Evolution of autoantibody responses in individuals at risk of rheumatoid arthritis

Implications of Post-Translational Modifications in Autoimmunity with Emphasis on Citrullination, Homocitrullination and Acetylation for the Pathogenesis, Diagnosis and Prognosis of Rheumatoid Arthritis

Post-translational modifications (PTMs) influence cellular processes and consequently, their dysregulation is related to the etiologies of numerous diseases. It is widely known that a variety of autoimmune responses in human diseases depend on PTMs of self-proteins. In this review we summarize the latest findings about the role of PTMs in the generation of autoimmunity and, specifically, we address the most relevant PTMs in rheumatic diseases that occur in synovial tissue. Citrullination, homocitrullination (carbamylation) and acetylation are responsible for the generation of Anti-Modified Protein/Peptide Antibodies (AMPAs family), autoantibodies which have been implicated in the etiopathogenesis, diagnosis and prognosis of rheumatoid arthritis (RA). Synthetic peptides provide complete control over the exact epitopes presented as well as the specific positions in their sequence where post-translationally modified amino acids are located and are key to advancing the detection of serological RA biomarkers that could be useful to stratify RA patients in order to pursue a personalized rheumatology. In this review we specifically address the latest findings regarding synthetic peptides post-translationally modified for the specific detection of autoantibodies in RA patients.

Current view on the pathogenic role of anti-citrullinated protein antibodies in rheumatoid arthritis

Epidemiological findings suggest a potential role for anti-citrullinated protein antibodies (ACPAs) in rheumatoid arthritis (RA) pathogenesis. ACPA-positive RA is associated with unique genetical and environmental risk factors, in contrast to seronegative RA. ACPA-positive healthy individuals are at risk of developing RA and can develop joint pain and bone loss already before disease onset. ACPA injection triggered bone loss and pain-like behaviour in mice and, in the presence of additional arthritis inducers, exacerbated joint inflammation. In cell culture experiments, ACPAs could bind to and modulate a variety of cellular targets, such as macrophages, osteoclasts, synovial fibroblasts, neutrophil granulocytes, mast cells, dendritic cells and platelets, further underlying a potential role for these autoantibodies in triggering pathogenic pathways and providing clues for their mechanisms of action. Patient-derived ACPA clones have been characterised by unique cellular effects and multiple ways to act on the target cells. ACPAs might directly induce stimulatory signals by ligating key citrullinated cell surface molecules or, alternatively, act as immune complexes on Fc receptors and potentially other molecules that recognise carbohydrate moieties. On the contrary to experimentally manufactured ACPA clones, patient-derived ACPAs are highly promiscuous and cross-reactive, suggesting a simultaneous binding to a range of functionally relevant and irrelevant targets. Moreover, several ACPA clones recognise carbamylated or acetylated targets as well. These features complicate the identification and description of ACPA-induced pathogenic mechanisms. In the current review, we summarise recent data on the functional properties of patient-derived ACPAs and present mechanistic models on how these antibodies might contribute to RA pathogenesis.

NRF2 activator A-1396076 ameliorates inflammation in autoimmune disease models by inhibiting antigen dependent T cell activation

Nuclear factor (erythroid-derived 2) like 2 (NRF2) is a nuclear transcription factor activated in response to oxidative stress that induces a gene program that dampens inflammation and can limit cell damage that perpetuates the inflammatory response. We have identified A-1396076, a potent and selective NRF2 activator with demonstrated KEAP1 binding and modulation of cellular NRF2 mediated effects. In vivo administration of A-1396076 inhibits inflammation across several rodent models of autoimmunity when administered at or before the time of antigen challenge while also inducing NRF2 modulated gene transcription in the liver of the animals. It was not effective when administered after the time of antigen challenge or in a T cell independent model of arthritis induced by passive transfer of anti-collagen antibodies. A-1396076 inhibited antigen dependent T cell activation as measured by IFN-γ production in an ex vivo re-stimulation assay and following anti-CD3 challenge of MOG-sensitized mice. A-1396076 reduced costimulatory molecule expression on dendritic cells in the lungs of OVA LPS challenged mice suggesting that the mechanism of T cell inhibition was mediated at least partially by interfering with antigen presentation. These data suggest that NRF2 activation may be an effective strategy to dampen inflammation for treatment of autoimmune disease.

Diet as a Modulator of Intestinal Microbiota in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic immune-driven inflammatory disease characterised by synovial inflammation, leading to progressive cartilage and bone destruction, impacting patients' functional capacity and quality of life. Patients with RA have significant differences in gut microbiota composition when compared to controls. Intestinal dysbiosis influences the intestinal barrier strength, integrity and function, and diet is considered the main environmental factor impacting gut microbiota. Over the last few years, researchers have focused on the influence of single components of the diet in the modulation of intestinal microbiota in RA rather than whole dietary patterns. In this review, we focus on how the Mediterranean diet (MD), a whole dietary pattern, could possibly act as an adjuvant therapeutic approach, modulating intestinal microbiota and intestinal barrier function in order to improve RA-related outcomes. We also review the potential effects of particular components of the MD, such as n-3 polyunsaturated fatty acids (PUFAs), polyphenols and fibre.

Obstructive lung diseases and risk of rheumatoid arthritis

Introduction: Smoking is an established risk factor for both lung diseases and rheumatoid arthritis (RA). Chronic mucosal airway inflammation may result in immune tolerance loss, neoantigen formation, and production of RA-related autoantibodies that increase the subsequent risk of RA. In this review, we aimed to summarize the current evidence supporting the role of obstructive lung diseases and subsequent risk of RA.Areas covered: We identified scientific articles discussing the biologic mechanisms linking mucosal airway inflammation and RA risk. We also identified studies investigating asthma, chronic obstructive pulmonary disease, bronchiectasis, cystic fibrosis, chronic tuberculous and nontuberculous mycobacterial infections, and interstitial lung disease with subsequent risk for RA.Expert opinion: The current evidence supports the hypothesis that mucosal airway inflammation may increase the risk of developing RA. However, most studies investigating this relationship have been retrospective and may not have adequately addressed the role of smoking. Larger prospective studies may provide stronger evidence for obstructive lung disease and RA risk. Determining the role of obstructive lung disease in RA pathogenesis may provide opportunity for RA prevention and screening strategies, while identifying novel biologic mechanisms that could offer targets to improve treatment and outcomes.

The Role of Dietary Fiber in Rheumatoid Arthritis Patients: A Feasibility Study

Short-chain fatty acids are microbial metabolites that have been shown to be key regulators of the gut-joint axis in animal models. In humans, microbial dysbiosis was observed in rheumatoid arthritis (RA) patients as well as in those at-risk to develop RA, and is thought to be an environmental trigger for the development of clinical disease. At the same time, diet has a proven impact on maintaining intestinal microbial homeostasis. Given this association, we performed a feasibility study in RA patients using high-fiber dietary supplementation with the objective to restore microbial homeostasis and promote the secretion of beneficial immunomodulatory microbial metabolites. RA patients (n = 36) under routine care received daily high-fiber bars or cereals for 28 days. Clinical assessments and laboratory analysis of immune parameters in blood and stool samples from RA patients were done before and after the high-fiber dietary supplementation. We observed an increase in circulating regulatory T cell numbers, favorable Th1/Th17 ratios, as well as decreased markers of bone erosion in RA patients after 28 days of dietary intervention. Furthermore, patient-related outcomes of RA improved. Based on these results, we conclude that controlled clinical studies of high-fiber dietary interventions could be a viable approach to supplement or complement current pharmacological treatment strategies.

The Clinical Value of Autoantibodies in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a highly heterogeneous syndrome in terms of clinical presentation, progression, and response to therapy. In such a complicated context, the identification of disease-related biomarkers would be undoubtedly helpful in assisting tailored approaches for every patient. Despite remarkable efforts, however, progress in new biomarker development and validation is dramatically slow. At present, none of the candidate genetic, cellular, or molecular biomarker has yet surpassed the clinical value of RA-specific autoantibodies, including rheumatoid factor (RF) and anti-citrullinated protein autoantibodies (ACPA). Rather, recent years have witnessed significant advancements in our understanding of the multiple roles that RF and ACPA play in RA pathophysiology. This has helped clarifying the mechanistic basis of the clinical associations of autoantibodies in RA. In this short review, we will briefly summarize the effector functions of RF and ACPA, and analyse how autoantibodies may help subclassifying RA patients in terms of clinical presentation and response to therapy.

On the origin of rheumatoid factors: Insights from analyses of variable region sequences

OBJECTIVES

Rheumatoid factors (RFs) are thought to play an important role in rheumatoid arthritis (RA), but are also found in healthy donors (HDs). Previous studies examined variable region sequences of these autoantibodies at a time when knowledge of the human germline repertoire was incomplete. Here we collected and analyzed RF sequence data from the literature to elucidate how RFs develop and whether their characteristics differ between RA patients and HDs.

METHODS

A database was built containing nucleotide sequences of RF heavy and light chain variable domains and characteristics including affinity, isotype and specificity, all collected from published papers. Gene usage and mutation frequencies were analyzed using IMGT/HiV-QUEST. Selection strength was assessed with the BASELINe tool.

RESULTS

Sequences were retrieved for 183 RF clones (87 RA; 67 HDs; 29 other). No biased gene usage was observed for RA and HDs. However, there does appear to be skewed gene usage in RFs from patients with mixed cryoglobulinemia. Mutation frequency varies considerably between RFs, and isotype-switched clones have significantly more mutations. Monospecific RFs carry more mutations than polyspecific RFs; no difference was found for RA- versus HD-derived RFs. Overall, reported affinity is low (median 1 µM), with a non-significant trend toward higher affinity of RA-derived RFs. Mutation frequency and affinity did not appear to be correlated. BASELINe analysis suggests an overall lack of positive selection and less negative selection strength in RA-derived RFs.

CONCLUSIONS

RFs derived from RA patients have similar properties as those derived from HDs. The RF response can be characterized as a moderately matured autoantibody response, with variable levels of somatic hypermutation, but low affinity.