Human neutrophil Fcgamma receptors initiate and play specialized nonredundant roles in antibody-mediated inflammatory diseases

Clustering analyses of murine bone marrow-derived neutrophils reveal a phenotypic heterogeneity that can respond differentially to stimulation

Neutrophils are granulocytic cells produced in the bone marrow from a granulocytic progenitor cell. During infection, the production of chemokines and cytokines induces the recruitment of neutrophils to the infected tissue to promote the clearance of microbial pathogens. Several studies have shown that different subpopulations of neutrophils can be identified during infection. However, no previous studies evaluated subpopulations of neutrophils purified from the bone marrow (BM), which are typically used to study the biology of these cells based on the assumption that the neutrophil population is homogeneous. In the present study, responses of purified BM-derived neutrophils to various stimuli such as PMA, LPS, and Streptococcus pneumoniae were evaluated using flow cytometry and bh-SNE analyses. Further, neutrophil population heterogeneity was assessed by clustering analyses. Our data suggest that purified BM-derived neutrophils were not a homogeneous cell population and were clustered into 12 subsets, each displaying a unique marker profile, where CD11b and CD62L emerged as pivotal markers for neutrophil function. Importantly, the subsets responded differentially to each stimulus, suggesting a nuanced activation pattern. Changes in biomarker expression were analyzed via Ingenuity Pathway Analysis (IPA) to unravel functional implications of the identified clusters, revealing subsets associated with different neutrophil functions, such as "Migration of neutrophils" or "Phagocytosis in neutrophils". This study contributes to understanding the diversity of purified BM-derived neutrophils and the implications of using these cellular preparations to raise conclusions about the functionality of these cells in various infection models.

Immune complex deposition promotes NK cell accumulation in the kidney

In systemic lupus erythematosus, immune complexes deposited in the kidney vasculature represent a potent inflammatory trigger with a high potential to progress to glomerulonephritis and organ failure. These immune complexes can be recognized by multiple effector cells via complement and Fcγ receptors. The transcriptome of CD16-bearing NK cells has been documented in kidneys from patients with SLE. In this study, we show that NK cells accumulate in the kidney in response to immune complex deposition and modulate the behavior of local T cells. Depletion of NK cells transiently ameliorated disease, suggesting NK cells may play a role in lupus nephritis and other immune complex-mediated conditions.

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.

Association Between Cytokeratin 19-Specific IgG and Neutrophil Activation in Asthma

PURPOSE

Patients with non-eosinophilic asthma (NEA) are less responsive to anti-inflammatory drugs and suffer from frequent asthma exacerbations. The pathogenic mechanism of NEA is not fully understood; however, the roles of monocytes and autoimmune mechanisms targeting airway epithelial cell (AEC) antigens have been proposed.

METHODS

The effects of monocyte extracellular traps (MoETs) on cytokeratin 19 (CK19) production in AECs, as well as the impact of CK19-specific immunoglobulin (Ig) G on neutrophil and monocyte activation, were investigated both in vivo and in vitro. Sixty asthmatic patients and 15 healthy controls (HCs) were enrolled, and the levels of serum immune complexes containing CK19-specific IgG and neutrophil extracellular trap (NET)-specific IgG were measured using enzyme-linked immunoassay.

RESULTS

MoETs induced CK19 and CK19-specific IgG production. Furthermore, the levels of serum CK19-specific IgG were significantly higher in the NEA group than in the eosinophilic asthma group. Among patients with NEA, asthmatics with high levels of CK19-specific IgG had higher levels of myeloperoxidase and NET-specific IgG than those with low levels of CK19-specific IgG (P = 0.020 and P = 0.017; respectively). Moreover, the immune complexes from asthmatics with high CK19-specific IgG enhanced NET formation and reactive oxygen species production (neutrophil activation), which were suppressed by N-acetylcysteine and anti-CD16 antibody treatment.

CONCLUSIONS

These findings suggest that circulating CK19 and CK19-specific IgG may contribute to NET formation, leading to airway inflammation and steroid resistance in NEA.

Single-cell profiling reveals kidney CD163+ dendritic cell participation in human lupus nephritis

OBJECTIVES

The current work aimed to provide a comprehensive single-cell landscape of lupus nephritis (LN) kidneys, including immune and non-immune cells, identify disease-associated cell populations and unravel their participation within the kidney microenvironment.

METHODS

Single-cell RNA and T cell receptor sequencing were performed on renal biopsy tissues from 40 patients with LN and 6 healthy donors as controls. Matched peripheral blood samples from seven LN patients were also sequenced. Multiplex immunohistochemical analysis was performed on an independent cohort of 60 patients and validated using flow cytometric characterisation of human kidney tissues and in vitro assays.

RESULTS

We uncovered a notable enrichment of CD163+ dendritic cells (DC3s) in LN kidneys, which exhibited a positive correlation with the severity of LN. In contrast to their counterparts in blood, DC3s in LN kidney displayed activated and highly proinflammatory phenotype. DC3s showed strong interactions with CD4+ T cells, contributing to intrarenal T cell clonal expansion, activation of CD4+ effector T cell and polarisation towards Th1/Th17. Injured proximal tubular epithelial cells (iPTECs) may orchestrate DC3 activation, adhesion and recruitment within the LN kidneys. In cultures, blood DC3s treated with iPTECs acquired distinct capabilities to polarise Th1/Th17 cells. Remarkably, the enumeration of kidney DC3s might be a potential biomarker for induction treatment response in LN patients.

CONCLUSION

The intricate interplay involving DC3s, T cells and tubular epithelial cells within kidneys may substantially contribute to LN pathogenesis. The enumeration of renal DC3 holds potential as a valuable stratification feature for guiding LN patient treatment decisions in clinical practice.

Human neutrophil Fc gamma receptors: different buttons for different responses

Neutrophils are fundamental cells in host defense. These leukocytes are quickly recruited from the blood to sites of infection or tissue damage. At these sites, neutrophils initiate several innate immune responses, including phagocytosis, production of reactive oxygen species, degranulation to release proteases and other antimicrobial compounds, production of inflammatory mediators, and formation of neutrophil extracellular traps. In addition to their role in innate immunity, neutrophils are now recognized as cells that also regulate adaptive immunity, via interaction with dendritic cells and lymphocytes. Neutrophils also respond to adaptive immunity by interacting with antibody molecules. Indeed, antibody molecules allow neutrophils to have antigen-specific responses. Neutrophils express different receptors for antibodies. The receptors for immunoglobulin G molecules are known as Fcγ receptors. Upon Fcγ receptor aggregation on the cell membrane, these receptors trigger distinct signal transduction cascades that activate particular cellular responses. In this review, we describe the major Fcγ receptors expressed on human neutrophils and discuss how each Fcγ receptor activates a choice of signaling pathways to stimulate particular neutrophil responses.

EGF-Receptor-Dependent TLR7 Signaling in Macrophages Promotes Glomerular Injury in Crescentic Glomerulonephritis

Glomerulonephritis (GN) is a group of inflammatory diseases and an important cause of morbidity and mortality worldwide. The initiation of the inflammatory process is quite different for each type of GN; however, each GN is characterized commonly and variably by acute inflammation with neutrophils and macrophages and crescent formation, leading to glomerular death. Toll-like receptor (TLR) 7 is a sensor for self-RNA and implicated in the pathogenesis of human and murine GN. Here, we show that TLR7 exacerbates glomerular injury in nephrotoxic serum nephritis (NTN), a murine model of severe crescentic GN. TLR7-/- mice were resistant to NTN, although TLR7-/- mice manifested comparable immune-complex deposition to wild-type mice without significant defects in humoral immunity, suggesting that endogenous TLR7 ligands accelerate glomerular injury. TLR7 was expressed exclusively in macrophages in glomeruli in GN but not in glomerular resident cells or neutrophils. Furthermore, we discovered that epidermal growth factor receptor (EGFR), a receptor-type tyrosine kinase, is essential for TLR7 signaling in macrophages. Mechanistically, EGFR physically interacted with TLR7 upon TLR7 stimulation, and EGFR inhibitor completely blocked the phosphorylation of TLR7 tyrosine residue(s). EGFR inhibitor attenuated glomerular damage in wild-type mice, and no additional glomerular protective effects by EGFR inhibitor were observed in TLR7-/- mice. Finally, mice lacking EGFR in macrophages were resistant to NTN. This study clearly demonstrated that EGFR-dependent TLR7 signaling in macrophages is essential for glomerular injury in crescentic GN.

TCM "medicine and food homology" in the management of post-COVID disorders

Background

The World Health Organization declared that COVID-19 is no longer a public health emergency of global concern on May 5, 2023. Post-COVID disorders are, however, becoming more common. Hence, there lies a growing need to develop safe and effective treatment measures to manage post-COVID disorders. Investigating the use of TCM medicinal foods in the long-term therapy of post-COVID illnesses may be beneficial given contemporary research's emphasis on the development of medicinal foods.

Scope and approach

The use of medicinal foods for the long-term treatment of post-COVID disorders is highlighted in this review. Following a discussion of the history of the TCM "Medicine and Food Homology" theory, the pathophysiological effects of post-COVID disorders will be briefly reviewed. An analysis of TCM medicinal foods and their functions in treating post-COVID disorders will then be provided before offering some insight into potential directions for future research and application.

Key findings and discussion

TCM medicinal foods can manage different aspects of post-COVID disorders. The use of medicinal foods in the long-term management of post-COVID illnesses may be a safe and efficient therapy choice because they are typically milder in nature than chronic drug use. These findings may also be applied in the long-term post-disease treatment of similar respiratory disorders.

CAR-neutrophil mediated delivery of tumor-microenvironment responsive nanodrugs for glioblastoma chemo-immunotherapy

Glioblastoma (GBM) is one of the most aggressive and lethal solid tumors in human. While efficacious therapeutics, such as emerging chimeric antigen receptor (CAR)-T cells and chemotherapeutics, have been developed to treat various cancers, their effectiveness in GBM treatment has been hindered largely by the blood-brain barrier and blood-brain-tumor barriers. Human neutrophils effectively cross physiological barriers and display effector immunity against pathogens but the short lifespan and resistance to genome editing of primary neutrophils have limited their broad application in immunotherapy. Here we genetically engineer human pluripotent stem cells with CRISPR/Cas9-mediated gene knock-in to express various anti-GBM CAR constructs with T-specific CD3ζ or neutrophil-specific γ-signaling domains. CAR-neutrophils with the best anti-tumor activity are produced to specifically and noninvasively deliver and release tumor microenvironment-responsive nanodrugs to target GBM without the need to induce additional inflammation at the tumor sites. This combinatory chemo-immunotherapy exhibits superior and specific anti-GBM activities, reduces off-target drug delivery and prolongs lifespan in female tumor-bearing mice. Together, this biomimetic CAR-neutrophil drug delivery system is a safe, potent and versatile platform for treating GBM and possibly other devastating diseases.

Smad3 is essential for polarization of tumor-associated neutrophils in non-small cell lung carcinoma

Neutrophils are dynamic with their phenotype and function shaped by the microenvironment, such as the N1 antitumor and N2 pro-tumor states within the tumor microenvironment (TME), but its regulation remains undefined. Here we examine TGF-β1/Smad3 signaling in tumor-associated neutrophils (TANs) in non-small cell lung carcinoma (NSCLC) patients. Smad3 activation in N2 TANs is negatively correlate with the N1 population and patient survival. In experimental lung carcinoma, TANs switch from a predominant N2 state in wild-type mice to an N1 state in Smad3-KO mice which associate with enhanced neutrophil infiltration and tumor regression. Neutrophil depletion abrogates the N1 anticancer phenotype in Smad3-KO mice, while adoptive transfer of Smad3-KO neutrophils reproduces this protective effect in wild-type mice. Single-cell analysis uncovers a TAN subset showing a mature N1 phenotype in Smad3-KO TME, whereas wild-type TANs mainly retain an immature N2 state due to Smad3. Mechanistically, TME-induced Smad3 target genes related to cell fate determination to preserve the N2 state of TAN. Importantly, genetic deletion and pharmaceutical inhibition of Smad3 enhance the anticancer capacity of neutrophils against NSCLC via promoting their N1 maturation. Thus, our work suggests that Smad3 signaling in neutrophils may represent a therapeutic target for cancer immunotherapy.

Functional antibody delivery: Advances in cellular manipulation

The current therapeutic antibody market in the U.S. consists of 100 antibody-based products and their market value is expected to explode beyond $300 billion by 2025. These therapies are presently limited to extracellular targets due to the innate inability of antibodies to transverse membranes. To expand the number of accessible therapeutic targets, intracellular antibody delivery is necessary. Many delivery vehicles for antibodies have been used with some promising results, such as nanoparticles and cell penetrating polymers. Despite the success of these delivery platforms using model antibody cargo, there is a surprisingly small number of studies that focus on functional antibody delivery into the cytosol that also measures a cellular response. Antibodies can be designed for essentially unlimited targets, including proteins and DNA, that will ultimately control cell function once delivered inside cells. Advancement in cellular manipulation depends on the application of intracellularly delivering functional antibodies to achieve a desired result. This review focuses on the emerging field of functional antibody delivery which enables various cellular responses and cell manipulation.

Therapeutic effects of Fc gamma RIV inhibition are mediated by selectively blocking immune complex-induced neutrophil activation in epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a subepidermal autoimmune bullous disease caused by autoantibodies targeting type VII collagen (COL7). It is characterized by inflammation and subepidermal blistering mainly through immune complex (IC)-mediated activation of neutrophils. In experimental EBA, binding of neutrophils to ICs in the skin and induction of clinical disease depends on the expression of the Fc gamma receptor (FcγR) IV. As activating FcγR mediate both neutrophil extravasation and activation, we used multiphoton imaging to obtain further insights into the mechanistic contribution of FcγRIV in the pathogenesis of EBA. First, we demonstrated that blocking FcγRIV function completely protects LysM-eGFP mice against induction of antibody transfer-induced EBA. To visualize the interactions of anti-COL7 IgG and neutrophils in vivo, fluorescently labeled anti-COL7 IgG was injected into LysM-eGFP mice. Multiphoton microscopy was sequentially performed over a period of 8 days. At all time points, we observed a significantly higher extravasation of neutrophils into the skin of mice treated with anti-FcγRIV antibody compared to controls. However, the percentage of detected neutrophils localized to the target antigen along the dermal-epidermal junction was comparable between both groups. Additionally, reactive oxygen release and migration in vitro assay data demonstrate that FcγRIV antibody treatment inhibits the activation, but not the migration, of neutrophils. Our findings underscore the importance of advanced in vivo imaging techniques to understand the complexity of IC-mediated neutrophil-dependent inflammation, and indicate that the therapeutic utility of FcγRIV blockade is achieved through impairment of IC-mediated neutrophil activation.

Single-cell multi-omics of human clonal hematopoiesis reveals that DNMT3A R882 mutations perturb early progenitor states through selective hypomethylation

Somatic mutations in cancer genes have been detected in clonal expansions across healthy human tissue, including in clonal hematopoiesis. However, because mutated and wild-type cells are admixed, we have limited ability to link genotypes with phenotypes. To overcome this limitation, we leveraged multi-modality single-cell sequencing, capturing genotype, transcriptomes and methylomes in progenitors from individuals with DNMT3A R882 mutated clonal hematopoiesis. DNMT3A mutations result in myeloid over lymphoid bias, and an expansion of immature myeloid progenitors primed toward megakaryocytic-erythroid fate, with dysregulated expression of lineage and leukemia stem cell markers. Mutated DNMT3A leads to preferential hypomethylation of polycomb repressive complex 2 targets and a specific CpG flanking motif. Notably, the hypomethylation motif is enriched in binding motifs of key hematopoietic transcription factors, serving as a potential mechanistic link between DNMT3A mutations and aberrant transcriptional phenotypes. Thus, single-cell multi-omics paves the road to defining the downstream consequences of mutations that drive clonal mosaicism.

Overexpressed angiotensin-converting enzyme in neutrophils suppresses glomerular damage in crescentic glomerulonephritis

While angiotensin-converting enzyme (ACE) regulates blood pressure by producing angiotensin II as part of the renin-angiotensin system, we recently reported that elevated ACE in neutrophils promotes an effective immune response and increases resistance to infection. Here, we investigate if such neutrophils protect against renal injury in immune complex (IC)-mediated crescentic glomerulonephritis (GN) through complement. Nephrotoxic serum nephritis (NTN) was induced in wild-type and NeuACE mice that overexpress ACE in neutrophils. Glomerular injury of NTN in NeuACE mice was attenuated with much less proteinuria, milder histological injury, and reduced IC deposits, but presented with more glomerular neutrophils in the early stage of the disease. There were no significant defects in T and B cell functions in NeuACE mice. NeuACE neutrophils exhibited enhanced IC uptake with elevated surface expression of FcγRII/III and complement receptor CR1/2. IC uptake in neutrophils was enhanced by NeuACE serum containing elevated complement C3b. Given no significant complement activation by ACE, this suggests that neutrophil ACE indirectly preactivates C3 and that the C3b-CR1/2 axis and elevated FcγRII/III play a central role in IC elimination by neutrophils, resulting in reduced glomerular injury. The present study identified a novel renoprotective role of ACE in glomerulonephritis; elevated neutrophilic ACE promotes elimination of locally formed ICs in glomeruli via C3b-CR1/2 and FcγRII/III, ameliorating glomerular injury.NEW & NOTEWORTHY We studied immune complex (IC)-mediated crescentic glomerulonephritis in NeuACE mice that overexpress ACE only in neutrophils. Such mice show no significant defects in humoral immunity but strongly resist nephrotoxic serum nephritis (less proteinuria, milder histological damage, reduced IC deposits, and more glomerular neutrophils). NeuACE neutrophils enhanced IC uptake via increased surface expression of CR1/2 and FcgRII/III, as well as elevated serum complement C3b. These results suggest neutrophil ACE as a novel approach to reducing glomerulonephritis.

Immunologic phenotype of patients with long-COVID syndrome of 1-year duration

Background

The pathophysiology of long-COVID remains unknown, and information is particularly limited for symptoms of very long duration. We aimed to assess the serological, T-cell immune responses and ANA titers of patients with long-COVID-19 syndrome of 1-year duration.

Methods

Prospective, longitudinal study of hospitalized COVID-19 patients followed-up for 12 months. Sequential blood samples and COVID-19 symptom questionnaires (CSQ) were obtained, and humoral and cellular immune responses, antinuclear antibodies (ANA) and inflammation biomarkers were analyzed.

Results

Of 154 patients discharged from hospital, 72 non-vaccinated with available CSQ in all visits were included. Of them, 14 (19.4%) reported persistent symptoms both at 6-months and 12-months, mainly asthenia (15.3%), myalgia (13.9%), and difficulty concentrating/memory loss (13.9%). Symptomatic patients were more frequently women, smokers, showed higher WHO severity score, and a trend to higher ICU admission. In the adjusted analysis, long-COVID syndrome was associated with lower frequency of detectable neutralizing antibodies (adjusted hazard ratio [aHR] 0.98; 95% confidence interval [CI], 0.97-0.99) and lower SARS-CoV-2-S1/S2 titers (aHR [95%CI] 0.14 [0.03–0.65]). T-cell immune response measured with a SARS-CoV-2-interferon-γ release assay was not different between groups. There was a higher frequency of positive ANA titers (≥160) in symptomatic patients (57.1% vs 29.3%, p=0.04), that was attenuated after adjustment aHR [95% CI] 3.37 [0.84-13.57], p=0.087. Levels of C-reactive protein and D-dimer were higher during follow-up in symptomatic patients, but with no differences at 12 months.

Conclusion

Patients with 1-year duration long-COVID-19 syndrome exhibit a distinct immunologic phenotype that includes a poorer SARS-CoV-2 antibody response, low-degree chronic inflammation that tends to mitigate, and autoimmunity.

Lysophosphatidylcholine Alleviates Acute Lung Injury by Regulating Neutrophil Motility and Neutrophil Extracellular Trap Formation

Sepsis is predominantly initiated by bacterial infection and can cause systemic inflammation, which frequently leads to rapid death of the patient. However, this acute systemic inflammatory response requires further investigation from the perspectives of clinical judgment criteria and early treatment strategies for the relief of symptoms. Lysophosphatidylcholine (LPC) 18:0 may relieve septic symptoms, but the relevant mechanism is not clearly understood. Therefore, we aimed to assess the effectiveness of LPC as a therapeutic treatment for acute inflammation in the lung induced by lipopolysaccharide in mice. Systemic inflammation of mice was induced by lipopolysaccharide (LPS) inoculation to investigate the role of LPC in the migration and the immune response of neutrophils during acute lung injury. By employing two-photon intravital imaging of the LPS-stimulated LysM-GFP mice and other in vitro and in vivo assays, we examined whether LPC alleviates the inflammatory effect of sepsis. We also tested the effect of LPC to human neutrophils from healthy control and sepsis patients. Our data showed that LPC treatment reduced the infiltration of innate immune cells into the lung. Specifically, LPC altered neutrophil migratory patterns and enhanced phagocytic efficacy in the damaged lung. Moreover, LPC treatment reduced the release of neutrophil extracellular trap (NET), which can damage tissue in the inflamed organ and exacerbate disease. It also reduced human neutrophil migration under inflammatory environment. Our results suggest that LPC can alleviate sepsis-induced lung inflammation by regulating the function of neutrophils. These findings provide evidence for the beneficial application of LPC treatment as a potential therapeutic strategy for sepsis.

The role of neutrophils in antibody-driven autoimmune cytopenias

Autoimmune cytopenias are a consequence of autoantibodies that target blood cell lineages and mark them for their accelerated destruction, mostly through phagocytosis by monocytes and macrophages and complement activation. Neutrophils, although equipped with Fc and complement receptors and effector mechanisms that are critical in other autoimmune conditions, remained long overlooked. Recent reports, however, propose a new and possibly critical role of neutrophils. In this review, we gathered available evidence on the contribution of neutrophils to the development, onset, and consequences of autoantibody-dependent cytopenias.

Monocytes transition to macrophages within the inflamed vasculature via monocyte CCR2 and endothelial TNFR2

Monocytes undergo phenotypic and functional changes in response to inflammatory cues, but the molecular signals that drive different monocyte states remain largely undefined. We show that monocytes acquire macrophage markers upon glomerulonephritis and may be derived from CCR2+CX3CR1+ double-positive monocytes, which are preferentially recruited, dwell within glomerular capillaries, and acquire proinflammatory characteristics in the nephritic kidney. Mechanistically, the transition to immature macrophages begins within the vasculature and relies on CCR2 in circulating cells and TNFR2 in parenchymal cells, findings that are recapitulated in vitro with monocytes cocultured with TNF-TNFR2-activated endothelial cells generating CCR2 ligands. Single-cell RNA sequencing of cocultures defines a CCR2-dependent monocyte differentiation path associated with the acquisition of immune effector functions and generation of CCR2 ligands. Immature macrophages are detected in the urine of lupus nephritis patients, and their frequency correlates with clinical disease. In conclusion, CCR2-dependent functional specialization of monocytes into macrophages begins within the TNF-TNFR2-activated vasculature and may establish a CCR2-based autocrine, feed-forward loop that amplifies renal inflammation.

Neutrophil Protein Kinase R Mediates Endothelial Adhesion and Migration by the Promotion of Neutrophil Actin Polymerization

Neutrophils protect against bacterial and fungal infections, but tight regulation of cell activation is essential for avoiding tissue damage in autoimmune disorders. Protein kinase R (PKR) is a serine/threonine kinase originally characterized by its role in the defense mechanisms against viral infection. Although PKR is involved in the signaling pathways of neurodegenerative diseases and metabolic disorders, its function in neutrophils is not well delineated. In this study, we demonstrate that human neutrophil PKR mediates adhesion to endothelial cells under physiological flow conditions but does not mediate rolling on those cells. Also, neutrophil PKR activation contributes to migration toward chemoattractants. Mechanistically, neutrophil PKR mediates the cell spreading and binding to ICAM-1 in static condition. Moreover, Ab microarray reveals that calcium/calmodulin-dependent protein kinase II is phosphorylated downstream of PKR and affects actin polymerization that is a cytoskeleton rearrangement indispensable for neutrophil migration induced by fMLF. In vivo, neutrophil recruitment into the dorsal air pouch of mice is reduced by PKR inhibitor treatment. Also, in mice with nephrotoxic serum nephritis, the compound treatment suppresses neutrophil accumulation in kidney glomerulus and subsequent development of albuminuria. Thus, in vascular inflammation, neutrophil PKR plays a critical role in the recruitment process, including endothelial adhesion and migration via leukocyte actin polymerization.

Neutrophils are key mediators in crescentic glomerulonephritis and targets for new therapeutic approaches

Crescentic glomerulonephritis (CGN) results from a diverse set of diseases associated with immune dysregulation and the breakdown of self-tolerance to a wide range of autoantigens, some known and some that remain unknown. Experimental data demonstrate that neutrophils have an important role in the pathogenesis of CGN. Upon activation, neutrophils generate reactive oxygen species, release serine proteases and form neutrophil extracellular traps (NETs), all of which can induce direct tissue damage. In addition, serine proteases such as myeloperoxidase and proteinase 3, presented on NETs, can be processed and recognized as autoantigens, leading to the generation and maintenance of autoimmune responses in susceptible individuals. The basis of the specificity of autoimmune responses in different patients to NET proteins is unclear, but relates at least in part to differences in human leucocyte antigen expression. Conditions associated with CGN are often characterized by aberrant neutrophil activation and NETosis and, in some, impaired NET degradation. Targeting neutrophil degranulation and NETosis is now possible using a variety of novel compounds and may provide a promising therapeutic alternative to glucocorticoid use, which has been a mainstay of management in CGN for decades and is associated with significant adverse effects. In this review, we discuss the evidence supporting the role of neutrophils in the development of CGN and the pathways identified in neutrophil degranulation and NETosis that may translate to novel therapeutic applications.

Mice Treated Subcutaneously with Mouse LPS-Converted PrPres or LPS Alone Showed Brain Gene Expression Profiles Characteristic of Prion Disease

Previously, we showed that bacterial lipopolysaccharide (LPS) converts mouse PrP^C protein to a beta-rich isoform (moPrP^res) resistant to proteinase K. In this study, we aimed to test if the LPS-converted PrP^res is infectious and alters the expression of genes related to prion pathology in brains of terminally sick mice. Ninety female FVB/N mice at 5 weeks of age were randomly assigned to 6 groups treated subcutaneously (sc) for 6 weeks either with: (1) Saline (CTR); (2) LPS from Escherichia coli 0111:B4 (LPS), (3) one-time sc administration of de novo generated mouse recombinant prion protein (moPrP; 29-232) rich in beta-sheet by incubation with LPS (moPrP^res), (4) LPS plus one-time sc injection of moPrP^res, (5) one-time sc injection of brain homogenate from Rocky Mountain Lab (RLM) scrapie strain, and (6) LPS plus one-time sc injection of RML. Results showed that all treatments altered the expression of various genes related to prion disease and neuroinflammation starting at 11 weeks post-infection and more profoundly at the terminal stage. In conclusion, sc administration of de novo generated moPrPres, LPS, and a combination of moPrP^res with LPS were able to alter the expression of multiple genes typical of prion pathology and inflammation.

Identifying Lung Cancer Cell Markers with Machine Learning Methods and Single-Cell RNA-Seq Data

Non-small cell lung cancer is a major lethal subtype of epithelial lung cancer, with high morbidity and mortality. The single-cell sequencing technique plays a key role in exploring the pathogenesis of non-small cell lung cancer. We proposed a computational method for distinguishing cell subtypes from the different pathological regions of non-small cell lung cancer on the basis of transcriptomic profiles, including a group of qualitative classification criteria (biomarkers) and various rules. The random forest classifier reached a Matthew’s correlation coefficient (MCC) of 0.922 by using 720 features, and the decision tree reached an MCC of 0.786 by using 1880 features. The obtained biomarkers and rules were analyzed in the end of this study.

FcγR engagement reprograms neutrophils into antigen cross-presenting cells that elicit acquired anti-tumor immunity

Classical dendritic cells (cDC) are professional antigen-presenting cells (APC) that regulate immunity and tolerance. Neutrophil-derived cells with properties of DCs (nAPC) are observed in human diseases and after culture of neutrophils with cytokines. Here we show that FcγR-mediated endocytosis of antibody-antigen complexes or an anti-FcγRIIIB-antigen conjugate converts neutrophils into nAPCs that, in contrast to those generated with cytokines alone, activate T cells to levels observed with cDCs and elicit CD8+ T cell-dependent anti-tumor immunity in mice. Single cell transcript analyses and validation studies implicate the transcription factor PU.1 in neutrophil to nAPC conversion. In humans, blood nAPC frequency in lupus patients correlates with disease. Moreover, anti-FcγRIIIB-antigen conjugate treatment induces nAPCs that can activate autologous T cells when using neutrophils from individuals with myeloid neoplasms that harbor neoantigens or those vaccinated against bacterial toxins. Thus, anti-FcγRIIIB-antigen conjugate-induced conversion of neutrophils to immunogenic nAPCs may represent a possible immunotherapy for cancer and infectious diseases.

Antibody Response to SARS-CoV-2 is Associated with Long-term Clinical Outcome in Patients with COVID-19: a Longitudinal Study

Background

The relationship of host immune response and viral replication with health outcomes in patients with COVID-19 remains to be defined. We aimed to characterize the medium and long-term clinical, virological, and serological outcomes after hospitalization for COVID-19, and to identify predictors of long-COVID.

Methods

Prospective, longitudinal study conducted in COVID-19 patients confirmed by RT-PCR. Serial blood and nasopharyngeal samples (NPS) were obtained for measuring SARS-CoV-2 RNA and S-IgG/N-IgG antibodies during hospital stay, and at 1, 2, and 6 months post-discharge. Genome sequencing was performed where appropriate. Patients filled out a COVID-19 symptom questionnaire (CSQ) at 2-month and 6-month visits, and those with highest scores were characterized.

Results

Of 146 patients (60% male, median age 64 years) followed-up, 20.6% required hospital readmission and 5.5% died. At 2 months and 6 months, 9.6% and 7.8% patients, respectively, reported moderate/severe persistent symptoms. SARS-CoV-2 RT-PCR was positive in NPS in 11.8% (median Ct = 38) and 3% (median Ct = 36) patients at 2 months and 6 months, respectively, but no reinfections were demonstrated. Antibody titers gradually waned, with seroreversion occurring at 6 months in 27 (27.6%) patients for N-IgG and in 6 (6%) for S-IgG. Adjusted 2-month predictors of the highest CSQ scores (OR [95%CI]) were lower peak S-IgG (0.80 [0.66–0.94]) and higher WHO severity score (2.57 [1.20–5.86]); 6-month predictors were lower peak S-IgG (0.89 [0.79–0.99]) and female sex (2.41 [1.20–4.82]); no association was found with prolonged viral RNA shedding.

Conclusions

Long-COVID is associated with weak anti-SARS-CoV-2 antibody response, severity of illness, and female gender. Late clinical events and persistent symptoms in the medium and long term occur in a significant proportion of patients hospitalized for COVID-19.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10875-021-01083-7.

Mired in the glomeruli: witnessing live neutrophil recruitment in the kidney

Inflammation of the kidney is a key contributor to proliferative glomerulonephritis, and kidney damage during glomerulonephritis can lead to renal failure. The immune response associated with glomerulonephritis episodes is a major determinant of patient outcomes, and understanding this response is paramount for effective therapeutic treatment. Neutrophils are the first responders to sites of infection or tissue injury and are a significant cellular infiltrate during proliferative glomerulonephritis. This immune cell was initially recognized as a "blunt" nonspecific effector cell that was recruited to kill pathogens and then die quickly. However, recent studies have shown that the behavior and function of neutrophils are substantially more complex. Neutrophil recruitment to inflammatory sites must be carefully regulated so that these potent cells accurately arrive at tissue sites and perform their functions without nonspecific injury to other locations. As the kidney contains unique microvasculature befitting their specialized role in blood filtration, the recruitment of neutrophils in the renal environment differs from other organs. This Mini-Review will describe how advances in live-animal (intravital) imaging led to the discovery of novel recruitment pathways in the kidney, particularly in the glomeruli, and highlight these differences to canonical neutrophil recruitment. In addition, molecular engagement of surface molecules that lead to intracellular signaling, which is followed by neutrophil capture in the glomeruli, is also briefly discussed. Finally, the contribution of other immune cells in renal neutrophil recruitment, the fate of the emigrated neutrophils after inflammation, and the relevance of mouse models compared with human glomerulonephritides will also be explored.

Immune-Related Urine Biomarkers for the Diagnosis of Lupus Nephritis

The kidney is one of the main organs affected by the autoimmune disease systemic lupus erythematosus. Lupus nephritis (LN) concerns 30-60% of adult SLE patients and it is significantly associated with an increase in the morbidity and mortality. The definitive diagnosis of LN can only be achieved by histological analysis of renal biopsies, but the invasiveness of this technique is an obstacle for early diagnosis of renal involvement and a proper follow-up of LN patients under treatment. The use of urine for the discovery of non-invasive biomarkers for renal disease in SLE patients is an attractive alternative to repeated renal biopsies, as several studies have described surrogate urinary cells or analytes reflecting the inflammatory state of the kidney, and/or the severity of the disease. Herein, we review the main findings in the field of urine immune-related biomarkers for LN patients, and discuss their prognostic and diagnostic value. This manuscript is focused on the complement system, antibodies and autoantibodies, chemokines, cytokines, and leukocytes, as they are the main effectors of LN pathogenesis.

Inhibitory affinity modulation of FcγRIIA ligand binding by glycosphingolipids by inside-out signaling

The interaction of the human FcγRIIA with immune complexes (ICs) promotes neutrophil activation and thus must be tightly controlled to avoid damage to healthy tissue. Here, we demonstrate that a fungal-derived soluble β-1,3/1,6-glucan binds to the glycosphingolipid long-chain lactosylceramide (LacCer) to reduce FcγRIIA-mediated recruitment to immobilized ICs under flow, a process requiring high-affinity FcγRIIA-immunoglobulin G (IgG) interactions. The inhibition requires Lyn phosphorylation of SHP-1 phosphatase and the FcγRIIA immunotyrosine-activating motif. β-glucan reduces the effective 2D affinity of FcγRIIA for IgG via Lyn and SHP-1 and, in vivo, inhibits FcγRIIA-mediated neutrophil recruitment to intravascular IgG deposited in the kidney glomeruli in a glycosphingolipid- and Lyn-dependent manner. In contrast, β-glucan did not affect FcγR functions that bypass FcγR affinity for IgG. In summary, we have identified a pathway for modulating the 2D affinity of FcγRIIA for ligand that relies on LacCer-Lyn-SHP-1-mediated inhibitory signaling triggered by β-glucan, a previously described activator of innate immunity.

Okubo et al. demonstrate that β-glucan binding to the glycosphingolipid lactosylceramide engages a Lyn kinase to SHP-1 phosphatase pathway that reduces FcγRIIA binding propensity for IgG, which suggests FcγRIIA affinity regulation by “inside-out” signaling. The β-glucan-lactosylceramide-Lyn axis prevents FcγRIIA-dependent neutrophil recruitment in vitro and to intravascular IgG deposits following glomerulonephritis.

Fcγ receptors on aging neutrophils

OBJECTIVE

Neutrophils are key effector cells of the innate immune system. They recognize antigens through membrane receptors, which are expressed during their maturation and activation. Neutrophils express FcγRII (CD32), FcγRIII (CD16), and FcγRI (CD64) after being activated by different factors such as cytokines and bacterial products. These receptors are involved with phagocytosis of IgG-opsonized microbes and enhance defense mechanisms. Based on that, our study seeks to compare the expression of FcγRII, FcγRIII, FcγRI, and CD11b on neutrophils from elderly and young subjects and their expression after in vitro activation with cytokines and LPS.

METHODOLOGY

Neutrophils were isolated from human peripheral blood and from mice bone marrow by density gradient. After isolation, FCγRs expression was immediately analyzed by flow cytometry or after in vitro stimulation.

RESULTS

In freshly isolated cells, the percentage of FcγRIIIb+ and CD11b+ neutrophils were higher in samples from young individuals; FcγRIIIa expression was more prominent on aged neutrophils; FcγRIA expression was similar in all samples analyzed. Exposure to CXCL8 and LPS resulted in a higher percentage of FcγRIa+ neutrophils on elderly individuals' samples but lower when compared with neutrophils from young donors. We observed that LPS caused an increase in FcγRIIa expression on aging human neutrophils. In contrast, FcγRIIIb expression in response to CXCL8 and LPS stimulation was not altered in the four groups. CD11b expression was lower in neutrophils from elderly individuals even in response to LPS and CXCL8. In mice, we observed differences only regarding CD11b expression, which was increased on aged neutrophils. LPS exposure caused an increase in all FcγRs.

CONCLUSIONS

Our results suggest that, in humans, the overall pattern of FcγR expression and integrin CD11b are altered during aging and immunosenescence might contribute to age-related infection.

Pathogenicity of Proteinase 3-Anti-Neutrophil Cytoplasmic Antibody in Granulomatosis With Polyangiitis: Implications as Biomarker and Future Therapies

Granulomatosis with polyangiitis (GPA) is a rare but serious necrotizing auto-immune vasculitis. GPA is mostly associated with the presence of Anti-Neutrophil Cytoplasmic Antibody (ANCA) targeting proteinase 3 (PR3-ANCA), a serine protease contained in neutrophil granules but also exposed at the membrane. PR3-ANCAs have a proven fundamental role in GPA: they bind neutrophils allowing their auto-immune activation responsible for vasculitis lesions. PR3-ANCAs bind neutrophil surface on the one hand by their Fab binding PR3 and on the other by their Fc binding Fc gamma receptors. Despite current therapies, GPA is still a serious disease with an important mortality and a high risk of relapse. Furthermore, although PR3-ANCAs are a consistent biomarker for GPA diagnosis, relapse management currently based on their level is inconsistent. Indeed, PR3-ANCA level is not correlated with disease activity in 25% of patients suggesting that not all PR3-ANCAs are pathogenic. Therefore, the development of new biomarkers to evaluate disease activity and predict relapse and new therapies is necessary. Understanding factors influencing PR3-ANCA pathogenicity, i.e. their potential to induce auto-immune activation of neutrophils, offers interesting perspectives in order to improve GPA management. Most relevant factors influencing PR3-ANCA pathogenicity are involved in their interaction with neutrophils: level of PR3 autoantigen at neutrophil surface, epitope of PR3 recognized by PR3-ANCA, isotype and glycosylation of PR3-ANCA. We detailed in this review the advances in understanding these factors influencing PR3-ANCA pathogenicity in order to use them as biomarkers and develop new therapies in GPA as part of a personalized approach.

Meta-analysis of global and high throughput public gene array data for robust vascular gene expression discovery in chronic rhinosinusitis: Implications in controlled release

BACKGROUND

Chronic inflammation is known to cause alterations in vascular homeostasis that directly affects blood vessel morphogenesis, angiogenesis, and tissue permeability. These phenomena have been investigated and exploited for targeted drug delivery applications in the context of cancers and other disease processes. Vascular pathophysiology and its associated genes and signaling pathways, however, have not been systematically investigated in patients with chronic rhinosinusitis (CRS). Understanding the interplay between key vascular signaling pathways and top biomarkers associated with CRS may facilitate the development of new targeted delivery strategies and treatment paradigms. Herein, we report findings from a gene meta-analysis to identify key vascular pathways and top genes involved in CRS.

METHODS

Proprietary software (Illumina BaseSpace Correlation Engine) and open-access data sets were used to perform a gene meta-analysis to systematically determine significant differences between key vascular biomarkers and vascular signaling pathways expressed in sinonasal tissue biopsies of controls and patients with CRS.

RESULTS

Thirteen studies were initially identified, and then reduced to five after applying exclusion principle algorithms. Genes associated with vasculature development and blood vessel morphogenesis signaling pathways were identified to be overexpressed among the top 15 signaling pathways. Out of many significantly upregulated genes, the levels of pro angiogenic genes such as early growth response (EGR3), platelet endothelial cell adhesion molecule (PECAM1) and L-selectin (SELL) were particularly significant in patients with CRS compared to controls.

DISCUSSION

Key vascular biomarkers and signaling pathways were significantly overexpressed in patients with CRS compared to controls, suggesting a contribution of vascular dysfunction in CRS pathophysiology. Vascular dysregulation and permeability may afford opportunities to develop drug delivery systems to improve efficacy and reduce toxicity of CRS treatment.

IgG-aggregates rapidly upregulate FcgRI expression at the surface of human neutrophils in a FcgRII-dependent fashion: A crucial role for FcgRI in the generation of reactive oxygen species

Autoimmune complexes are an important feature of several autoimmune diseases such as lupus, as they contribute to tissue damage through the activation of immune cells. Neutrophils, key players in lupus, interact with immune complexes through Fc gamma receptors (FcgR). Incubation of neutrophils with aggregated-IgGs caused degranulation and increased the surface expression of FcgRI within minutes in a concentration-dependent fashion. After 30 minutes, IgG aggregates (1 mg/mL) upregulated FcgRI by 4.95 ± 0.45-fold. FcgRI-positive neutrophils reached 67.24% ± 6.88% on HA-IgGs stimulated neutrophils, from 3.12% ± 1.62% in non-stimulated cells, ranking IgG-aggregates among the most potent known agonists. FcgRIIa, and possibly FcgRIIIa, appeared to mediate this upregulation. Also, FcgRI-dependent signaling proved necessary for reactive oxygen species (ROS) production in response to IgG-aggregates. Finally, combinations of bacterial materials with aggregates dramatically boosted ROS production. This work suggests FcgRI as an essential component in the response of human neutrophils to immune complexes leading to the production of ROS, which may help explain how neutrophils contribute to tissue damage associated with immune complex-associated diseases, such as lupus.

VISTA deficiency protects from immune complex-mediated glomerulonephritis by inhibiting neutrophil activation

V-type immunoglobulin domain-containing suppressor of T-cell activation (VISTA) is a negative checkpoint regulator of T cells. We assessed VISTA deficient mice in the murine nephrotoxic nephritis models of acute and chronic immune-complex mediated glomerulonephritis. We show that VISTA deficiency protects from crescentic glomerulonephritis, with no effect on the nephritogenic adaptive immune response. The early neutrophil influx was unaffected but proteinuria was reduced suggesting a reduction in neutrophil activation. In vivo, there was reduced neutrophil degranulation in VISTA deficienct mice and, in vitro, VISTA-deficient neutrophils had an impaired response to immune complexes but not to fMLP or PMA. Mice with a genetic deficiency of neutrophils due to myeloid-specific deletion of myeloid cell leukemia 1 (Mcl-1) were also protected from crescentic glomerulonephritis, indicating an essential role for neutrophils. Therefore, VISTA deficiency inhibits neutrophil activation by immune complexes and neutrophil-dependent crescentic glomerulonephritis. This suggests that VISTA is a therapeutic target for inflammatory disease. However, this would need to be balanced against a potential enhancing effect on autoimmunity.

Role of Opsonophagocytosis in Immune Protection against Malaria

The quest for immune correlates of protection continues to slow vaccine development. To date, only vaccine-induced antibodies have been confirmed as direct immune correlates of protection against a plethora of pathogens. Vaccine immunologists, however, have learned through extensive characterizations of humoral responses that the quantitative assessment of antibody responses alone often fails to correlate with protective immunity or vaccine efficacy. Despite these limitations, the simple measurement of post-vaccination antibody titers remains the most widely used approaches for vaccine evaluation. Developing and performing functional assays to assess the biological activity of pathogen-specific responses continues to gain momentum; integrating serological assessments with functional data will ultimately result in the identification of mechanisms that contribute to protective immunity and will guide vaccine development. One of these functional readouts is phagocytosis of antigenic material tagged by immune molecules such as antibodies and/or complement components. This review summarizes our current understanding of how phagocytosis contributes to immune defense against pathogens, the pathways involved, and defense mechanisms that pathogens have evolved to deal with the threat of phagocytic removal and destruction of pathogens.

Genetic Variation in Low-To-Medium-Affinity Fcγ Receptors: Functional Consequences, Disease Associations, and Opportunities for Personalized Medicine

Fc-gamma receptors (FcγR) are the cellular receptors for Immunoglobulin G (IgG). Upon binding of complexed IgG, FcγRs can trigger various cellular immune effector functions, thereby linking the adaptive and innate immune systems. In humans, six classic FcγRs are known: one high-affinity receptor (FcγRI) and five low-to-medium-affinity FcγRs (FcγRIIA, -B and -C, FcγRIIIA and -B). In this review we describe the five genes encoding the low-to-medium -affinity FcγRs (FCGR2A, FCGR2B, FCGR2C, FCGR3A, and FCGR3B), including well-characterized functionally relevant single nucleotide polymorphisms (SNPs), haplotypes as well as copy number variants (CNVs), which occur in distinct copy number regions across the locus. The evolution of the locus is also discussed. Importantly, we recommend a consistent nomenclature of genetic variants in the FCGR2/3 locus. Next, we focus on the relevance of genetic variation in the FCGR2/3 locus in auto-immune and auto-inflammatory diseases, highlighting pathophysiological insights that are informed by genetic association studies. Finally, we illustrate how specific FcγR variants relate to variation in treatment responses and prognosis amongst autoimmune diseases, cancer and transplant immunology, suggesting novel opportunities for personalized medicine.

CD36 identified by weighted gene co-expression network analysis as a hub candidate gene in lupus nephritis

Lupus nephritis (LN) is a severe manifestation of systemic lupus erythematosus (SLE), which often progresses to end-stage renal disease (ESRD) and ultimately leads to death. At present, there are no definitive therapies towards LN, so that illuminating the molecular mechanism behind the disease has become an urgent task for researchers. Bioinformatics has become a widely utilized method for exploring genes related to disease. This study set out to conduct weighted gene co-expression network analysis (WGCNA) and screen the hub gene of LN. We performed WGCNA on the microarray expression profile dataset of GSE104948 from the Gene Expression Omnibus (GEO) database with 18 normal and 21 LN samples of glomerulus. A total of 5,942 genes were divided into 5 co-expression modules, one of which was significantly correlated to LN. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were conducted on the LN-related module, and the module was proved to be associated mainly with the activation of inflammation, immune response, cytokines, and immune cells. Genes in the most significant GO terms were extracted for sub-networks of WGNCA. We evaluated the centrality of genes in the sub-networks by Maximal Clique Centrality (MCC) method and CD36 was ultimately screened out as a hub candidate gene of the pathogenesis of LN. The result was verified by its differentially expressed level between normal and LN in GSE104948 and the other three multi-microarray datasets of GEO. Moreover, we further demonstrated that the expression level of CD36 is related to the WHO Lupus Nephritis Class of LN patients with the help of Nephroseq database. The current study proposed CD36 as a vital candidate gene in LN for the first time and CD36 may perform as a brand-new biomarker or therapeutic target of LN in the future.

Expression, Role, and Regulation of Neutrophil Fcγ Receptors

Neutrophils are best known for their critical role in host defense, for which they utilize multiple innate immune mechanisms, including microbe-associated pattern recognition, phagocytosis, production of reactive oxygen species, and the release of potent proteases, mediators, antimicrobials, and neutrophil extracellular traps. Beyond their well-established contribution to innate immunity, neutrophils were more recently reported to interact with various other cell types, including cells from the adaptive immune system, thereby enabling neutrophils to tune the overall immune response of the host. Neutrophils express different receptors for IgG antibodies (Fcγ receptors), which facilitate the engulfment of IgG-opsonized microbes and trigger cell activation upon cross-linking of several receptors. Indeed, FcγRs (via IgG antibodies) confer neutrophils with a key feature of the adaptive immunity: an antigen-specific cell response. This review summarizes the expression and function of FcγRs on human neutrophils in health and disease and how they are affected by polymorphisms in the FCGR loci. Additionally, we will discuss the role of neutrophils in providing help to marginal zone B cells for the production of antibodies, which in turn may trigger neutrophil effector functions when engaging FcγRs.

An IgG-induced neutrophil activation pathway contributes to human drug-induced anaphylaxis

Anaphylaxis is a systemic acute hypersensitivity reaction that is considered to depend on allergen-specific immunoglobulin E (IgE) antibodies and histamine release by mast cells and basophils. Nevertheless, allergen-specific IgG antibodies have been proposed to contribute when the allergen is an abundant circulating large molecule, e.g., after infusions of therapeutic antibodies or dextran. Data from animal models demonstrate a pathway involving platelet-activating factor (PAF) release by monocytes/macrophages and neutrophils activated via their Fc gamma receptors (FcγRs). We hypothesized that such a pathway may also apply to small drugs and could be responsible for non–IgE-mediated anaphylaxis and influence anaphylaxis severity in humans. We prospectively conducted a multicentric study of 86 patients with suspected anaphylaxis to neuromuscular-blocking agents (NMBAs) during general anesthesia and 86 matched controls. We found that concentrations of anti-NMBA IgG and markers of FcγR activation, PAF release, and neutrophil activation correlated with anaphylaxis severity. Neutrophils underwent degranulation and NETosis early after anaphylaxis onset, and plasma-purified anti-NMBA IgG triggered neutrophil activation ex vivo in the presence of NMBA. Neutrophil activation could also be observed in patients lacking evidence of classical IgE-dependent anaphylaxis. This study supports the existence of an IgG-neutrophil pathway in human NMBA-induced anaphylaxis, which may aggravate anaphylaxis in combination with the IgE pathway or underlie anaphylaxis in the absence of specific IgE. These results reconcile clinical and experimental data on the role of antibody classes in anaphylaxis and could inform diagnostic approaches to NMBA-induced acute hypersensitivity reactions.

Understanding Fc Receptor Involvement in Inflammatory Diseases: From Mechanisms to New Therapeutic Tools

Fc receptors (FcRs) belong to the ITAM-associated receptor family. FcRs control the humoral and innate immunity which are essential for appropriate responses to infections and prevention of chronic inflammation or auto-immune diseases. Following their crosslinking by immune complexes, FcRs play various roles such as modulation of the immune response by released cytokines or of phagocytosis. Here, we review FcR involvement in pathologies leading notably to altered intracellular signaling with functionally relevant consequences to the host, and targeting of Fc receptors as therapeutic approaches. Special emphasis will be given to some FcRs, such as the FcαRI, the FcγRIIA and the FcγRIIIA, which behave like the ancient god Janus depending on the ITAM motif to inhibit or activate immune responses depending on their targeting by monomeric/dimeric immunoglobulins or by immune complexes. This ITAM duality has been recently defined as inhibitory or activating ITAM (ITAMi or ITAMa) which are controlled by Src family kinases. Involvement of various ITAM-bearing FcRs observed during infectious or autoimmune diseases is associated with allelic variants, changes in ligand binding ability responsible for host defense perturbation. During auto-immune diseases such as rheumatoid arthritis, lupus or immune thrombocytopenia, the autoantibodies and immune complexes lead to inflammation through FcR aggregation. We will discuss the role of FcRs in autoimmune diseases, and focus on novel approaches to target FcRs for resolution of antibody-mediated autoimmunity. We will finally also discuss the down-regulation of FcR functionality as a therapeutic approach for autoimmune diseases.

Humanised effector-null FcγRIIA antibody inhibits immune complex-mediated proinflammatory responses

OBJECTIVE

Immune complexes (ICs) play a critical role in the pathology of autoimmune diseases. The aim of this study was to generate and characterise a first-in-class anti-FcγRIIA antibody (Ab) VIB9600 (previously known as MEDI9600) that blocks IgG immune complex-mediated cellular activation for clinical development.

METHODS

VIB9600 was humanised and optimised from the IV.3 Ab. Binding affinity and specificity were determined by Biacore and ELISA. Confocal microscopy, Flow Cytometry-based assays and binding competition assays were used to assess the mode of action of the antibody. In vitro cell-based assays were used to demonstrate suppression of IC-mediated inflammatory responses. In vivo target suppression and efficacy was demonstrated in FcγRIIA-transgenic mice. Single-dose pharmacokinetic (PK)/pharmacodynamic study multiple dose Good Laboratory Practice (GLP) toxicity studies were conducted in non-human primates.

RESULTS

We generated a humanised effector-deficient anti-FcγRIIA antibody (VIB9600) that potently blocks autoantibody and IC-mediated proinflammatory responses. VIB9600 suppresses FcγRIIA activation by blocking ligand engagement and by internalising FcγRIIA from the cell surface. VIB9600 inhibits IC-induced type I interferons from plasmacytoid dendritic cells (involved in SLE), antineutrophil cytoplasmic antibody (ANCA)-induced production of reactive oxygen species by neutrophils (involved in ANCA-associated vasculitis) and IC-induced tumour necrosis factor α and interleukin-6 production (involved in rheumatoid arthritis). In FcγRIIA transgenic mice, VIB9600 suppressed antiplatelet antibody-induced thrombocytopaenia, acute anti-GBM Ab-induced nephritis and anticollagen Ab-induced arthritis. VIB9600 also exhibited favourable PK and safety profiles in cynomolgus monkey studies.

CONCLUSIONS

VIB9600 is a specific humanised antibody antagonist of FcγRIIA with null effector function that warrants further clinical development for the treatment of IC-mediated diseases.

Urinary levels of the leukocyte surface molecule CD11b associate with glomerular inflammation in lupus nephritis

Noninvasive biomarkers of disease activity are needed to monitor response to therapy and predict disease recurrence in patients with glomerulonephritis. The leukocyte surface markers integrin Mac-1 and CD16b have been implicated in the pathogenesis of lupus nephritis (LN). Mac-1 comprises a unique α subunit (CD11b) complexed with a common β2 subunit, which are released along with CD16b from specific leukocyte subsets under inflammatory conditions including glomerulonephritis. We investigated the association of urinary CD11b and CD16b with histopathological activity in 272 patients with biopsy-proven glomerular diseases, including 118 with LN. Urine CD11b and CD16b were measured via enzyme-linked immunosorbent assay. Urinary levels of both markers were increased in LN, but only urinary CD11b was correlated with the number of glomerular leukocytes and with overall histopathological activity. In a subset of patients with samples available from the time of biopsy and subsequent clinical remission of LN, urinary levels of CD11b decreased with successful glucocorticoid treatment. Receiver-operating characteristic curve analysis demonstrated that urinary CD11b was superior to CD16b, the scavenger receptor CD163, and monocyte chemotactic protein-1 for the prediction of proliferative LN. In anti-mouse nephrotoxic serum glomerulonephritis, urinary CD11b correlated with histologic damage and decreased with corticosteroid treatment. In vitro, CD11b levels were decreased on activated mouse neutrophils displaying Fcγ receptor clustering and transendothelial migration, suggesting that leukocyte activation and transmigration are required for CD11b shedding in urine. Together, our results suggest that urinary CD11b may be a useful biomarker to estimate histopathological activity, particularly glomerular leukocyte accumulation, in LN.

FcγRIIIb Restricts Antibody-Dependent Destruction of Cancer Cells by Human Neutrophils

The function of the low-affinity IgG-receptor FcγRIIIb (CD16b), which is uniquely and abundantly expressed on human granulocytes, is not clear. Unlike the other Fcγ receptors (FcγR), it is a glycophosphatidyl inositol (GPI) -anchored molecule and does not have intracellular signaling motifs. Nevertheless, FcγRIIIb can cooperate with other FcγR to promote phagocytosis of antibody-opsonized microbes by human neutrophils. Here we have investigated the role of FcγRIIIb during antibody-dependent cellular cytotoxicity (ADCC) by neutrophils toward solid cancer cells coated with either trastuzumab (anti-HER2) or cetuximab (anti-EGFR). Inhibiting FcγRIIIb using CD16-F(ab')₂ blocking antibodies resulted in substantially enhanced ADCC. ADCC was completely dependent on FcγRIIa (CD32a) and the enhanced ADCC seen after FcγRIIIb blockade therefore suggested that FcγRIIIb was competing with FcγRIIa for IgG on the opsonized target cells. Interestingly, the function of neutrophil FcγRIIIb as a decoy receptor was further supported by using neutrophils from individuals with different gene copy numbers of FCGR3B causing different levels of surface FcγRIIIb expression. Individuals with one copy of FCGR3B showed higher levels of ADCC compared to those with two or more copies. Finally, we show that therapeutic antibodies intended to improve FcγRIIIa (CD16a)-dependent natural killer (NK) cell ADCC due to the lack of fucosylation on the N-linked glycan at position N297 of the IgG₁ heavy chain Fc-region, show decreased ADCC as compared to regularly fucosylated antibodies. Together, these data confirm FcγRIIIb as a negative regulator of neutrophil ADCC toward tumor cells and a potential target for enhancing tumor cell destruction by neutrophils.

Primary Human Neutrophils Exhibit a Unique HIV-Directed Antibody-Dependent Phagocytosis Profile

The only clinical HIV vaccine trial to demonstrate efficacy, RV144, correlated protection with the antibodies (Abs) mediating function via the "constant" immunoglobulin region, the crystallizable fragment (Fc). These data have supported a focus on the induction of Abs by vaccines that trigger antiviral activities by relevant leukocytes via Fc receptors (FcRs). Neutrophils are phagocytes that comprise > 50% of leukocytes and display unique FcRs. We sought to compare the Ab-dependent cellular phagocytosis (ADCP) activity of human neutrophils to the commonly assayed THP-1 cell line. HIV-specific Abs were employed to elicit ADCP of beads coated with HIV envelope protein. Overall, trends were noted among neutrophil donors and the ADCP profile was different from that of THP-1 cells. mAb ELISA titers correlated with ADCP by THP-1 cells but not neutrophils. Monoclonal (m)Abs were also tested with primary monocytes. Donor-to-donor variation was high, and hindered the analysis of this dataset, but it was, in itself, an important finding. This study illustrates the concept that the assessment of FcR-mediated Ab activity with a frequently used cell line such as THP-1 is not necessarily indicative of relevant Ab functionality in vivo, and this calls for in-depth study of the properties of the HIV antibodies best-suited to eliciting antiviral activities by primary cells.

Cis interaction between sialylated FcγRIIA and the αI-domain of Mac-1 limits antibody-mediated neutrophil recruitment

Vascular-deposited IgG immune complexes promote neutrophil recruitment, but how this process is regulated is still unclear. Here we show that the CD18 integrin Mac-1, in its bent state, interacts with the IgG receptor FcγRIIA in cis to reduce the affinity of FcγRIIA for IgG and inhibit FcγRIIA-mediated neutrophil recruitment under flow. The Mac-1 rs1143679 lupus-risk variant reverses Mac-1 inhibition of FcγRIIA, as does a Mac-1 ligand and a mutation in Mac-1’s ligand binding αI-domain. Sialylated complex glycans on FcγRIIA interact with the αI-domain via divalent cations, and this interaction is required for FcγRIIA inhibition by Mac-1. Human neutrophils deficient in CD18 integrins exhibit augmented FcγRIIA-dependent recruitment to IgG-coated endothelium. In mice, CD18 integrins on neutrophils dampen IgG-mediated neutrophil accumulation in the kidney. In summary, cis interaction between sialylated FcγRIIA and the αI-domain of Mac-1 alters the threshold for IgG-mediated neutrophil recruitment. A disruption of this interaction may increase neutrophil influx in autoimmune diseases.

Deposited immune complexes (IC) promote neutrophil recruitment, but the fine tuning of this process is still unclear. Here the authors show that the cis interaction of the IC receptor, FcγRIIA and CD18 integrin, Mac-1, on the neutrophil surface modulates neutrophil adhesion, with FcγRIIA sialylation specifically implicated in this interaction.

Burning controversies in NETs and autoimmunity: The mysteries of cell death and autoimmune disease

The causes and mechanisms of autoimmune disease pose continuing challenges to the scientific community. Recent clues implicate a peculiar feature of neutrophils, their ability to release nuclear chromatin in the form of neutrophil extracellular traps (NETs), in the induction or progression of autoimmune disease. Efforts to define the beneficial versus detrimental effects of NET release have, as yet, only partially revealed mechanisms that guide this process. Evidence suggests that the process of NET release is highly regulated, but the details of regulation remain controversial and obscure. Without a better understanding of the factors that initiate and control NET formation, the judicious modification of neutrophil behaviour for medically useful purposes appears remote. We highlight gaps and inconsistencies in published work, which make NETs and their role in health and disease a puzzle that deserves more focused attention.

Engineered hexavalent Fc proteins with enhanced Fc-gamma receptor avidity provide insights into immune-complex interactions

Autoantibody-mediated diseases are currently treated with intravenous immunoglobulin, which is thought to act in part via blockade of Fc gamma receptors, thereby inhibiting autoantibody effector functions and subsequent pathology. We aimed to develop recombinant molecules with enhanced Fc receptor avidity and thus increased potency over intravenous immunoglobulin. Here we describe the molecular engineering of human Fc hexamers and explore their therapeutic and safety profiles. We show Fc hexamers were more potent than IVIG in phagocytosis blockade and disease models. However, in human whole-blood safety assays incubation with IgG1 isotype Fc hexamers resulted in cytokine release, platelet and complement activation, whereas the IgG4 version did not. We used a statistically designed mutagenesis approach to identify the key Fc residues involved in these processes. Cytokine release was found to be dependent on neutrophil FcγRIIIb interactions with L234 and A327 in the Fc. Therefore, Fc hexamers provide unique insights into Fc receptor biology.

Tania Rowley et al. present multivalent Fc molecules with enhanced avidity for Fc gamma receptors in order to improve the treatment of autoantibody-mediated human diseases. They found several key amino acids involved in Fc receptor binding interactions.

Mechanisms of Tissue Injury in Lupus Nephritis

Disease heterogeneity remains a major challenge for the understanding of systemic lupus erythematosus (SLE). Recent work has revealed the important role of nonimmune factors in the development of end-organ damage involvement, shifting the current paradigm that views SLE as a disease inflicted by a disturbed immune system on passive target organs. Here, we discuss the pathogenesis of lupus nephritis in a comprehensive manner, by incorporating the role that target organs play by withstanding and modulating the local inflammatory response. Moreover, we consider the effects that genetic variants exert on immune and nonimmune cells in order to shape the phenotype of the disease in each affected individual.

PRN473, an inhibitor of Bruton's tyrosine kinase, inhibits neutrophil recruitment via inhibition of macrophage antigen-1 signalling

BACKGROUND AND PURPOSE

Following inflammatory stimuli, neutrophils are recruited to sites of inflammation and exert effector functions that often have deleterious effects on tissue integrity, which can lead to organ failure. Bruton's tyrosine kinase (Btk) is expressed in neutrophils and constitutes a promising pharmacological target for neutrophil-mediated tissue damage. Here, we evaluate a selective reversible inhibitor of Btk, PRN473, for its ability to dampen neutrophil influx via inhibition of adhesion receptor signalling pathways.

EXPERIMENTAL APPROACH

In vitro assays were used to assess fMLP receptor 1 (Fpr-1)-mediated binding of ligands to the adhesion receptors macrophage antigen-1 (Mac-1) and lymphocyte function antigen-1. Intravital microscopy of the murine cremaster was used to evaluate post-adhesion strengthening and endoluminal crawling. Finally, neutrophil influx was visualized in a clinically relevant model of sterile liver injury in vivo. Btk knockout animals were used as points of reference for Btk functions.

KEY RESULTS

Pharmacological inhibition of Btk by PRN473 reduced fMLP-induced phosphorylation of Btk and Mac-1 activation. Biochemical experiments demonstrated the specificity of the inhibitor. PRN473 (20 mg·kg^-1 ) significantly reduced intravascular crawling and neutrophil recruitment into inflamed tissue in a model of sterile liver injury, down to levels seen in Btk-deficient animals. A higher dose did not provide additional reduction of intravascular crawling and neutrophil recruitment.

CONCLUSIONS AND IMPLICATIONS

PRN473, a highly selective inhibitor of Btk, potently attenuates sterile liver injury by inhibiting the activation of the β₂ -integrin Mac-1 and subsequently neutrophil recruitment into inflamed tissue.

IFN-γ alters the expression of diverse immunity related genes in a cell culture model designed to represent maturing neutrophils

The cytokine interferon-γ (IFN-γ) is approved as a drug to treat chronic granulomatous disease (CGD) and osteopetrosis and is also used in hyperimmunoglobulin E syndromes. Patients with CGD have defects in proteins of the NOX2 NADPH oxidase system. This leads to reduced production of microbicidal ROS by PMNs and recurrent life threatening infections. The goal of this study was to better understand how IFN-γ might support phagocyte function in these diseases, and to obtain information that might expand potential uses for IFN-γ. Neutrophils mature in the bone marrow and then enter the blood where they quickly undergo apoptotic cell death with a half-life of only 5–10 hours. Therefore we reasoned that IFN-γ might exert its effects on neutrophils via prolonged exposure to cells undergoing maturation in the marrow rather than by its brief exposure to short-lived circulating cells. To explore this possibility we made use of PLB-985 cells, a myeloblast-like myeloid cell line that can be differentiated into a mature, neutrophil-like state by treatment with various agents including DMSO. In initial studies we investigated transcription and protein expression in PLB-985 cells undergoing maturation in the presence or absence of IFN-γ. We observed IFN-γ induced differences in expression of genes known to be involved in classical aspects of neutrophil function (transmigration, chemotaxis, phagocytosis, killing and pattern recognition) as well as genes involved in apoptosis and other mechanisms that regulating neutrophil number. We also observed differences for genes involved in the major histocompatibility complex I (MHCI) and MHCII systems whose involvement in neutrophil function is controversial and not well defined. Finally, we observed significant changes in expression of genes encoding guanylate binding proteins (Gbps) that are known to have roles in immunity but which have not as yet been linked to neutrophil function. We propose that changes in the expression within these classes of genes could help explain the immune supportive effects of IFN-γ. Next we explored if the effect of IFN-γ on expression of these genes is dependent on whether the cells are undergoing maturation; to do this we compared the effects of IFN-γ on cells cultured with and without DMSO. For a subset of genes the expression level changes caused by IFN-γ were much greater in maturing cells than non-maturing cells. These findings indicate that developmental changes associated with cell maturation can modulate the effects of IFN-γ but that this is gene specific. Since the effects of IFN-γ depend on whether cells are maturing, the gene expression changes observed in this study must be due to more than just prolonged application of IFN-γ and are instead the result of interplay between cell maturation and changes caused by the chemokine. This supports our hypothesis that the effects of IFN-γ on developing neutrophils in the bone marrow may be very different from its effects on mature cells in the blood. Collectively the findings in this study enhance our understanding of the effects of IFN-γ on maturing myeloid cells and indicate possible mechanisms by which this cytokine could support immune function.