The multifaceted role of mast cells in the pathogenesis of rheumatoid arthritis.

Mast cells (MC) are tissue duelling cells playing an active role in both innate and adaptive immune system. They act as first players in different microbial infections and exert a crucial role in allergy, chronic inflammation, fibrosis, and rheumatic diseases (RD), including rheumatoid arthritis (RA). MC are normally present in human synovia and they increase in the joints of RA patients, contributing to inflammatory and remodelling processes. Due to their great plasticity and multifunctionality, MC exert a wide range of roles in different stages of the disease. To date, the results obtained by in-vitro and in-vivo studies have contributed to better clarify the dynamic role of MC in local arthritis of RA and have improved our knowledge on different aspect of the disease. Although different mice models have been extensively used to investigate the contribution of MC in different stages of RA, those models often fail to reproduce the complexity and the heterogeneity of the human disease. Here, we provide an overview on different roles of MC in RA pathogenesis and how these cells might influence some clinical features of the disease.

CXCL12/SDF-1 in IgG4-Related Disease.

Background: SDF-1/CXCL12 is a chemokine with pleiotropic functions in hematopoietic stem cell niche homeostasis, germinal center architecture, B cell maturation, neoangiogenesis, and fibrosis. Recently, the CXCL12/CXCR4/CXCR7 axis was associated with cancer metastasis and autoimmune diseases. The IgG4-related disease (IgG4-RD) is a pathological condition characterized by IgG4+ plasma cells infiltrating fibrotic lesions. The aim of this research is to investigate the relevance of SDF-1/CXCL12 in IgG4-RD. Materials and Methods: Peripheral blood samples were collected before therapy from a single-center cohort of 28 IgG4-RD patients, fulfilling the ACR-EULAR classification criteria. Clinical and serological data were obtained for each patient. In total, 14 healthy donors (NHS), 9 patients with pancreatic ductal adenocarcinoma (PDAC), and 9 with Sjogren syndrome (SSj) were recruited as controls and screened for circulating SDF-1/CXCL12 by ELISA. Moreover, paraffin-embedded pancreatic biopsies obtained from patients with IgG4-RD (n = 7), non-autoimmune pancreatitis (n = 3), PDAC (n = 5), and control tissues (n = 4) were analyzed to study the tissue expression and localization of SDF-1/CXCL12 and one of its receptors, CXCR4, and their potential relation with neutrophil extracellular traps (NETs). Results: IgG4-RD patients had higher serum levels of SDF-1/CXCL12 than normal controls (p = 0.0137). Cytokine levels did not differ between the IgG4-RD autoimmune pancreatitis (AIP) and retroperitoneal fibrosis nor between the single- and multiple-organ involvement. No correlation was seen with the IgG4-RD Responder Index, IgG4 levels, white blood cells, or inflammatory markers in the serum. When compared to SSj, the IgG4-RD AIP subgroup presents higher amounts of serum SDF-1/CXCL12 (p = 0.0275), while no differences are seen in comparison with PDAC. The expression of SDF-1/CXCL12 in the tissue was significantly higher in the IgG4-RD tissue than the normal pancreas, and the tissue with the high SDF-1/CXCL12 expression is characterized by the overall inflammatory cell infiltration, fibrosis, and high level of NETs. Conclusion: Modulating B cell development, neoangiogenesis and fibrosis, and SDF-1/CXCL12 may play a role in IgG4-RD. The higher levels observed in IgG4-RD, as compared to SSj, which closely mimics the disease, can be related to a different pattern of lesions, with prevalent fibrosis seen in IgG4-RD. Taken together, these findings suggest that drugs acting on the CXCL12/CXCR4/CXCR7 axis may affect IgG4-RD.

Evaluation of neutrophil extracellular trap deregulated formation in pyoderma gangrenosum.

Pyoderma gangrenosum (PG) is a neutrophilic dermatose (ND) characterized by a dense neutrophilic infiltrate in the affected tissue. Neutrophil extracellular traps (NETs) are web-like structures released by neutrophils and composed of cytosolic and granule proteins assembled on a scaffold of decondensed chromatin. Very little is known about the role of NETosis in PG. Here, we assessed the possible implication of NETosis in the pathogenesis of PG by investigating the NETosis in the ulcers of 26 PG patients. We demonstrated that neutrophils in the PG skin lesions undergo an aberrant level of NETosis in 100% of the analysed cases (N = 26). All control and abscess biopsies were instead negative for the NETosis. In addition, neutrophils from peripheral blood of PG patients showed a significantly higher rate of spontaneous, but not induced, NETosis. Overall, this study suggests that the NETosis may contribute to systemic inflammation and tissue destruction in PG, thus representing a possible novel therapeutic target.

Renal Involvement in IgG4-Related Disease: From Sunlight to Twilight.

IgG4-Related Disease (IgG4-RD) is a fibroinflammatory condition characterized by a typical histopathological pattern (dense lymphoplasmacytic infiltrate with prevalent IgG4+ plasma cells and storiform fibrosis), which may involve the kidney both directly (IgG4-related kidney disease, IgG4-RKD) or indirectly, as a consequence of post-renal ureteral obstruction due to retroperitoneal fibrosis (IgG4-RD RF). The most frequent presentation of IgG4-RKD is IgG4-related tubulointerstitial nephritis (TIN), but a glomerular disease can be present, in most of the cases a membranous nephropathy. Albeit steroid-responsive, in some cases renal manifestations may lead to progressive and permanent organ damage. In this review we describe four clinical cases representative of typical and less typical renal manifestations of IgG4-RD, emphasizing a potential, subclinical, early involvement of the kidney in the disease.

Unique expansion of IL-21+ Tfh and Tph cells under control of ICOS identifies Sjögren's syndrome with ectopic germinal centres and MALT lymphoma.

OBJECTIVES: To explore the relevance of T-follicular-helper (Tfh) and pathogenic peripheral-helper T-cells (Tph) in promoting ectopic lymphoid structures (ELS) and B-cell mucosa-associated lymphoid tissue (MALT) lymphomas (MALT-L) in Sjögren's syndrome (SS) patients. METHODS: Salivary gland (SG) biopsies with matched peripheral blood were collected from four centres across the European Union. Transcriptomic (microarray and quantitative PCR) analysis, FACS T-cell immunophenotyping with intracellular cytokine detection, multicolor immune-fluorescence microscopy and in situ hybridisation were performed to characterise lesional and circulating Tfh and Tph-cells. SG-organ cultures were used to investigate functionally the blockade of T-cell costimulatory pathways on key proinflammatory cytokine production. RESULTS: Transcriptomic analysis in SG identified Tfh-signature, interleukin-21 (IL-21) and the inducible T-cell co-stimulator (ICOS) costimulatory pathway as the most upregulated genes in ELS+SS patients, with parotid MALT-L displaying a 400-folds increase in IL-21 mRNA. Peripheral CD4+CXC-motif chemokine receptor 5 (CXCR5)+programmed cell death protein 1 (PD1)+ICOS+ Tfh-like cells were significantly expanded in ELS+SS patients, were the main producers of IL-21, and closely correlated with circulating IgG and reduced complement C4. In the SG, lesional CD4+CD45RO+ICOS+PD1+ cells selectively infiltrated ELS+ tissues and were aberrantly expanded in parotid MALT-L. In ELS+SG and MALT-L parotids, conventional CXCR5+CD4+PD1+ICOS+Foxp3- Tfh-cells and a uniquely expanded population of CXCR5-CD4+PD1hiICOS+Foxp3- Tph-cells displayed frequent IL-21/interferon-γ double-production but poor IL-17 expression. Finally, ICOS blockade in ex vivo SG-organ cultures significantly reduced the production of IL-21 and inflammatory cytokines IL-6, IL-8 and tumour necrosis factor-α (TNF-α). CONCLUSIONS: Overall, these findings highlight Tfh and Tph-cells, IL-21 and the ICOS costimulatory pathway as key pathogenic players in SS immunopathology and exploitable therapeutic targets in SS.

Biomarkers In Chronic Spontaneous Urticaria: Current Targets And Clinical Implications.

Chronic urticaria (CU) is a mast cell-driven disease characterized by the development of wheals, angioedema, or both for more than 6 weeks. The two major sub-types are chronic spontaneous urticaria (CSU) and inducible urticaria. In the last decade different pathophysiological mechanisms, potentially responsible for the development of the disease, have been described. It is likely that the activation of mast cells and basophils in CSU can be the results of immune system dysregulation, activation of the inflammatory cascade, and of the extrinsic coagulation pathway. Some of the mediators involved in the pathophysiological mechanisms of CSU have recently been identified as potential biomarkers useful for the diagnosis, follow-up, and management of the disease, even if they are not yet available in clinical practice. Thus, in this review we discuss new insights in the mediators involved in the pathogenesis of CSU, highlighting their potential role as biomarkers in the activity and progression of the disease and response to therapies.

One year in review 2019: Sjögren's syndrome.

Primary Sjögren's syndrome (pSS) is a complex and heterogeneous disorder characterised by a wide spectrum of glandular and extra-glandular features. Novel insights into disease pathogenesis and the discovery of novel biomarkers are allowing us to characterise the disease not only phenotypically on the basis of clinical presentation, but also on the basis of the endotype. Ultimately, a better stratification of patients may pave new avenues for novel targeted therapies, opening new possibilities for the application of personalised medicine in pSS.

Neutrophil extracellular traps (NET) induced by different stimuli: A comparative proteomic analysis.

Neutrophil extracellular traps (NET) formation is part of the neutrophil response to infections, but excessive or inappropriate NETosis may trigger the production of autoantibodies and cause organ damage in autoimmune disorders. Spontaneously netting neutrophils are not frequent and induction of NET in vitro by selected stimuli is necessary to investigate their structure. In the present work, the protein composition and post-translational modifications of NET produced under different stimuli have been studied by means of proteomic analysis. Neutrophils from healthy donors were stimulated by PMA, A23187, Escherichia coli LPS or untreated; after three hours, cells were washed, treated with DNase and supernatants collected for mass spectrometry. Data were analyzed by unsupervised hierarchical clustering analyses. We identified proteins contained in NETs of any source or exclusive of one stimulus: LPS-induced and spontaneous NET diverge in protein composition, while PMA- and A23187-induced NET appear more similar. Among the post-translational modifications we examined, methionine sulfoxidation is frequent especially in PMA- and LPS-induced NETs. Myeloperoxidase is the protein more extensively modified. Thus, proteomic analysis indicates that NETs induced by different stimuli are heterogeneous in terms of both protein composition and post-translational modifications, suggesting that NET induced in different conditions may have different biological effects.

One year in review 2019: pathogenesis of rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease influenced by both genetic and environmental factors. Over the last few years, particular attention has been given to novel genes and to the close interaction between genetic factors and epigenetic mechanisms. Research has also focused on the influence of environmental factors on disease development, and on new mechanisms of the innate and adaptive immune system that can influence the different stages of RA. However, there are still several aspects of the disease that need further investigation. Shedding some light on the different aspects of RA pathogenesis will help to improve the current diagnostic tools and to identify new targets for the development of disease-modifying therapies. Thus, in this review we summarise the new insights in RA pathogenesis, resulting from literature research data published in the last year.

NK cell recruitment in salivary glands provides early viral control but is dispensable for tertiary lymphoid structure formation.

Salivary glands (SGs) represent a permissive site for several sialotropic viruses whose persistence is linked to the development of autoimmunity. Natural Killer (NK) cells play a key role in viral clearance but their involvement in viral infection control and in tertiary lymphoid structures (TLS) development within SGs is unknown. By using an inducible model of TLS in the SGs of wild-type C57BL/6 mice, induced by the local delivery of a replication-defective adenovirus (AdV), we demonstrated that circulating NK cells are rapidly recruited to SGs and highly enrich the early inflammatory infiltrate prior to TLS development. NK cells migrating to SGs in response to AdV infection up-regulate NKp46, undergo proliferation, acquire cytotoxic potential, produce Granzyme-B and IFN-γ, and reduce viral load in the acute phase of the infection. Nonetheless, the selective depletion of both circulating and infiltrating NK cells in AdV-infected mice neither affect the development and frequency of TLS nor the onset of autoimmunity. These data demonstrate that, upon local viral delivery of AdV, peripheral NK cells homing to SGs can exert an early control of the viral infection but are dispensable for the formation of TLS and breach of immunologic tolerance.

A clinical and histopathological analysis of the anti-centromere antibody positive subset of primary Sjögren's syndrome.

OBJECTIVES: ACA-positive/primary Sjögren's syndrome (pSS) represents a distinct overlapping entity with intermediate features in between limited systemic sclerosis (lSSc) and pSS. Few data are available on their general risk for lymphoproliferative complications, specifically regarding adverse predictors at the level of minor salivary gland (MSG) histology. The objectives of this work are: a) to characterise, through a detailed immunohistochemistry study, the organisation of the lymphomonocitic infiltrates in ACA-positive/pSS patient vs. ACA-negative/pSS patients focusing on the presence of GC-like structures in minor salivary gland biopsies; b) to compare the frequency of traditional clinical and serological risk factors for lymphoma between the two subgroups. METHODS: We analysed 28 MSG samples from ACA-positive/pSS patients and 43 consecutive MSGs from ACA-negative/pSS, using sequential IHC staining for CD3, CD20 and CD21 in order to define the T/B cell segregation within the periductal infiltrates and presence of ectopic GC-like on the detection of GC-like structures. Clinical and serological data of all the patients were retrieved and analysed. RESULTS: Ectopic lymphoid structures (ELS) with GC-like structures were observed in 7 out of 28 ACA-positive/pSS patients (25%) and in 13 out of 43 ACA-negative/pSS patients (30.2%). Similarly, no statistical significant difference was found between the two groups as far as the classical pSS risk factors for lymphoproliferative complications was concerned (i.e. salivary gland enlargement, purpura, low C4, leukocytopenia, clonal gammopathy). Finally, the 3 cases of non-Hodgkin's lymphoma observed were equally distributed between the two subsets. CONCLUSIONS: Overall, this study indicates that ACA-positive/and ACA-negative pSS patients apparently present a similar risk for lymphoproliferative complications as suggested indirectly by the analogies between the two groups observed at the histopathology level.

Implication of Epstein-Barr virus infection in disease-specific autoreactive B cell activation in ectopic lymphoid structures of Sjögren's syndrome.

OBJECTIVE: To examine whether the B cell tropic γ-herpesvirus Epstein-Barr virus (EBV) is aberrantly expressed in its latent and lytic forms within ectopic lymphoid structures (ELS) in the salivary glands of patients with Sjögren's syndrome (SS), and to investigate the relationship between EBV dysregulation, B cell activation, in situ differentiation of autoreactive plasma cells, disease-specific autoantibody production, and cytotoxicity. METHODS: Latent and lytic EBV infection in the salivary glands of 28 patients with SS and 38 patients with nonspecific chronic sialadenitis (NSCS), characterized for the presence or absence of ELS, was investigated by reverse transcription-polymerase chain reaction, in situ hybridization, and immunohistochemical/immunofluorescence staining. Glandular versus synovial production of anti-Ro 52, anti-citrullinated protein antibodies (ACPAs), and anti-EBV peptide antibodies was analyzed in situ or in vivo in human SS/SCID and human rheumatoid arthritis/SCID mouse chimeras. RESULTS: EBV dysregulation within inflammatory infiltrates was observed exclusively in ELS+ SS salivary gland tissue, as revealed by latent EBV infection and lytic EBV infection in B cells and plasma cells, respectively. Conversely, epithelial latent membrane protein 2A expression was observed in both patients with SS and patients with NSCS. Importantly, perifollicular plasma cells displaying Ro 52 immunoreactivity were frequently infected by EBV. Furthermore, ELS-containing SS salivary gland tissue that was transplanted into SCID mice supported the production of anti-Ro 52/anti-La 48 and anti-EBV antibodies but not ACPAs. Analysis of CD4+ and CD8+ T cell localization and granzyme B expression demonstrated that the persistence of EBV in ELS-containing SS salivary glands was associated with follicular exclusion of CD8+ T cells and impaired CD8-mediated cytotoxicity. CONCLUSION: Active EBV infection is selectively associated with ELS in the salivary glands of patients with SS and appears to contribute to local growth and differentiation of disease-specific autoreactive B cells.

Epstein-Barr virus persistence and infection of autoreactive plasma cells in synovial lymphoid structures in rheumatoid arthritis.

OBJECTIVES: Rheumatoid arthritis (RA) is associated with an increased Epstein-Barr virus (EBV) blood DNA load, a robust immune response to EBV and cross-reactive circulating antibodies to viral and self-antigens. However, the role of EBV in RA pathogenesis remains elusive. Here, we investigated the relationship between synovial EBV infection, ectopic lymphoid structures (ELS) and immunity to citrullinated self and EBV proteins. METHODS: Latent and lytic EBV infection was investigated in 43 RA synovial tissues characterised for presence/absence of ELS and in 11 control osteoarthritis synovia using RT-PCR, in situ hybridisation and immunohistochemistry. Synovial production of anti-citrullinated protein (ACPA) and anti-citrullinated EBV peptide (VCP1/VCP2) antibodies was investigated in situ and in vivo in the severe combined immunodeficiency (SCID)/RA chimeric model. RESULTS: EBV dysregulation was observed exclusively in ELS+ RA but not osteoarthritis (OA) synovia, as revealed by presence of EBV latent (LMP2A, EBV-encoded small RNA (EBER)) transcripts, EBER+ cells and immunoreactivity for EBV latent (LMP1, LMP2A) and lytic (BFRF1) antigens in ELS-associated B cells and plasma cells, respectively. Importantly, a large proportion of ACPA-producing plasma cells surrounding synovial germinal centres were infected with EBV. Furthermore, ELS-containing RA synovia transplanted into SCID mice supported production of ACPA and anti-VCP1/VCP2 antibodies. Analysis of CD4+ and CD8+ T-cell localisation and granzyme B expression suggests that EBV persistence in ELS-containing synovia may be favoured by exclusion of CD8+ T cells from B-cell follicles and impaired CD8-mediated cytotoxicity. CONCLUSIONS: We demonstrated active EBV infection within ELS in the RA synovium in association with local differentiation of ACPA-reactive B cells.

The role of eight polymorphisms in three candidate genes in determining the susceptibility, phenotype, and response to anti-TNF therapy in patients with rheumatoid arthritis.

OBJECTIVES: Several single nucleotide polymorphisms (SNPs) have been associated with rheumatoid arthritis (RA) such as peptidylarginine deiminase-4 (PADI4), osteopontin (OPN), and perforin (PRF1) genes. Thus, we aimed at analysing the influence of eight SNPs in these candidate genes on RA susceptibility and their association with laboratory and clinical features in terms of response to anti-TNF therapy. METHODS: We performed a case-control study on 377 Caucasian RA patients and 391 healthy, ethnicity-matched, population-based controls. All subjects were genotyped for PADI4_89/94, PADI4_92, PADI4_104, PADI4_100 in PADI4; -156G/GG and +1239A/C in OPN and A91V and N252S in PRF1 genes. The patients were stratified for shared epitope (SE) HLA-DRB1. rheumatoid factor (RF) and anti-citrullinated protein/peptide antibodies (ACPA) were analysed. The patients started anti-TNF treatment and they were evaluated at baseline and after 12 weeks. Disease activity was evaluated with DAS28 and response to treatment with EULAR criteria. RESULTS: A statistically significant association between RA and OPN -156G/GG was found (p=0.023). SE was firmly confirmed to be associated with RA (OR=3.68; p<10-10). No other statistically significant association with clinical and laboratory features were observed. CONCLUSIONS: For the first time, in an Italian cohort, we report the association between -156G/GG in OPN gene and RA susceptibility. Short-term response to anti-TNF therapy was not influenced by the genetic variants studied.