Neutrophil activation in patients with anti-neutrophil cytoplasmic autoantibody-associated vasculitis and large-vessel vasculitis

The platelet-mitochondria nexus in autoimmune and musculoskeletal diseases

Platelets are crucial for thrombosis and hemostasis. Importantly, they contain mitochondria that are responsible for energy generation and therefore vital for platelet survival and activation. Activated platelets can release mitochondria that may be free or encapsulated in platelet extracellular vesicles (EVs). Extruded mitochondria are a well-known source of mitochondrial DNA, and mitochondrial antigens that can be targeted by autoantibodies forming immune complexes (IC). Interaction of IC with the platelet cell surface FcγRIIA receptor results in platelet activation and release of platelet granule components. In this review, we summarize how platelets and mitochondria may contribute to the pathogenesis of different autoimmune and musculoskeletal diseases. Targeting key drivers of mitochondrial extrusion may ultimately lead to urgently needed targeted pharmacological interventions for treating inflammation and thrombotic diathesis, and halting organ damage in some of these rheumatological conditions.

Exogenous serpin B1 restricts immune complex-mediated NET formation via inhibition of a chymotrypsin-like protease and enhances microbial phagocytosis

Immune complex (IC)-driven formation of neutrophil extracellular traps (NETs) is a major contributing factor to the pathogenesis of autoimmune diseases including systemic lupus erythematosus (SLE). Exogenous recombinant human serpin B1 (rhsB1) can regulate NET formation; however, its mechanism(s) of action is currently unknown as is its ability to regulate IC-mediated NET formation and other neutrophil effector functions. To investigate this, we engineered or post-translationally modified rhsB1 proteins that possessed specific neutrophil protease inhibitory activities and pretreated isolated neutrophils with them prior to inducing NET formation with ICs derived from patients with SLE, PMA, or the calcium ionophore A23187. Neutrophil activation and phagocytosis assays were also performed with rhsB1 pretreated and IC-activated neutrophils. rhsB1 dose-dependently inhibited NET formation by all three agents in a process dependent on its chymotrypsin-like inhibitory activity, most likely cathepsin G. Only one variant (rhsB1 C344A) increased surface levels of neutrophil adhesion/activation markers on IC-activated neutrophils and boosted intracellular ROS production. Further, rhsB1 enhanced complement-mediated neutrophil phagocytosis of opsonized bacteria but not ICs. In conclusion, we have identified a novel mechanism of action by which exogenously administered rhsB1 inhibits IC, PMA, and A2138-mediated NET formation. Cathepsin G is a well-known contributor to autoimmune disease but to our knowledge, this is the first report implicating it as a potential driver of NET formation. We identified the rhsB1 C334A variant as a candidate protein that can suppress IC-mediated NET formation, boost microbial phagocytosis, and potentially impact additional neutrophil effector functions including ROS-mediated microbial killing in phagolysosomes.

A Glimpse into Humoral Response and Related Therapeutic Approaches of Takayasu's Arteritis

Takayasu's arteritis (TAK) manifests as an insidiously progressive and debilitating form of granulomatous inflammation including the aorta and its major branches. The precise etiology of TAK remains elusive, with current understanding suggesting an autoimmune origin primarily driven by T cells. Notably, a growing body of evidence bears testimony to the widespread effects of B cells on disease pathogenesis and progression. Distinct alterations in peripheral B cell subsets have been described in individuals with TAK. Advancements in technology have facilitated the identification of novel autoantibodies in TAK. Moreover, emerging data suggest that dysregulated signaling cascades downstream of B cell receptor families, including interactions with innate pattern recognition receptors such as toll-like receptors, as well as co-stimulatory molecules like CD40, CD80 and CD86, may result in the selection and proliferation of autoreactive B cell clones in TAK. Additionally, ectopic lymphoid neogenesis within the aortic wall of TAK patients exhibits functional characteristics. In recent decades, therapeutic interventions targeting B cells, notably utilizing the anti-CD20 monoclonal antibody rituximab, have demonstrated efficacy in TAK. Despite the importance of the humoral immune response, a systematic understanding of how autoreactive B cells contribute to the pathogenic process is still lacking. This review provides a comprehensive overview of the biological significance of B cell-mediated autoimmunity in TAK pathogenesis, as well as insights into therapeutic strategies targeting the humoral response. Furthermore, it examines the roles of T-helper and T follicular helper cells in humoral immunity and their potential contributions to disease mechanisms. We believe that further identification of the pathogenic role of autoimmune B cells and the underlying regulation system will lead to deeper personalized management of TAK patients. We believe that further elucidation of the pathogenic role of autoimmune B cells and the underlying regulatory mechanisms holds promise for the development of personalized approaches to managing TAK patients.

FPR1: A critical gatekeeper of the heart and brain

G protein-coupled receptors (GPCRs) are currently the most widely focused drug targets in the clinic, exerting their biological functions by binding to chemicals and activating a series of intracellular signaling pathways. Formyl-peptide receptor 1 (FPR1) has a typical seven-transmembrane structure of GPCRs and can be stimulated by a large number of endogenous or exogenous ligands with different chemical properties, the first of which was identified as formyl-methionine-leucyl-phenylalanine (fMLF). Through receptor-ligand interactions, FPR1 is involved in inflammatory response, immune cell recruitment, and cellular signaling regulation in key cell types, including neutrophils, neural stem cells (NSCs), and microglia. This review outlines the critical roles of FPR1 in a variety of heart and brain diseases, including myocardial infarction (MI), ischemia/reperfusion (I/R) injury, neurodegenerative diseases, and neurological tumors, with particular emphasis on the milestones of FPR1 agonists and antagonists. Therefore, an in-depth study of FPR1 contributes to the research of innovative biomarkers, therapeutic targets for heart and brain diseases, and clinical applications.

Current Insights into Tissue Injury of Giant Cell Arteritis: From Acute Inflammatory Responses towards Inappropriate Tissue Remodeling

Giant cell arteritis (GCA) is an autoimmune disease affecting large vessels in patients over 50 years old. It is an exemplary model of a classic inflammatory disorder with IL-6 playing the leading role. The main comorbidities that may appear acutely or chronically are vascular occlusion leading to blindness and thoracic aorta aneurysm formation, respectively. The tissue inflammatory bulk is expressed as acute or chronic delayed-type hypersensitivity reactions, the latter being apparent by giant cell formation. The activated monocytes/macrophages are associated with pronounced Th1 and Th17 responses. B-cells and neutrophils also participate in the inflammatory lesion. However, the exact order of appearance and mechanistic interactions between cells are hindered by the lack of cellular and molecular information from early disease stages and accurate experimental models. Recently, senescent cells and neutrophil extracellular traps have been described in tissue lesions. These structures can remain in tissues for a prolonged period, potentially favoring inflammatory responses and tissue remodeling. In this review, current advances in GCA pathogenesis are discussed in different inflammatory phases. Through the description of these-often overlapping-phases, cells, molecules, and small lipid mediators with pathogenetic potential are described.

The Contribution of Innate Immunity in Large-Vessel Vasculitis: Detangling New Pathomechanisms beyond the Onset of Vascular Inflammation

Large-vessel vasculitis (LVV) are autoimmune and autoinflammatory diseases focused on vascular inflammation. The central core of the intricate immunological and molecular network resides in the disruption of the "privileged immune state" of the arterial wall. The outbreak, initially primed by dendritic cells (DC), is then continuously powered in a feed-forward loop by the intimate cooperation between innate and adaptive immunity. If the role of adaptive immunity has been largely elucidated, knowledge of the critical function of innate immunity in LVV is still fragile. A growing body of evidence has strengthened the active role of innate immunity players and their key signaling pathways in orchestrating the complex pathomechanisms underlying LVV. Besides DC, macrophages are crucial culprits in LVV development and participate across all phases of vascular inflammation, culminating in vessel wall remodeling. In recent years, the variety of potential pathogenic actors has expanded to include neutrophils, mast cells, and soluble mediators, including the complement system. Interestingly, new insights have recently linked the inflammasome to vascular inflammation, paving the way for its potential pathogenic role in LVV. Overall, these observations encourage a new conceptual approach that includes a more in-depth study of innate immunity pathways in LVV to guide future targeted therapies.

Distinguishing laboratory characteristics in giant cell arteritis: a real-world retrospective cohort study

BACKGROUND

Untreated Giant Cell Arteritis (GCA) has the potential to cause serious complications such as vision loss. Appropriate initial assessment by General Practitioners, early treatment and specialist referral are therefore essential in reducing morbidity. However, lack of awareness around the range of presentations can lead to a delay in diagnosis.

OBJECTIVE

We aim to evaluate the discriminative diagnostic performance of laboratory characteristics associated with GCA in our population over a period of 18 months.

DISCUSSION

This is a real-world retrospective review of patients referred to ophthalmology services with concern for GCA. The pre-test probability of a patient referred with suspected GCA was 13.9% to have GCA, highlighting the need for specialist referrals to continue. White Cell Count (p = 0.01), Platelet Count (p = 0.02), Erythrocyte sedimentation rate (p = 0.004) and C-reactive protein (p = 0.002) were significantly different between GCA and non-GCA cases. Moreover, this study demonstrates that absolute neutrophil count (p = 0.02) can be a useful parameter in initial investigations for GCA.

Mitochondrial-mediated inflammation and platelet activation in giant cell arteritis

Markers of extracellular mitochondria are present in giant cell arteritis (GCA) patients. However, their role in promoting inflammation and platelet activation is no known. To investigate this, isolated mitochondria were opsonized with plasma from GCA patients or healthy individuals and incubated with peripheral blood mononuclear cells (PBMCs) or platelets and assessed for inflammatory cytokine production and platelet activation. Plasma from GCA patients promoted increased mitochondrial-mediated cytokine production by PBMCs as compared to healthy controls (p < 0.05). Mitochondria opsonized with plasma factors from patients with GCA induced higher platelet activation as compared to mitochondria opsonized with plasma factors from healthy individuals (p = 0.0015). Platelet levels of P-selectin were associated with disease activity in GCA (r = 0.34, p = 0.01). GCA patients have impaired ability to regulate the clearance of extracellular mitochondria, possibly contributing to excessive inflammation and platelet activation. Targeting key drivers of mitochondrial extrusion and/or their clearance could lead to new therapeutic interventions in GCA.

Serum calprotectin and renal function decline in ANCA-associated vasculitides: a post hoc analysis of MAINRITSAN trial

OBJECTIVE

Serum calprotectin appears to be an interesting biomarker associated with renal vascular disease activity in antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV). The aim of this study was to assess whether serum calprotectin levels can predict decline in renal function in AAV patients receiving maintenance therapy.

METHODS

Serum calprotectin levels were assessed at inclusion and month 6 in AAV patients, in complete remission after induction therapy, randomly assigned to rituximab or azathioprine. Renal function decline was defined as a 25% decrease in estimated glomerular filtration rate (eGFR) and a change in the eGFR category, or a decrease of 15 mL/min/1.73 m2. Relapse was defined as a Birmingham Vasculitis Activity Score >0 attributable to active vasculitis.

RESULTS

Seventy-six AAV were included. Serum calprotectin increased from baseline to month 6 in patients with renal function decline (7940 (-226.0, 28 691) ng/ml vs -4800 (-18 777, 3708) ng/ml; p<0.001). An increase of calprotectin level was associated with a higher risk of subsequent renal function decline even after adjustment (OR 6.50 (95% CI 1.7 to 24.9) p=0.006). A significantly higher risk of relapse was observed in proteinase 3- AAV patients with an increase of serum calprotectin levels (OR 5.6 (95% CI 1.0 to 31.2), p=0.03).

CONCLUSION

An increase in serum calprotectin by month 6 compared with inclusion during remission-maintenance therapy in AAV was associated with a higher risk of renal function decline in the following 12 months.

TRIAL REGISTRATION NUMBER

NCT00748644.

Immune complex-mediated neutrophil activation in patients with polymyalgia rheumatica

OBJECTIVE

Neutrophils are important in host defence. However, neutrophils are also linked to inflammation and organ damage. The purpose of this study was to assess whether markers of neutrophil activation are increased in PMR.

METHODS

Levels of immune complexes (IC), calprotectin and neutrophil extracellular traps (NETs) were measured in plasma of healthy individuals (n = 30) and patients with PMR (n = 60), at flare and upon treatment with glucocorticoids using ELISA. Plasma-mediated neutrophil activation was assessed in presence of an FcγRIIA inhibitory antibody (IV.3).

RESULTS

Plasma levels of calprotectin and NETs were elevated in PMR (P < 0.001). Mechanistically, neutrophil activation was driven by ICs, present in plasma, able to up-regulate neutrophil activation markers CD66b and CD11b (P < 0.0001) in an FcγRIIA-dependent manner (P < 0.01). Of note, circulating levels of IC correlated with plasma induced CD66b and CD11b (r = 0.51, P = 0.004, and r = 0.46, P = 0.01, respectively) and decreased after glucocorticoid therapy. In contrast to NETs, calprotectin significantly decreased after glucocorticoid therapy (P < 0.001) and was higher in PMR without overlapping GCA compared with patients with overlapping disease (P = 0.014). Interestingly, musculoskeletal involvement was associated with elevated levels of calprotectin before initiation of glucocorticoid therapy (P = 0.036).

CONCLUSIONS

Neutrophil activation, including NET formation, is increased in PMR, through IC-mediated engagement of FcγRIIA. Clinically, neutrophil activation is associated with musculoskeletal involvement, with calprotectin, but not NETs, being a biomarker of treatment response in PMR patients. In all, IC-mediated neutrophil activation is a central process in PMR pathogenesis identifying potential novel therapeutic targets (FcγRIIA), as well as soluble markers for disease monitoring (calprotectin).

Neutrophil extracellular trap formation in anti-neutrophil cytoplasmic antibody-associated and large-vessel vasculitis

Levels of neutrophil extracellular traps (NETs) were measured in plasma of healthy controls (HC, n = 30) and patients with granulomatosis with polyangiitis (GPA, n = 123), microscopic polyangiitis (MPA, n = 61), Takayasu's arteritis (TAK, n = 58), and giant cell arteritis (GCA, n = 68), at times of remission or activity and correlated with levels of the platelet-derived thrombospondin-1 (TSP-1). Levels of NETs were elevated during active disease in patients with GPA (p < 0.0001), MPA (p = 0.0038), TAK (p < 0.0001), and GCA (p < 0.0001), and in remission for GPA, p < 0.0001, MPA, p = 0.005, TAK, p = 0.03, and GCA, p = 0.0009. All cohorts demonstrated impaired NET degradation. Patients with GPA (p = 0.0045) and MPA (p = 0.005) had anti-NET IgG antibodies. Patients with TAK had anti-histone antibodies (p < 0.01), correlating with presence of NETs. Levels of TSP-1 were increased in all patients with vasculitis, and associated with NET formation. NET formation is a common process in vasculitides. Targeting NET formation or degradation could be potential therapeutic approaches for vasculitides.

Circulating Calprotectin (cCLP) in autoimmune diseases

BACKGROUND AND AIM

Calprotectin (CLP) is a heterodimeric complex formed by two S100 proteins (S100A8/A9), which plays a pivotal role in innate immunity. Due to its intrinsic cytotoxic and proinflammatory properties, CLP controls cell differentiation, proliferation and NETosis and has been associated with a wide range of rheumatic diseases. Our review summarizes the widespread interest in circulating CLP (cCLP) as a biomarker of neutrophil-related inflammation, in autoimmune rheumatic disease (ARD) and non-ARD.

METHODS

A thorough literature review was performed using PubMed and EMBASE databases searching for circulating calprotectin and synonyms S100A8/A9, myeloid-related protein 8/14 (MRP8/MRP14), calgranulin A/B and L1 protein in addition to specific ARDs and autoimmune non-rheumatic diseases. We selected only English-language articles and excluded abstracts without the main text.

RESULTS

High cCLP serum levels are associated with worse structural outcomes in rheumatoid arthritis and to a lesser extent, in spondyloarthritis. In addition, cCLP can predict disease relapse in some autoimmune diseases including systemic lupus erythematosus (SLE), anti-neutrophil cytoplasmic antibodies-associated vasculitis (AAV) and some severe manifestations of connective tissue diseases, such as glomerulonephritis in SLE, AAV, juvenile idiopathic arthritis, adult-onset Still's disease and lung fibrosis in systemic sclerosis. Therefore, cCLP levels enable the identification of patients who need an accurate and tight follow-up. The clinical usefulness of cCLP as an inflammatory marker has been suggested for inflammatory/autoimmune non-rheumatic diseases, and especially for the monitoring of the inflammatory bowel diseases patients. Currently, there are only a few studies that evaluated the cCLP efficacy as a clinical biomarker in inflammatory/autoimmune non-rheumatic diseases with controversial results. Future studies are warranted to better clarify the role of cCLP in relation to the disease severity in myasthenia gravis, multiple sclerosis, chronic inflammatory demyelinating polyneuropathy, Graves' orbitopathy, autoimmune bullous diseases and uveitis.

CONCLUSION

Our literature review supports a relevant role of cCLP as potential prognostic biomarker mirroring local or systemic inflammation, especially in chronic inflammatory rheumatic diseases.

Rs867228 in FPR1 accelerates the manifestation of luminal B breast cancer

Formyl peptide receptor-1 (FPR1) is a pathogen recognition receptor involved in the detection of bacteria, in the control of inflammation, as well as in cancer immunosurveillance. A single nucleotide polymorphism in FPR1, rs867228, provokes a loss-of-function phenotype. In a bioinformatic study performed on The Cancer Genome Atlas (TCGA), we observed that homo-or heterozygosity for rs867228 in FPR1 (which affects approximately one-third of the population across continents) accelerates age at diagnosis of specific carcinomas including luminal B breast cancer by 4.9 years. To validate this finding, we genotyped 215 patients with metastatic luminal B mammary carcinomas from the SNPs To Risk of Metastasis (SToRM) cohort. The first diagnosis of luminal B breast cancer occurred at an age of 49.2 years for individuals bearing the dysfunctional TT or TG alleles (n = 73) and 55.5 years for patients the functional GG alleles (n = 141), meaning that rs867228 accelerated the age of diagnosis by 6.3 years (p=0.0077, Mann & Whitney). These results confirm our original observation in an independent validation cohort. We speculate that it may be useful to include the detection of rs867228 in breast cancer screening campaigns for selectively increasing the frequency and stringency of examinations starting at a relatively young age.

Pathogenesis of giant cell arteritis with focus on cellular populations

Giant cell arteritis (GCA), the most common non-infectious vasculitis, mainly affects elderly individuals. The disease usually affects the aorta and its main supra-aortic branches causing both general symptoms of inflammation and specific ischemic symptoms because of the limited blood flow due to arterial structural changes in the inflamed arteries. The pathogenesis of the GCA is complex and includes a dysregulated immune response that affects both the innate and the adaptive immunity. During the last two decades several studies have investigated interactions among antigen-presenting cells and lymphocytes, which contribute to the formation of the inflammatory infiltrate in the affected arteries. Toll-like receptor signaling and interactions through the VEGF-Notch-Jagged1 pathway are emerging as crucial events of the aberrant inflammatory response, facilitating among others the migration of inflammatory cells to the inflamed arteries and their interactions with the local stromal milieu. The increased use of checkpoint inhibitors in cancer immunotherapy and their immune-related adverse events has fed interest in the role of checkpoint dysfunction in GCA, and recent studies suggest a dysregulated check point system which is unable to suppress the inflammation in the previously immune-privileged arteries, leading to vasculitis. The role of B-cells is currently reevaluated because of new reports of considerable numbers of plasma cells in inflamed arteries as well as the formation of artery tertiary lymphoid organs. There is emerging evidence on previously less studied cell populations, such as the neutrophils, CD8+ T-cells, T regulatory cells and tissue residing memory cells as well as for stromal cells which were previously considered as innocent bystanders. The aim of this review is to summarize the evidence in the literature regarding the cell populations involved in the pathogenesis of GCA and especially in the context of an aged, immune system.