Diverse mechanisms of IRF5 action in inflammatory responses

Recent advances in anti-inflammation via AMPK activation

Inflammation is a complex physiological phenomenon, which is the body's defensive response, but abnormal inflammation can have adverse effects, and many diseases are related to the inflammatory response. AMPK, as a key sensor of cellular energy status, plays a crucial role in regulating cellular energy homeostasis and glycolipid metabolism. In recent years, the anti-inflammation effect of AMPK and related signalling cascade has begun to enter everyone's field of vision - not least the impact on metabolic diseases. A great number of studies have shown that anti-inflammatory drugs work through AMPK and related pathways. Herein, this article summarises recent advances in compounds that show anti-inflammatory effects by activating AMPK and attempts to comment on them.

The Role of Interferon Regulatory Factors in Liver Diseases

The interferon regulatory factors (IRFs) family comprises 11 members that are involved in various biological processes such as antiviral defense, cell proliferation regulation, differentiation, and apoptosis. Recent studies have highlighted the roles of IRF1-9 in a range of liver diseases, including hepatic ischemia-reperfusion injury (IRI), alcohol-induced liver injury, Con A-induced liver injury, nonalcoholic fatty liver disease (NAFLD), cirrhosis, and hepatocellular carcinoma (HCC). IRF1 is involved in the progression of hepatic IRI through signaling pathways such as PIAS1/NFATc1/HDAC1/IRF1/p38 MAPK and IRF1/JNK. The regulation of downstream IL-12, IL-15, p21, p38, HMGB1, JNK, Beclin1, β-catenin, caspase 3, caspase 8, IFN-γ, IFN-β and other genes are involved in the progression of hepatic IRI, and in the development of HCC through the regulation of PD-L1, IL-6, IL-8, CXCL1, CXCL10, and CXCR3. In addition, IRF3-PPP2R1B and IRF4-FSTL1-DIP2A/CD14 pathways are involved in the development of NAFLD. Other members of the IRF family also play moderately important functions in different liver diseases. Therefore, given the significance of IRFs in liver diseases and the lack of a comprehensive compilation of their molecular mechanisms in different liver diseases, this review is dedicated to exploring the molecular mechanisms of IRFs in various liver diseases.

Exploring the polarization of M1 and M2 macrophages in the context of skin diseases

Macrophages are critical components of the immune system and play vital roles in pathogen defense, immune regulation, and tissue repair. These cells exhibit different polarization states depending on environmental signals, and the M1/M2 paradigm is a useful tool for comprehending these states. This review article comprehensively presents the underlying mechanisms of M1 and M2 macrophage polarization and examines their polarization in various skin diseases. Additionally, this paper discusses therapeutic strategies that target M1 and M2 macrophage polarization in skin diseases. A more profound understanding of macrophage polarization in skin diseases could provide valuable insights for the development of innovative therapeutic strategies.

UBR5 promotes antiviral immunity by disengaging the transcriptional brake on RIG-I like receptors

The Retinoic acid-Inducible Gene I (RIG-I) like receptors (RLRs) are the major viral RNA sensors essential for the initiation of antiviral immune responses. RLRs are subjected to stringent transcriptional and posttranslational regulations, of which ubiquitination is one of the most important. However, the role of ubiquitination in RLR transcription is unknown. Here, we screen 375 definite ubiquitin ligase knockout cell lines and identify Ubiquitin Protein Ligase E3 Component N-Recognin 5 (UBR5) as a positive regulator of RLR transcription. UBR5 deficiency reduces antiviral immune responses to RNA viruses, while increases viral replication in primary cells and mice. Ubr5 knockout mice are more susceptible to lethal RNA virus infection than wild type littermates. Mechanistically, UBR5 mediates the Lysine 63-linked ubiquitination of Tripartite Motif Protein 28 (TRIM28), an epigenetic repressor of RLRs. This modification prevents intramolecular SUMOylation of TRIM28, thus disengages the TRIM28-imposed brake on RLR transcription. In sum, UBR5 enables rapid upregulation of RLR expression to boost antiviral immune responses by ubiquitinating and de-SUMOylating TRIM28.

IRF5 governs macrophage adventitial infiltration to fuel abdominal aortic aneurysm formation

Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease characterized by the expansion of the aortic wall. One of the most significant features is the infiltration of macrophages in the adventitia, which drives vasculature remodeling. The role of macrophage-derived interferon regulatory factor 5 (IRF5) in macrophage infiltration and AAA formation remains unknown. RNA sequencing of AAA adventitia identified Irf5 as the top significantly increased transcription factor that is predominantly expressed in macrophages. Global and myeloid cell-specific deficiency of Irf5 reduced AAA progression, with a marked reduction in macrophage infiltration. Further cellular investigations indicated that IRF5 promotes macrophage migration by direct regulation of downstream phosphoinositide 3-kinase γ (PI3Kγ, Pik3cg). Pik3cg ablation hindered AAA progression, and myeloid cell-specific salvage of Pik3cg restored AAA progression and macrophage infiltration derived from Irf5 deficiency. Finally, we found that IRF5 and PI3Kγ expression in the adventitia is significantly increased in patients with AAA. These findings reveal that the IRF5-dependent regulation of PI3Kγ is essential for AAA formation.

Viral recognition and the antiviral interferon response

Interferons (IFNs) are antiviral cytokines that play a key role in the innate immune response to viral infections. In response to viral stimuli, cells produce and release interferons, which then act on neighboring cells to induce the transcription of hundreds of genes. Many of these gene products either combat the viral infection directly, e.g., by interfering with viral replication, or help shape the following immune response. Here, we review how viral recognition leads to the production of different types of IFNs and how this production differs in spatial and temporal manners. We then continue to describe how these IFNs play different roles in the ensuing immune response depending on when and where they are produced or act during an infection.

Peli1 deletion in macrophages attenuates myocardial ischemia/reperfusion injury by suppressing M1 polarization

The polarization of macrophages to the M1 or M2 phenotype has a pivotal role in inflammatory response following myocardial ischemia/reperfusion injury. Peli1, an E3 ubiquitin ligase, is closely associated with inflammation and autoimmunity as an important regulatory protein in the Toll-like receptor signaling pathway. We aimed to explore the function of Peli1 in macrophage polarization under myocardial ischemia/reperfusion injury and elucidate the possible mechanisms. We show here that Peli1 is upregulated in peripheral blood mononuclear cells from patients with myocardial ischemia/reperfusion, which is correlated with myocardial injury and cardiac dysfunction. We also found that the proportion of M1 macrophages was reduced and myocardial infarct size was decreased, paralleling improvement of cardiac function in mice with Peli1 deletion in hematopoietic cells or macrophages. Macrophage Peli1 deletion lessened M1 polarization and reduced the migratory ability in vitro. Mechanistically, Peli1 contributed to M1 polarization by promoting K63-linked ubiquitination and nuclear translocation of IRF5. Moreover, Peli1 deficiency in macrophages reduced the apoptosis of cardiomyocytes in vivo and in vitro. Together, our study demonstrates that Peli1 deficiency in macrophages suppresses macrophage M1 polarization and alleviates myocardial ischemia/reperfusion injury by inhibiting the nuclear translocation of IRF5, which may serve as a potential intervention target for myocardial ischemia/reperfusion injury.

Depression Exacerbates Dextran Sulfate Sodium-Induced Colitis via IRF5-Mediated Macrophage Polarization

BACKGROUND AND AIMS

Patients with inflammatory bowel disease (IBD) and concurrent depression are predisposed to severer disease activity and a worse prognosis. Macrophage polarization toward the M1 phenotype may contribute to the exacerbation of IBD with comorbid depression. Moreover, interferon regulatory factor 5 (IRF5) is involved in the pathogenesis of IBD. The aim of this study was to explore the role of IRF5 in macrophage polarization in the impact of depression upon colitis.

METHODS

Depressive-like behavior was induced by repeated forced swim stress. Colon length, disease activity index (DAI), colon morphology, histology, ultrastructure of epithelial barrier, lamina propria macrophage polarization, and expression of IRF5 were compared between DSS colitis rats with and without depressive-like behavior. IRF5 shRNA was constructed to affect the rat peritoneal macrophages polarization in vitro. After IRF5 shRNA lentivirus was introduced into colon by enema, the colitis severity, lamina propria macrophage polarization, and TNF-α, IL-1β, and IL-10 of colon tissues were measured.

RESULTS

The study found severer colonic inflammation in depressed versus non-depressed DSS-colitis rats. Depressed DSS-colitis rats exhibited smaller subepithelial macrophages size and reduced intracellular granule diversity compared with nondepressed DSS-colitis rats. Increased polarization toward the M1 phenotype, elevated expression of IRF5, and co-expression of IRF5 with CD86 were found in depressed versus nondepressed DSS-colitis rats. Lentivirus-mediated shRNA interference with IRF5 expression switched rat peritoneal macrophage polarization from the M1 to the M2 phenotype, downregulated TNF-α, IL-1β expression to a greater extent in depressed versus nondepressed colitis rats.

CONCLUSIONS

IRF5-mediated macrophage polarization may likely underlie the deterioration of DSS-induced colitis caused by depression.

Berberine regulates PADI4-related macrophage function to prevent lung cancer

Coptis chinensis Franch (CCF) has been widely used by Chinese old herbalist doctor to treat internal and external diseases including malignant sore and cancer. Berberine (BBR) is a major bioactive compound in CCF and may exert anti-tumor and anti-inflammatory effects like CCF. However, the prevention effect of berberine against lung cancer and its relevance of anti-inflammation property to cancer-preventing effect are still obscure. Protein arginine deaminase 4 (PAD4) played an important role in macrophage related inflammatory response, the purpose of this study was to identify whether berberine can prevent lung cancer and explore its effect on PADI4-related macrophage function. In vitro, PADI4 overexpression affects cell-activated state in macrophages. PADI4 overexpressed macrophages promote epithelial-mesenchymal transition (EMT) of A549 lung cancer cells and inhibit cell apoptosis. Berberine at the experiment dose had no effect on cell viability of U937-derived macrophages, but could significantly inhibit PADI4 expression to reverse the macrophage-activated state and the lung cancer -promoting effect of PADI4-overexpressed macrophages. Unlike GSK484, berberine had a little effect on the PADI4 citrullination activity at the experimental doses, its IC50 for PADI4 inhibition is 45.07 μM (44.03-46.12 μM). In the mouse lung carcinogenetic model, PADI4 expression was directly related to the number of lung nodules. Berberine had the similar role to GSK484 in reducing the number of lung tumor nodules with the improved lung pathology in a dose-dependent manner and significantly inhibited PADI4 expression. Further, we found that PADI4 overexpression could inhibit IRF5 expression, up-regulate CD163 and CD206 and down-regulate CD86 in macrophages, which could be reversed by berberine. Our results suggest that berberine may regulate PADI4-related macrophage function to prevent lung cancer.

Physiological and Pathological Inflammation Induced by Antibodies and Pentraxins

Macrophages play a key role in induction of inflammatory responses. These inflammatory responses are mostly considered to be instigated by activation of pattern recognition receptors (PRRs) or cytokine receptors. However, recently it has become clear that also antibodies and pentraxins, which can both activate Fc receptors (FcRs), induce very powerful inflammatory responses by macrophages that can even be an order of magnitude greater than PRRs. While the physiological function of this antibody-dependent inflammation (ADI) is to counteract infections, undesired activation or over-activation of this mechanism will lead to pathology, as observed in a variety of disorders, including viral infections such as COVID-19, chronic inflammatory disorders such as Crohn's disease, and autoimmune diseases such as rheumatoid arthritis. In this review we discuss how physiological ADI provides host defense by inducing pathogen-specific immunity, and how erroneous activation of this mechanism leads to pathology. Moreover, we will provide an overview of the currently known signaling and metabolic pathways that underlie ADI, and how these can be targeted to counteract pathological inflammation.

Pharmacological Activation of p53 during Human Monocyte to Macrophage Differentiation Attenuates Their Pro-Inflammatory Activation by TLR4, TLR7 and TLR8 Agonists

Simple Summary

Pharmacological activation of tumor suppressor p53 is a promising therapeutic strategy for a range of hematologic and solid cancers. Whether p53 activation augments or suppresses anti-tumor innate immunity is less understood. Here we show that treatment of differentiating human macrophages with a p53 activator idasanutlin suppresses their inflammatory responses to activators of toll-like receptors (TLR) -4 and -7/8. This is accompanied by reduced expression of TLR7, TLR8, as well as TLR4 co-receptor CD14. These data help evaluating the possibilities of combining p53-targeting and immunostimulatory anti-cancer therapies.

Abstract

The transcription factor p53 has well-recognized roles in regulating cell cycle, DNA damage repair, cell death, and metabolism. It is an important tumor suppressor and pharmacological activation of p53 by interrupting its interaction with the ubiquitin E3 ligase mouse double minute 2 homolog (MDM2) is actively explored for anti-tumor therapies. In immune cells, p53 modulates inflammatory responses, but the impact of p53 on macrophages remains incompletely understood. In this study, we used the MDM2 antagonist idasanutlin (RG7388) to investigate the responses of primary human macrophages to pharmacological p53 activation. Idasanutlin induced a robust p53-dependent transcriptional signature in macrophages, including several pro-apoptotic genes. However, idasanutlin did not generally sensitize macrophages to apoptosis, except for an enhanced response to a Fas-stimulating antibody. In fully differentiated macrophages, idasanutlin did not affect pro-inflammatory gene expression induced by toll-like receptor 4 (TLR4), TLR3, and TLR7/8 agonists, but inhibited interleukin-4-induced macrophage polarization. However, when present during monocyte to macrophage differentiation, idasanutlin attenuated inflammatory responses towards activation of TLR4 and TLR7/8 by low doses of lipopolysaccharide or resiquimod (R848). This was accompanied by a reduced expression of CD14, TLR7, and TLR8 in macrophages differentiated in the presence of idasanutlin. Our data suggest anti-inflammatory effects of pharmacological p53 activation in differentiating human macrophages.

IRF5 Acts as a Potential Therapeutic Marker in Inflammatory Bowel Diseases

BACKGROUND

Inflammatory bowel diseases (IBDs), including ulcerative colitis (UC) and Crohn's disease (CD), are chronic inflammatory disorders. As is well known, interferon regulatory factor (IRF) 5 is closely associated with the pathogenesis of various inflammatory diseases. But the exact role of IRF5 in IBD remains unclear.

METHODS

In this study, we detected IRF5 expression in peripheral blood mononuclear cells (PBMCs) and inflamed mucosa from IBD patients by immunohistochemistry, western blot, and quantitative real-time polymerase chain reaction. Peripheral blood CD4+ T cells were stimulated with inflammatory cytokines and transfected by lentivirus.

RESULTS

In active IBD patients, the expression of IRF5 in PBMCs and inflamed colonic tissues was obviously increased and significantly associated with disease activity. Ectopic overexpression of IRF5 could promote the differentiation of IBD CD4+ T cells into Th1 and Th17 cells by regulating T-bet and RAR related orphan receptor C, whereas knockdown of IRF5 had the opposite effects. Tumor necrosis factor (TNF)-α upregulated expression of IRF5 in CD4+ T cells, but anti-TNF treatment with infliximab could markedly reduce IRF5 expression in CD4+ T cells and intestinal mucosa of CD patients.

CONCLUSION

Our study reveals a novel mechanism that IRF5 levels are correlated with disease activity in IBD and might function as a possible marker for the management of IBD via regulating Th1 and Th17 immune responses and cytokine production.

Stevioside Activates AMPK to Suppress Inflammation in Macrophages and Protects Mice from LPS-Induced Lethal Shock

Stevioside, a diterpenoid glycoside, is widely used as a natural sweetener; meanwhile, it has been proven to possess various pharmacological properties as well. However, until now there were no comprehensive evaluations focused on the anti-inflammatory activity of stevioside. Thus, the anti-inflammatory activities of stevioside, both in macrophages (RAW 264.7 cells, THP-1 cells, and mouse peritoneal macrophages) and in mice, were extensively investigated for the potential application of stevioside as a novel anti-inflammatory agent. The results showed that stevioside was capable of down-regulating lipopolysaccharide (LPS)-induced expression and production of pro-inflammatory cytokines and mediators in macrophages from different sources, such as IL-6, TNF-α, IL-1β, iNOS/NO, COX2, and HMGB1, whereas it up-regulated the anti-inflammatory cytokines IL-10 and TGF-β1. Further investigation showed that stevioside could activate the AMPK -mediated inhibition of IRF5 and NF-κB pathways. Similarly, in mice with LPS-induced lethal shock, stevioside inhibited release of pro-inflammatory factors, enhanced production of IL-10, and increased the survival rate of mice. More importantly, stevioside was also shown to activate AMPK in the periphery blood mononuclear cells of mice. Together, these results indicated that stevioside could significantly attenuate LPS-induced inflammatory responses both in vitro and in vivo through regulating several signaling pathways. These findings further strengthened the evidence that stevioside may be developed into a therapeutic agent against inflammatory diseases.

Full-length transcriptome sequencing combined with RNA-seq analysis revealed the immune response of fat greenling (Hexagrammos otakii) to Vibrio harveyi in early infection

Fat greenling (Hexagrammos otakii) is an important commercial marine fish species cultured in northeast Asia, but its available gene sequences are limited. Vibrio harveyi is a causative agent of vibriosis in fat greenling and also causes severe losses to the aquaculture industry in China. In order to obtain more high-quality transcript information and investigate the early immune response of fat greenling against V. harveyi, the fish were artificially infected with V. harveyi, and five sampling points were set within 48 h. Iso-Seq combined with RNA-Seq were applied in the comprehensive transcriptome analysis of V. harveyi-infected fat greenling. Total 42,225 consensus isoforms were successfully extracted from the result of Iso-Seq, and more than 19,000 ORFs were predicted. In addition, total three modules were identified by WGCNA which significantly positive correlated to the infection time, and the KEGG analysis showed that the immune-related genes in these modules mainly enriched in TLR signaling pathway, NF-κB signaling pathway and Endocytosis. The activation of inflammation and endocytosis was the most significant characteristics of fat greenling immune response during the early infection. Based on the WGCNA, a series of high-degree nodes in the networks were identified as hub genes. The protein structures of cold-inducible RNA-binding protein (CIRBP), poly [ADP-ribose] polymerase 1 (PARP1) and protein arginine N-methyl transferase 1 (PRMT1) were subsequently found to be highly conserved in vertebrate, and the gene expression pattern of CIRBP, PARP1, PRMT1 and a part of TLR/NF-κB pathway-related genes indicated that these proteins might have similar biological functions in regulation of inflammatory response in teleost fish. The results of this study provided the first systematical full-length transcriptome profile of fat greenling and characterized its immune responses in early infection of V. harvey, which will serve as the foundation for further exploring the molecular mechanism of immune defense against bacterial infection in fat greenling.

The risk of rheumatoid arthritis among patients with inflammatory bowel disease: a systematic review and meta-analysis

Background

Studies have suggested that patients with inflammatory bowel disease (IBD) have an increased risk of rheumatoid arthritis (RA). However, the available data on this association are inconsistent. This meta-analysis aimed to determine the association between IBD and the risk of RA.

Methods

Observational studies investigating the RA risk among patients with IBD (Crohn disease (CD) and/or ulcerative colitis (UC)) were searched in PubMed, Embase, and Web of Science from the date of inception to December 2019. The methodological quality of the included studies was assessed using the Newcastle-Ottawa Scale. Relative risks (RRs) and corresponding 95% confidential intervals (CIs) were pooled with a random-effects model. Heterogeneity was evaluated using I² statistics while publication bias was determined using Begg’s and Egger’s tests. Subgroup and sensitivity analyses were performed.

Results

A total of three cohort studies, three cross-sectional studies, and two case-control studies were included in the meta-analyses. Compared to the non-IBD control or general population, there was a significantly higher risk of RA among patients with IBD (RR = 2.59; 95% CI: 1.93–3.48). Moreover, both CD (RR = 3.14; 95% CI: 2.46–4.01) and UC (RR = 2.29; 95% CI: 1.76–2.97) were associated with a significantly increased risk of RA. However, heterogeneity was substantial across studies and the subgroup analyses failed to identify the potential source of heterogeneity.

Conclusions

Patients with IBD have a greater risk of developing RA. Rheumatologists should be consulted when patients with IBD present with undifferentiated joint complaints. However, more prospective cohort studies are needed to validate these results.

IRF5 Promotes Influenza Virus-Induced Inflammatory Responses in Human Induced Pluripotent Stem Cell-Derived Myeloid Cells and Murine Models

The inflammatory response to influenza A virus (IAV) participates in infection control but contributes to disease severity. After viral detection, intracellular pathways are activated, initiating cytokine production, but these pathways are incompletely understood. We show that interferon regulatory factor 5 (IRF5) mediates IAV-induced inflammation and, in mice, drives pathology. This was independent of antiviral type 1 IFN and virus replication, implying that IRF5 could be specifically targeted to treat influenza virus-induced inflammation. We show for the first time that human iPSC technology can be exploited in genetic studies of virus-induced immune responses. Using this technology, we deleted IRF5 in human myeloid cells. These IRF5-deficient cells exhibited impaired influenza virus-induced cytokine production and revealed that IRF5 acts downstream of Toll-like receptor 7 and possibly retinoic acid-inducible gene I. Our data demonstrate the importance of IRF5 in influenza virus-induced inflammation, suggesting that genetic variation in the IRF5 gene may influence host susceptibility to viral diseases.

Recognition of influenza A virus (IAV) by the innate immune system triggers pathways that restrict viral replication, activate innate immune cells, and regulate adaptive immunity. However, excessive innate immune activation can exaggerate disease. The pathways promoting excessive activation are incompletely understood, with limited experimental models to investigate the mechanisms driving influenza virus-induced inflammation in humans. Interferon regulatory factor 5 (IRF5) is a transcription factor that plays important roles in the induction of cytokines after viral sensing. In an in vivo model of IAV infection, IRF5 deficiency reduced IAV-driven immune pathology and associated inflammatory cytokine production, specifically reducing cytokine-producing myeloid cell populations in Irf5^−/− mice but not impacting type 1 interferon (IFN) production or virus replication. Using cytometry by time of flight (CyTOF), we identified that human lung IRF5 expression was highest in cells of the myeloid lineage. To investigate the role of IRF5 in mediating human inflammatory responses by myeloid cells to IAV, we employed human-induced pluripotent stem cells (hIPSCs) with biallelic mutations in IRF5, demonstrating for the first time that induced pluripotent stem cell-derived dendritic cells (iPS-DCs) with biallelic mutations can be used to investigate the regulation of human virus-induced immune responses. Using this technology, we reveal that IRF5 deficiency in human DCs, or macrophages, corresponded with reduced virus-induced inflammatory cytokine production, with IRF5 acting downstream of Toll-like receptor 7 (TLR7) and, possibly, retinoic acid-inducible gene I (RIG-I) after viral sensing. Thus, IRF5 acts as a regulator of myeloid cell inflammatory cytokine production during IAV infection in mice and humans and drives immune-mediated viral pathogenesis independently of type 1 IFN and virus replication.

IMPORTANCE The inflammatory response to influenza A virus (IAV) participates in infection control but contributes to disease severity. After viral detection, intracellular pathways are activated, initiating cytokine production, but these pathways are incompletely understood. We show that interferon regulatory factor 5 (IRF5) mediates IAV-induced inflammation and, in mice, drives pathology. This was independent of antiviral type 1 IFN and virus replication, implying that IRF5 could be specifically targeted to treat influenza virus-induced inflammation. We show for the first time that human iPSC technology can be exploited in genetic studies of virus-induced immune responses. Using this technology, we deleted IRF5 in human myeloid cells. These IRF5-deficient cells exhibited impaired influenza virus-induced cytokine production and revealed that IRF5 acts downstream of Toll-like receptor 7 and possibly retinoic acid-inducible gene I. Our data demonstrate the importance of IRF5 in influenza virus-induced inflammation, suggesting that genetic variation in the IRF5 gene may influence host susceptibility to viral diseases.

Antibody response to homologous epitopes of Epstein-Barr virus, Mycobacterium avium subsp. paratuberculosis and IRF5 in patients with different connective tissue diseases and in mouse model of antigen-induced arthritis

Background

Improved knowledge of different biomarkers is crucial for early diagnosis of rheumatic diseases and to provide important insights for clinical management. In this study, we evaluated the seroreactivity of patients with different connective tissue diseases (CTDs) (rheumatoid arthritis, RA; systemic lupus erythematosus, SLE; systemic sclerosis, SSc; and Sjogren’s syndrome, SSj) to interferon regulatory factor 5 (IRF5) peptide and homologs derived from Epstein-Barr virus (EBV) and Mycobacterium avium subsp. paratuberculosis (MAP). Antigen-induced arthritis (AIA) experiments have been performed in control and IRF5 conditional knockout mice to reinforce the hypothesis that antibodies generated against the three homologous peptides are cross-reactive.

Methods

Reactivity against wild-type (wt) and citrullinated (cit) IRF5 (IRF5_424-434), MAP (MAP_4027_18-32) and EBV (BOLF1_305-320) peptides were tested by indirect ELISA in sera from 100 RA patients, 54 patients with other CTDs (14 SLE, 28 SSc and 12 SSj) and 100 healthy subjects (HCs). Antibody responses to the same wt peptides have been tested in AIA mouse sera after immunization with complete Freud’s adjuvant (CFA) and methylated bovine serum albumin (mBSA) to induce arthritis in the knee joint.

Results

BOLF1, MAP_4027 and IRF5 peptides triggered different antibody responses in CTD diseases with a stronger reactivity in RA (p=0.0001). Similar trends were observed in AIA mice with significantly higher reactivity after 7 days from induction of arthritis. We also found statistically significant differences in antibody responses between SSc and HCs for BOLF1 (p=0.003), MAP_4027 (p=0.0076) and IRF5 (p=0.0042). Peripheral reactivity to cit peptides was lower compared to their wt counterparts, except for cit-MAP_4027_18-32, which induced stronger responses in RA than wt-MAP_4027_18-32 (46% vs. 26%, p=0.0170).

Conclusion(s): Our results show differential antibody responses to BOLF1, MAP_4027 and IRF5 peptides among CTDs, highlighting their potential as diagnostic biomarkers in these diseases. Experiments performed in IRF5 conditional knockout mice support the hypothesis of cross-reactivity between the investigated homologous antigens.

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Serum IgG anti-BOLF1, MAP_4027 and IRF5 Abs responses are significantly higher in RA than in other rheumatic conditions.

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Antibody responses to epitopes of EBV, IRF5 and MAP in AIA mouse model is comparable to results obtained in humans.

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Antigens present in the CFA are homologous to MAP, EBV and IRF5 peptides trigger cross-reactive responses.

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MAP might be a possible triggering factor in the etiology of systemic sclerosis and RA.

PtpA and PknG Proteins Secreted by Mycobacterium avium subsp. paratuberculosis are Recognized by Sera from Patients with Rheumatoid Arthritis: A Case-Control Study

Purpose

Rheumatoid arthritis (RA) can result from complex interactions between the affected person’s genetic background and environment. Viral and bacterial infections may play a pathogenetic role in RA through different mechanisms of action. We aimed to evaluate the presence of antibodies (Abs) directed against two proteins of Mycobacterium avium subsp. paratuberculosis (MAP) in sera of RA subjects, which are crucial for the survival of the pathogen within macrophages. Moreover, we analyzed the correlation of immune response to both proteins with the following homologous peptides: BOLF1_305–320, MAP_4027_18–32 and IRF5_424–434 to understand how the synergic role of Epstein–Barr virus (EBV) and MAP infection in genetically predisposed subjects may lead to a possible deregulation of interferon regulatory factor 5 (IRF5).

Materials and methods

The presence of Abs against protein tyrosine phosphatase A (PtpA) and protein kinase G (PknG) in sera from Sardinian RA patients (n=84) and healthy volunteers (HCs, n=79) was tested by indirect ELISA.

Results

RA sera showed a remarkably high frequency of reactivity against PtpA in comparison to HCs (48.8% vs 7.6%; p<0.001) and lower but statistically significant responses towards PknG (27.4% vs 10.1%; p=0.0054). We found a significant linear correlation between the number of swollen joints and the concentrations of antibodies against PtpA (p=0.018). Furthermore, a significant bivariate correlation between PtpA and MAP MAP_4027_18–32 peptide has been found, suggesting that MAP infection may induce a secondary immune response through cross-reaction with IRF5 (R²=0.5).

Conclusion

PtpA and PknG are strongly recognized in RA which supports the hypothesis that MAP infection may be involved in the pathogenesis of RA.