaliana plants, which were fed to H-2(q) -restricted DBA/1 mice to assess the preventive effect on collagen-induced arthritis (CIA). The treatment resulted in fewer mice exhibiting disease and arthritis scores were significantly reduced. Immune suppression was evident in treated mice, and serum biomarkers for inflammation as well as anticollagen IgG responses were reduced. In spleen and draining lymph nodes, CD4(+) T-cell responses were reduced. Concomitant with a reduced effector T-cell activity with lower IFNγ, IL-13 and IL-17A production, we observed an increase in IL-10 production to recall antigen stimulation in vitro, suggesting reduced Th1, Th2 and Th17 activity subsequent to up-regulated IL-10 and regulatory T-cell (Treg) functions. This study shows that edible plants expressing a tolerogen were effective at stimulating CD4 T-cell tolerance and in protecting against CIA disease. Our study conveys optimism as to the potential of using edible plants for oral treatment of rheumatoid arthritis.

Collagen Specific T-Cell Repertoire and HLA-DR Alleles: Biomarkers of Active Refractory Rheumatoid Arthritis

Rheumatoid arthritis (RA) is characterized by chronic joint inflammation and associates with HLA-DRB1*04. The Collagen IIp_261-273-specific T cell repertoire in the peripheral blood of DR4 + patients at the onset of the disease shows a restricted TCR-beta chain usage among which the most frequent is TRBV25.

To define whether this group of DR4-restricted collagen-specific shared T cell could represent markers of active-severe disease and response to therapy, 90 subjects affected by early-RA were enrolled in the study; peripheral blood mononuclear cells were cultured with or without the human collagen II peptide p261-273 and were examined by immunoscope analysis for the usage of the previously identified shared TCR-beta chains.

We report that the presence of T cells carrying rearrangement TRBV25 associated with HLA-DR haplotype and disease activity. HLA-DRB1* haplotypes 04–04, 04–01 and 04–11 were significantly associated with usage of TRBV25, higher disease activity at the onset of disease and poor response to DMARDs.

Finally, the HLA-DRB1* haplotype appeared complementary with current serologic tools to predict good and poor responders in a treat to target strategy. The data reported here offer clues to predict the course of the disease and to foresee personalized treatments in RA patients.

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In DR4 + RA patients disease activity is associated with detection of Collagen_261-273-specific T cells carrying TRBV25.

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HLA-DR 04/04, 04/01 and 04/11 alleles were associated with TRBV25, DAS at the onset, and poor response to DMARDs.

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These findings could lead to tailor the treatment in the subgroup of patients with an active refractory disease.

In the era of costly medical care with monoclonal antibodies and new molecules, and of an increasing request of a personalized medicine, a relevant socio-economic problem in the management of Rheumatoid Arthritis patients is the possible identification of the subgroups of poor responders to treatment. Our study aimed to detect the refractory active patients using an HLA-DR test (available in most hospital centers) combined with a relatively new biomarker of active disease expressed on the cell surface of autoreactive T cells. These tests appear complementary tools to identify the best and the poor responders to a “treat to target strategy”.

Immunological evaluation of rheumatoid arthritis patients treated with itolizumab

Rheumatoid arthritis is an autoimmune disease characterized by joint inflammation that affects approximately 1% of the general population. Itolizumab, a monoclonal antibody specific for the human CD6 molecule mainly expressed on T lymphocytes, has been shown to inhibit proliferation of T cells and proinflammatory cytokine production in psoriasis patients. We have now assessed the immunological effect of itolizumab in combination with methotrexate in rheumatoid arthritis by analyzing clinical samples taken from 30 patients enrolled in a clinical trial. T and B cell subpopulations were measured at different time points of the study. Plasma cytokine levels and anti-idiotypic antibody response to itolizumab were also evaluated. The combined treatment of itolizumab and methotrexate led to a reduction in the frequency of T cell subpopulations, and plasma levels of proinflammatory cytokines showed a significant decrease up to at least 12 weeks after treatment ended. No anti-idiotypic antibody response was detected. These results support the relevance of the CD6 molecule as a therapeutic target for the treatment of this disease.

T Cell Migration in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation in joints, associated with synovial hyperplasia and with bone and cartilage destruction. Although the primacy of T cell-related events early in the disease continues to be debated, there is strong evidence that autoantigen recognition by specific T cells is crucial to the pathophysiology of rheumatoid synovitis. In addition, T cells are key components of the immune cell infiltrate detected in the joints of RA patients. Initial analysis of the cytokines released into the synovial membrane showed an imbalance, with a predominance of proinflammatory mediators, indicating a deleterious effect of Th1 T cells. There is nonetheless evidence that Th17 cells also play an important role in RA. T cells migrate from the bloodstream to the synovial tissue via their interactions with the endothelial cells that line synovial postcapillary venules. At this stage, selectins, integrins, and chemokines have a central role in blood cell invasion of synovial tissue, and therefore in the intensity of the inflammatory response. In this review, we will focus on the mechanisms involved in T cell attraction to the joint, the proteins involved in their extravasation from blood vessels, and the signaling pathways activated. Knowledge of these processes will lead to a better understanding of the mechanism by which the systemic immune response causes local joint disorders and will help to provide a molecular basis for therapeutic strategies.

Coeliac disease and rheumatoid arthritis: similar mechanisms, different antigens

Rheumatoid arthritis (RA) and coeliac disease are inflammatory diseases that both have a strong association with class II HLAs: individuals carrying HLA-DQ2.5 and/or HLA-DQ8 alleles have an increased risk of developing coeliac disease, whereas those carrying HLA-DR shared epitope alleles exhibit an increased risk of developing RA. Although the molecular basis of the association with specific HLA molecules in RA remains poorly defined, an immune response against post-translationally modified protein antigens is a hallmark of each disease. In RA, understanding of the pathogenetic role of B-cell responses to citrullinated antigens, including vimentin, fibrinogen and α-enolase, is rapidly growing. Moreover, insight into the role of HLAs in the pathogenesis of coeliac disease has been considerably advanced by the identification of T-cell responses to deamidated gluten antigens presented in conjunction with predisposing HLA-DQ2.5 molecules. This article briefly reviews these advances and draws parallels between the immune mechanisms leading to RA and coeliac disease, which point to a crucial role for T-cell-B-cell cooperation in the development of full-blown disease. Finally, the ways in which these novel insights are being exploited therapeutically to re-establish tolerance in patients with RA and coeliac disease are described.

A circulating reservoir of pathogenic-like CD4+ T cells shares a genetic and phenotypic signature with the inflamed synovial micro-environment

Objectives

Systemic immunological processes are profoundly shaped by the micro-environments where antigen recognition occurs. Identifying molecular signatures distinctive of such processes is pivotal to understand pathogenic immune responses and manipulate them for therapeutic purposes. Unfortunately, direct investigation of peripheral tissues, enriched in pathogenic T cells, is often impossible or imposingly invasive in humans. Conversely, blood is easily accessible, but pathogenic signatures are diluted systemically as a result of the strict compartmentalisation of immune responses. In this work, we aimed at defining immune mediators shared between the bloodstream and the synovial micro-environment, and relevant for disease activity in autoimmune arthritis.

Methods

CD4⁺ T cells from blood and synovium of patients with juvenile idiopathic arthritis (JIA) were immunophenotyped by flow cytometry. The TCR repertoire of a circulating subset showing similarity with the synovium was analysed through next-generation sequencing of TCR β-chain CDR3 to confirm enrichment in synovial clonotypes. Finally, clinical relevance was established by monitoring the size of this subset in the blood of patients with JIA and rheumatoid arthritis (RA).

Results

We identified a small subset of circulating CD4⁺ T cells replicating the phenotypical signature of lymphocytes infiltrating the inflamed synovium. These circulating pathogenic-like lymphocytes (CPLs) were enriched in synovial clonotypes and they exhibited strong production of pro-inflammatory cytokines. Importantly, CPLs were expanded in patients with JIA, who did not respond to therapy, and also correlated with disease activity in patients with RA.

Conclusions

CPLs provide an accessible reservoir of pathogenic cells recirculating into the bloodstream and correlating with disease activity, to be exploited for diagnostic and research purposes.

Induction of bone loss in DBA/1J mice immunized with citrullinated autologous mouse type II collagen in the absence of adjuvant

Joint damage in rheumatoid arthritis (RA) is characterized by cartilage and bone loss resulting in pain, deformity, and loss of joint function. Anti-citrullinated protein antibody (ACPA) has been implicated in RA pathogenesis and predicts radiographical joint damage and clinical severity. Therefore, the purpose of this study was to assess bone loss by micro-CT, histological joint damage, and ACPA levels using a mouse model of RA. Arthritis was induced by immunizing DBA/1 mice with autologous citrullinated type II mouse collagen (CIT-CII) weekly for 4 weeks. Mice immunized with autologous CII served as controls. At week 5, mice were killed, ACPA levels determined, and micro-CT performed to quantitatively analyze bone damage. Micro-CT analysis revealed significant loss of bone density, volume, and surface (p < 0.05) in bone peripheral to the inflamed joints of CIT-CII animals compared to CII controls. Histological staining demonstrated cartilage, proteoglycan, joint collagen, and bone collagen loss in the CIT-CII group compared to CII. Serum ACPA levels were increased (p = 0.03) in the CIT-CII group compared to CII, and these levels were inversely correlated with bone quantity and quality. In this study, we demonstrate that immunization with autologous CIT-CII initiates significant systemic bone and articular cartilage loss in the absence of adjuvant. Significant inverse correlations of circulating ACPA and bone quality/quantity were present. ACPA levels predict the adverse bone morphological changes in this model of early RA.

Lungs, joints and immunity against citrullinated proteins in rheumatoid arthritis

Rheumatoid arthritis (RA) is a prototype for a criterion-defined inflammatory disease, for which the aetiology and initial molecular pathogenesis has been elusive for a long time. We describe in this Review how studies on the interplay between specific immunity, alongside genetic and environmental predisposing factors, provide new tools to understand the molecular basis of distinct subsets of the disease. A particular emphasis is on the possibility that pathogenic immune reactions might be initiated at other sites than the joints, and that the lungs could harbour such sites. New data strengthen this concept, showing that local immunity towards citrullinated proteins and accompanying inflammation might be present in the lungs early during disease development. This progress makes RA an interesting case for the future development of therapies that might be directed against disease-inducing immunity even before inflammation and destruction of joints has begun.

The lung may play a role in the pathogenesis of rheumatoid arthritis

Multiple studies have identified strong associations between the lung and rheumatoid arthritis (RA). Such studies identify a high prevalence of lung disease, both airways and parenchymal disease, in subjects with clinically classifiable RA. It has been suggested that lung disease in RA results from targeting of the lung from circulating autoimmunity or other factors such as medications. However, findings that lung disease, specifically inflammatory airways disease, and lung generation of autoimmunity can be present before the onset of joint symptoms suggest that immune reactions in the lung may be involved in the initial development of RA-related autoimmunity. Herein we review these issues in detail, as well as outline a potential research agenda to understand the natural history of lung involvement in RA and its relation to the overall pathogenesis of RA.

Pathogenesis and prevention of rheumatic disease: focus on preclinical RA and SLE

Established and emerging data demonstrate that a 'preclinical' period of disease precedes the onset of clinical rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), as well as other autoimmune rheumatic diseases (ARDs).This preclinical stage of development of disease is characterized by abnormalities in disease-related biomarkers before the onset of the clinically apparent signs and symptoms. Numerous genetic and environmental risk factors for ARDs have also been identified, and many of these factors are likely to act before the clinical appearance of tissue injury to initiate and/or propagate autoimmunity and autoimmune disease. Thus, biomarkers representative of these autoimmune processes could potentially be used in conjunction with other clinical parameters during the preclinical period of ARDs to predict the future development of clinically apparent disease. This Review focuses on the preclinical stages of RA and SLE, as our current understanding of these diseases can be used to present an overall model of the development of ARDs that might ultimately be used to develop screening programmes and preventive strategies. Important considerations for the future development of such approaches, in particular, the issues that require additional research and how they might be addressed, are also discussed.

Of mice and men: how animal models advance our understanding of T-cell function in RA

The involvement of autoreactive T cells in the pathogenesis of rheumatoid arthritis (RA) as well as in autoimmune animal models of arthritis has been well established; however, unanswered questions, such as the role of joint-homing T cells, remain. Animal models of arthritis are superb experimental tools in demonstrating how T cells trigger joint inflammation, and thus can help to further our knowledge of disease mechanisms and potential therapies. In this Review, we discuss the similarities and differences in T-cell subsets and functions between RA and mouse arthritis models. For example, various T-cell subsets are involved in both human and mouse arthritis, but differences might exist in the cytokine regulation and plasticity of these cells. With regard to joint-homing T cells, an abundance of synovial T cells is present in humans compared with mice. On the other hand, local expansion of type 17 T-helper (TH17) cells is observed in some animal models, but not in RA. Finally, whereas T-cell depletion therapy essentially failed in RA, antibody targeting of T cells can work, at least preventatively, in most arthritis models. Clearly, additional human and animal studies are needed to fill the gap in our understanding of the specific contribution of T-cell subsets to arthritis in mice and men.

Exposure to mimivirus collagen promotes arthritis

Collagens, the most abundant proteins in animals, also occur in some recently described nucleocytoplasmic large DNA viruses such as Mimiviridae, which replicate in amoebae. To clarify the impact of viral collagens on the immune response of animals exposed to Mimiviridae, we have investigated the localization of collagens in Acanthamoeba polyphaga mimivirus particles and the response of mice to immunization with mimivirus particles. Using protein biotinylation, we have first shown that viral collagen encoded by open reading frame L71 is present at the surface of mimivirus particles. Exposure to mimivirus collagens elicited the production of anti-collagen antibodies in DBA/1 mice immunized intradermally with mimivirus protein extracts. This antibody response also targeted mouse collagen type II and was accompanied by T-cell reactivity to collagen and joint inflammation, as observed in collagen-induced arthritis following immunization of mice with bovine collagen type II. The broad distribution of nucleocytoplasmic large DNA viruses in the environment suggests that humans are constantly exposed to such large virus particles. A survey of blood sera from healthy human subjects and from rheumatoid arthritis patients indeed demonstrated that 30% of healthy-subject and 36% of rheumatoid arthritis sera recognized the major mimivirus capsid protein L425. Moreover, whereas 6% of healthy-subject sera recognized the mimivirus collagen protein L71, 22% of rheumatoid arthritis sera were positive for mimivirus L71. Accordingly, our study shows that environmental exposure to mimivirus represents a risk factor in triggering autoimmunity to collagens.

Th17 memory cells: live long and proliferate

The development of immune memory is a double-edged sword, helping to maintain health by preventing repeated infections but also driving chronic inflammation when dysregulated. Th17 cells are now well-known as major drivers of autoimmune disease but also play roles in protective immune responses against pathogens. This mini-review will focus on the recent evidence for long-lived, robust Th17 memory cell populations in mouse models and humans, and their functional roles in mediating host protection and chronic disease states.

T cells out of control--impaired immune regulation in the inflamed joint

Since the discovery of FOXP3+ regulatory T (T(REG)) cells over 15 years ago, intensive research has focused on their presence, phenotype and function in autoimmune disease. Whether deficiencies in T(REG) cells underlie autoimmune pathology and whether, or how, therapeutic approaches based on these cells might be successful is still the subject of debate. The potential role of T(REG)-cell extrinsic factors, such as proinflammatory cytokines and resistance of effector T cells to suppression, as the cause of regulatory defects in chronic autoimmune inflammation is an intensive area of research. It is now clear that, at the site of inflammation, antigen presenting cells (APCs) and proinflammatory cytokines drive effector T cell skewing and plasticity, and that these T cells can become unresponsive to regulation. In addition, expansion and function of T(REG) cells is affected by the inflammatory environment; indeed, new data suggest that, in certain conditions, T(REG) cells promote inflammation. This Review summarizes the latest findings on changes in effector T cell homeostasis in autoimmune disease and focuses on how mechanisms that normally regulate these cells are affected in the inflamed joints of patients with arthritis. These findings have important clinical implications and will affect the development of new therapeutic strategies for autoimmune arthritis.

Comparative analysis of collagen type II-specific immune responses during development of collagen-induced arthritis in two B10 mouse strains

Introduction

Immune responses against collagen type II (CII) are crucial for the development of collagen-induced arthritis (CIA). The aim of the present study was to evaluate and compare the CII-directed T cell and antibody specificity at different time points in the course of CIA using two mouse strains on the B10 genetic background - B10.Q, expressing A^q MHC class II molecules, and B10.DR4.Ncf1^*/*, expressing human rheumatoid arthritis-associated MHC II DR4 molecules (DRA*0101/DRB*0401).

Methods

B10.Q and B10.DR4.Ncf1^*/* mice were immunized with CII emulsified in adjuvant and development of CIA was assessed. T cells from draining lymph nodes were restimulated in vitro with CII peptides and interferon-gamma (IFN-γ) levels in culture supernatants were evaluated by ELISA. CII-specific antibody levels in serum samples were measured by ELISA.

Results

At four different CIA time points we analyzed T cell specificity to the immunodominant CII epitope 259-273 (CII259-273) and several posttranslationally modified forms of CII259-273 as well as antibody responses to three B cell immunodominant epitopes on CII (C1, U1, J1). Our data show that CII-specific T and B cell responses increase dramatically after disease onset in both strains and are sustained during the disease course. Concerning anti-CII antibody fine specificity, during all investigated stages of CIA the B10.Q mice responded predominantly to the C1 epitope, whereas the B10.DR4.Ncf1^*/* mice also recognized the U1 epitope. In the established disease phase, T cell reactivity toward the galactosylated CII259-273 peptide was similar between the DR4- and the A^q-expressing strains whereas the response to the non-modified CII peptide was dramatically enhanced in the DR4 mice compared with the B10.Q. In addition, we show that the difference in the transgenic DR4-restricted T cell specificity to CII259-273 is not dependent on the degree of glycosylation of the collagen used for immunization.

Conclusions

The present study provides important evaluation of CII-specific immune responses at different phases during CIA development as well as a comparative analysis between two CIA mouse models. We indicate significant differences in CII T cell and antibody specificities between the two strains and highlight a need for improved humanized B10.DR4 mouse model for rheumatoid arthritis.

C57BL/6 mice need MHC class II Aq to develop collagen-induced arthritis dependent on autoreactive T cells

INTRODUCTION

Collagen-induced arthritis (CIA) has traditionally been performed in MHC class II A(q)-expressing mice, whereas most genetically modified mice are on the C57BL/6 background (expressing the b haplotype of the major histocompatibility complex (MHC) class II region). However, C57BL/6 mice develop arthritis after immunisation with chicken-derived collagen type II (CII), but arthritis susceptibility has been variable, and the immune specificity has not been clarified.

OBJECTIVE

To establish a CIA model on the C57BL/6 background with a more predictable and defined immune response to CII.

RESULTS

Both chicken and rat CII were arthritogenic in C57BL/6 mice provided they were introduced with high doses of Mycobacterium tuberculosis adjuvant. However, contaminating pepsin was strongly immunogenic and was essential for arthritis development. H-2(b)-restricted T cell epitopes on chicken or rat CII could not be identified, but expression of A(q) on the C57BL/6 background induced T cell response to the CII260-270 epitope, and also prolonged the arthritis to be more chronic.

CONCLUSIONS

The putative (auto)antigen and its arthritogenic determinants in C57BL/6 mice remains undisclosed, questioning the value of the model for addressing T cell-driven pathological pathways in arthritis. To circumvent this impediment, we recommend MHC class II congenic C57BL/6N.Q mice, expressing A(q), with which T cell determinants have been thoroughly characterised.