Fc receptors gone wrong: A comprehensive review of their roles in autoimmune and inflammatory diseases

Human cerebrospinal fluid monoclonal CASPR2 autoantibodies induce changes in electrophysiology, functional MRI, and behavior in rodent models

Anti-contactin associated protein receptor 2 (CASPR2) encephalitis is a severe autoimmune encephalitis with a variable clinical phenotype including behavioral abnormalities, cognitive decline, epileptic seizures, peripheral nerve hyperexcitability and neuropathic pain. The detailed mechanisms of how CASPR2 autoantibodies lead to synaptic dysfunction and clinical symptoms are largely unknown. Aiming for analyses from the molecular to the clinical level, we isolated antibody-secreting cells from the cerebrospinal fluid of two patients with CASPR2 encephalitis. From these we cloned four anti-CASPR2 human monoclonal autoantibodies (mAbs) with strong binding to brain and peripheral nerves. All were highly hypermutated and mainly of the IgG4 subclass. Mutagenesis studies determined selective binding to the discoidin domain of CASPR2. Surface plasmon resonance revealed affinities with dissociation constants KD in the pico- to nanomolar range. CASPR2 mAbs interrupted the interaction of CASPR2 with its binding partner contactin 2 in vitro and were internalized after binding to CASPR2-expressing cells. Electrophysiological recordings of rat hippocampal slices after stereotactic injection of CASPR2 mAbs showed characteristic afterpotentials following electrical stimulation. In vivo experiments with intracerebroventricular administration of human CASPR2 mAbs into mice and rats showed EEG-recorded brain hyperexcitability but no spontaneous recurrent seizures. Behavioral assessment of infused mice showed a subtle clinical phenotype, mainly affecting sociability. Mouse brain MRI exhibited markedly reduced resting-state functional connectivity without short-term structural changes. Together, the experimental data support the direct pathogenicity of CASPR2 autoantibodies. The minimally invasive EEG and MRI techniques applied here may serve as novel objective, quantifiable tools for improved animal models, in particular for subtle neuropsychiatric phenotypes or repeated measurements.

Novel therapeutic approach for psoriasis: Upregulating FcRn to inhibit ferroptosis and alleviate lesional skin

Psoriasis, a chronic inflammatory skin disease, is characterized by complex immune dysregulation and oxidative stress responses. The neonatal Fc receptor (FcRn) plays a crucial role in the development of autoimmune diseases. Analysis of clinical psoriasis samples demonstrated a negative correlation between FcRn expression in skin lesions and disease severity. However, the role of FcRn in this process remains unclear. This study aimed to investigate the involvement of FcRn in the pathogenesis and progression of psoriasis. In an imiquimod (IMQ)-induced psoriasis-like mouse model, FcRn expression was significantly decreased in the lesional skin, and transcriptome sequencing of the skin revealed activation of the ferroptosis pathway in psoriasis. This led to the hypothesis that FcRn could potentially regulate ferroptosis via the signal transducer and activating transcription factor 3 (STAT3)/solute carrier family 7 member 11 (SLC7A11) axis. Further experiments showed exacerbated psoriasis-like lesional skin and ferroptosis in FcRn-knockout mice, whereas intervention with the ferroptosis inhibitor Fer-1 or STAT3 inhibitor Stattic alleviated these symptoms. Critical binding sites for the transcription factor STAT3 were identified in the SLC7A11 promoter region at positions -1185 and -564 using the luciferase reporter assays and chromatin immunoprecipitation. The administration of 1,4-naphthoquinone (NQ), an FcRn agonist, effectively alleviated psoriasis-like skin lesions by inhibiting ferroptosis. This study highlights the molecular mechanisms of action of FcRn in psoriasis and provides an experimental basis for the development of novel therapeutic strategies targeting FcRn.

Current development of Fc gamma receptors (FcγRs) in diagnostics: a review

The ability of the immune system to fight against pathogens relies on the intricate collaboration between antibodies and Fc gamma receptors (FcγRs). These receptors are a group of transmembrane glycoprotein molecules, which can specifically detect and bind to the Fc portion of immunoglobulin G (IgG) molecules. They are distributed on a diverse array of immune cells, forming a strong defence system to eliminate invading threats. FcγRs have gained increasing attention as potential biomarkers for various diseases in recent years due to their ability to reflect immune dysregulation and disease pathogenesis. Increasing lines of evidence have shed new light on the remarkable association of FcγRs polymorphisms with the susceptibility of autoimmune diseases such as systemic lupus erythematosus (SLE) and lupus nephritis. Several studies have also reported the application of FcγR as a novel biomarker for the diagnosis of infection and cancer. Due to the surge in interest and concern regarding the potential of FcγRs as promising diagnostic biomarkers, this review, thereby, serves to provide a comprehensive overview of the structural characteristics, functional roles, and expression patterns of FcγRs, with a particular focus on their evolving role as diagnostic and prognostic biomarkers.

Genetic variability of three common NK and γδ T cell receptor genes (FCγ3R, NCR3, and DNAM-1) and their role in Polish patients with rheumatoid arthritis and ankylosing spondylitis

Various lymphocyte subpopulations, including NK cells as well as γδ T cells, have been considered an important element in the pathogenesis of autoimmune, inflammatory, rheumatic diseases, such as rheumatoid arthritis (RA) and ankylosing spondylitis (AS). The aim of this study was to assess the potential role of polymorphic variations in the genes coding for three NK and γδ T cell receptors: NCR3, FCγR3A, and DNAM-1 (rs1052248, rs396991, and rs763361, respectively) in the disease susceptibility and the efficacy of treatment with TNF inhibitors. The study included 461 patients with RA, 168 patients with AS, and 235 voluntary blood donors as controls. The NCR3 rs1052248 AA homozygosity prevailed in RA in patients lacking rheumatoid factor (p = 0.044) as well as in those who manifested the disease at a younger age (p = 0.005) and had higher CRP levels after 12 weeks of anti-TNF therapy (p = 0.021). The FCγR3A rs396991 polymorphism was associated with pain visual analogue scale (VAS) values before the initiation of anti-TNF treatment. Lower VAS values were observed in the GG homozygous RA patients (p = 0.024) and in AS patients with the TT genotype (p = 0.012). Moreover, AS heterozygous patients with the TG genotype presented higher CRP levels in the 12th week of anti-TNF treatment (p = 0.021). The findings suggest that the NCR3 rs1052248 AA homozygosity may have an adverse effect on RA, while the T allele potentially plays a protective role in the development of AS. Moreover, the rs1052248 T allele and TT genotype appear to have a favorable impact on the response to anti-TNF therapy in RA patients.

Animal models of studying the pathogenesis of multi-organ tissue damage in lupus

Moderate-to-severe systemic lupus erythematosus (SLE) is characterized by extensive autoantibody deposition and persistent autoinflammation. As the existing animal models are limited in accurately reproducing the pathological characteristics of human SLE, we introduced a novel animal model simulating multi-organ autoinflammation through intra-organ injections. The model closely mimicked key features of SLE, including IgG deposition, inflammation, and tissue damage. The model could be used to assess the roles of IgG, immune cells, cytokines, and Fc gamma receptor (FcγR) in the pathogenesis of autoinflammation. The results obtained from this model could be confirmed by lupus MRL/lpr mice. The review suggested that the diagnostic criteria should be reconsidered to incorporate IgG deposition in tissues and highlighted the limitations of current T-cell and B-cell-focused treatments. To summarize, the IgG deposition model can be used to investigate the pathogenesis and treatment of multi-organ tissue damage associated with SLE.

Efgartigimod as rescue treatment in acute phase of neuromyelitis optica spectrum disorder: A Case Report

Introduction

Neuromyelitis optica spectrum disorder (NMOSD) is a central nervous system demyelinating disease. Current therapy methods, however, have limited effect on acute attacks except for intravenous methylprednisolone (IVMP). Efgartigimod is a first-in-class novel human immunoglobulin G1 (IgG1) Fc fragment approved for the treatment of generalized myasthenia gravis. Its capacity to rapidly decrease serum IgG levels, including pathogenic autoantibodies, positions it as a potentially effective option for managing the acute phase of NMOSD.

Case presentation

We report the case of a 59-year-old female patient with acute NMOSD, presenting with vision loss and numbness in all four limbs. Despite an initial inadequate response to intravenous methylprednisolone (IVMP), the addition of Efgartigimod to her treatment regimen led to rapid improvement, notably including a significant reduction in serum aquaporin-4 antibody titers, total IgG levels, and inflammation cytokine levels. Furthermore, no adverse events were reported during a four-month follow-up period.

Conclusion

As an adjunct to glucocorticoid therapy, Efgartigimod has proven effective and safe for this patient. However, to ascertain its potential as a novel therapeutic option for acute NMOSD, larger-scale prospective clinical trials are required.

Human Fc gamma receptor IIIA blockade inhibits platelet destruction in a humanized murine model of ITP

ABSTRACT

Fc gamma receptor (FcγR) IIIA is an important receptor for immunoglobulin G (IgG) and is involved in immune defense mechanisms as well as tissue destruction in some autoimmune diseases including immune thrombocytopenia (ITP). FcγRIIIA on macrophages can trigger phagocytosis of IgG-sensitized platelets, and prior pilot studies observed blockade of FcγRIIIA increased platelet counts in patients with ITP. Unfortunately, although blockade of FcγRIIIA in patients with ITP increased platelet counts, its engagement by the blocking antibody drove serious adverse inflammatory reactions. These adverse events were postulated to originate from the antibody's Fc and/or bivalent nature. The blockade of human FcγRIIIA in vivo with a monovalent construct lacking an active Fc region has not yet been achieved. To effectively block FcγRIIIA in vivo, we developed a high affinity monovalent single-chain variable fragment (scFv) that can bind and block human FcγRIIIA. This scFv (17C02) was expressed in 3 formats: a monovalent fusion protein with albumin, a 1-armed human IgG1 antibody, and a standard bivalent mouse (IgG2a) antibody. Both monovalent formats were effective in preventing phagocytosis of ITP serum-sensitized human platelets. In vivo studies using FcγR-humanized mice demonstrated that both monovalent therapeutics were also able to increase platelet counts. The monovalent albumin fusion protein did not have adverse event activity as assessed by changes in body temperature, whereas the 1-armed antibody induced some changes in body temperature even though the Fc region function was impaired by the Leu234Ala and Leu235Ala mutations. These data demonstrate that monovalent blockade of human FcγRIIIA in vivo can potentially be a therapeutic strategy for patients with ITP.

Immunoglobulin G genetic variation can confound assessment of antibody levels via altered binding to detection reagents

Objectives

Amino acid variations across more than 30 immunoglobulin (Ig) allotypes may introduce structural changes that influence recognition by anti-Ig detection reagents, consequently confounding interpretation of antibody responses, particularly in genetically diverse cohorts. Here, we assessed a panel of commercial monoclonal anti-IgG1 clones for capacity to universally recognise two dominant IgG1 haplotypes (G1m-1,3 and G1m1,17).

Methods

Four commercial monoclonal anti-human IgG1 clones were assessed via ELISAs and multiplex bead-based assays for their ability to bind G1m-1,3 and G1m1,17 IgG1 variants. Detection antibodies were validated against monoclonal IgG1 allotype standards and tested for capacity to recognise antigen-specific plasma IgG1 from G1m-1,3 and G1m1,17 homozygous and heterozygous SARS-CoV-2 BNT162b2 vaccinated (n = 28) and COVID-19 convalescent (n = 44) individuals. An Fc-specific pan-IgG detection antibody corroborated differences between hinge- and Fc-specific anti-IgG1 responses.

Results

Hinge-specific anti-IgG1 clone 4E3 preferentially bound G1m1,17 compared to G1m-1,3 IgG1. Consequently, SARS-CoV-2 Spike-specific IgG1 levels detected in G1m1,17/G1m1,17 BNT162b2 vaccinees appeared 9- to 17-fold higher than in G1m-1,3/G1m-1,3 vaccinees. Fc-specific IgG1 and pan-IgG detection antibodies equivalently bound G1m-1,3 and G1m1,17 IgG1 variants, and detected comparable Spike-specific IgG1 levels between haplotypes. IgG1 responses against other human coronaviruses and influenza were similarly poorly detected by 4E3 anti-IgG1 in G1m-1,3/G1m-1,3 subjects.

Conclusion

Anti-IgG1 clone 4E3 confounds assessment of antibody responses in clinical cohorts owing to bias towards detection of G1m1,17 IgG1 variants. Validation of anti-Ig clones should include evaluation of binding to relevant antibody variants, particularly as the role of immunogenetics upon humoral immunity is increasingly explored in diverse populations.

Pharmacokinetics and pharmacodynamics across infusion rates of intravenously administered nipocalimab: results of a phase 1, placebo-controlled study

Introduction

Nipocalimab is a high-affinity, fully human, aglycosylated, effectorless, immunoglobulin G (IgG) 1 monoclonal antibody that targets the neonatal Fc receptor (FcRn), decreases systemic IgG including autoantibodies, and is under development in several IgG autoantibody- and alloantibody-mediated diseases, including generalized myasthenia gravis, chronic inflammatory demyelinating polyneuropathy, maternal-fetal medicine, and multiple other therapeutic areas. An initial phase 1 study with single and multiple ascending doses of nipocalimab infused intravenously (IV) over 2 h demonstrated dose-dependent serum pharmacokinetics and IgG reductions, with an adverse event (AE) profile comparable to placebo.

Methods

The current investigation evaluates the safety, tolerability, pharmacokinetics, and pharmacodynamics of single doses of nipocalimab across various IV infusion rates in a randomized, double-blind, placebo-controlled, sequential-dose study. Forty participants were randomized to receive nipocalimab 30 mg/kg over 60, 30, 15 or 7.5 min (0.5, 1, 2, or 4 mg/kg/min); nipocalimab 60 mg/kg over 15 min (4 mg/kg/min); or matching placebo.

Results

At doses up to 60 mg/kg and infusion rates up to 4 mg/kg/min (maximum clinically feasible rate), single doses of nipocalimab were tolerable, with 12 (40%) participants experiencing AEs across nipocalimab cohorts compared with 1 (10%) participant in the placebo cohort. AEs deemed treatment related occurred in 6 (20%) participants receiving nipocalimab and 1 (10%) participant receiving placebo. None of the AEs were severe, and no participants discontinued treatment due to AEs. Nipocalimab provided consistent, dose-dependent serum pharmacokinetics and IgG reductions, regardless of infusion rate.

Discussion

This study supports the use of shortened durations of nipocalimab infusion for future studies.

Interactions of the anti-FcRn monoclonal antibody, rozanolixizumab, with Fcγ receptors and functional impact on immune cells in vitro

Rozanolixizumab is a humanized anti-neonatal Fc receptor (FcRn) monoclonal antibody (mAb) of the immunoglobulin G4 (IgG4) sub-class, currently in clinical development for the treatment of IgG autoantibody-driven diseases. This format is frequently used for therapeutic mAbs due to its intrinsic lower affinity for Fc gamma receptors (FcγR) and lack of C1q engagement. However, with growing evidence suggesting that no Fc-containing agent is truly "silent" in this respect, we explored the engagement of FcγRs and potential functional consequences with rozanolixizumab. In the study presented here, rozanolixizumab was shown to bind to FcγRs in both protein-protein and cell-based assays, and the kinetic data were broadly as expected based on published data for an IgG4 mAb. Rozanolixizumab was also able to mediate antibody bipolar bridging (ABB), a phenomenon that led to a reduction of labeled FcγRI from the surface of human macrophages in an FcRn-dependent manner. However, the presence of exogenous human IgG, even at low concentrations, was able to prevent both binding and ABB events. Furthermore, data from in vitro experiments using relevant human cell types that express both FcRn and FcγRI indicated no evidence for functional sequelae in relation to cellular activation events (e.g., intracellular signaling, cytokine production) upon either FcRn or FcγR binding of rozanolixizumab. These data raise important questions about whether therapeutic antagonistic mAbs like rozanolixizumab would necessarily engage FcγRs at doses typically administered to patients in the clinic, and hence challenge the relevance and interpretation of in vitro assays performed in the absence of competing IgG.

A case report of transcatheter aortic valve replacement in a patient with Sjögren's syndrome and aortic stenosis

Background

The co-existence of Sjögren's syndrome and aortic stenosis (AS) is infrequent, and there lack cases of transcatheter aortic valve replacement (TAVR) for these patients with detailed management decision-making.

Case summary

We report a case of a female patient who had AS and Sjögren's syndrome with leukopaenia and thrombocytopaenia. To overcome co-existing hyper-coagulation and high thrombogenesis risk, difficult lifetime valve management, and high infection risk, we performed TAVR with 3D printing and formulated antithrombotic and antibiotic schemes.

Conclusion

This case provided a successful experience of TAVR in patients with Sjögren's syndrome. Long-term follow-up will be conducted, and optimization of the therapeutic regimen requires further exploration.

Platelets are a major player and represent a therapeutic opportunity in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by immune dysregulation and organ injury with a premature mortality due to cardiovascular diseases. Platelets, that are primarily known for their role in hemostasis, have been shown to play an active role in the pathogenesis and in the progression of immune-mediated inflammatory diseases. Here we summarize the evidence of their roles in SLE pathogenesis which supports the development of targeted treatments. Platelets and their precursors, the megakaryocytes, are intrinsically different in SLE patients compared with healthy controls. Different triggers related to innate and adaptive immunity activate platelets which release extracellular vesicles, soluble factors and interact with immune cells, thereby perpetuating inflammation. Platelets are involved in organ damage in SLE, especially in lupus nephritis and participate in the heightened cardiovascular mortality. They also play a clear role in antiphospholipid syndrome which can be associated with both thrombocytopenia and thrombosis. To tackle platelet activation and their interactions with immune cells now constitute promising therapeutic strategies in SLE.

The role of platelets in immune-mediated inflammatory diseases

Immune-mediated inflammatory diseases (IMIDs) are characterized by excessive and uncontrolled inflammation and thrombosis, both of which are responsible for organ damage, morbidity and death. Platelets have long been known for their role in primary haemostasis, but they are now also considered to be components of the immune system and to have a central role in the pathogenesis of IMIDs. In patients with IMIDs, platelets are activated by disease-specific factors, and their activation often reflects disease activity. Here we summarize the evidence showing that activated platelets have an active role in the pathogenesis and the progression of IMIDs. Activated platelets produce soluble factors and directly interact with immune cells, thereby promoting an inflammatory phenotype. Furthermore, platelets participate in tissue injury and promote abnormal tissue healing, leading to fibrosis. Targeting platelet activation and targeting the interaction of platelets with the immune system are novel and promising therapeutic strategies in IMIDs.

Basophils Predict Mite Sensitization in Patients with Kawasaki Disease

Background: Patients with Kawasaki disease (KD) are at a significantly increased risk of allergic diseases. Immunoglobulin E (IgE) is an immunoglobulin that mediates allergic sensitization to various allergens and is related to various allergic diseases. However, few studies have analyzed specific IgE on allergy biomarkers after KD is diagnosed. Objective: This study aimed to investigate the pattern of specific IgE levels against food and inhalant allergens. Methods: This retrospective study was conducted in Taiwan to identify patients admitted with KD. A subset of 453 admitted KD children younger than or equal to five years of age with intravenous immunoglobulin (IVIG) was followed up at our clinic with available specific IgE data. Results: The most common allergens were Dermatophagoides farina or pteronyssinus, house-dust, and cockroach mix. Positive specific IgE for Dermatophagoides farina or pteronyssinus was less common in children diagnosed with KD who were two years old or younger (p = 0.028). KD patients with higher basophils before IVIG (p = 0.010 and 0.018 for two different mites) and higher C-reactive protein (CRP, p = 0.030 and 0.028) after IVIG were at higher risk of mite sensitization. Integrated mite sensitization demonstrated higher basophils before IVIG, age at KD diagnosis, and the male sex to be clinically meaningful after logistic regression models. Conclusions: This study is the first to suggest that specific IgE in KD patients may be correlated with age at KD diagnosis, as well as basophils. Further longitudinal prospective studies are warranted to clarify the unique profile of specific IgE in KD patients.

Sepsis - it is all about the platelets

Sepsis is accompanied by thrombocytopenia and the severity of the thrombocytopenia is associated with mortality. This thrombocytopenia is characteristic of disseminated intravascular coagulation (DIC), the sepsis-associated coagulopathy. Many of the pathogens, both bacterial and viral, that cause sepsis also directly activate platelets, which suggests that pathogen-induced platelet activation leads to systemic thrombosis and drives the multi-organ failure of DIC. In this paper we review the mechanisms of platelet activation by pathogens and the evidence for a role for anti-platelet agents in the management of sepsis.

The interferon in idiopathic inflammatory myopathies: Different signatures and new therapeutic perspectives. A literature review

Idiopathic inflammatory myopathies (IIM), even though sharing common clinical manifestations, are characterized by diversified molecular pathogenetic mechanisms which may account for the partial inefficacy of currently used immunomodulatory drugs. In the last decades, the role of interferon (IFN) in IIM has been extensively elucidated thanks to genomic and proteomic studies which have assessed the molecular signature at the level of affected tissues or in peripheral blood across distinct IIM subtypes. A predominant type I IFN response has been shown in dermatomyositis (DM), being especially enhanced in MDA5+ DM, while a type 2 IFN profile characterizes anti-synthetase syndrome (ASyS) and inclusion body myositis (IBM); conversely, a less robust IFN footprint has been defined for immune-mediated necrotizing myopathy (IMNM). Intracellular IFN signaling is mediated by the janus kinase/signal transducer and activator of transcription (JAK/STAT) through dedicated transmembrane receptors and specific cytoplasmic molecular combinations. These results may have therapeutic implications and led to evaluating the efficacy of new targeted drugs such as the recently introduced janus kinase inhibitors (JAKi), currently approved for the treatment of rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis. In this review we aim to summarize the most significant evidence of IFN role in IIM pathogenesis and to describe the current state of the art about the ongoing clinical trials on IFN-targeting drugs, with particular focus on JAKi.

FcγRIIIA activation-mediated up-regulation of glycolysis alters MDSCs modulation in CD4+ T cell subsets of Sjögren syndrome

Our and other researchers' previous studies found that myeloid-derived suppressor cells (MDSCs) were increased, and these MDSCs, supposed to play immunosuppressive roles, showed significant pro-inflammatory effects in Sjögren's syndrome (SS). However, the key factors and potential mechanisms leading MDSCs to be inflammatory remain unclear. In this study, we found that MDSCs from SS patients were positively correlated with the percentages of Th17 cells, disease activity and serum autoantibodies, and showed higher levels of Fc gamma receptor (FcγR) IIIA and glycolysis. Most importantly, SS MDSCs or heat-aggregated IgG (HAIG)-treated MDSCs down-regulated Th1/Th2 ratio and up-regulated Th17/Treg ratio, which could be obviously rescued by IgG monomer or glycolysis inhibitor 2-DG. As well, the levels of FcγRIV and glycolysis in MDSCs and the ratio of Th17/Treg were increased, and the ratio of Th1/Th2 was decreased in SS-like NOD mice. Our study indicated that MDSCs showed pro-inflammatory phenotypes by disturbing CD4⁺ T-cell balances in SS. The pro-inflammatory effects of MDSCs might be directly linked to the enhanced glycolysis mediated by FcγRIIIA activation.

The Genetics of Primary Biliary Cholangitis: A GWAS and Post-GWAS Update

Primary biliary cholangitis (PBC) is a chronic, progressive cholestatic liver disease in which the small intrahepatic bile ducts are destroyed by autoimmune reactions. Among autoimmune diseases, which are polygenic complex traits caused by the combined contribution of genetic and environmental factors, PBC exhibits the strongest involvement of genetic heritability in disease development. As at December 2022, genome-wide association studies (GWASs) and associated meta-analyses identified approximately 70 PBC susceptibility gene loci in various populations, including those of European and East Asian descent. However, the molecular mechanisms through which these susceptibility loci affect the pathogenesis of PBC are not fully understood. This study provides an overview of current data regarding the genetic factors of PBC as well as post-GWAS approaches to identifying primary functional variants and effector genes in disease-susceptibility loci. Possible mechanisms of these genetic factors in the development of PBC are also discussed, focusing on four major disease pathways identified by in silico gene set analyses, namely, (1) antigen presentation by human leukocyte antigens, (2) interleukin-12-related pathways, (3) cellular responses to tumor necrosis factor, and (4) B cell activation, maturation, and differentiation pathways.

Macrophages in Lupus Nephritis: Exploring a potential new therapeutic avenue

Lupus nephritis (LN) is a serious complication of systemic lupus erythematosus (SLE) that occurs in about half of patients. LN is characterized by glomerular deposition of immune complexes, leading to subendothelial, mesangial and subepithelial electron dense deposits, triggering immune cell infiltration and glomerular as well as tubulointerstitial injury. Monocytes and macrophages are abundantly present in inflammatory lesions, both in glomeruli and the tubulointerstitium. Here we discuss how monocytes and macrophages are involved in this process and how monocytes and macrophages may represent specific therapeutic targets to control LN.

The neutrophil: A key resourceful agent in immune‐mediated vasculitis

The term "vasculitis" refers to a group of rare immune-mediated diseases characterized by the dysregulated immune system attacking blood vessels located in any organ of the body, including the skin, lungs, and kidneys. Vasculitides are classified according to the size of the vessel that is affected. Although this observation is not specific to small-, medium-, or large-vessel vasculitides, patients show a high circulating neutrophil-to-lymphocyte ratio, suggesting the direct or indirect involvement of neutrophils in these diseases. As first responders to infection or inflammation, neutrophils release cytotoxic mediators, including reactive oxygen species, proteases, and neutrophil extracellular traps. If not controlled, this dangerous arsenal can injure the vascular system, which acts as the main transport route for neutrophils, thereby amplifying the initial inflammatory stimulus and the recruitment of immune cells. This review highlights the ability of neutrophils to "set the tone" for immune cells and other cells in the vessel wall. Considering both their long-established and newly described roles, we extend their functions far beyond their direct host-damaging potential. We also review the roles of neutrophils in various types of primary vasculitis, including immune complex vasculitis, anti-neutrophil cytoplasmic antibody-associated vasculitis, polyarteritis nodosa, Kawasaki disease, giant cell arteritis, Takayasu arteritis, and Behçet's disease.