Roles of Fc receptors in autoimmunity

64Cu-labeled minibody D2101 visualizes CDH17-positive gastric cancer xenografts with short waiting time

OBJECTIVE

We previously reported In-labeled anti-cadherin17 (CDH17) IgG visualized CDH17-positive gastric cancer xenografts. Unfortunately, a long waiting time was required to obtain high-contrast images due to long blood retention (blood half-life: 26 h). To accelerate blood clearance, we have developed anti-CDH17 minibody (D2101 minibody) and evaluated the pharmacokinetics in gastric cancer mouse models.

METHODS

Two different single chain Fvs (scFvs), D2101 mutant and D2111, were developed from each parental IgG. The binding ability to CDH17 and stability in plasma were evaluated. D2101 minibody, constructed based on D2101 mutant scFv, was labeled with Cu (Cu-D2101 minibody), and the in-vitro and in-vivo properties were evaluated by cell ELISA, biodistribution experiments, and PET imaging in mice bearing CDH17-positive AGS and CDH17-negative MKN74 tumors.

RESULTS

D2101 mutant and D2111 scFvs showed similar affinities to CDH17. D2101 mutant scFv was more stable than D2111 scFv in plasma. No loss of binding affinity of the D2101 minibody by chelate conjugation and radiolabeling procedures was observed. The biodistribution of Cu-D2101 minibody showed high uptake in AGS tumors and low uptake in MKN74. The blood half-life of Cu-D2101 minibody was 6.5 h. Improved blood clearance of Cu-D2101 minibody provided high tumor-to-blood ratios compared with the previous results of parental IgG in AGS xenograft mice. PET studies showed consistent results with biodistribution studies.

CONCLUSIONS

Cu-D2101 minibody exhibited higher tumor-to-blood ratios at earlier time points than those of the radiolabeled parental IgG. Cu-D2101 minibody has potential as an immunoimaging agent for CDH17-positive tumors.

Whole genomes reveal multiple candidate genes and pathways involved in the immune response of dolphins to a highly infectious virus

Wildlife species are challenged by various infectious diseases that act as important demographic drivers of populations and have become a great conservation concern particularly under growing environmental changes. The new era of whole genome sequencing provides new opportunities and avenues to explore the role of genetic variants in the plasticity of immune responses, particularly in non-model systems. Cetacean morbillivirus (CeMV) has emerged as a major viral threat to cetacean populations worldwide, contributing to the death of thousands of individuals of multiple dolphin and whale species. To understand the genomic basis of immune responses to CeMV, we generated and analysed whole genomes of 53 Indo-Pacific bottlenose dolphins (Tursiops aduncus) exposed to Australia's largest known CeMV-related mortality event that killed at least 50 dolphins from three different species. The genomic data set consisted of 10,168,981 SNPs anchored onto 23 chromosome-length scaffolds and 77 short scaffolds. Whole genome analysis indicated that levels of inbreeding in the dolphin population did not influence the outcome of an individual. Allele frequency estimates between survivors and nonsurvivors of the outbreak revealed 15,769 candidate SNPs, of which 689 were annotated to 295 protein coding genes. These included 50 genes with functions related to innate and adaptive immune responses, and cytokine signalling pathways and genes thought to be involved in immune responses to other morbilliviruses. Our study characterised genomic regions and pathways that may contribute to CeMV immune responses in dolphins. This represents a stride towards clarifying the complex interactions of the cetacean immune system and emphasises the value of whole genome data sets in understanding genetic elements that are essential for species conservation, including disease susceptibility and adaptation.

FcγRIIA expression accelerates nephritis and increases platelet activation in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune inflammatory disease characterized by deposits of immune complexes (ICs) in organs and tissues. The expression of FcγRIIA by human platelets, which is their unique receptor for immunoglobulin G antibodies, positions them to ideally respond to circulating ICs. Whereas chronic platelet activation and thrombosis are well-recognized features of human SLE, the exact mechanisms underlying platelet activation in SLE remain unknown. Here, we evaluated the involvement of FcγRIIA in the course of SLE and platelet activation. In patients with SLE, levels of ICs are associated with platelet activation. Because FcγRIIA is absent in mice, and murine platelets do not respond to ICs in any existing mouse model of SLE, we introduced the FcγRIIA (FCGR2A) transgene into the NZB/NZWF1 mouse model of SLE. In mice, FcγRIIA expression by bone marrow cells severely aggravated lupus nephritis and accelerated death. Lupus onset initiated major changes to the platelet transcriptome, both in FcγRIIA-expressing and nonexpressing mice, but enrichment for type I interferon response gene changes was specifically observed in the FcγRIIA mice. Moreover, circulating platelets were degranulated and were found to interact with neutrophils in FcγRIIA-expressing lupus mice. FcγRIIA expression in lupus mice also led to thrombosis in lungs and kidneys. The model recapitulates hallmarks of human SLE and can be used to identify contributions of different cellular lineages in the manifestations of SLE. The study further reveals a role for FcγRIIA in nephritis and in platelet activation in SLE.

Polymorphisms in Fc Gamma Receptors and Susceptibility to Malaria in an Endemic Population

Repeated infections by Plasmodium falciparum result in a humoral response that could reduce disease symptoms and prevent the development of clinical malaria. The principal mechanism underlying this humoral response is that immunoglobulin G (IgG) binds directly to the parasites, thus causing their neutralization. However, the action of antibodies alone is not always sufficient to eliminate pathogens from an organism. One key element involved in the recognition of IgG that plays a crucial role in the destruction of the parasites responsible for spreading malaria is the family of Fc gamma receptors. These receptors are expressed on the surface of immune cells. Several polymorphisms have been detected in the genes encoding these receptors, associated with susceptibility or resistance to malaria in different populations. In this review, we describe identified polymorphisms within the family of Fc gamma receptors and the impact of these variations on the response of a host to infection as well as provide new perspectives for the design of an effective vaccine for malaria.

Bone Marrow Endothelial Cells Take Up Blood-Borne Immune Complexes via Fcγ Receptor IIb2 in an Erythropoietin-Dependent Manner

Immune complexes (ICs) in blood are efficiently removed mainly by liver reticuloendothelial systems consisting of sinusoidal endothelial cells and Kupffer cells expressing FcγR. The bone marrow (BM) also has sinusoidal vasculatures, and sinusoidal BM endothelial cells (BMECs) bear unique function, including hematopoietic niches and traffic regulation of hematopoietic cells. In this study, we found that sinusoidal BMECs express FcγRIIb2, which is markedly increased in anemic conditions or by the administration of erythropoietin (Epo) in healthy mice. BMECs expressed Epo receptor (EpoR), and the Epo-induced increase in FcγRIIb2 expression was abolished in Epor^-/- ::HG1-Epor transgenic mice, which lack EpoR in BMECs except for BM erythroblasts, suggesting the effect was directly mediated via EpoR on BMECs. Further, although BMECs hardly captured i.v.-injected soluble ICs in healthy mice, Epo administration induced a remarkable increase in the uptake of ICs in a FcγRIIb-dependent manner. Enhancement of the IC incorporation capacity by Epo was also observed in cultured BMECs in vitro, suggesting the direct effect of Epo on BMECs. Moreover, we found that i.v.-injected ICs in Epo-treated mice were more rapidly removed from the circulation than in PBS-treated mice. These results reveal a novel function of BMECs to efficiently remove circulating blood-borne ICs in an FcγRIIb2-mediated manner.

IgG immune complexes with Staphylococcus aureus protein A enhance osteoclast differentiation and bone resorption by stimulating Fc receptors and TLR2

Staphylococcus aureus is a main pathogen of osteomyelitis and protein A is a virulence factor with high affinity for IgG. In this study, we investigated whether S. aureus affects the differentiation and bone resorption of osteoclasts through the IgG-binding capacity of protein A. Staphylococcus aureus pre-treated with serum or IgG showed marked enhancement in osteoclastogenesis and bone resorption compared to non-treated S. aureus or a protein A-deficient mutant. Blocking of the Fc receptor and deletion of the Fcγ receptor gene in osteoclast precursor cells showed that enhanced osteoclastogenesis stimulated by S. aureus IgG immune complexes (ICs) was mediated by the Fc receptor on osteoclast precursor cells. In addition, osteoclastogenesis stimulated by S. aureus ICs but not the protein A-deficient mutant was markedly reduced in osteoclast precursor cells of Myd88-knockout mice. Moreover, NFATc1, Syk and NF-κB signals were necessary for osteoclastogenesis stimulated by S. aureus ICs. The results suggest the contribution of a of Toll-like receptor 2 (TLR2)-Myd88 signal to the activity of S. aureus ICs. We further examined the expression of pro-inflammatory cytokines that is known to be enhanced by FcγR-TLR cross-talk. Osteoclasts induced by S. aureus ICs showed higher expression of TNF-α and IL-1β, and marked stimulation of proton secretion of osteoclasts activated by pro-inflammatory cytokines. Finally, injection of S. aureus, but not the protein A-deficient mutant, exacerbated bone loss in implantation and intra-peritoneal administration mouse models. Our results provide a novel mechanistic aspect of bone loss induced by S. aureus in which ICs and both Fc receptors and TLR pathways are involved.

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.

Lupus IgG deposition causes arthritis but inhibits bone destruction through competitive occupation of FcγRI and reduced RANKL signalling

Objectives

Bone destruction is a remarkable feature of inflammatory arthritis. It remains unknown why arthritis associated with the systemic autoimmune/inflammatory condition systemic lupus erythematosus (SLE) does not result in erosion and destruction. We aimed to determine the role of autoantibody in the pathogenesis of non-erosive arthritis in SLE.

Methods

We analysed medical record of SLE patients, investigated whether autoantibody induces arthritis lacking bone destruction in animal models and determined whether SLE autoantibody inhibits osteoclastogenesis induced by RANKL in vitro experiments.

Results

We found that arthritis lacking bone erosions is common in SLE patients and lupus-prone mice. Intraarticular injection of lupus serum or IgG induces immune complex deposition and arthritis, but does not result in bone destruction. Deposition of IgG, monocytes/macrophages and TNF-α is all required for the development of arthritis. Lupus serum or IgG inhibits RANKL-induced differentiation of monocytes into osteoclast in a dose-dependent manner. FcγR acts as co-receptors for RANKL and is involved in osteoclastogenesis. Deficiency of FcγRII or FcγRIII does not affect osteoclastogenesis in the presence of SLE IgG. However, lupus IgG competes for FcγRI binding with RANKL, thereby reducing osteoclastogenesis.

Conclusion

Observations from this study demonstrate that IgG from SLE patients can induce arthritis and inhibits RANKL-induced osteoclastogenesis through competitive occupation of FcγRI on monocytes/macrophages. This study improves the understanding of the pathophysiology of SLE-associated arthritis and offers a protective mechanism (FcγRI inhibition) that may be targeted in other forms of autoimmune/inflammatory arthritis, such as RA, to prevent or limit bone erosion and inflammatory bone loss.

Beyond Allotypes: The Influence of Allelic Diversity in Antibody Constant Domains

Polymorphic diversity in antibody constant domains has long been defined by allotypic motifs that cross react with the sera of other individuals. Improvements in sequencing technologies have led to the discovery of a large number of new allelic sequences that underlie this diversity. Many of the point mutations lie outside traditional allotypic motifs suggesting they do not elicit immunogenic responses. As antibodies play an important role in immune defense and biotechnology, understanding how this newly resolved diversity influences the function of antibodies is important. This review investigates the current known diversity of antibody alleles at a protein level for each antibody isotype as well as the kappa and lambda light chains. We focus on evidence emerging for how these mutations perturb antibody interactions with antigens and Fc receptors that are critical for function, as well as the influence this might have on the use of antibodies as therapeutics and reagents.

Sialylated Immunoglobulins for the Treatment of Immuno-Inflammatory Diseases

Immunoglobulins are the potent effector proteins of the humoral immune response. In the course of evolution, immunoglobulins have formed extremely diverse types of molecular structures with antigen-recognizing, antigen-binding, and effector functions embedded in a single molecule. Polysaccharide moiety of immunoglobulins plays the essential role in immunoglobulin functioning. There is growing evidence that the carbohydrate composition of immunoglobulin-linked glycans, and especially their terminal sialic acid residues, provide a key effect on the effector functions of immunoglobulins. Possibly, sialylation of Fc glycan is a common mechanism of IgG anti-inflammatory action in vivo. Thus, the post-translational modification (glycosylation) of immunoglobulins opens up significant possibilities in the diagnosis of both immunological and inflammatory disorders and in their therapies. This review is focused on the analysis of glycosylation of immunoglobulins, which can be a promising addition to improve existing strategies for the diagnosis and treatment of various immuno-inflammatory diseases.

A method combining blue native polyacrylamide gel electrophoresis with liquid chromatography tandem-mass spectrometry to detect circulating immune complexes between therapeutic monoclonal antibodies and anti-drug antibodies in animals

Therapeutic monoclonal antibodies can potentially induce unwanted immune responses, resulting in the production of anti-drug antibodies (ADAs). The binding of ADAs to drugs and subsequent formation of immune complexes (ICs) can trigger various responses, dependent on the size, concentration, and subclass of ADAs. To better understand the impact of ADAs on pharmacokinetics, pharmacodynamics, and toxicological profiles, a bioanalytical method was developed for the detection of ICs between human monoclonal immunoglobulin G (IgG) and ADAs in biological samples. Regarding the experimental procedure, in brief, the human antibody-specific ICs and unbound human antibody in biological samples are separated through blue native polyacrylamide gel electrophoresis (BN-PAGE). The target fractions are then cut from the gel, followed by in-gel trypsin digestion and subsequent liquid chromatography tandem-mass spectrometry (LC-MS/MS) to monitor the human IgG-specific peptide. This method was able to detect various types of human antibodies with a lower limit of detection of 10 μg/mL in monkey serum. The assay performance for the detection of ICs was demonstrated using spiked samples, and pre-incubated ICs in monkey serum were clearly detected. Taken together, these findings indicate that our method enables a semi-quantitative analysis for estimating the ratio of human antibody included ICs in comparison to the total antibody. This method was successfully applied to an in vivo study using mice, and the data helped explain the unexpectedly rapid clearance of a humanized antibody due to the formation of large ICs. The combination of the separation of ICs by BN-PAGE and the detection of the human IgG-specific peptide by LC-MS/MS is a useful general bioanalytical approach for the detection of ICs in animals.

Innate Immune Defense Mechanisms by Myeloid Cells That Hamper Cancer Immunotherapy

Over the past decade, cancer immunotherapy has been steering immune responses toward cancer cell eradication. However, these immunotherapeutic approaches are hampered by the tumor-promoting nature of myeloid cells, including monocytes, macrophages, and neutrophils. Despite the arsenal of defense strategies against foreign invaders, myeloid cells succumb to the instructions of an established tumor. Interestingly, the most primordial defense responses employed by myeloid cells against pathogens, such as complement activation, antibody-dependent cell cytotoxicity and phagocytosis, actually seem to favor cancer progression. In this review, we discuss how rudimentary defense mechanisms deployed by myeloid cells can promote tumor progression.

Human Fcγ-receptor IIb modulates pathogen-specific versus self-reactive antibody responses in lyme arthritis

Pathogen-specific antibody responses need to be tightly regulated to generate protective but limit self-reactive immune responses. While loss of humoral tolerance has been associated with microbial infections, the pathways involved in balancing protective versus autoreactive antibody responses in humans are incompletely understood. Studies in classical mouse model systems have provided evidence that balancing of immune responses through inhibitory receptors is an important quality control checkpoint. Genetic differences between inbred mouse models and the outbred human population and allelic receptor variants not present in mice; however, argue for caution when directly translating these findings to the human system. By studying Borrelia burgdorferi infection in humanized mice reconstituted with human hematopoietic stem cells from donors homozygous for a functional or a non-functional FcγRIIb allele, we show that the human inhibitory FcγRIIb is a critical checkpoint balancing protective and autoreactive immune responses, linking infection with induction of autoimmunity in the human immune system.

The Role of Syk in Inflammatory Response of Human Abdominal Aortic Aneurysm Tissue

Objective: Inflammatory response is central to pathogenesis of abdominal aortic aneurysm (AAA). Recently, we reported that Syk, a signaling molecule in inflammatory cells, promotes AAA development in a mouse model. In this study, we aimed to investigate the role of Syk in human AAA pathogenesis.

Materials and Methods: We obtained human AAA wall samples during open surgical aortic repair at Kurume University Hospital. Immunohistochemical analyses of AAA samples were performed for Syk activation and cell type markers. Ex vivo culture of human AAA tissue was utilized to evaluate the effect of P505-15, a Syk inhibitor, on secretions of interleukin-6 (IL-6) and matrix metalloproteinases (MMPs).

Results: Immunohistochemical analysis showed infiltration of B cells, T cells, and macrophages in AAA samples. Syk activation was localized mainly in B cells and part of macrophages. AAA tissue in culture secreted IL-6, MMP-9, and MMP-2 without any stimulation. The unstimulated secretions of IL-6, MMP-9, and MMP-2 were insensitive to P505-15. Secretions of IL-6 and MMP-9 were enhanced by exogenous normal human immunoglobulin G (IgG), which was suppressed by P505-15, whereas secretion of MMP-2 was insensitive to IgG or P505-15.

Conclusion: These results demonstrate an important role of Syk for IgG-dependent inflammatory response in human AAA.

Targeting the blood-nerve barrier for the management of immune-mediated peripheral neuropathies

Healthy peripheral nerves encounter, with increased frequency, numerous chemical, biological, and biomechanical forces. Over time and with increasing age, these forces collectively contribute to the pathophysiology of a spectrum of traumatic, metabolic, and/or immune-mediated peripheral nerve disorders. The blood-nerve barrier (BNB) serves as a critical first-line defense against chemical and biologic insults while biomechanical forces are continuously buffered by a dense array of longitudinally orientated epineural collagen fibers exhibiting high-tensile strength. As emphasized throughout this Experimental Neurology Special Issue, the BNB is best characterized as a functionally dynamic multicellular vascular unit comprised of not only highly specialized endoneurial endothelial cells, but also associated perineurial cells, pericytes, Schwann cells, basement membrane, and invested axons. The composition of the BNB, while anatomically distinct, is not functionally dissimilar to that of the well characterized neurovascular unit of the central nervous system. While the BNB lacks a glial limitans and an astrocytic endfoot layer, the primary function of both vascular units is to establish, maintain, and protect an optimal endoneurial (PNS) or interstitial (CNS) fluid microenvironment that is vital for proper neuronal function. Altered endoneurial homeostasis as a secondary consequence of BNB dysregulation is considered an early pathological event in the course of a variety of traumatic, immune-mediated, or metabolically acquired peripheral neuropathies. In this review, emerging experimental advancements targeting the endoneurial microvasculature for the therapeutic management of immune-mediated inflammatory peripheral neuropathies, including the AIDP variant of Guillain-Barré syndrome, are discussed.

Fc-gamma IIIa-V158F receptor polymorphism contributes to the severity of Guillain-Barré syndrome

Objective

Guillain‐Barré syndrome (GBS) is a rare, life‐threatening disorder of the peripheral nervous system. Immunoglobulin G Fc‐gamma receptors (FcγRs) mediate and regulate diverse effector functions and are involved in the pathogenesis of GBS. We investigated whether the FcγR polymorphisms FcγRIIa H/R131 (rs1801274), FcγRIIIa V/F158 (rs396991), and FcγRIIIb NA1/NA2, and their haplotype patterns affect the affinity of IgG‐FcγR interactivity and influence GBS susceptibility and severity.

Methods

We determined FcγR polymorphisms in 303 patients with GBS and 302 ethnically matched healthy individuals from Bangladesh by allele‐specific polymerase chain reaction. Pairwise linkage disequilibrium and haplotype patterns were analyzed based on D ´statistics and the genotype package of R statistics, respectively. Logistic regression analysis and Fisher’s exact test with corrected P (Pc) values were employed for statistical comparisons.

Results

FcγRIIIa‐V158F was associated with the severe form of GBS compared to the mild form (P = 0.005, OR = 2.24, 95% CI = 1.28–3.91; Pc = 0.015); however, FcγR genotypes and haplotype patterns did not show any association with GBS susceptibility compared to healthy controls. FcγRIIIa‐V/V158 and FcγRIIIb‐NA2/2 were associated with recent Campylobacter jejuni infection (P ≤ 0.001, OR = 0.36, 95% CI = 0.23–0.56; Pc ≤ 0.003 and P = 0.004, OR = 1.70, 95% CI = 1.18–2.44; Pc ≤ 0.012, respectively). Haplotype 1 (FcγRIIa‐H131R‐ FcγRIIIa‐V158F‐ FcγRIIIb‐NA1/2) and the FcγRIIIb‐NA2/2 genotype were more prevalent among anti‐GM1 antibody‐positive patients (P = 0.031, OR = 9.61, 95% CI = 1.24–74.77, Pc = 0.279; P = 0.027, OR = 1.62, 95% CI = 1.06–2.5, Pc = 0.081, respectively).

Interpretation

FcγR polymorphisms and haplotypes are not associated with susceptibility to GBS, though the FcγRIIIa‐V158F genotype is associated with the severity of GBS.

Immune Complex-Driven Generation of Human Macrophages with Anti-Inflammatory and Growth-Promoting Activity

To maintain homeostasis, macrophages must be capable of assuming either an inflammatory or an anti-inflammatory phenotype. To better understand the latter, we stimulated human macrophages in vitro with TLR ligands in the presence of high-density immune complexes (IC). This combination of stimuli resulted in a broad suppression of inflammatory mediators and an upregulation of molecules involved in tissue remodeling and angiogenesis. Transcriptomic analysis of TLR stimulation in the presence of IC predicted the downstream activation of AKT and the inhibition of GSK3. Consequently, we pretreated LPS-stimulated human macrophages with small molecule inhibitors of GSK3 to partially phenocopy the regulatory effects of stimulation in the presence of IC. The upregulation of DC-STAMP and matrix metalloproteases was observed on these cells and may represent potential biomarkers for this regulatory activation state. To demonstrate the presence of these anti-inflammatory, growth-promoting macrophages in a human infectious disease, biopsies from patients with leprosy (Hanseniasis) were analyzed. The lepromatous form of this disease is characterized by hypergammaglobulinemia and defective cell-mediated immunity. Lesions in lepromatous leprosy contained macrophages with a regulatory phenotype expressing higher levels of DC-STAMP and lower levels of IL-12, relative to macrophages in tuberculoid leprosy lesions. Therefore, we propose that increased signaling by FcγR cross-linking on TLR-stimulated macrophages can paradoxically promote the resolution of inflammation and initiate processes critical to tissue growth and repair. It can also contribute to infectious disease progression.

Different clinical characteristics of longitudinally extensive transverse myelitis with and without connective tissue disorders: a single-center retrospective study

BACKGROUND AND OBJECTIVE

Autoimmune longitudinal extensive transverse myelitis (LETM) is often combined with connective tissue disorders (CTD). The purpose of this study was to compare the clinical characteristics of autoimmune LETM with and without CTD.

METHODS

Ninety-two patients diagnosed with autoimmune LETM were enrolled from our clinical database and divided into two groups depending on whether they had a concomitant diagnosis of CTD. Differences in clinical, serological, and imaging characteristics between the two groups were evaluated and compared.

RESULTS

Fifty-nine LETM patients without CTD and 33 LETM patients with CTD were included. LETM patients with CTD had higher Kurtzke Expanded Disability Status Scale at nadir and more severe sensory dysfunction (p < 0.05) than those without CTD. It was also found that LETM patients with CTD, compared with those without CTD, had elevated levels of immune inflammation markers such as IgG, IgA, and globulins (p < 0.05). These abovementioned characteristics were more prominent in patients with aquaporin-4 antibodies (AQP4-ab) than in those without them. In addition, the most common type of CTD in LETM was Sjögren syndrome (SS), which was usually diagnosed at the time of LETM or later.

CONCLUSION

LETM patients with CTD, especially those with AQP4-ab, had greater sensory dysfunction and higher levels of inflammatory markers than did LETM patients without CTD. Multicenter cooperation and long-term follow-up are necessary to further study the inherent implications and prognosis of the disease.

Identification of differentially expressed circulating exosomal lncRNAs in IgA nephropathy patients

Background

Although immunoglobulin A nephropathy (IgAN) is one of the foremost primary glomerular disease, treatment of IgAN is still in infancy. Non-invasive biomarkers are urgently needed for IgAN diagnosis. We investigate the difference in expression profiles of exosomal long non-coding-RNAs (lncRNAs) in plasma from IgAN patients compared with their healthy first-degree relatives, which may reveal novel non-invasive IgAN biomarkers.

Methods

We isolated exosomes from the plasma of both IgAN patients and their healthy first-degree relatives. High-throughput RNA sequencing and real-time quantitative polymerase chain reaction (qRT-PCR) was used to validate lncRNA expression profiles. Pathway enrichment analysis was used to predict their nearest protein-coding genes.

Results

lncRNA-G21551 was significantly down-regulated in IgAN patients. Interestingly, the nearest protein-coding gene of lncRNA-G21551 was found to be encoding the low affinity receptor of the Fc segment of immunoglobulin G (FCGR3B).

Conclusions

Exosomal lncRNA-G21551, with FCGR3B as the nearest protein-coding gene, was down-regulated in IgAN patients, indicating its potential to serve as a non-invasive biomarker for IgAN.

Immune surveillance for vaccine-preventable diseases

INTRODUCTION

Immunesurveillance is an important tool to monitor the protection of the population against vaccine-preventable diseases, which is currently mostly based on the detection of specific serum antibodies. However, the landscape of immune surveillance is changing, driven by emerging and evolving pathogens, changes in the age distribution of the population and scientific understanding of protective immunity, necessitating a comprehensive review.

AREAS COVERED

To anticipate these changes, reliable and high-throughput detection of antibody levels is desired to enable screening in larger population settings. Antibody levels alone do not always equate with protection and may require additional functional testing of the antibodies or immune cell-based assays. In addition, the location (systemic or locally mucosal) of the infection and whether the antibodies are induced through infection or vaccination have implications for both immune protection and assessing immune status.

EXPERT COMMENTARY

In order to perform multicenter studies on many samples for multiple antigens, more validated reference materials and wider adoption of high-throughput techniques are needed. The field of serosurveillance will also benefit from better correlates of protection and understanding of (local) mechanisms of protection. Here we give an overview of the current state-of-the-art of serosurveillance and how the field could move forward.

The Diverse Functions of the Ubiquitous Fcγ Receptors and Their Unique Constituent, FcRγ Subunit

Fc gamma receptors (FcγRs) are widely expressed on a variety of immune cells and play a myriad of regulatory roles in the immune system because of their structural diversity. Apart from their indispensable role in specific binding to the Fc portion of antibody subsets, FcγRs manifest diverse biological functions upon binding to their putative ligands. Examples of such manifestation include phagocytosis, presentation of antigens, mediation of antibody-dependent cellular cytotoxicity, anaphylactic reactions, and the promotion of apoptosis of T cells and natural killer cells. Functionally, the equilibrium between activating and inhibiting FcγR maintains the balance between afferent and efferent immunity. The γ subunit of the immunoglobulin Fc receptor (FcRγ) is a key component of discrete immune receptors and Fc receptors including the FcγR family. Furthermore, FcγRs exert a key role in terms of crosslinking the innate and adaptive workhorses of immunity. Ablation of one of these receptors might positively or negatively influence the immune response. Very recently, we discovered that FcRγ derived from natural cytotoxicity triggering receptor 1 (NCR1) curtails CD8⁺ T cell expansion and thereby turns an acute viral infection into a chronic one. Such a finding opens a new avenue for targeting the FcγRs as one of the therapeutic regimens to boost the immune response. This review highlights the structural heterogeneity and functional diversity of the ubiquitous FcγRs along with their featured subunit, FcRγ.

Serum IgA Fc effector functions in infectious disease and cancer

Immunoglobulin (Ig) A is the most abundant antibody isotype present at mucosal surfaces and the second most abundant in human serum. In addition to preventing pathogen entry at mucosal surfaces, IgA can control and eradicate bacterial and viral infections through a variety of antibody‐mediated innate effector cell mechanisms. The role of mucosal IgA in infection (e.g. neutralization) and in inflammatory homeostasis (e.g. allergy and autoimmunity) has been extensively investigated; by contrast, serum IgA is comparatively understudied. IgA binding to fragment crystallizable alpha receptor plays a dual role in the activation and inhibition of innate effector cell functions. Mounting evidence suggests that serum IgA induces potent effector functions against various bacterial and some viral infections including Neisseria meningitidis and rotavirus. Furthermore, in the era of immunotherapy, serum IgA provides an interesting alternative to classical IgG monoclonal antibodies to treat cancer and infectious pathogens. Here we discuss the role of serum IgA in infectious diseases with reference to bacterial and viral infections and the potential for IgA as a monoclonal antibody therapy.

Antibodies to the RNA binding protein heterogeneous nuclear ribonucleoprotein A1 contribute to neuronal cell loss in an animal model of multiple sclerosis

Neurodegeneration, including loss of neurons and axons, is a feature of progressive forms of multiple sclerosis (MS). The mechanisms underlying neurodegeneration are mostly unknown. Research implicates autoimmunity to nonmyelin self-antigens as important contributors to disease pathogenesis. Data from our lab implicate autoimmunity to the RNA binding protein (RBP) heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) as a possible mechanism of neurodegeneration in MS. MS patients make antibodies to hnRNP A1, which have been shown to lead to neuronal dysfunction in vitro. Using an animal model of MS, experimental autoimmune encephalomyelitis (EAE), we show here that injection of anti-hnRNP A1 antibodies, in contrast to control antibodies, resulted in worsened disease and increased neurodegeneration. We found a reduction of NeuN⁺ neuronal cell bodies in areas of the ventral gray matter of the spinal cord where anti-hnRNP A1 antibodies localized. Neurons displayed increased levels of hnRNP A1 nucleocytoplasmic mislocalization and stress granule formation, both markers of neuronal injury. Anti-hnRNP A1 antibodies were found to surround neuronal cell bodies and interact with CD68⁺ immune cells via Fc receptors. Additionally, anti-hnRNP A1 antibodies were found within neuronal cell bodies including those of the ventral spinocerebellar tract (VSCT), a tract previously shown to undergo neurodegeneration in anti-hnRNP A1 antibody injected EAE mice. Finally, both immune cells and neurons showed increased levels of inducible nitric oxide synthase, another indicator of cell damage. These findings suggest that autoimmunity to RBPs, such as hnRNP A1, play a role in neurodegeneration in EAE with important implications for the pathogenesis of MS.

Contribution of Fcγ receptor IIB to creating a suppressive tumor microenvironment in a mouse model

Various immune cells are recruited in the tumor microenvironment. It is well established that cellular immune responses, such as cytotoxic or suppressive activities, play an important role in regulating tumor growth and metastasis. However, the contribution of humoral immune responses against tumors is poorly understood. Fc receptors constitute critical elements for the up- or downregulation of immune responses through immune complexes. Here, we examined the potential role of the inhibitory Fc receptor, Fcγ receptor IIB (FcγRIIB), in tumor immunity using a mouse model. Our findings indicated that tumor-specific antibodies are induced in tumor-bearing mice and control tumor immunity. FcγRIIB deletion significantly improved both cellular and humoral immunity against tumors and delayed tumor growth. These findings indicated that spontaneous antibodies against tumors create a suppressive tumor microenvironment through FcγRIIB signaling, thus suggesting an attractive therapeutic target for cancer immunotherapy.

111In-labeled anti-cadherin17 antibody D2101 has potential as a noninvasive imaging probe for diagnosing gastric cancer and lymph-node metastasis

OBJECTIVE

Cadherin-17 (CDH17) is a transmembrane protein that mediates cell-cell adhesion and is frequently expressed in adenocarcinomas, including gastric cancer. CDH17 may be an effective diagnostic marker for the staging of gastric cancer. Here, we developed an ¹¹¹In-labeled anti-CDH17 monoclonal antibody (Mab) as an imaging tracer and performed biodistribution and single-photon emission computed tomography (SPECT)/computed tomography (CT) imaging studies using mice with CDH17-positive gastric cancer xenografts. CDH17 expression in gastric cancer specimens was also analyzed.

METHODS

The cross-reactivity and affinity of our anti-CDH17 Mab D2101 was evaluated by surface plasmon resonance analysis and cell enzyme-linked immunosorbent assay, respectively. Biodistribution and SPECT/CT studies of ¹¹¹In-labeled D2101 (¹¹¹In-D2101) were performed. CDH17 expression in gastric cancer specimens was evaluated by immunohistochemistry.

RESULTS

Surface plasmon resonance analysis revealed that D2101 specifically recognizes human CDH17, but not murine CDH17. The affinity of D2101 slightly decreased as a result of the radiolabeling procedures. The biodistribution study revealed high uptake of ¹¹¹In-D2101 in tumors (maximum, 39.2 ± 9.5% ID/g at 96 h postinjection), but low uptake in normal organs, including the stomach. Temporal SPECT/CT imaging with ¹¹¹In-D2101 visualized tumors with a high degree of tumor-to-nontumor contrast. Immunohistochemical analysis revealed that, compared with HER2, which is a potential marker of N-stage, CDH17 had a higher frequency of positivity in specimens of primary and metastatic gastric cancer.

CONCLUSION

Our ¹¹¹In-anti-CDH17 Mab D2101 depicted CDH17-positive gastric cancer xenografts in vivo and has the potential to be an imaging probe for the diagnosis of primary lesions and lymph-node metastasis in gastric cancer.

FcgRIII Deficiency and FcgRIIb Defeciency Promote Renal Injury in Diabetic Mice

The immune system is involved in the development of diabetes complications and IgG Fc gamma receptors (FcgRs) are key immune receptors responsible for the effective control of both humoral and innate immunity. We investigated the effects of members of the FcgR superfamily into both the streptozotocin plus high fat-induced type 2 diabetes and high fat diet (HFD) models. FcgRIII^-/- diabetic mice and FcgRIIb^-/- diabetic mice had elevated levels of serum creatinine compared with wildtype (WT) diabetic mice. Renal histology of diabetic FcgRIII knockout and FcgRIIb knockout mice showed mesangial expansion and GBM thickening; the mechanistic study indicated a higher expression of TGF-β1, TNF-α, and p-NFκB-p65 compared with wild type mouse. The HFD mouse with FcgRIII knockout or FcgRIIb knockout had increased biochemical and renal injury factors, but oxLDL deposition was higher than in FcgRIII^-/- diabetic mice and FcgRIIb^-/- diabetic mice. In vitro we further examined the mechanism by which the Fc gamma receptor promoted renal injury and transfected glomerular mesangial cells (GMCs) with FcgRI siRNA attenuated the level of TGF-β1, TNF-α expression. In summary, FcgRI knockdown downregulated kidney inflammation and fibrosis and FcgRIIb knockout accelerated inflammation, fibrosis, and the anomalous deposition of oxLDL whereas FcgRIII deficiency failed to protect kidney from diabetic renal injury. These observations suggested that FcgRs might represent a novel target for the therapeutic intervention of diabetic nephropathy.

Proinflammatory Differentiation of Macrophages Through Microparticles That Form Immune Complexes Leads to T- and B-Cell Activation in Systemic Autoimmune Diseases

Patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) demonstrate increased circulating microparticles (MP). These vesicles, primarily those that form immune complexes (MP-IC), may activate monocytes. We evaluated the effect of MP and MP-IC in the differentiation of monocytes to macrophages (monocyte-derived macrophages; MDM) and for consequences in autologous lymphocyte activation. Monocytes from healthy controls (HC) and patients with RA and SLE that differentiated into MDM in the presence of MP-IC showed a proinflammatory (M1-like) profile, which was more evident using MP-IC from patients with RA than those from patients with SLE. Notably, MDM from HC and patients with RA that differentiated with MP-IC were more prone to M1-like profile than those from patients with SLE. In HC and patients with RA, monocyte differentiation using MP-IC decreased the frequency of MDM that bound/internalized latex beads. The M1-like profile did not completely revert following IL-4 treatment. The effect of M1-like MDM on T lymphocytes stimulated with phytohemagglutinin was further evaluated. MDM differentiated with MP enhanced the proliferation of T cells obtained from patients with RA compared with those differentiated with MP-IC or without vesicles. Neither MP nor MP-IC induced interferon (IFN)-γ+ and tumor necrosis factor (TNF)-α+ T cells in patients with RA. Conversely, unlike MDM differentiated with or without MP, MP-IC enhanced the proliferation and increased the frequencies of IFN-γ+CD4+ T, TNF-α+CD4+ T, and IFN-γ+CD8+ T cells in patients with SLE. The co-culture of B cells with MDM obtained from patients with RA and SLE and differentiated with MP-IC increased the expression of B-cell activation markers and prevented B lymphocyte death. Strikingly, only for patients with SLE, these responses seemed to be associated with a significant increase in B-cell activating factor levels, high plasmablast frequency and immunoglobulin production. These results showed that MP-IC from patients with systemic autoimmune diseases favored the polarization of MDM into a proinflammatory profile that promotes T-cell activation, and additionally induced B-cell activation and survival. Therefore, the effect of MP-IC in mononuclear phagocytes may be an important factor for modulating adaptive responses in systemic autoimmune diseases.

Elimination of activating Fcγ receptors in spontaneous autoimmune peripheral polyneuropathy model protects from neuropathic disease

Spontaneous autoimmune peripheral polyneuropathy (SAPP) is a reproducible mouse model of chronic inflammatory peripheral neuropathy in female non-obese diabetic mice deficient in co-stimulatory molecule, B7-2 (also known as CD86). There is evidence that SAPP is an interferon-γ, CD4+ T-cell-mediated disorder, with autoreactive T-cells and autoantibodies directed against myelin protein zero involved in its immunopathogenesis. Precise mechanisms leading to peripheral nerve system inflammation and nerve injury including demyelination in this model are not well defined. We examined the role of activating Fc-gamma receptors (FcγRs) by genetically ablating Fcγ-common chain (Fcer1g) shared by all activating FcγRs in the pathogenesis of this model. We have generated B7-2/ Fcer1g-double null animals for these studies and found that the neuropathic disease is substantially ameliorated in these animals as assessed by behavior, electrophysiology, immunocytochemistry, and morphometry. Our current studies focused on characterizing systemic and endoneurial inflammation in B7-2-null and B7-2/ Fcer1g-double nulls. We found that accumulation of endoneurial inflammatory cells was significantly attenuated in B7-2/ Fcer1g-double nulls compared to B7-2-single nulls. Whereas, systemically the frequency of CD4+ regulatory T cells and expression of immunosuppressive cytokine, IL-10, were significantly enhanced in B7-2/ Fcer1g-double nulls. Overall, these findings suggest that elimination of activating FcγRs modulate nerve injury by altering endoneurial and systemic inflammation. These observations raise the possibility of targeting activating FcγRs as a treatment strategy in acquired inflammatory demyelinating neuropathies.

Unique-region phosphorylation targets LynA for rapid degradation, tuning its expression and signaling in myeloid cells

The activity of Src-family kinases (SFKs), which phosphorylate immunoreceptor tyrosine-based activation motifs (ITAMs), is a critical factor regulating myeloid-cell activation. We reported previously that the SFK LynA is uniquely susceptible to rapid ubiquitin-mediated degradation in macrophages, functioning as a rheostat regulating signaling (Freedman et al., 2015). We now report the mechanism by which LynA is preferentially targeted for degradation and how cell specificity is built into the LynA rheostat. Using genetic, biochemical, and quantitative phosphopeptide analyses, we found that the E3 ubiquitin ligase c-Cbl preferentially targets LynA via a phosphorylated tyrosine (Y32) in its unique region. This distinct mode of c-Cbl recognition depresses steady-state expression of LynA in macrophages derived from mice. Mast cells, however, express little c-Cbl and have correspondingly high LynA. Upon activation, mast-cell LynA is not rapidly degraded, and SFK-mediated signaling is amplified relative to macrophages. Cell-specific c-Cbl expression thus builds cell specificity into the LynA checkpoint.

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.

[Cryoglobulinemic vasculitis in chronic hepatitis C: Genetic aspects]

Cryoglobulinemia (CG) is detected in more than 50% of patients with chronic hepatitis C (CHC); however, only 15-25% of them develop cryoglobulinemic vasculitis (CV) that is a systemic vasculitis due to the formation of immune deposits, which affects small (less than medium-sized) vessels and which is frequently fatal for the patient. The causes of CG only in some patients with CHC and the pathogenesis of CV remain unstudied; however, the accumulated data allow one to identify the special contribution of the patient's genetic factors to the development of the disease. The paper considers the genetic aspects of the development of CG and CV in CHC.

Improvement in dysmyelination by the inhibition of microglial activation in a mouse model of Sandhoff disease

Sandhoff disease (SD) is a genetic disorder caused by a mutation of the β-subunit gene β-hexosaminidase B (HexB) in humans, which results in the massive accumulation of the ganglioside GM2 and related glycosphingolipids in the nervous system. SD causes progressive neurodegeneration and changes in white matter in human infants. An animal model of SD has been established, Hexb-deficient (Hexb) mice, which shows abnormalities resembling the severe phenotype found in human infants. Previously, we reported that the activation state of microglia caused astrogliosis in the early stage of Hexb mouse development. To study how the symptoms of SD develop, we explored the difference in gene expression between 4-week-old Hexb and Hexb mouse cerebral cortices by microarray analysis. The data indicated not only the upregulation of immune system-related genes but also the downregulation of myelin-related genes in the 4-week-old Hexb mouse cerebral cortices. To test the correlation between inflammation and dysmyelination, we generated double-knockout mice of Hexb and the Fc receptor γ gene (Fcrγ), which is a regulator of autoimmune responses. Dysmyelination recovered in these double-knockout mice. The number of oligodendrocyte progenitors, which expressed platelet-derived growth factor receptor-α, did not change in the 2-week-old mouse brain. These results indicate that microglial activation plays an important role in the myelination process, without influencing the number of oligodendrocyte progenitors, in the development of Hexb mice.

Sweet SIGNs: IgG glycosylation leads the way in IVIG-mediated resolution of inflammation

A hallmark of many chronic inflammatory and autoimmune diseases is that there is an impaired resolution of inflammation and return to the steady state. The infusion of high doses of pooled serum IgG preparations from thousands of donors [intravenous immunoglobulin (IVIG) therapy] has been shown to induce resolution of inflammation in a variety of chronic inflammatory and autoimmune diseases, suggesting that IgG molecules can instruct the immune system to stop inflammatory processes and initiate the return to the steady state. The aim of this review is to discuss how insights into the mechanism of IVIG activity may help to understand the molecular and cellular pathways underlying resolution of inflammation. We will put a special emphasis on pathways dependent on the IgG FC domain and IgG sialylation, as several recent studies have provided new insights into how this glycosylation-dependent pathway modulates innate and adaptive immune responses through different sets of C-type or I-type lectins.

Fully galactosyl-fucosyl-bisected IgG1 reduces anti-HBV efficacy and liver histological improvement

N-glycosylation on the crystallizable fragment (Fc) governs antibody-mediated immune responses. This study addressed the relevance of N-acetylglucosamine (GlcNAc)-bisected IgG₁ on the disease progression and treatment efficacy in the immune active phase of chronic hepatitis B virus (HBV) infection. Serum IgG₁N-glycan patterns from 166 HBV e antigen (HBeAg)-positive patients were analyzed using liquid chromatography-tandem mass spectrometry. The proportion of GlcNAc-bisected IgG₁ on the disease severity and efficacy of nucleos(t)ide analogue treatment were investigated. Cytokine-dependent regulations of IgG₁ GlcNAc bisection were also addressed using mouse IgG₁-producing hybridoma cells. We found that IgG₁ bearing a fully galactosyl-fucosyl-N-acetylglucosamine-bisected (G2FN) glycoform in HBeAg-positive patients was associated with high levels of HBV DNA or HBV surface antigen, alanine aminotransferase <2 upper limits of normal, and a mild liver injury. Moreover, baseline IgG₁-G2FN ≧ 1.5% was linked to lower probabilities of virological response (HBV DNA undetectable in serum), HBeAg seroconversion, HBV core antigen loss, and liver histological improvement after treatment. Cox and logistic regression analyses revealed that IgG₁-G2FN was an unfavorable factor for the virological response (hazard ratio = 0.620, 95% confidence interval = 0.466-0.825, P = 0.001) or liver histological improvement (odds ratio = 0.513, 95% confidence interval = 0.279-0.943, P = 0.032), respectively. Results from in vitro studies showed that transforming growth factor (TGF)-β1 treatment downregulated mannosyl β-1,4-N-acetylglucosaminyltransferase 3 and β-1,4-galactosyltransferase 1 activities and thereby IgG₁-G2FN production, and this phenomenon reflected an inverse correlation between IgG₁-G2FN and TGF-β1 in sera of patients (r = -0.431, P < 0.001). In conclusion, IgG₁-G2FN was related to an attenuated liver inflammation and unfavorable treatment responses in patients with HBeAg-positive chronic hepatitis B.

CD32 Ligation Promotes the Activation of CD4+ T Cells

Low affinity receptors for the Fc portion of IgG (FcγRs) represent a critical link between innate and adaptive immunity. Immune complexes (ICs) are the natural ligands for low affinity FcγRs, and high levels of ICs are usually detected in both, chronic viral infections and autoimmune diseases. The expression and function of FcγRs in myeloid cells, NK cells and B cells have been well characterized. By contrast, there are controversial reports about the expression and function of FcγRs in T cells. Here, we demonstrated that ~2% of resting CD4+ T cells express cell surface FcγRII (CD32). Analysis of CD32 expression in permeabilized cells revealed an increased proportion of CD4+CD32+ T cells (~9%), indicating that CD4+ T cells store a CD32 cytoplasmic pool. Activation of CD4+ T cells markedly increased the expression of CD32 either at the cell surface or intracellularly. Analysis of CD32 mRNA transcripts in activated CD4+ T cells revealed the presence of both, the stimulatory FcγRIIa (CD32a) and the inhibitory FcγRIIb (CD32b) isoforms of CD32, being the CD32a:CD32b mRNA ratio ~5:1. Consistent with this finding, we found not only that CD4+ T cells bind aggregated IgG, used as an IC model, but also that CD32 ligation by specific mAb induced a strong calcium transient in CD4+ T cells. Moreover, we found that pretreatment of CD4+ T cells with immobilized IgG as well as cross-linking of CD32 by specific antibodies increased both, the proliferative response of CD4+ T cells and the release of a wide pattern of cytokines (IL-2, IL-5, IL-10, IL-17, IFN-γ, and TNF-α) triggered by either PHA or anti-CD3 mAb. Collectively, our results indicate that ligation of CD32 promotes the activation of CD4+ T cells. These findings suggest that ICs might contribute to the perpetuation of chronic inflammatory responses by virtue of its ability to directly interact with CD4+ T cells through CD32a, promoting the activation of T cells into different inflammatory profiles.

Lack of ethnic differences in the pharmacokinetics and pharmacodynamics of evolocumab between Caucasian and Asian populations

AIMS

To evaluate the potential ethnic differences in the pharmacokinetics (PK) and pharmacodynamics (PD) of evolocumab in Caucasian and Asian populations using population PK/PD modelling analysis.

METHODS

Data from different ethnic groups in 5 Phase I clinical trials, including two American studies, one Japanese study and two Chinese studies, were chosen for model building and evaluation. A target-mediated drug disposition model together with an indirect response model best captured evolocumab binding and the removal of unbound proprotein convertase subtilisin/kexin type 9 (PCSK9) as well as a reduction in circulating low-density lipoprotein cholesterol (LDL-C). Ethnicity and other related factors (body weight, target expression level etc.) were analysed as potential covariates.

RESULTS

The estimated linear clearance and volume of evolocumab were 0.24 l day^-1 and 2.75 l, respectively, which was consistent with the previous modelling results from the American trials. The time course of the LDL-C reduction was described by an indirect response model with the elimination rate of LDL-C being modulated by unbound PCSK9. The concentration of unbound PCSK9 associated with the half-maximal inhibition of LDL-C elimination was 1.28 nmol l^-1 . Both the PK and PD characteristics were consistent between the Caucasian and Asian populations.

CONCLUSION

The target-mediated drug disposition model successfully described the PK and PD characteristics of evolocumab, and this analysis found no significant differences in the PK/PD relationship for its LDL-C lowering effects between Caucasians and Asians.

Fc gamma receptor IIa suppresses type I and III interferon production by human myeloid immune cells

Type I and type III interferons (IFNs) are fundamental for antiviral immunity, but prolonged expression is also detrimental to the host. Therefore, upon viral infection high levels of type I and III IFNs are followed by a strong and rapid decline. However, the mechanisms responsible for this suppression are still largely unknown. Here, we show that IgG opsonization of model viruses influenza and respiratory syncytial virus (RSV) strongly and selectively suppressed type I and III IFN production by various human antigen-presenting cells. This suppression was induced by selective inhibition of TLR, RIG-I-like receptor, and STING-dependent type I and III IFN gene transcription. Surprisingly, type I and III IFN suppression was mediated by Syk and PI3K independent inhibitory signaling via FcγRIIa, thereby identifying a novel non-canonical FcγRIIa pathway in myeloid cells. Together, these results indicate that IgG opsonization of viruses functions as a novel negative feedback mechanism in humans, which may play a role in the selective suppression of type I and III IFN responses during the late-phase of viral infections. In addition, activation of this pathway may be used as a tool to limit type I IFN-associated pathology.

Leukocyte Immunoglobulin-Like Receptors A2 and A6 are Expressed in Avian Macrophages and Modulate Cytokine Production by Activating Multiple Signaling Pathways

The activating leukocyte immunoglobulin-like receptors (LILRAs) play an important role in innate immunity. However, most of the LILRA members have not been characterized in avian species including chickens. The present study is the first attempt at cloning, structural analysis and functional characterization of two LILRAs (LILRA2 and LILRA6) in chickens. Multiple sequence alignments and construction of a phylogenetic tree of chicken LILRA2 and LILRA6 with mammalian proteins revealed high conservation between chicken LILRA2 and LILRA6 and a close relationship between the chicken and mammalian proteins. The mRNA expression of LILRA2 and LILRA6 was high in chicken HD11 macrophages and the small intestine compared to that in several other tissues and cells tested. To examine the function of LILRA2 and LILRA6 in chicken immunity, LILRA2 and LILRA6 were transfected into HD11 cells. Our findings indicated that LILRA2 and LILRA6 are associated with the phosphorylation of Src kinases and SHP2, which play a regulatory role in immune functions. Moreover, LILRA6 associated with and activated MHC class I, β2-microglobulin and induced the expression of transporters associated with antigen processing but LILRA2 did not. Furthermore, both LILRA2 and LILRA6 activated JAK-STAT, NF-κB, PI3K/AKT and ERK1/2 MAPK signaling pathways and induced Th1-, Th2- and Th17-type cytokines and Toll-like receptors. Collectively, this study indicates that LILRA2 and LILRA6 are essential for macrophage-mediated immune responses and they have the potential to complement the innate and adaptive immune system against pathogens.

The protein tyrosine phosphatase PTPN22 negatively regulates presentation of immune complex derived antigens

A C1858T single nucleotide polymorphism within PTPN22 (which encodes PTPN22^R620W) is associated with an enhanced susceptibility to multiple autoimmune diseases including type 1 diabetes and rheumatoid arthritis. Many of the associated autoimmune diseases have an autoantibody component to their pathology. Fc receptors (FcRs) recognise autoantibodies when they bind to autoantigens and form immune complexes. After immune complex binding and receptor crosslinking, FcRs signal via Src and Syk family kinases, leading to antigen uptake, presentation and cytokine secretion. Ptpn22 encodes a protein tyrosine phosphatase that negatively regulates Src and Syk family kinases proximal to immunoreceptor signalling cascades. We therefore hypothesised that PTPN22 regulates immune complex stimulated FcR responses in dendritic cells (DCs). Bone marrow derived DCs (BMDCs) from wild type (WT) or Ptpn22^-/- mice were pulsed with ovalbumin:anti-ovalbumin immune complexes (ova ICs). Co-culture with WT OT-II T cells revealed that ova IC pulsed Ptpn22^-/- BMDCs have an enhanced capability to induce T cell proliferation. This was associated with an increased capability of Ptpn22^-/- BMDCs to present immune complex derived antigens and to form ova IC dependent DC-T cell conjugates. These findings highlight PTPN22 as a regulator of FcR mediated responses and provide a link between the association of PTPN22^R620W with autoantibody associated autoimmune diseases.

Aristolochic acid I determine the phenotype and activation of macrophages in acute and chronic kidney disease

Acute and chronic kidney injuries are multifactorial traits that involve various risk factors. Experimental animal models are crucial to unravel important aspects of injury and its pathophysiological mechanisms. Translating knowledge obtained from experimental approaches into clinically useful information is difficult; therefore, significant attention needs to be paid to experimental procedures that mimic human disease. Herein, we compared aristolochic acid I (AAI) acute and chronic kidney injury model with unilateral ischemic-reperfusion injury (uIRI), cisplatin (CP)- or folic acid (FA)-induced renal damage. The administration of AAI showed significant changes in serum creatinine and BUN upon CKD. The number of neutrophils and macrophages were highly increased as well as AAI-induced CKD characterized by loss of tubular epithelial cells and fibrosis. The in vitro and in vivo data indicated that macrophages play an important role in the pathogenesis of AA-induced nephropathy (AAN) associated with an excessive macrophage accumulation and an alternative activated macrophage phenotype. Taken together, we conclude that AA-induced injury represents a suitable and relatively easy model to induce acute and chronic kidney injury. Moreover, our data indicate that this model is appropriate and superior to study detailed questions associated with renal macrophage phenotypes.

The promise and challenges of immune agonist antibody development in cancer

Immune cell functions are regulated by co-inhibitory and co-stimulatory receptors. The first two generations of cancer immunotherapy agents consist primarily of antagonist antibodies that block negative immune checkpoints, such as programmed cell death protein 1 (PD1) and cytotoxic T lymphocyte protein 4 (CTLA4). Looking ahead, there is substantial promise in targeting co-stimulatory receptors with agonist antibodies, and a growing number of these agents are making their way through various stages of development. This Review discusses the key considerations and potential pitfalls of immune agonist antibody design and development, their differentiating features from antagonist antibodies and the landscape of agonist antibodies in clinical development for cancer treatment.

Polymorphisms of immunoglobulin receptors and the effects on clinical outcome in cancer immunotherapy and other immune diseases: a general review

Receptors for the Fc domain of immunoglobulins [Fc receptors (FcRs)] are essential for the maintenance of antibody-mediated immune responses. FcRs consist of activating- and inhibitory-type receptors that regulate adequate thresholds for various immune cells. In particular, polymorphisms and/or gene copy-number variations of FcRs for IgG (FcγRs) are closely associated with the development of inflammatory disorders, including autoimmune diseases. Recent evidence has implicated polymorphisms of FcRs in the efficacy of monoclonal antibody (mAb)-mediated therapy. This review provides an overview of genetic variations in human FcγRs and the clinical contribution of FcγR polymorphisms in mAb treatments for cancer, autoimmune diseases and allergies.

Soluble fibrinogen like protein 2 (sFGL2), the novel effector molecule for immunoregulation

Soluble fibrinogen-like protein 2 (sFGL2) is the soluble form of fibrinogen-like protein 2 belonging to the fibrinogen-related protein superfamily. It is now well characterized that sFGL2 is mainly secreted by regulatory T cell (Treg) populations, and exerts potently immunosuppressive activities. By repressing not only the differentiation and proliferation of T cells but also the maturation of dendritic cells (DCs), sFGL2 acts largely as an immunosuppressant. Moreover, sFGL2 also induces apoptosis of B cells, tubular epithelial cells (TECs), sinusoidal endothelial cells (SECs), and hepatocytes. This mini-review focuses primarily on the recent literature with respect to the signaling mechanism of sFGL2 in immunomodulation, and discusses the clinical implications of sFGL2 in transplantation, hepatitis, autoimmunity, and tumors.

Comprehensive proteome analysis of lysosomes reveals the diverse function of macrophages in immune responses

Phagocytosis and autophagy in macrophages have been shown to be essential to both innate and adaptive immunity. Lysosomes are the main catabolic subcellular organelles responsible for degradation and recycling of both extracellular and intracellular material, which are the final steps in phagocytosis and autophagy. However, the molecular mechanisms underlying lysosomal functions after infection remain obscure. In this study, we conducted a quantitative proteomics analysis of the changes in constitution and glycosylation of proteins in lysosomes derived from murine RAW 264.7 macrophage cells treated with different types of pathogens comprising examples of bacteria (Listeria monocytogenes, L. m), DNA viruses (herpes simplex virus type-1, HSV-1) and RNA viruses (vesicular stomatitis virus, VSV). In total, 3,704 lysosome-related proteins and 300 potential glycosylation sites on 193 proteins were identified. Comparative analysis showed that the aforementioned pathogens induced distinct alterations in the proteome of the lysosome, which is closely associated with the immune functions of macrophages, such as toll-like receptor activation, inflammation and antigen-presentation. The most significant changes in proteins and fluctuations in glycosylation were also determined. Furthermore, Western blot analysis showed that the changes in expression of these proteins were undetectable at the whole cell level. Thus, our study provides unique insights into the function of lysosomes in macrophage activation and immune responses.

Potential Involvement of Platelet-Derived Microparticles and Microparticles Forming Immune Complexes during Monocyte Activation in Patients with Systemic Lupus Erythematosus

Microparticles (MPs) are vesicles derived from the plasma membrane of different cells, are considered a source of circulating autoantigens, and can form immune complexes (MPs-ICs). The number of MPs and MPs-ICs increases in patients with systemic lupus erythematosus (SLE). MPs activate myeloid cells by inducing IL-6 and TNF-α in both SLE and other diseases. Therefore, we propose that the recognition of MPs-ICs by monocytes rather that MPs may define their phenotype and contribute to the inflammatory process in patients with SLE. Thus, the aims of this study were to evaluate the association among circulating MPs-ICs from different cell sources, alterations observed in monocyte subsets, and disease activity in patients with SLE and to establish whether monocytes bind and respond to MPs-ICs in vitro. Circulating MPs and monocyte subsets were characterized in 60 patients with SLE and 60 healthy controls (HCs) using multiparametric flow cytometry. Patients had higher MP counts and frequencies of MPs-CD41a + (platelet-derived) compared with HCs, regardless of disease activity. MPs from patients with SLE were C1q + and formed ICs with IgM and IgG. MPs-IgG + were positively correlated with active SLE (aSLE), whereas MPs-IgM + were negatively correlated. Most of the circulating total ICs-IgG + were located on MPs. The proportion and number of non-classical monocytes were significantly decreased in patients with SLE compared with HCs and in patients with aSLE compared with patients with the inactive disease. Non-classical monocytes obtained from patients with SLE exhibited increased levels of CD64 associated with MPs-IgG +, MPs-C1q +, total circulating ICs-IgG +, and disease activity. The direct effects of MPs and MPs-IgG + on monocytes were evaluated in cell culture. Monocytes from both HCs and patients bound to and internalized MPs and MPs-IgG + independent of CD64. These vesicles derived from platelets (PMPs), mainly PMPs-IgG +, activated monocytes in vitro and increased the expression of CD69, CD64, and pro-inflammatory cytokines such as IL-1β, TNF-α, and IFN-α. Therefore, MPs are one of the most representative sources of the total amount of circulating ICs-IgG + in patients with SLE. MPs-IgG + are associated with SLE activity, and PMPs-IgG + stimulate monocytes, changing their phenotype and promoting pro-inflammatory responses related to disease activity.

The Potential Role of Trained Immunity in Autoimmune and Autoinflammatory Disorders

During induction of trained immunity, monocytes and macrophages undergo a functional and transcriptional reprogramming toward increased activation. Important rewiring of cellular metabolism of the myeloid cells takes place during induction of trained immunity, including a shift toward glycolysis induced through the mTOR pathway, as well as glutaminolysis and cholesterol synthesis. Subsequently, this leads to modulation of the function of epigenetic enzymes, resulting in important changes in chromatin architecture that enables increased gene transcription. However, in addition to the beneficial effects of trained immunity as a host defense mechanism, we hypothesize that trained immunity also plays a deleterious role in the induction and/or maintenance of autoimmune and autoinflammatory diseases if inappropriately activated.

Anti-CD11b antibody treatment suppresses the osteoclast generation, inflammatory cell infiltration, and autoantibody production in arthritis-prone FcγRIIB-deficient mice

BACKGROUND

Previously we established an arthritis-prone FcγRIIB-deficient mouse strain (designated KO1). Anti-mouse CD11b mAb (5C6) has been reported to inhibit the recruitment of peripheral CD11b⁺ myelomonocytic cells from the blood to the inflammatory site. These cells include neutrophils and monocytes, both of which play important roles in the development of arthritis. Here we treated KO1 mice with 5C6 mAb in order to study its effect on arthritis development.

METHODS

To evaluate the disease-preventive effect of 5C6, 4-month-old preclinical KO1 mice were divided into three groups: the first treated with 5C6 for 6 months, the second treated with normal rat IgG for 6 months, as a control, and the third left untreated. Arthritis severity and immunological abnormalities were compared among the groups, along with transcriptional levels of several important arthritis-related factors in ankle joints, spleen, and peripheral blood cells.

RESULTS

The 5C6 treatment ameliorated arthritis in KO1 mice, showing decreases in inflammatory cell infiltration and osteoclast formation. Analysis of transcriptional levels in ankle joints revealed that compared with the two control groups, the 5C6-treated group showed downregulated expression of RANK, RANKL, MCP-1, RANTES, TNFα, and IL-6, and at the same time showed significantly up-regulated expression of the decoy receptor for RANKL, i.e. osteoprotegerin. In addition, the disease suppression was associated with the lower serum levels of autoantibodies, and the decreased frequencies of activated B cells and plasma cells. The expression levels of B cell activation/differentiation-related cytokines were suppressed in spleen and peripheral leukocytes of the 5C6-treated mice. Intriguingly, while untreated KO1 mice spontaneously developed marked monocytosis, the 5C6-treated mice showed the significantly down-regulated frequency of monocytes.

CONCLUSIONS

The outcome of 5C6 treatment was complex, in which the 5C6-mediated disease-preventive effect is likely due on one hand to the decrease in the recruitment of inflammatory cells and osteoclast precursor monocytes from the periphery into the joints, and on the other hand to the suppression of B cell activation/maturation and of autoantibody production via the suppression of B cell stimulating cytokine production. The lower levels of these cytokines may be the secondary effect of the lower frequency of monocytes, since monocytes/macrophages are the major producers of these cytokines.

Role of Malt1 protease activity in pathogenesis of inflammatory disorders mediated by FcγR signaling

MALT lymphoma-translocation protein 1 (Malt1) protease activity is triggered by stimulation of various immune receptors. Activation of Malt1 protease induces cleavage of negative regulators for immune responses, resulting in lymphocytes activation. Although Malt1 protease mediates the signaling process downstream of the T cell, B cell, and dectin receptors, its contribution in Fcγ receptor (FcγR) signaling has not been elucidated. In this study, we investigated the role of Malt1 protease activity in FcγR signaling using Malt1 protease-deficient (PD) mouse. In addition, role of Malt1 protease for the development of FcγR-mediated autoimmune disease was also investigated in vivo. Malt1 protease cleaves their substrates, such as RelB and cylindromatosis (CYLD). However, the Malt1 proteolytic activity was silenced in the Malt1 PD mice. Production of inflammatory cytokines via FcγR stimulation was decreased on dendritic cells prepared from Malt1 PD mice. In FcγR-dependent murine immune thrombocytopenia (ITP) model, gene expressions of the inflammatory cytokines in the spleen of Malt1 PD mice were lower than those of WT mice. Then, Malt1 PD mice protected the development of thrombocytopenia. These results clearly figured out that Malt1 protease activity plays an important role in the activation of innate immune cells via FcγR, and the development of FcγR-mediated autoimmune diseases. Therefore, Malt1 is an attractive target for the treatment of inflammatory diseases mediated by FcγR.

C5aR activation in the absence of C5a: A new disease mechanism of autoimmune hemolytic anemia in mice

IgG Fc receptors (FcγRs) and the C5a anaphylatoxin receptor (C5aR) were identified as key regulators of type II autoimmune injury in mice. However, and with respect to C5aR, the relative importance of C5a for IgG autoantibody-induced cellular destruction remained unclear. Using an experimental model of autoimmune hemolytic anemia (AIHA), we here report marked differences in the development of AIHA between mice lacking C5aR and C5-deficient (Hc⁰ ) strain, indicating a limited role of C5 in this type of C5aR-regulated disease. Ex-vivo-analyses of liver homogenates from anemic Hc⁰ mice demonstrate C5a-independent C5aR activation, upregulation of FcγR expression and amplification of erythrophagocytosis by macrophages. As assessed by pharmacological inhibition studies, targeting of C5aR, but not of C5, is effective in treating experimental AIHA. Collectively, these results define a previously unrecognized disease mechanism of C5aR activation in AIHA that does not necessarily involve C5 and C5a.

(5R)-5-hydroxytriptolide ameliorates anti-glomerular basement membrane glomerulonephritis in NZW mice by regulating Fcγ receptor signaling

(5R)-5-hydroxytriptolide (LLDT-8) is a novel triptolide analog that has been identified as a promising candidate for treating autoimmune diseases and has been shown to be effective in treating murine collagen-induced arthritis and lupus nephritis. In the present study, we investigated the therapeutic effect and possible mechanism of action of LLDT-8 in a murine anti-glomerular basement membrane (GBM) glomerulonephritis model. NZW mice were injected with rabbit anti-GBM serum (500 μL, ip). The mice were orally treated with LLDT-8 (0.125 mg/kg, every other day) or a positive control prednisolone (2 mg/kg every day) for 14 d. Blood and urine samples as well as spleen and kidney tissues were collected for analyses. LLDT-8 treatment did not affect the generation of mouse anti-rabbit antibodies. LLDT-8 significantly reversed established proteinuria, improved renal histopathology and attenuated renal dysfunction in glomerulonephritis mice. Furthermore, LLDT-8 inhibited inflammation in the kidney evidenced by significantly decreasing C3 and IgG deposition, reducing the levels of the pathogenic cytokines TNF-α, IL-6, IL-17, and IFN-γ, and reducing related chemokine expression and leukocyte infiltration in kidneys. Moreover, LLDT-8 treatment significantly increased the expression of FcγRIIB in the kidney and spleen. In addition, the treatment restored the reduced expression of FcγRIIB on the surface of kidney effector cells, CD11b⁺ cells, and interfered with FcγR-dependent signaling, especially FcγRIIB-mediated downstream kinases, such as BTK. These results demonstrate that LLDT-8 ameliorates anti-GBM glomerulonephritis by regulating the Fcγ receptor signaling.