Cutting edge: the conversion of arginine to citrulline allows for a high-affinity peptide interaction with the rheumatoid arthritis-associated HLA-DRB1*0401 MHC class II molecule

Mucosal immunity and rheumatoid arthritis: An update on mechanisms and therapeutic potential

Rheumatoid Arthritis (RA) is a persistent autoimmune inflammatory disorder that arises from the intricate interaction between genetic predisposition and environmental influences. The progression of RA can be delineated into four distinct phases: initially, the influence of genetic and environmental risk factors; followed by the emergence of systemic autoimmunity; subsequently, an asymptomatic inflammatory phase; and ultimately, the manifestation of clinical arthritis. Recently, the role of mucosal immunity in RA has gained significant attention in research. Evidence from published studies suggests that mucosal immunity not only influences the onset of RA but also plays a crucial role in its progression. Scholars have begun to unravel the intricate links between RA and the mucosal barriers of the gastrointestinal tract, respiratory system, and oral cavity. Specifically, shifts in the mucosal microbiota, dysfunction of mucosal barriers, and the abnormal activation of mucosal immune tissues are all implicated in the pathogenesis of RA.Despite this growing body of knowledge, a comprehensive review of the abnormal mucosal immunity in RA and its therapeutic implications is yet to be conducted. This review emphasizes the driving role of mucosal immune abnormalities in the development of systemic autoimmunity in rheumatoid arthritis (RA). It further explores the therapeutic potential of mucosal immunity in RA, as well as the issues and challenges that need to be addressed in the current research field, providing a new perspective and potential therapeutic targets for the prevention and treatment of RA.

Rheumatoid arthritis - the role of T cells in this complex systemic autoimmune disease

Rheumatoid arthritis (RA) is a chronic inflammatory disease of the joints that can affect individuals at any age of life. While involvement of the immune system in RA has long been clear, current treatments remain limited to interventions that broadly suppress immune responses with a lack of personalization. This review highlights recent advances in our understanding of immune dysregulation in RA in three settings: (1) before disease onset; (2) in synovial tissue the site of inflammation; and (3) during disease flares after drug withdrawal. These findings provide a detailed view of T cell subsets correlated with the presence or imminent onset of RA, which provides guidance for future investigations to validate new biomarkers that would allow clinicians to diagnose and intercede earlier. It suggests mechanisms that could be leveraged for novel targeted therapeutic approaches and individualized precision treatment wherein clinicians would be able to predict effective treatments for each patient.

A Potential Link Between HLA-DRB1/DQB1 Alleles and Response to Treatment in Rheumatoid Arthritis Patients

The present study aimed to determine the association of HLA-DRB1/-DQB1 alleles with response to treatment and anti-citrullinated peptide antibody (ACPA) status in Iranian rheumatoid arthritis (RA) patients. A total of 167 RA patients, including 114 good responders (GRs) and 53 poor responders (PRs) as well as 330 ethnic-matched healthy controls, participated in this study. Disease activity and treatment response were assessed using the Disease Activity Score 28-joint (DAS28) scores during the 9-month post-treatment. HLA-DRB1/-DQB1 alleles were identified using polymerase chain reaction with a sequence-specific primers (PCR-SSP) method and compared between the study groups. Of the patients, 106 (63.5%) were ACPA-positive, 88 (52.7%) human leucocyte antigen (HLA)-shared epitope (SE)-positive, 64 (38.3%) ACPA+SE+ and 37 (22.2%) ACPA-SE-. HLA-SE alleles were significantly more frequent in patients (p = 3.2e - 05), in PR versus GR patients (p = 0.01) and in ACPA+ versus ACPA- patients (p = 0.009). PR patients had a higher prevalence of ACPA+SE+ compared to GR patients (p = 0.02). Higher frequencies of DRB1*04:02 (pc = 0.03), *04:04 (pc = 0.007), *04:05 (pc = 5.0e - 05), *10:01 (pc = 1.0e - 04), DQB1*03:02 (pc = 0.002) and *05:01 (pc = 0.002) alleles, and lower frequencies of DRB1*04:01 (pc = 0.007), *11:01 (pc = 0.03), *13:01 (pc = 0.03) and DQB1*06:03 (pc = 0.03) alleles were observed in patients compared to healthy controls. These findings suggest a relationship between HLA-SE alleles and ACPA development and a potential link between HLA-SE/non-SE alleles and therapeutic responses in RA patients.

Antigen presentation of post-translationally modified peptides in major histocompatibility complexes

T cells of the adaptive immune system recognize pathogens and malignantly transformed cells through a process called antigen presentation. During this process, peptides are displayed on major histocompatibility complex (MHC) class I and II molecules. Self-reactive T cells are typically removed or suppressed during T-cell development and through peripheral tolerance mechanisms, ensuring that only T cells recognizing peptides that are either absent or present in low abundance under normal conditions remain. This selective process allows T cells to respond to peptides derived from foreign proteins while ignoring those from self-proteins. However, T cells can also respond to peptides derived from proteins that have undergone post-translational modifications (PTMs). Over 200 different PTMs have been described, and while they are essential for protein function, localization and stability, their dysregulation is often associated with disease conditions. PTMs can affect the proteolytic processing of proteins and prevent MHC binding, thereby changing the repertoire of peptides presented on MHC molecules. However, it is also increasingly evident that many peptides presented on MHC molecules carry PTMs, which can alter their immunogenicity. As a result, the presentation of post-translationally modified peptides by MHC molecules plays a significant role in various diseases, as well as autoimmune disorders and allergies. This review will provide an overview of the impact of PTMs on antigen presentation and their implications for immune recognition and disease.

Exploring Anticitrullinated Antibodies (ACPAs) and Serum-Derived Exosomes Cargoes

BACKGROUND

Autoantibodies such as rheumatoid factor (RF) and anticitrullinated protein autoantibodies (ACPAs) are useful tools for rheumatoid arthritis (RA). The presence of ACPAs against citrullinated proteins (CPs), especially citrullinated fibrinogen (cFBG), seems to be a useful serological marker for diagnosing RA. RA patients' sera were found to be enriched in exosomes that can transmit many proteins. Exosomes have been found to express citrullinated protein such as cFBG.

OBJECTIVE

We conducted this study in two stages. In the first phase, we aimed to evaluate the association between autoantibodies and risk factors. In the next step, ACPA-positive serum samples from the first phase were subjected to exosomal studies to explore the presence of cFBG, which is a frequent target for ACPAs.

METHODS

We investigated the autoantibodies in one hundred and sixteen Saudi RA patients and correlated with host-related risk factors. Exosomes were extracted from patients' sera and examined for the presence of cFBG using monoclonal antibodies.

RESULTS

The study reported a high female-to-male ratio of 8:1, and seropositive RA (SPRA) was more frequent among included RA patients. The frequency and the levels of ACPAs were similar in both genders. Autoantibodies incidences have a direct correlations with patient age, while the average titers decreased as the age increased. Further, the highest incidence and levels of autoantibodies were reported in patients with RA duration between 5 and 10 years. Smoking and family history have no impact on autoantibody, except for ACPAs titers among smokers' RA. Our analysis of serum exosomes revealed that about 50% of SPRA patients expressed cFBG.

CONCLUSIONS

The female-to-male ratio is 8:1, which is higher than the global ratio. We can conclude that patients' age and disease duration contribute to the autoantibodies, particularly RF and anti-MCV, whereas smoking and family history had no effects on autoantibodies. We detected cFBG in all exosomes from SPRA patients; thus, we suggest that the precise mechanism of exosomes in RA pathogenesis can be investigated to develop effective treatment strategies.

Gut Microbes as the Major Drivers of Rheumatoid Arthritis: Our Microbes Are Our Fortune!

Rheumatoid arthritis (RA) is an autoimmune disease with an unknown etiology. While certain genes provide strong susceptibility factors, the role of environmental factors is becoming increasingly recognized. Among genetic factors, human leukocyte antigen (HLA) genes, encoded within the major histocompatibility complex (MHC), have been linked to predisposition to RA, while among environmental factors, smoking, infections and diet are the major contributors. Genetic and environmental factors impact microbial composition in the host. Based on the dysbiosis observed in the gut and lung microbiome, a mucosal origin of RA has been suggested. However, proving whether genes or microbes provide a stronger risk factor has been difficult. Studies from RA patients and various mouse models, specifically humanized mice expressing HLA class II genes, have been instrumental in defining the role of environmental factors such as smoking and endogenous small intestinal microbes in modulating arthritis severity. The consensus based on most studies support an interaction between host genetic and environmental factors in the onset and severity of disease. However, until now, no microbial markers for disease prognosis or treatment efficacy have been available. Here, the role of gut microbes as markers of disease severity, and the potential for using endogenous commensals for modulating immune responses to suppress inflammation in the context of genetic factors, are discussed.

Antigen-specific T-cell frequency and phenotype mirrors disease activity in DRB1*04:04+ rheumatoid arthritis patients

Rheumatoid arthritis (RA) is associated with high-risk HLA class II alleles known as the "RA shared epitope." Among prevalent shared epitope alleles, study of DRB1*04:04 has been limited. To define relevant epitopes, we identified citrullinated peptide sequences from synovial antigens that were predicted to bind to HLA-DRB1*04:04 and utilized a systematic approach to confirm their binding and assess their recognition by CD4 T cells. After confirming the immunogenicity of 13 peptides derived from aggrecan, cartilage intermediate layer protein (CILP), α-enolase, vimentin, and fibrinogen, we assessed their recognition by T cells from a synovial tissue sample, observing measurable responses to 8 of the 13 peptides. We then implemented a multicolor tetramer panel to evaluate the frequency and phenotype of antigen-specific CD4 T cells in individuals with anti-citrullinated protein antibody-positive RA and controls. In subjects with RA, CILP-specific T-cell frequencies were significantly higher than those of other antigens. The surface phenotypes exhibited by antigen-specific T cells were heterogeneous, but Th1-like and Th2-like cells predominated. Stratifying based on disease status and activity, antigen-specific T cells were more frequent and most strongly polarized in RA subjects with high disease activity. In total, these findings identify novel citrullinated epitopes that can be used to interrogate antigen-specific CD4 T cells and show that antigen-specific T-cell frequency is elevated in subjects with high disease activity.

Fibroblasts in rheumatoid arthritis: novel roles in joint inflammation and beyond

High-throughput technologies in human and animal studies have revealed novel molecular and cellular pathways involved in tissue inflammation of rheumatoid arthritis (RA). Fibroblasts have been in the forefront of research for several decades. Subpopulations with specific phenotypic and functional properties have been characterized both in mouse models and human disease. Data supporting the active involvement of fibroblasts in immune responses and tissue remodeling processes, as well as their central role in promoting clinical relapses and contributing to treatment resistance, have clearly reshaped their role in disease evolution. The lung is an important non-synovial component of RA both from a clinical and an immunopathogenic aspect. Interstitial lung disease (ILD) is a significant contributor to disease burden affecting morbidity and mortality. Although our knowledge of ILD has progressed, significant gaps in both basic and clinical science remain, posing hurdles to efficient diagnosis, prediction of disease course and its effective treatment. The specific role and contribution of fibroblasts to this process has not been clearly defined. The focus of this review is on fibroblasts and their contribution to RA and RA-ILD, presenting data on genetics and immune responses associated with RA-ILD in humans and animal models.

Silica-mediated exacerbation of inflammatory arthritis: A novel murine model

Objective

The mucosal origin hypothesis in rheumatoid arthritis (RA) posits that inhalant exposures, such as cigarette smoke and crystalline silica (c-silica), trigger immune responses contributing to disease onset. Despite the established risk posed by these exposures, the mechanistic link between inhalants, lung inflammation, and inflammatory arthritis remains poorly understood, partly from the lack of a suitable experimental model. As c-silica accelerates autoimmune phenotypes in lupus models and is a recognized risk factor for several autoimmune diseases, we investigated whether c-silica exposure could induce RA-like inflammatory arthritis in mice.

Methods

Two arthritis-prone mouse strains, BXD2/TyJ and HLA-DR4 transgenic (DR4-Tg), were exposed to c-silica or PBS via oropharyngeal instillation. Arthritis was evaluated by clinical signs and histopathology. Autoimmunity was further evaluated by serological analysis, including autoantibodies and cytokines and chemokines. Lung pathology was evaluated by histopathology and immunofluorescent staining for lymphocyte and macrophages.

Results

C-silica exposure induced chronic pulmonary silicosis in all mice. In BXD2 mice, this was associated with rapid arthritis development, marked by synovitis, bone erosion, and elevated serum autoantibody levels targeting various antigens, including snRNP and citrullinated protein. Additionally, BXD2 mice exhibited inducible bronchus-associated lymphoid tissue (iBALT) formation and elevated autoantibodies in bronchoalveolar lavage fluid (BALF). Conversely, DR4-Tg mice had no significant arthritis, negligible autoantibody responses, and milder lung inflammation lacking iBALT.

Conclusion

We introduce a novel model of c-silica-mediated inflammatory arthritis, creating a novel platform to unravel the molecular and cellular underpinnings of RA and advance understanding of the mucosal origin hypothesis.

Bioinformatics identification based on causal association inference using multi-omics reveals the underlying mechanism of Gui-Zhi-Shao-Yao-Zhi-Mu decoction in modulating rheumatoid arthritis

OBJECT

Rheumatoid arthritis (RA) is a prevalent and currently incurable autoimmune disease. Existing conventional medical treatments are limited in their efficacy, prolonged disease may lead to bone destruction, joint deformity, and loss of related functions, which places a huge burden on RA patients and their families. For millennia, the use of traditional Chinese medicine (TCM), exemplified by the Gui-Zhi-Shao-Yao-Zhi-Mu decoction (GZSYZM), has been demonstrated to offer distinct therapeutic advantages in the management of RA. Exploring the potential mechanism of GZSYZM in the treatment of RA is a hot topic in the field of TCM.

METHOD

High-throughput sequencing data of RA at bulk level and single cell level and Chinese Materia Medica target-related databases were used as data sources. Ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry was employed for the identification of the most relevant compounds to the active ingredients present in the GZSYZM granules. Potential disease genes were identified using a combination of differential expression analysis and weighted gene co-expression network analysis, and the "Chinese Materia Medica-Ingredient-Target" network was constructed to obtain candidate drug target genes. The GZSYZM-RA hub genes were then identified based on Molecular Complex Detection algorithm. To explore the associations and potential mechanisms between the GZSYZM-RA hub gene set and RA, Mendelian randomization (MR) analysis and Bayesian co-localization analysis were used to further identify the GZSYZM-RA core genes that were causally associated with RA. A nomogram was constructed based on a multifactorial logistic regression model using the GZSYZM-RA core genes as predictors of RA. To evaluate its diagnostic value, receiver operating characteristic (ROC) curves, calibration curves, and decision curves were plotted. The potential downstream regulatory mechanisms of the gene of interest in GZSYZM in RA therapy were finally investigated using single- gene set enrichment analysis and molecular docking. The aim was to model the optimal conformation of its target protein receptor binding to the small molecule ligand in GZSYZM to identify the key constituents.

RESULT

Functional enrichment analysis revealed that the GZSYZM-RA hub gene set is enriched in several autoimmune-related mechanistic pathways, with a particular emphasis on the phosphoinositide 3 kinase (PI3K)‑serine/threonine kinase (AKT) signaling pathway. AUCell scores demonstrated active expression of the GZSYZM-RA hub gene set with the PI3K-AKT signaling pathway on monocytes, especially non-classical monocytes. Immunol infiltration analysis based on the CIBERSORT algorithm also showed a strong correlation between several genes in the GZSYZM-RA hub gene set and monocytes by calculating Spearman's rank correlation coefficients. MR analysis with co-localization analysis further identified seven core genes (CASP8, PPARG, IKBKB, PPARA, IFNG, MYC, and STAT3) causally associated with RA. Diagnostic value for clinical decision making was demonstrated by a multivariable logistic regression model constructed with GZSYZM-RA core genes. Molecular docking analysis indicates that CASP8 and GZSYZM have high docking scores, with three key constituents (quercetin, kaempferol, and diosmetin) exhibiting strong binding affinities.

CONCLUSION

GZSYZM may regulate the abnormal over-proliferation and apoptotic imbalance of fibroblast-like synoviocytes in RA patients by inhibiting signaling of the PI3K-AKT signaling pathway while activating CASP8-mediated pro-apoptotic effects. And it may be effective in directly or indirectly inhibiting monocyte-to-osteoclast differentiation, ultimately improving the poor prognosis of joint destruction in RA patients.

The Role of Vimentin Peptide Citrullination in the Structure and Dynamics of HLA-DRB1 Rheumatoid Arthritis Risk-Associated Alleles

Citrullination, a post-translational modification (PTM), plays a critical role in rheumatoid arthritis (RA) by triggering immune responses to citrullinated self-antigens. Some HLA-DRB1 genes encode molecules with the shared epitope (QKRAA/QRRAA) sequence in the peptide-binding groove which preferentially presents citrulline-modified peptides, like vimentin, that intensifies the immune response in RA. In this study, we used computational approaches to evaluate intermolecular interactions between vimentin peptide-ligands (with/without PTM) and HLA-DRB1 alleles associated with a significantly increased risk for RA development. Crystal structures for HLA-DRB1*04:01, *04:04, and *04:05 bound to citrullinated peptides (PDB ID: 4MCY, 4MD5, 6BIR) were retrieved from the Protein Data Bank and non-citrullinated 3D structures were generated by mutating citrulline to arginine. The pHLA complexes were submitted to four rounds (50 ns each) of molecular dynamic simulations (MD) with Gromacs v.2022. Our results show that citrulline strengthens the interaction between vimentin and the HLA-DRB1 molecules, therefore impacting both the peptide affinity to the HLAs and pHLA stability; it also induces more intermolecular hydrogen bond formation during MD in the pHLA. Citrulline prevents repulsion between amino acid 71β and the P4-residue of native vimentin. Thus, vimentin citrullination seems to affect pHLA binding and dynamics, which may influence RA-related immune responses.

Genetics of rheumatoid arthritis

In the past four decades, a plethora of genetic association studies have been carried out in cohorts of patients with rheumatoid arthritis. These studies have highlighted key aspects of disease pathogenesis and suggested causal mechanisms. In this review, we discuss major advances in our understanding of the genetic architecture of rheumatoid arthritis susceptibility, severity and treatment response and explain how genetics supports current models of disease pathogenesis and outcome. We outline future research directions, like Mendelian randomisation, and present a number of potential avenues for clinical translation, including risk and outcome prediction, patient stratification into treatment response groups and pharmacological applications.

Tetraspanin32 (TSPAN32) is downregulated in rheumatoid arthritis: Evidence from animal models and patients

This study aimed to investigate the role of TSPAN32, a member of the tetraspanin family, in rheumatoid arthritis (RA). The objective was to assess the expression levels of TSPAN32 in experimental RA models and in RA patient immune cells, exploring its potential as a regulatory factor in RA pathogenesis. The study employed adjuvant-induced arthritis in rats and collagen-induced arthritis (CIA) in mice as experimental models. Ex vivo analyses included evaluating TSPAN32 expression in immune cells at different stages of the disease. In silico data analysis involved examining transcriptomic datasets from drug-naïve and treated RA patients to correlate TSPAN32 expression with clinical parameters. TSPAN32 overexpression experiments in splenocytes from CIA mice aimed to demonstrate its functional impact on antigen-specific immune responses. The animal models revealed a significant downregulation of TSPAN32, particularly in synovial-infiltrating T cells. Also, TSPAN32 overexpression inhibited pro-inflammatory cytokine production in splenocytes. In RA patients, TSPAN32 was consistently downregulated in circulating and synovial-infiltrating T cells, as well as in CD8+ T cells, B cells and NK cells. Drug treatment did not significantly alter TSPAN32 levels. Negative correlations were observed between TSPAN32 expression and inflammatory markers (CRP, ESR) and clinical scores (SDAI) in RA patients. This study suggests that reduced TSPAN32 expression characterizes pathogenic T-cell populations in RA, highlighting its potential as biomarker for inflammation and disease activity. TSPAN32 may play a crucial role in shaping adaptive immune responses in RA, opening avenues for novel therapeutic strategies targeting this tetraspanin family member.

Elevated Anti-Cyclic Citrullinated Peptide Levels Associated with Filamentary Keratitis

PURPOSE

To assess two cases of filamentary keratitis with elevated serum levels of anti-cyclic citrullinated peptide (anti-CCP) antibodies without known rheumatoid arthritis (RA).

METHODS

A retrospective chart review was conducted on cases with filamentary keratitis and elevated anti-CCP antibodies between January 2021 and January 2023. Patient demographics, clinical characteristics, and serological test results were reviewed.

RESULTS

The first patient, a 77-year-old man, presented with foreign body sensation and eye redness. He reported mild dry mouth but no joint pain or known autoimmune disease, though he had a family history of RA. Schirmer test scores were 7 and 12 mm in the right and left eyes, with an ocular staining score (OSS) of 12 in each eye. His serum anti-CCP antibody level was >2,777 U. Over 3 years of follow-up, he showed no signs of RA development. The second patient, an 84-year-old man, presented with severe burning and light sensitivity but no dry mouth or joint pain. Schirmer test scores were 2 and 3 mm in the right and left eyes, with OSS of 9 and 5, respectively. His serum anti-CCP level was 1330 U. He developed inflammatory arthritis and was diagnosed with RA 16 months after initial presentation.

CONCLUSION

This report suggests that filamentary keratitis with elevated serum anti-CCP antibody levels may indicate early RA. These findings underscore the importance of anti-CCP testing in filamentary keratitis patients, even without typical RA symptoms. Further research is needed to explore the link between anti-CCP antibodies and ocular surface diseases in RA.

A Chemical Approach to Assess the Impact of Post-translational Modification on MHC Peptide Binding and Effector Cell Engagement

The human major histocompatibility complex (MHC) plays a pivotal role in the presentation of peptidic fragments from proteins, which can originate from self-proteins or from nonhuman antigens, such as those produced by viruses or bacteria. To prevent cytotoxicity against healthy cells, thymocytes expressing T cell receptors (TCRs) that recognize self-peptides are removed from circulation (negative selection), thus leaving T cells that recognize nonself-peptides. Current understanding suggests that post-translationally modified (PTM) proteins and the resulting peptide fragments they generate following proteolysis are largely excluded from negative selection; this feature means that PTMs can generate nonself-peptides that potentially contribute to the development of autoreactive T cells and subsequent autoimmune diseases. Although it is well-established that PTMs are prevalent in peptides present on MHCs, the precise mechanisms by which PTMs influence the antigen presentation machinery remain poorly understood. In the present work, we introduce chemical modifications mimicking PTMs on synthetic peptides. This is the first systematic study isolating the impact of PTMs on MHC binding and also their impact on TCR recognition. Our findings reveal various ways PTMs alter antigen presentation, which could have implications for tumor neoantigen presentation.

Tumor antigen presentation and the associated signal transduction during carcinogenesis

Numerous developments have been achieved in the study and treatment of cancer throughout the decades that it has been common. After decades of research, about 100 different kinds of cancer have been found, each with unique subgroups within certain organs. This has significantly expanded our understanding of the illness. A mix of genetic, environmental, and behavioral variables contribute to the complicated and diverse process of cancer formation. Mutations, or changes in the DNA sequence, are crucial to the development of cancer. These mutations have the ability to downregulate the expression and function of Major Histocompatibility Complex class I (MHC I) and MHCII receptors, as well as activate oncogenes and inactivate tumor suppressor genes. Cancer cells use this tactic to avoid being recognized by cytotoxic CD8+T lymphocytes, which causes issues with antigen presentation and processing. This review goes into great length into the PI3K pathway, changes to MHC I, and positive impacts of tsMHC-II on disease-free survival and overall survival and the involvement of dendritic cells (DCs) in different tumor microenvironments. The vital functions that the PI3K pathway and its link to the mTOR pathway are highlighted and difficulties in developing effective cancer targeted therapies and feedback systems has also been mentioned, where resistance mechanisms include RAS-mediated oncogenic changes and active PI3K signalling.

The molecular basis underlying T cell specificity towards citrullinated epitopes presented by HLA-DR4

CD4+ T cells recognising citrullinated self-epitopes presented by HLA-DRB1 bearing the shared susceptibility epitope (SE) are implicated in rheumatoid arthritis (RA). However, the underlying T cell receptor (TCR) determinants of epitope specificity towards distinct citrullinated peptide antigens, including vimentin-64cit59-71 and α-enolase-15cit10-22 remain unclear. Using HLA-DR4-tetramers, we examine the T cell repertoire in HLA-DR4 transgenic mice and observe biased TRAV6 TCR gene usage across these two citrullinated epitopes which matches with TCR bias previously observed towards the fibrinogen β-74cit69-81 epitope. Moreover, shared TRAV26-1 gene usage is evident in four α-enolase-15cit10-22 reactive T cells in three human samples. Crystal structures of mouse TRAV6+ and human TRAV26-1+ TCR-HLA-DR4 complexes presenting vimentin-64cit59-71 and α-enolase-15cit10-22, respectively, show three-way interactions between the TCR, SE, citrulline, and the basis for the biased selection of TRAV genes. Position 2 of the citrullinated epitope is a key determinant underpinning TCR specificity. Accordingly, we provide a molecular basis of TCR specificity towards citrullinated epitopes.

Autoantibodies Serum Level and 10-Year Risk of Fractures Evaluated by FRAX® Tool in Rheumatoid Arthritis Patients

Purpose

FRAX® is a tool used for evaluation of risk of fracture in RA and non-RA patients and to identify those eligible for intervention. One of the limitations of FRAX in RA settings is that it does not consider factors known to contribute to osteoporosis such as autoantibodies. This study analysed the association of anti-mutated citrullinated vimentin antibody (anti-MCV), anti-cyclic citrullinated peptide antibody (anti-CCP), IgM rheumatoid factor (RF), IgA RF with 10-year risk of major osteoporosis and hip fracture.

Methods

FRAX® tool was used to estimate 10-year risk of major osteoporosis fracture and hip fracture in 189 RA patients over 40 years of age. Anti-MCV, anti-CCP, IgM RF and IgA RF were tested using enzyme immunoassay and analysed at different levels. Results were adjusted for various confounders including disease activity.

Results

Fifty-one (26.9%) RA patients had high (≥20%) 10-year risk of major osteoporosis fracture and 67 (35.4%) had high (>3%) 10-year risk of hip fracture. Among all the tested autoantibodies, only IgM RF at elevated levels was associated with high 10-year risk of major osteoporosis fracture (adjusted OR = 4.1, 95% CI = 1.5-11.3, p = 0.006) and of hip fracture (adjusted OR = 17.4, 95% CI = 3.7-81.3, p < 0.0001). There was no agreement between FRAX and femoral neck (FN) BMD. None of the autoantibodies tested were associated with FN osteopenia or osteoporosis including IgM RF at high levels.

Conclusion

Our study highlights the importance of quantitative measurement of autoantibodies in assessment of risk for fractures among RA patients. Our preliminary findings need to be assessed in prospective studies to determine the actual predictive value of high IgM RF levels among patients with RA.

Protein Citrullination by Peptidyl Arginine Deiminase/Arginine Deiminase Homologs in Members of the Human Microbiota and Its Recognition by Anti-Citrullinated Protein Antibodies

The human microbiome exists throughout the body, and it is essential for maintaining various physiological processes, including immunity, and dysbiotic events, which are associated with autoimmunity. Peptidylarginine deiminase (PAD) enzymes can citrullinate self-proteins related to rheumatoid arthritis (RA) that induce the production of anti-citrullinated protein antibodies (ACPAs) and lead to inflammation and joint damage. The present investigation was carried out to demonstrate the expression of homologs of PADs or arginine deiminases (ADs) and citrullinated proteins in members of the human microbiota. To achieve the objective, we used 17 microbial strains and specific polyclonal antibodies (pAbs) of the synthetic peptide derived from residues 100-200 of human PAD2 (anti-PAD2 pAb), and the recombinant fragment of amino acids 326 and 611 of human PAD4 (anti-PAD4 pAb), a human anti-citrulline pAb, and affinity ACPAs of an RA patient. Western blot (WB), enzyme-linked immunosorbent assay (ELISA), elution, and a test with Griess reagent were used. This is a cross-sectional case-control study on patients diagnosed with RA and control subjects. Inferential statistics were applied using the non-parametric Kruskal-Wallis test and Mann-Whitney U test generated in the SPSS program. Some members of phyla Firmicutes and Proteobacteria harbor homologs of PADs/ADs and citrullinated antigens that are reactive to the ACPAs of RA patients. Microbial citrullinome and homolog enzymes of PADs/ADs are extensive in the human microbiome and are involved in the production of ACPAs. Our findings suggest a molecular link between microorganisms of a dysbiotic microbiota and RA pathogenesis.

Neutrophil extracellular traps in rheumatoid arthritis and periodontitis: Contribution of PADI4 gene polymorphisms

AIM

We sought to investigate the release of neutrophil extracellular traps (NETs) in neutrophils from individuals with rheumatoid arthritis (RA) and controls and compare the presence of NETs in gingival tissues according to periodontal status. Also, the association between single nucleotide polymorphisms (SNPs) of the peptidyl arginine deaminase type 4 (PADI4) gene and the GTG haplotype with RA, periodontitis and NETs was evaluated in vitro.

MATERIALS AND METHODS

Peripheral neutrophils were isolated by density gradient, and NET concentration was determined by the PicoGreen method. Immunofluorescence was studied to identify NETs by co-localization of myeloperoxidase (MPO)-citrullinated histone H3 (H3Cit). Genotyping for SNPs (PADI4_89; PADI4_90; PADI4_92; and PADI4_104) was performed in 87 individuals with RA and 111 controls.

RESULTS

The release of NETs in vitro was significantly higher in individuals with RA and periodontitis and when stimulated with Porphyromonas gingivalis. Gingival tissues from subjects with RA and periodontitis revealed increased numbers of MPO-H3Cit-positive cells. Individuals with the GTG haplotype showed a higher release of NETs in vitro and worse periodontal parameters.

CONCLUSIONS

The release of NETs by circulating neutrophils is associated with RA and periodontitis and is influenced by the presence of the GTG haplotype.

The Role of Citrullination Modification in CD4+ T Cells in the Pathogenesis of Immune-Related Diseases

The post-translational modifications (PTMs) of proteins play a crucial role in increasing the functional diversity of proteins and are associated with the pathogenesis of various diseases. This review focuses on a less explored PTM called citrullination, which involves the conversion of arginine to citrulline. This process is catalyzed by peptidyl arginine deiminases (PADs). Different members of the PAD family have distinct tissue distribution patterns and functions. Citrullination is a post-translational modification of native proteins that can alter their structure and convert them into autoantigens; thus, it mediates the occurrence of autoimmune diseases. CD4+ T cells, including Th1, Th2, and Th17 cells, are important immune cells involved in mediating autoimmune diseases, allergic reactions, and tumor immunity. PADs can induce citrullination in CD4+ T cells, suggesting a role for citrullination in CD4+ T cell subset differentiation and function. Understanding the role of citrullination in CD4+ T cells may provide insights into immune-related diseases and inflammatory processes.

Anti-cytokine autoantibodies: mechanistic insights and disease associations

Anti-cytokine autoantibodies (ACAAs) are increasingly recognized as modulating disease severity in infection, inflammation and autoimmunity. By reducing or augmenting cytokine signalling pathways or by altering the half-life of cytokines in the circulation, ACAAs can be either pathogenic or disease ameliorating. The origins of ACAAs remain unclear. Here, we focus on the most common ACAAs in the context of disease groups with similar characteristics. We review the emerging genetic and environmental factors that are thought to drive their production. We also describe how the profiling of ACAAs should be considered for the early diagnosis, active monitoring, treatment or sub-phenotyping of diseases. Finally, we discuss how understanding the biology of naturally occurring ACAAs can guide therapeutic strategies.

The effect of HLA-DRB1*04:01 on a mouse model of atherosclerosis

Objectives

HLA-DRB1 is associated with an increased risk of cardiovascular disease in patients with rheumatoid arthritis (RA). This study aimed to determine the effect of HLA-DRB1 on atherosclerotic cardiovascular disease (ASCVD) using a novel mouse model.

Methods

Mice transgenic for HLA-DRB1*04:01 (DR4tg) were crossed with low density lipoprotein receptor knock-out (Ldlr^-/-) mice that develop atherosclerosis when fed a high fat, high cholesterol (HFHC) diet. Male and female DR4tgLdlr^-/- (n = 48), Ldlr^-/- (n = 24), DR4tg (n = 24), and C57Bl/6 (B6) background (n = 24) mice were fed HFHC or regular diet (RD) for 12 weeks. Blood samples were analyzed for serum lipoproteins using a colorimetric assay. C-reactive protein (CRP) and oxidized LDL (OxLDL) were measured using ELISA. Atherosclerosis in the aortas was assessed using the lipid stain, Sudan IV. The presence of citrulline in atherosclerotic plaque was determined by immunohistochemistry.

Results

Sera low-density lipoprotein cholesterol (LDL-C) levels were higher in HFHC-fed Ldlr^-/- versus DR4tgLdlr^-/--; p = 0.0056, but the aortic plaque burden and degree of citrullination in the plaque were similar for these two strains. The ratio of pro-atherogenic OxLDL to LDL levels was higher in DR4tgLdlr^-/- than Ldlr^-/-mice; p = 0.0017. All mice had an increase in CRP when fed a HFHC diet, most pronounced for DR4tgLdlr^-/-; p = 0.0009. There were no significant sex differences for DR4tgLdlr^-/- mice; however, male Ldlr^-/- mice had worse atherosclerosis. B6 and DR4tg mice did not have significant elevations in serum cholesterol levels and did not develop atherosclerosis.

Conclusions

Expression of HLA-DRB1 resulted in an elevation of OxLDL and a reduction in the male bias for atherosclerosis, mimicking what is observed in RA.

Protein citrullination: inhibition, identification and insertion

Protein citrullination is a post-translational modification (PTM) that is catalysed by the protein arginine deiminase (PAD) family of enzymes. This PTM involves the transformation of an arginine residue into citrulline. Protein citrullination is associated with several physiological processes, including the epigenetic regulation of gene expression, neutrophil extracellular trap formation and DNA damage-induced apoptosis. Aberrant protein citrullination is relevant to several autoimmune and neurodegenerative diseases and certain forms of cancer. PAD inhibitors have shown remarkable efficacy in a range of diseases including rheumatoid arthritis (RA), lupus, atherosclerosis and ulcerative colitis. In RA, anti-citrullinated protein antibodies can be detected prior to disease onset and are thus a valuable diagnostic tool for RA. Notably, citrullinated proteins may serve more generally as biomarkers of specific disease states; however, the identification of citrullinated protein residues remains challenging owing to the small 1 Da mass change that occurs upon citrullination. Herein, we highlight the progress made so far in the development of pan-PAD and isozyme selective inhibitors as well as the identification of citrullinated proteins and the site-specific incorporation of citrulline into proteins. This article is part of the Theo Murphy meeting issue 'The virtues and vices of protein citrullination'.

Peripheral CD4+ /CD8+ T cell composition distinct from healthy individuals is shared by ankylosing spondylitis and rheumatoid arthritis

OBJECTIVE

Ankylosing spondylitis (AS) and rheumatoid arthritis (RA) are chronic inflammatory joint diseases, linking to the alterations of immune cells. We attempted to assess whether the alterations in the composition of CD4+ /CD8+ T cells are different between AS and RA and identify the characteristic cells between male and female patients.

METHODS

The proportions of CD3+ or double positive T cells, 6 CD4+ T subsets and 9 CD8+ T cell subsets were detected by flow cytometry and compared in 30 healthy individuals, 42 AS patients and 45 RA patients. The differentially altered cells were individually analyzed for associations with disease activity parameters. In addition, their proportions were compared between different genders in the 3 groups.

RESULTS

The proportions of CD4+ T cells, naive CD4+ T cells and central memory CD4+ T cells were lower in AS patients (P = 0.001, P = 0.002 and P = 0.007, respectively) and RA patients (P = 0.032, P < 0.001 and P = 0.016, respectively), but the proportion of effector memory ones was higher when compared with healthy populations (both P < 0.001), as were the decrease of naive/central memory CD8+ T cells in AS (P = 0.003 and P = 0.016, respectively) and RA (P < 0.001 and P = 0.006, respectively), and the increased tendency of terminally differentiated CD8+ T cells. However, these above-mentioned cells, regulatory T (Treg) cells and CD8+ T cells with different CD127 expressions between AS and RA were similar in proportion. Furthermore, naive CD4+ T cells were positively associated with C-reactive protein (CRP) in AS, whereas CD4+ T cells and terminally differentiated CD8+ T of RA patients were associated with CRP in RA. The gender-related alterations predominantly displayed the overexpressions of Treg cells and naive CD8+ T cells in female patients with AS and RA, respectively.

CONCLUSIONS

AS patients and RA patients have some similar peripheral CD4+ /CD8+ T cell subsets but are distinct from healthy individuals, which may contribute to disease severity. Females are respectively characterized by the up-regulation of Treg cells and naive CD8+ T cells in AS patients and RA patients. The study offers an in-depth understanding of the role of T cell subsets in the similarities of the disorders and helps us to monitor disease changes and may offer a theoretical basis of developing novel therapies against common targets.

Advancement in nanotechnology for treatment of rheumatoid arthritis: scope and potential applications

Rheumatoid arthritis is a hyperactive immune disorder that results in severe inflammation in synovial joints, cartilage, and bone deterioration, resulting in immobilization of joints. Traditional approaches for the treatment of rheumatoid arthritis are associated with some limiting factors such as suboptimal patient compliance, inability to control the progression of disorder, and safety concerns. Therefore, innovative drug delivery carriers for efficient therapeutic delivery at inflamed synovial sites with better safety assessment are urgently needed to address these issues. From this perspective, nanotechnology is an outstanding alternative to traditional drug delivery approaches, and it has shown great promise in developing novel carriers to treat rheumatoid arthritis. Considering the current research and future application of nanocarriers, it is believed that nanocarriers can be a crucial element in rheumatoid arthritis treatment. This paper covers all currently available pathophysiological aspects of rheumatoid arthritis and treatment options. Future research for the reduction of synovial inflammation should focus on developing multifunction nanoparticles capable of delivering therapeutic agents with improved safety, efficacy, and cost-effectiveness to be commercialized.

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.

Citrullination modulates antigen processing and presentation by revealing cryptic epitopes in rheumatoid arthritis

Cryptic peptides, hidden from the immune system under physiologic conditions, are revealed by changes to MHC class II processing and hypothesized to drive the loss of immune tolerance to self-antigens in autoimmunity. Rheumatoid arthritis (RA) is an autoimmune disease characterized by immune responses to citrullinated self-antigens, in which arginine residues are converted to citrullines. Here, we investigate the hypothesis that citrullination exposes cryptic peptides by modifying protein structure and proteolytic cleavage. We show that citrullination alters processing and presentation of autoantigens, resulting in the generation of a unique citrullination-dependent repertoire composed primarily of native sequences. This repertoire stimulates T cells from RA patients with anti-citrullinated protein antibodies more robustly than controls. The generation of this unique repertoire is achieved through altered protease cleavage and protein destabilization, rather than direct presentation of citrulline-containing epitopes, suggesting a novel paradigm for the role of protein citrullination in the breach of immune tolerance in RA.

Hypercitrullination and anti-citrullinated protein antibodies in chronic apical periodontitis, a laboratory investigation. Does autoimmunity contribute to the pathogenesis?

AIM

The presence of Gram-negative anaerobic bacteria, in particular, Porphyromonas gingivalis (P. gingivalis) in periapical granulomas predicts the generation of citrullinated proteins in the lesion. Citrullination of proteins may lead to the formation of anti-citrullinated autoantibodies (ACPA-s) initiating the formation of an autoimmune loop which may contribute to the perpetuation of inflammatory reactions and tissue damage in chronic apical periodontitis. The objective of this study was to demonstrate the formation of citrullinated proteins in chronic apical periodontitis and whether they can act as autoantigens.

METHODOLOGY

Twenty-five periapical granulomas (n = 25) were investigated in the study. Healthy periodontal tissue samples served as normal control tissue (n = 6). The peptidyl-citrulline level was determined with the dot blot method. ACPA levels were analysed using anti-citrullinated cyclic peptide (anti-CCP) EDIA kit. Differences between periapical granuloma and control samples were assessed using Mann-Whitney U tests. p Values <.05 were considered as statistically significant.

RESULTS

Protein concentrations, peptidyl-citrulline levels and anti-CCP ratios were compared between periapical granuloma and healthy control groups. Multiple linear regression analysis revealed significant (p = .042) hypercitrullination in periapical granuloma samples. Moreover, there was a significant difference in the ACPA ratios between periapical granuloma (2.03 ± 0.30) and healthy control (0.63 ± 0.17) groups (p = .01). Seventeen of 25 periapical granuloma samples (17/25; 68%), whereas one out of six control samples (1/6; 17%) were shown to be positive for the presence of ACPA.

CONCLUSIONS

This is the first study detecting the presence of citrullinated peptides and APCA in periapical granuloma, suggesting the contribution of autoimmune reactions in the pathogenesis and perpetuation of chronic apical periodontitis.

C-terminal citrullinated peptide alters antigen-specific APC:T cell interactions leading to breach of immune tolerance

In rheumatoid arthritis, the emergence of anti-citrullinated autoimmunity is associated with HLA-antigen-T cell receptor complexes. The precise mechanisms underpinning this breach of tolerance are not well understood. Porphyromonas gingivalis expresses an enzyme capable of non-endogenous C-terminal citrullination with potential to generate citrullinated autoantigens. Here we document how C-terminal citrullination of ovalbumin peptide^323-339 alters the interaction between antigen-presenting cells and OTII T cells to induce functional changes in responding T cells. These data reveal that C-terminal citrullination is sufficient to breach T cell peripheral tolerance in vivo and reveal the potential of C-terminal citrullination to lower the threshold for T cell activation. Finally, we demonstrate a role for the IL-2/STAT5/CD25 signalling axis in breach of tolerance. Together, our data identify a tractable mechanism and targetable pathways underpinning breach of tolerance in rheumatoid arthritis and provide new conceptual insight into the origins of anti-citrullinated autoimmunity.

Cytotoxic CD8+ T cells target citrullinated antigens in rheumatoid arthritis

The immune mechanisms that mediate synovitis and joint destruction in rheumatoid arthritis (RA) remain poorly defined. Although increased levels of CD8+ T cells have been described in RA, their function in pathogenesis remains unclear. Here we perform single cell transcriptome and T cell receptor (TCR) sequencing of CD8+ T cells derived from anti-citrullinated protein antibodies (ACPA)+ RA blood. We identify GZMB+CD8+ subpopulations containing large clonal lineage expansions that express cytotoxic and tissue homing transcriptional programs, while a GZMK+CD8+ memory subpopulation comprises smaller clonal expansions that express effector T cell transcriptional programs. We demonstrate RA citrullinated autoantigens presented by MHC class I activate RA blood-derived GZMB+CD8+ T cells to expand, express cytotoxic mediators, and mediate killing of target cells. We also demonstrate that these clonally expanded GZMB+CD8+ cells are present in RA synovium. These findings suggest that cytotoxic CD8+ T cells targeting citrullinated antigens contribute to synovitis and joint tissue destruction in ACPA+ RA.

MHC Class II Presentation in Autoimmunity

Antigen presentation by major histocompatibility complex class II (MHC-II) molecules is crucial for eliciting an efficient immune response by CD4+ T cells and maintaining self-antigen tolerance. Some MHC-II alleles are known to be positively or negatively associated with the risk of the development of different autoimmune diseases (ADs), including those characterized by the emergence of autoreactive T cells. Apparently, the MHC-II presentation of self-antigens contributes to the autoimmune T cell response, initiated through a breakdown of central tolerance to self-antigens in the thymus. The appearance of autoreactive T cell might be the result of (i) the unusual interaction between T cell receptors (TCRs) and self-antigens presented on MHC-II; (ii) the posttranslational modifications (PTMs) of self-antigens; (iii) direct loading of the self-antigen to classical MHC-II without additional nonclassical MHC assistance; (iv) the proinflammatory environment effect on MHC-II expression and antigen presentation; and (v) molecular mimicry between foreign and self-antigens. The peculiarities of the processes involved in the MHC-II-mediated presentation may have crucial importance in the elucidation of the mechanisms of triggering and developing ADs as well as for clarification on the protective effect of MHC-II alleles that are negatively associated with ADs.

The differences between broad bean koji fermented in laboratory and factory conditions by an efficient Aspergillus oryzae

Broad bean paste-meju was fermented by a mixture of broad bean koji and saline; koji fermentation is an essential process for the production of broad bean paste-meju. Aspergillus oryzae was the most widely used in sauce fermentation. The purpose of this study was to research the factory adaptability of the highly efficient A. oryzae PNM003 and further evaluate the effect of fermentation conditions and fermentation strains on koji. A. oryzae PNM003 was compared with the widely used strain HN 3.042 not only in the laboratory but also in factory conditions (large scale). Results showed that the koji made with the same starter in the factory had a greater amount of fungi than that in the laboratory. Bacteria and yeast levels in HN_L koji were higher than in PN_L koji. As for fungi constitution, almost only Aspergillus survived in the end through the microorganism self-purification process during koji fermentation. As for the bacterial constitution, koji was grouped by fermentation conditions instead of fermentation starter. PN koji had higher protease activity and a higher content of total acids, amino acid nitrogen, amino acids, and organic acids in the laboratory conditions. Nevertheless, in factory conditions, PN koji and HN koji had similar indexes. As for volatile flavor compounds, koji made with the two starters in the same condition was grouped together. As for the same starter, there were more flavor compounds metabolized in the factory condition than in the laboratory condition, especially esters and alcohols. The results showed PN was a highly efficient strain to ferment koji, but the advantages were expressed more remarkably in laboratory conditions. In brief, the fermented condition had a greater influence than the fermentation starter for broad bean koji.

Immune Responses at Host Barriers and Their Importance in Systemic Autoimmune Diseases

Host barriers such as the skin, the lung mucosa, the intestinal mucosa and the oral cavity are crucial at preventing contact with potential threats and are populated by a diverse population of innate and adaptive immune cells. Alterations in antigen recognition driven by genetic and environmental factors can lead to autoimmune systemic diseases such rheumatoid arthritis, systemic lupus erythematosus and food allergy. Here we review how different immune cells residing at epithelial barriers, host-derived signals and environmental signals are involved in the initiation and progression of autoimmune responses in these diseases. We discuss how regulation of innate responses at these barriers and the influence of environmental factors such as the microbiota can affect the susceptibility to develop local and systemic autoimmune responses particularly in the cases of food allergy, systemic lupus erythematosus and rheumatoid arthritis. Induction of pathogenic autoreactive immune responses at host barriers in these diseases can contribute to the initiation and progression of their pathogenesis.

Citrullinated glucose-regulated protein 78 is a candidate target for melanoma immunotherapy

Introduction

Post translational modification of proteins plays a significant role in immune recognition. In particular the modification of arginine to citrulline which is mediated by PAD enzymes is increased during cellular stress (autophagy) which permits the presentation of modified epitopes upon MHC class II molecules for recognition by CD4 T cells. Citrullination also occurs in tumour cells as a result of continuous environmental stresses and increased autophagy. We have shown in animal models the efficient stimulation of citrullinated epitope specific CD4 T cells resulting in dramatic elimination/regression of tumours. The ER chaperone glucose-regulated protein 78 (GRP78) is known to also be required for stress-induced autophagy and is directly linked to autophagosome formation. GRP78 is known to be highly expressed by many tumour types. In this study we investigate the potential of targeting citrullinated GRP78 for cancer therapy.

Methods

A citrullinated GRP78 specific antibody was used to assess citrullinated GRP78 expression in murine and human tumour cells by flow cytometry. Five peptides were selected and used to vaccinate HLA transgenic mice and immune responses were characterised by ex vivo cytokine ELISpot assay. T cell repertoire in humans was assessed through proliferation assays and cytokine ELISpot assay. Citrullinated peptide was identified in murine B16 melanoma by mass spectrometry and the peptide vaccine was assessed for tumour therapy in a mouse melanoma model.

Results

We show the identification CD4 T cell responses to one citrullinated GRP78 epitope that are restricted through HLA DP*0401 and HLA-DR*0101 alleles. This peptide is detected by mass spectrometry in B16 melanoma grown in vivo and citrulline specific CD4 responses to two peptides spanning this epitope mediate efficient therapy of established B16 melanoma tumours in HHDII/DP4 (p<0.0001) transgenic mouse model. Finally, we demonstrate the existence of a repertoire of responses to the citrullinated GRP78 peptide in healthy individuals (p=0.0023) with 13/17 (76%) individuals showing a response to this peptide.

Conclusion

We propose that citrullinated GRP78 is a candidate tumour antigen and vaccination against citrullinated GRP78 may provide a promising tumour therapy approach.

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.

Posttranslational modifications in diabetes: Mechanisms and functions

As one of the most widespread chronic diseases, diabetes and its accompanying complications affect approximately one tenth of individuals worldwide and represent a growing cause of morbidity and mortality. Accumulating evidence has proven that the process of diabetes is complex and interactive, involving various cellular responses and signaling cascades by posttranslational modifications (PTMs). Therefore, understanding the mechanisms and functions of PTMs in regulatory networks has fundamental importance for understanding the prediction, onset, diagnosis, progression, and treatment of diabetes. In this review, we offer a holistic summary and illustration of the crosstalk between PTMs and diabetes, including both types 1 and 2. Meanwhile, we discuss the potential use of PTMs in diabetes treatment and provide a prospective direction for deeply understanding the metabolic diseases.

Pulmonary Manifestations in Rheumatological Diseases

Pulmonary involvement complicates the various aspects of care in patients suffering from autoimmune disorders. The epidemiological data generated over the last 10 to 15 years have improved the overall understanding of the risk factors and pathophysiological mechanisms involved in pulmonary involvement in rheumatological conditions. Recent advances in genetics have provided superior insight into the pathogenesis of autoimmune diseases and the underlying pulmonary involvement. This review article provides a concise overview of the four most common rheumatological conditions associated with pulmonary involvement: systemic lupus erythematosus (SLE), dermatomyositis/polymyositis, rheumatoid arthritis (RA), and systemic sclerosis (SSc). The clinical, epidemiological, and genetic aspects of these diseases are summarized in this article with particular emphasis on the characteristic patterns of pulmonary involvement in radiological imaging and various treatment options for each of these autoimmune diseases and their lung manifestations.

Peptidylarginine Deiminase 2 Gene Polymorphisms in Subjects with Periodontitis Predispose to Rheumatoid Arthritis

Epidemiologic studies have shown associations between periodontitis and rheumatoid arthritis (RA), but a causal relationship has not been established. Citrullination of gingival proteins by human peptidylarginine deiminases (PADs) or PAD from Porphyromonas gingivalis has been proposed to generate autoantigens in anti-CCP-positive RA. This study investigated whether the association between periodontitis and RA is influenced by single nucleotide polymorphisms (SNPs) in the genes encoding PAD2 and PAD4 that catalyze aberrant citrullination in RA and often are overexpressed in inflamed gingival connective tissue in subjects with periodontitis. The study included 137 RA patients and 161 controls with self-reported periodontitis. Periodontitis onset preceded RA onset by 13 years on average and was not associated with any of the SNPs investigated. In subjects with periodontitis, carriage of the minor alleles of rs2057094 and rs2235912 in PADI2 significantly increased the risk of RA (odds ratios 1.42 [p = 0.03] and 1.48 [p = 0.02], respectively), and this effect was driven by the anti-CCP-negative RA patients. The minor alleles of these SNPs only increased risk of anti-CCP-positive RA in individuals with periodontitis and a history of smoking. These data suggest that individuals with periodontitis carrying the minor alleles of SNPs rs2057094, rs2076616 and rs2235912 in PADI2 may be at increased risk of RA.

Isolation of HLA-DR-naturally presented peptides identifies T-cell epitopes for rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) immunopathogenesis revolves around the presentation of poorly characterised self-peptides by human leucocyte antigen (HLA)-class II molecules on the surface of antigen-presenting cells to autoreactive CD4 +T cells. Here, we analysed the HLA-DR-associated peptidome of synovial tissue (ST) and of dendritic cells (DCs) pulsed with synovial fluid (SF) or ST, to identify potential T-cell epitopes for RA.

METHODS

HLA-DR/peptide complexes were isolated from RA ST samples (n=3) and monocyte-derived DCs, generated from healthy donors carrying RA-associated shared epitope positive HLA-DR molecules and pulsed with RA SF (n=7) or ST (n=2). Peptide sequencing was performed by high-resolution mass spectrometry. The immunostimulatory capacity of selected peptides was evaluated on peripheral blood mononuclear cells from patients with RA (n=29) and healthy subjects (n=12) by flow cytometry.

RESULTS

We identified between 103 and 888 HLA-DR-naturally presented peptides per sample. We selected 37 native and six citrullinated (cit)-peptides for stimulation assays. Six of these peptides increased the expression of CD40L on CD4 +T cells patients with RA, and specifically triggered IFN-γ expression on RA CD4 +T cells compared with healthy subjects. Finally, the frequency of IFN-γ-producing CD4 +T cells specific for a myeloperoxidase-derived peptide showed a positive correlation with disease activity.

CONCLUSIONS

We significantly expanded the peptide repertoire presented by HLA-DR molecules in a physiologically relevant context, identifying six new epitopes recognised by CD4 +T cells from patients with RA. This information is important for a better understanding of the disease immunopathology, as well as for designing tolerising antigen-specific immunotherapies.

CD4+ Cytotoxic T Cells Involved in the Development of EBV-Associated Diseases

Activated cytotoxic CD4 T cells (HLA-DR+) play an important role in the control of EBV infection, especially in cells with latency I (EBNA-1). One of the evasion mechanisms of these latency cells is generated by gp42, which, via peripherally binding to the β1 domain of the β chain of MHC class II (HLA-DQ, -DR, and -DP) of the infected B lymphocyte, can block/alter the HLA class II/T-cell receptor (TCR) interaction, and confer an increased level of susceptibility towards the development of EBV-associated autoimmune diseases or cancer in genetically predisposed individuals (HLA-DRB1* and DQB1* alleles). The main developments predisposing the factors of these diseases are: EBV infection; HLA class II risk alleles; sex; and tissue that is infiltrated with EBV-latent cells, forming ectopic lymphoid structures. Therefore, there is a need to identify treatments for eliminating cells with EBV latency, because the current treatments (e.g., antivirals and rituximab) are ineffective.

Effect of HTLV-1 Infection on the Clinical Course of Patients with Rheumatoid Arthritis

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The effects of HTLV-1 on health are not fully elucidated. Epidemiological studies have shown that the prevalence of HTLV-1 infection is high in patients with rheumatic diseases. The prevalence of comorbidities, such as Sjögren’s syndrome and rheumatoid arthritis (RA), is higher in patients with HAM/TSP than the in general population. Studies have shown the effects of HTLV-1-infection on the clinical course of RA. Major questions on the association between HTLV-1 infection and RA: (1) Is it possible that HTLV-1 infection causes RA? (2) Do patients with RA who are infected with HTLV-1 have different clinical features? (3) Are immunosuppressants associated with an increased prevalence of HAM/TSP or ATL in RA patients with HTLV-1 infection? Is ATL an immunosuppressive therapy-associated lymphoproliferative disorder? No large-scale studies have investigated the incidence of ATL in patients with RA. However, several studies have reported the development of ATL in patients with RA who have HTLV-1 infection. This review aimed to shed light on the association between HTLV-1 infection and RA and summarize the unmet medical needs of RA patients with HTLV-1 infection.

Peptidyl arginine deiminase expression and macrophage polarization following stimulation with citrullinated and malondialdehyde-acetaldehyde modified fibrinogen

OBJECTIVE

Post-translational modifications of extracellular matrix proteins such as fibrinogen may lead to tolerance loss and have been implicated in rheumatoid arthritis (RA) pathogenesis. The purpose of this study was to determine whether fibrinogen (FIB) modified with citrulline (CIT), malondialdehyde-acetaldehyde (MAA) or both leads to altered macrophage polarization, peptidyl arginine deiminase (PAD) expression, or production of citrullinated proteins.

METHODS

PMA-treated U-937 cells (M0 cells) were stimulated with MAA, CIT or MAA-CIT modified FIB. Macrophage (M1/M2) phenotypes were evaluated by flow cytometry, RT-PCR, and ELISA. PAD enzyme expression and protein citrullination was evaluated using RT-PCR and Western Blot.

RESULTS

Flow cytometry revealed that M0 macrophages stimulated with FIB-MAA-CIT resulted in mixed M1/M2 phenotypes as demonstrated by cell surface expression and mRNA levels of CD14, CD192, CD163, and CD206 (p < 0.001 vs. others), and the release of IL-18, IP-10, CCL22, and IL-13 (p < 0.001 vs. others). While FIB-MAA treated M0 cells demonstrated a mixed M1/M2 phenotype, cytokine and cell surface markers differed from FIB-MAA-CIT. Finally, M0 cells treated with FIB-CIT demonstrated markers and cytokines consistent with only the M1-like phenotype. Exposure of M0 cells to FIB-MAA-CIT (at 48 h) and FIB-MAA (at 24 h) led to increased mRNA expression and protein expression of PAD2 (p < 0.001) with increased protein citrullination.

CONCLUSION

These findings suggest that MAA-modification and citrullination of FIB, in isolation or combination, yield specific effects on macrophage polarization, PAD expression and citrullination that ultimately may induce inflammatory and fibrotic responses associated with RA.

How RA Associated HLA-DR Molecules Contribute to the Development of Antibodies to Citrullinated Proteins: The Hapten Carrier Model

The risk to develop ACPA positive rheumatoid arthritis (RA), the most destructive type of autoimmune arthritis, is carried by HLA-DRB1 alleles containing a 5 amino acid motif: the shared epitope (SE). RA is preceded by the emergence of disease specific anti citrullinated protein antibodies (ACPA). SE positive HLA-DRB1 alleles are associated with ACPA and ACPA positive RA, not with ACPA negative RA, suggesting that ACPA contribute to the pathogenesis of RA. Understanding how HLA-DRB1 genotypes influence ACPA could lead to a curative or preventive treatment of RA. The “Shared epitope binds citrullinated peptides “ hypothesis suggests that RA associated HLA-DR alleles present citrullinated peptides to T cells that help ACPA producing B cells. The “Hapten carrier model” suggests that PAD4 is the target of the T cells which help ACPA specific B cells through a hapten carrier mechanism in which PAD4 is the carrier and citrullinated peptides are the haptens. Direct binding assay of citrullinated peptides to purified HLA-DR molecules does not support the “shared epitope binds citrullinated peptides” hypothesis. The Odds Ratios to develop ACPA positive RA associated with each of 12 common HLA-DRB1 genotypes match the probability that the two HLA-DR molecules they encode can bind at least one peptide from PAD4, not from citrullinated fibrinogen. Thus, PAD4 tolerization might stop the carrier effect and switch off production of ACPA.

The Role of Exposomes in the Pathophysiology of Autoimmune Diseases II: Pathogens

In our continuing examination of the role of exposomes in autoimmune disease, we use this review to focus on pathogens. Infections are major contributors to the pathophysiology of autoimmune diseases through various mechanisms, foremost being molecular mimicry, when the structural similarity between the pathogen and a human tissue antigen leads to autoimmune reactivity and even autoimmune disease. The three best examples of this are oral pathogens, SARS-CoV-2, and the herpesviruses. Oral pathogens reach the gut, disturb the microbiota, increase gut permeability, cause local inflammation, and generate autoantigens, leading to systemic inflammation, multiple autoimmune reactivities, and systemic autoimmunity. The COVID-19 pandemic put the spotlight on SARS-CoV-2, which has been called “the autoimmune virus.” We explore in detail the evidence supporting this. We also describe how viruses, in particular herpesviruses, have a role in the induction of many different autoimmune diseases, detailing the various mechanisms involved. Lastly, we discuss the microbiome and the beneficial microbiota that populate it. We look at the role of the gut microbiome in autoimmune disorders, because of its role in regulating the immune system. Dysbiosis of the microbiota in the gut microbiome can lead to multiple autoimmune disorders. We conclude that understanding the precise roles and relationships shared by all these factors that comprise the exposome and identifying early events and root causes of these disorders can help us to develop more targeted therapeutic protocols for the management of this worldwide epidemic of autoimmunity.

Autoantigen Discovery in the Hair Loss Disorder, Alopecia Areata: Implication of Post-Translational Modifications

Alopecia areata (AA) is a chronic, multifactorial, polygenic, and heterogeneous disorder affecting growing hair follicles in susceptible individuals, which results in a non-scarring and reversible hair loss with a highly unpredictable course. Despite very considerable research effort, the nature of the precipitating factor(s) responsible for initiating AA in any given hair follicle remains unclear, due largely to significant gaps in our knowledge of the precise sequence of the etiopathogenic events in this dermatosis. However, disease-related changes in the immune-competence of the lower growing hair follicle, together with an active immune response (humoral and cellular) to hair follicle-associated antigens, are key associated phenomena. Confirmation of the hair follicle antigen(s) implicated in AA disease onset has remained stubbornly elusive. While it may be considered somewhat philosophical by some, it is also unclear whether immune-mediated hair loss in AA results from a) an ectopic (i.e., in an abnormal location) immune response to native (unmodified) self-antigens expressed by the healthy hair follicle, b) a normal immune response against modified self-antigens (or neoantigens), or c) a normal immune response against self-antigens (modified/non-modified) that were not previously visible to the immune system (because they were conformationally-hidden or sequestered) but become exposed and presentable in an MHC-I/-II molecule-restricted manner. While some candidate hair follicle antigen target(s) in AA are beginning to emerge, with a potential role for trichohyalin, it is not yet clear whether this represents the initial and immunodominant antigenic focus in AA or is simply one of an expanding repertoire of exposed hair follicle tissue damage-associated antigens that are secondary to the disease. Confirmation of autoantigen identity is essential for our understanding of AA etiopathogenesis, and consequently for developing a more informed therapeutic strategy. Major strides have been made in autoantigen discovery in other autoimmune conditions. In particular, some of these conditions may provide insights into how post-translational modifications (e.g., citrullination, deamidation, etc.) of hair follicle-restricted proteins may increase their antigenicity and so help drive the anti-hair follicle immune attack in AA.