Increased susceptibility to organic dust exposure-induced inflammatory lung disease with enhanced rheumatoid arthritis-associated autoantigen expression in HLA-DR4 transgenic mice

Insights into the complexities of Citrullination: From immune regulation to autoimmune disease

Citrullination, a post-translational modification that changes arginine to citrulline in proteins, is vital for immune response modulation and cell signaling. Catalyzed by peptidyl arginine deiminases (PADs), citrullination is linked to various diseases, particularly autoimmune disorders like rheumatoid arthritis (RA). Citrullinated proteins can trigger the production of anti-citrullinated protein antibodies (ACPAs), included in RA classification criteria. The immune response to citrullination involves both innate and adaptive immunity, affecting monocytes/macrophages, neutrophils, dendritic cells, natural killer cells, B cells, and T cells. Citrullination contributes to disease development in RA and other conditions such as multiple sclerosis, sepsis, and cancer. Therapeutic strategies targeting citrullination and its effects are being explored, including B cell depletion therapies, T cell-directed approaches, PAD inhibitors, and citrullinated peptide-based vaccines. Understanding the interplay between citrullination and the immune system may lead to novel diagnostic tools and targeted therapies for autoimmune diseases and beyond.

Antibodies to Malondialdehyde-Acetaldehyde Adduct Are Associated With Prevalent and Incident Rheumatoid Arthritis-Associated Interstitial Lung Disease in US Veterans

OBJECTIVE

The objective of this study is to determine the associations of protein-specific anti-malondialdehyde-acetaldehyde (MAA) antibodies with prevalent and incident rheumatoid arthritis-interstitial lung disease (RA-ILD).

METHODS

Within a multicenter, prospective cohort of US veterans with RA, RA-ILD was validated by medical record review of clinical diagnoses, chest imaging, and pathology. Serum antibodies to MAA-albumin, MAA-collagen, MAA-fibrinogen, and MAA-vimentin (IgA, IgM, and IgG) were measured by a standardized enzyme-linked immunosorbent assay. Associations of anti-MAA antibodies with prevalent and incident RA-ILD were assessed using multivariable regression models adjusting for established RA-ILD risk factors.

RESULTS

Among 2,739 participants with RA (88% male, mean age of 64 years), there were 114 with prevalent and 136 with incident RA-ILD (average time to diagnosis: 6.6 years). Higher IgM anti-MAA-collagen (per 1 SD: adjusted odds ratio [aOR] 1.28, 95% confidence interval [CI] 1.02-1.61), IgA anti-MAA-fibrinogen (aOR 1.48, 95% CI 1.14-1.92), and IgA (aOR 1.78, 95% CI 1.34-2.37) and IgG (aOR 1.48, 95% CI 1.14-1.92) anti-MAA-vimentin antibodies were associated with prevalent RA-ILD. In incident analyses, higher IgA (per one SD: adjusted hazards ratio [aHR] 1.40, 95% CI 1.11-1.76) and IgM (aHR 1.29, 95% CI 1.04-1.60) anti-MAA-albumin antibody concentrations were associated with increased ILD risk. Participants with IgA (aHR 2.13, 95% CI 1.16-3.90) or IgM (aHR 1.98, 95% CI 1.08-3.64) anti-MAA-albumin antibody concentrations in the highest quartile had an approximately two-fold increased risk of incident RA-ILD. Across all isotypes, anti-MAA-fibrinogen, anti-MAA-collagen, and anti-MAA-vimentin antibodies were not significantly associated with incident RA-ILD.

CONCLUSION

Protein-specific anti-MAA antibodies to collagen, fibrinogen, and vimentin were associated with prevalent RA-ILD. IgA and IgM anti-MAA-albumin antibodies were associated with a higher risk of incident RA-ILD. These findings suggest that MAA modifications and resultant immune responses may contribute to RA-ILD pathogenesis.

The immunomodulatory of interleukin-33 in rheumatoid arthritis: A systematic review

Rheumatoid arthritis (RA) is a systemic chronic autoimmune disease that primarily affects the joints and surrounding soft tissues, characterized by chronic inflammation and proliferation of the synovium. Various immune cells are involved in the pathophysiology of RA. The complex interplay of factors such as chronic inflammation, genetic susceptibility, dysregulation of serum antibody levels, among others, contribute to the complexity of the disease mechanism, disease activity, and treatment of RA. Recently, the cytokine storm leading to increased disease activity in RA has gained significant attention. Interleukin-33 (IL-33), a member of the IL-1 family, plays a crucial role in inflammation and immune regulation. ST2 (suppression of tumorigenicity 2 receptor), the receptor for IL-33, is widely expressed on the surface of various immune cells. When IL-33 binds to its receptor ST2, it activates downstream signaling pathways to exert immunoregulatory effects. In RA, IL-33 regulates the progression of the disease by modulating immune cells such as circulating monocytes, tissue-resident macrophages, synovial fibroblasts, mast cells, dendritic cells, neutrophils, T cells, B cells, endothelial cells, and others. We have summarized and analyzed these findings to elucidate the pathways through which IL-33 regulates RA. Furthermore, IL-33 has been detected in the synovium, serum, and synovial fluid of RA patients. Due to inconsistent research results, we conducted a meta-analysis on the association between serum IL-33, synovial fluid IL-33, and the risk of developing RA in patients. The pooled SMD was 1.29 (95% CI: 1.15-1.44), indicating that IL-33 promotes the onset and pathophysiological progression of RA. Therefore, IL-33 may serve as a biomarker for predicting the risk of developing RA and treatment outcomes. As existing drugs for RA still cannot address drug resistance in some patients, new therapeutic approaches are needed to alleviate the significant burden on RA patients and healthcare systems. In light of this, we analyzed the potential of targeting the IL-33/ST2-related signaling pathway to modulate immune cells associated with RA and alleviate inflammation. We also reviewed IL-33 and RA susceptibility-related single nucleotide polymorphisms, suggesting potential involvement of IL-33 and macrophage-related drug-resistant genes in RA resistance therapy. Our review elucidates the role of IL-33 in the pathophysiology of RA, offering new insights for the treatment of RA.

Clinical features associated with the presence of anti-Ro52 and anti-Ro60 antibodies in Jo-1 antibody-positive anti-synthetase syndrome

Introduction

Anti-SSA antibodies target two unrelated proteins, Ro52 (E3 ligase) and Ro60 (RNA binding protein). Previous studies indicate that anti-Ro52 antibodies are frequently associated with various myositis-specific autoantibodies (MSAs)-including anti-tRNA synthetase antibodies-and that the coexistence of MSAs and anti-Ro52 antibodies may portend worse clinical outcomes. Although not well-described in the setting of myositis, work from our animal model of HRS (histidyl-tRNA synthetase)-induced myositis suggests that anti-Ro60 antibodies may also be linked to specific MSAs such as anti-HRS/Jo-1. We therefore aimed to demonstrate the prevalence and clinical characteristics of Ro52 and Ro60 antibody positivity in patients possessing Jo-1 antibodies.

Methods

To establish the immunological link between anti-synthetase, anti-Ro52, and anti-Ro60 antibodies, we evaluated the relative titers of these antibodies in blood and bronchoalveolar lavage fluid (BALF) of mice following immunization with HRS/Jo-1. In parallel, we used ELISA-based approaches to assess sera from 177 anti-Jo1 antibody-positive patients for the presence of anti-Ro52 and/or anti-Ro60 antibodies. We then determined statistical associations between co-existing anti-Jo-1, anti-Ro52, and/or anti-Ro60 antibodies and clinical manifestations associated with the anti-synthetase syndrome.

Results

Mice immunized with HRS had higher levels of anti-Ro52 and anti-Ro60 antibodies in serum and BALF than PBS-immunized mice. In 177 anti-Jo-1 antibody-positive patients, the prevalence of anti-Ro52 and anti-Ro60 antibodies was 36% and 15%, respectively. The frequency of dry eye/dry mouth, interstitial pneumonia, and pulmonary events over time differed between patients with various combinations of anti-Ro52 and anti-Ro60 antibodies. While anti-Ro52 antibodies generally correlated with statistically significant increases in each of these clinical manifestations, the presence of Ro60 antibodies alone was associated with decreased frequency of ILD.

Discussion

Anti-Ro52 and/or anti-Ro60 antibodies are often co-expressed with anti-Jo1 antibodies, defining clinical subsets with different disease course/outcomes.

Targeting transitioning lung monocytes/macrophages as treatment strategies in lung disease related to environmental exposures

BACKGROUND

Environmental/occupational exposures cause significant lung diseases. Agricultural organic dust extracts (ODE) and bacterial component lipopolysaccharide (LPS) induce recruited, transitioning murine lung monocytes/macrophages, yet their cellular role remains unclear.

METHODS

CCR2 RFP+ mice were intratracheally instilled with high concentration ODE (25%), LPS (10 μg), or gram-positive peptidoglycan (PGN, 100 μg) for monocyte/macrophage cell-trafficking studies. CCR2 knockout (KO) mice and administration of intravenous clodronate liposomes strategies were employed to reduce circulating monocytes available for lung recruitment following LPS exposure. Lung tissues and bronchoalveolar lavage fluid (BALF) were collected. Pro-inflammatory and/or pro-fibrotic cytokines, chemokines, and lung extracellular matrix mediators were quantitated by ELISA. Infiltrating lung cells including monocyte/macrophage subpopulations, neutrophils, and lymphocytes were characterized by flow cytometry. Lung histopathology, collagen content, vimentin, and post-translational protein citrullination and malondialdehyde acetaldehyde (MAA) modification were quantitated. Parametric statistical tests (one-way ANOVA, Tukey'smultiple comparison) and nonparametric statistical (Kruskal-Wallis, Dunn's multiple comparison) tests were used following Shapiro-Wilk testing for normality.

RESULTS

Intratracheal instillation of ODE, LPS, or PGN robustly induced the recruitment of inflammatory CCR2+ CD11cintCD11bhi monocytes/macrophages and both CCR2+ and CCR2- CD11c-CD11bhi monocytes at 48 h. There were also increases in CCR2+ CD4+ and CD8+ T cells and NK cells. Despite reductions in LPS-induced lung infiltrating CD11cintCD11bhi cells (54% reduction), CCR2 knockout (KO) mice were not protected against LPS-induced inflammatory and pro-fibrotic consequences. Instead, compensatory increases in lung neutrophils and CCL2 and CCL7 release occurred. In contrast, the depletion of circulating monocytes through the administration of intravenous clodronate (vs. vehicle) liposomes 24 h prior to LPS exposure reduced LPS-induced infiltrating CD11cintCD11bhi monocyte-macrophage subpopulation by 59% without compensatory changes in other cell populations. Clodronate liposome pre-treatment significantly reduced LPS-induced IL-6 (66% reduction), matrix metalloproteinases (MMP)-3 (36%), MMP-8 (57%), tissue inhibitor of metalloproteinases (61%), fibronectin (38%), collagen content (22%), and vimentin (40%). LPS-induced lung protein citrullination and MAA modification, post-translational modifications implicated in lung disease, were reduced (39% and 48%) with clodronate vs. vehicle liposome.

CONCLUSION

Highly concentrated environmental/occupational exposures induced the recruitment of CCR2+ and CCR2- transitioning monocyte-macrophage and monocyte subpopulations and targeting peripheral monocytes may reduce the adverse lung consequences resulting from exposures to LPS-enriched inhalants.

Combined repetitive inhalant endotoxin and collagen-induced arthritis drive inflammatory lung disease and arthritis severity in a testosterone-dependent manner

Respiratory-related diseases are a leading cause of death in rheumatoid arthritis (RA) and are disproportionately higher in men, which may be attributable to environmental risk factors. Animal studies have demonstrated potentiated autoimmunity, arthritis, and profibrotic/inflammatory lung disease with a combination of airborne exposures and collagen-induced arthritis (CIA). This study aimed to determine whether hormone-dependent differences explained these observations. Arthritis-prone male intact and castrated DBA/1J mice received intranasal inhalation of lipopolysaccharide (LPS) daily for 5 wk and CIA induction. Arthritis scores and serum pentraxin-2 levels were increased in castrated versus intact mice. In contrast, airway cell influx, lung tissue infiltrates, and lung levels of proinflammatory and profibrotic markers (C5a, IL-33, and matrix metalloproteinases) were reduced in castrated versus intact mice. CIA + LPS-induced lung histopathology changes and the expression of lung autoantigens including malondialdehyde acetaldehyde (MAA)- and citrulline (CIT)-modified proteins and vimentin were reduced in castrated animals. There were no differences in serum anti-MAA or anti-CIT protein antibody (ACPA) levels or serum pentraxin levels between groups. Testosterone replacement led to a reversal of several lung inflammatory/profibrotic endpoints noted earlier in castrated male CIA + LPS-treated mice with testosterone supplementation promoting neutrophil influx, MAA expression, and TNF-α, IL-6, and MMP-9. These findings imply that testosterone contributes to lung and arthritis inflammatory responses following CIA + LPS coexposure, but not to systemic autoantibody responses. The CIA + LPS model provides a paradigm for investigations focused on the mechanistic underpinnings for epidemiologic and phenotypic sex differences in RA-related lung disease.NEW & NOTEWORTHY Our study shows that testosterone acts as a key immunomodulatory hormone contributing to critical features of rheumatoid arthritis (RA)-associated lung disease in the setting of airborne endotoxin (lipopolysaccharide; LPS) exposures and concomitant arthritis induction in mice. The exaggerated airway inflammation observed following combined exposures in male mice was accompanied by increases in profibrotic mediators, netosis, and increased expression of lung autoantigens, all relevant to the pathogenesis of lung disease in arthritis.

Post-endotoxin exposure-induced lung inflammation and resolution consequences beneficially impacted by lung-delivered IL-10 therapy

Although lung diseases typically result from long-term exposures, even a robust, one-time exposure can result in long-lasting consequences. Endotoxin is a ubiquitous environmental/occupational inflammatory agent often used to model airway inflammation. Using a murine model, the return to lung homeostasis following high dose inhalant lipopolysaccharide (LPS, 10-100 μg) exposure were delineated over 2 weeks. LPS-induced rapid weight loss, release of proinflammatory mediators, and inflammatory cell influx with prolonged persistence of activated macrophages CD11c⁺CD11b⁺ and recruited/transitioning CD11c^intCD11b⁺ monocyte-macrophages out to 2 weeks. Next, lung-delivered recombinant (r) interleukin (IL)-10 was intratracheally administered for 3 doses initiated 5 h following LPS (10 μg) exposure for 2 days. IL-10 therapy reduced LPS-induced weight loss and increased blood glucose levels. Whereas there was no difference in LPS-induced bronchoalveolar lavage airway fluid cellular influx, total lung cell infiltrates were reduced (37%) with rIL-10 treatment. Post-LPS exposure treatment with rIL-10 strikingly reduced lavage fluid and lung homogenate levels of tumor necrosis factor-α (88% and 93% reduction, respectively), IL-6 (98% and 94% reduction), CXCL1 (66% and 75% reduction), and CXCL2 (47% and 67% reduction). LPS-induced recruited monocyte-macrophages (CD11c^intCD11b⁺) were reduced (68%) with rIL-10. Correspondingly, LPS-induced lung tissue CCR2⁺ inflammatory monocyte-macrophage were reduced with rIL-10. There were also reductions in LPS-induced lung neutrophils, lymphocyte subpopulations, collagen content, and vimentin expression. These findings support the importance of studying resolution processes for the development of treatment after unintended environmental/occupational biohazard exposures. Short-term, lung-delivered rIL-10 favorably hastened inflammatory recovery processes following acute, high dose inhalant LPS exposure.