Association of the Fc gamma receptor IIA-R/R131 genotype with myasthenia gravis in Dutch patients

Cellular and Molecular Pathways of COVID-19 and Potential Points of Therapeutic Intervention

With the objective of linking early findings relating to the novel SARS-CoV-2 coronavirus with potentially informative findings from prior research literature and to promote investigation toward therapeutic response, a coherent cellular and molecular pathway is proposed for COVID-19. The pathway is consistent with a broad range of observed clinical features and biological markers and captures key mediators of pathophysiology. In this proposed pathway, membrane fusion and cytoplasmic entry of SARS-CoV-2 virus via ACE2 and TMPRSS2-expressing respiratory epithelial cells, including pulmonary type-II pneumocytes, provoke an initial immune response featuring inflammatory cytokine production coupled with a weak interferon response, particularly in IFN-λ-dependent epithelial defense. Differentiation of non-classic pathogenic T-cells and pro-inflammatory intermediate monocytes contributes to a skewed inflammatory profile, mediated by membrane-bound immune receptor subtypes (e.g., FcγRIIA) and downstream signaling pathways (e.g., NF-κB p65 and p38 MAPK), followed by chemotactic infiltration of monocyte-derived macrophages and neutrophils into lung tissue. Endothelial barrier degradation and capillary leakage contribute to alveolar cell damage. Inflammatory cytokine release, delayed neutrophil apoptosis, and NETosis contribute to pulmonary thrombosis and cytokine storm. These mechanisms are concordant with observed clinical markers in COVID-19, including high expression of inflammatory cytokines on the TNF-α/IL-6 axis, elevated neutrophil-to-lymphocyte ratio (NLR), diffuse alveolar damage via cell apoptosis in respiratory epithelia and vascular endothelia, elevated lactate dehydrogenase (LDH) and CRP, high production of neutrophil extracellular traps (NETs), depressed platelet count, and thrombosis. Although certain elements are likely to be revised as new findings emerge, the proposed pathway suggests multiple points of investigation for potential therapeutic interventions. Initial candidate interventions include prophylaxis to augment epithelial defense (e.g., AT1 receptor blockade, type III and type I interferons, melatonin, calcitriol, camostat, and lopinavir) and to reduce viral load (e.g., remdesivir, ivermectin, emetine, Abelson kinase inhibitors, dopamine D2 antagonists, and selective estrogen receptor modulators). Additional interventions focus on tempering inflammatory signaling and injury (e.g., dexamethasone, doxycycline, Ang1-7, estradiol, alpha blockers, and DHA/EPA, pasireotide), as well as inhibitors targeted toward molecular mediators of the maladaptive COVID-19 immune response (e.g., IL-6, TNF-α, IL-17, JAK, and CDK9).

Understanding Inter-Individual Variability in Monoclonal Antibody Disposition

Monoclonal antibodies (mAbs) are currently the largest and most dominant class of therapeutic proteins. Inter-individual variability has been observed for several mAbs; however, an understanding of the underlying mechanisms and factors contributing to inter-subject differences in mAb disposition is still lacking. In this review, we analyze the mechanisms of antibody disposition and the putative mechanistic determinants of inter-individual variability. Results from in vitro, preclinical, and clinical studies were reviewed evaluate the role of the neonatal Fc receptor and Fc gamma receptors (expression and polymorphism), target properties (expression, shedding, turnover, internalization, heterogeneity, polymorphism), and the influence of anti-drug antibodies. Particular attention is given to the influence of co-administered drugs and disease, and to the physiological relevance of covariates identified by population pharmacokinetic modeling, as determinants of variability in mAb pharmacokinetics.

Identifying the culprits in neurological autoimmune diseases

The target organ of neurological autoimmune diseases (NADs) is the central or peripheral nervous system. Multiple sclerosis (MS) is the most common NAD, whereas Guillain-Barré syndrome (GBS), myasthenia gravis (MG), and neuromyelitis optica (NMO) are less common NADs, but the incidence of these diseases has increased exponentially in the last few years. The identification of a specific culprit in NADs is challenging since a myriad of triggering factors interplay with each other to cause an autoimmune response. Among the factors that have been associated with NADs are genetic susceptibility, epigenetic mechanisms, and environmental factors such as infection, microbiota, vitamins, etc. This review focuses on the most studied culprits as well as the mechanisms used by these to trigger NADs.

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Neurological autoimmune diseases are caused by a complex interaction between genes, environmental factors, and epigenetic deregulation.

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Infectious agents can cause an autoimmune reaction to myelin epitopes through molecular mimicry and/or bystander activation.

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Gut microbiota dysbiosis contributes to neurological autoimmune diseases.

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Smoking increases the risk of NADs through inflammatory signaling pathways, oxidative stress, and Th17 differentiation.

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Deficiency in vitamin D favors NAD development through direct damage to the central and peripheral nervous system.

The Human FcγRII (CD32) Family of Leukocyte FcR in Health and Disease

FcγRs have been the focus of extensive research due to their key role linking innate and humoral immunity and their implication in both inflammatory and infectious disease. Within the human FcγR family FcγRII (activatory FcγRIIa and FcγRIIc, and inhibitory FcγRIIb) are unique in their ability to signal independent of the common γ chain. Through improved understanding of the structure of these receptors and how this affects their function we may be able to better understand how to target FcγR specific immune activation or inhibition, which will facilitate in the development of therapeutic monoclonal antibodies in patients where FcγRII activity may be desirable for efficacy. This review is focused on roles of the human FcγRII family members and their link to immunoregulation in healthy individuals and infection, autoimmunity and cancer.

The Rare Anaphylaxis-Associated FcγRIIa3 Exhibits Distinct Characteristics From the Canonical FcγRIIa1

FcγRIIa is an activating FcγR, unique to humans and non-human primates. It induces antibody-dependent proinflammatory responses and exists predominantly as FcγRIIa1. A unique splice variant, we designated FcγRIIa3, has been reported to be associated with anaphylactic reactions to intravenous immunoglobulins (IVIg) therapy. We aim to define the functional consequences of this FcγRIIa variant associated with adverse responses to IVIg therapy and evaluate the frequency of associated SNPs. FcγRIIa forms from macaque and human PBMCs were investigated for IgG-subclass specificity, biochemistry, membrane localization, and functional activity. Disease-associated SNPs were analyzed by sequencing genomic DNA from 224 individuals with immunodeficiency or autoimmune disease. FcγRIIa3 was identified in macaque and human PBMC. The FcγRIIa3 is distinguished from the canonical FcγRIIa1 by a unique 19-amino acid cytoplasmic insertion and these two FcγRIIa forms responded distinctly to antibody ligation. Whereas FcγRIIa1 was rapidly internalized, FcγRIIa3 was retained longer at the membrane, inducing greater calcium mobilization and cell degranulation. Four FCGR2A SNPs were identified including the previously reported intronic SNP associated with anaphylaxis, but in only 1 of 224 individuals. The unique cytoplasmic element of FcγRIIa3 delays internalization and is associated with enhanced cellular activation. The frequency of the immunodeficiency-associated SNP varies between disease populations but interestingly occurred at a lower frequency than previously reported. None-the-less enhanced FcγRIIa3 function may promote a proinflammatory environment and predispose to pathological inflammatory responses.

The Role and Function of Fcγ Receptors on Myeloid Cells

A key determinant for the survival of organisms is their capacity to recognize and respond efficiently to foreign antigens. This is largely accomplished by the orchestrated activity of the innate and adaptive branches of the immune system. Antibodies are specifically generated in response to foreign antigens, facilitating thereby the specific recognition of antigens of almost infinite diversity. Receptors specific for the Fc domain of antibodies, Fc receptors, are expressed on the surface of the various myeloid leukocyte populations and mediate the binding and recognition of antibodies by innate leukocytes. By directly linking the innate and the adaptive components of immunity, Fc receptors play a central role in host defense and the maintenance of tissue homeostasis through the induction of diverse proinflammatory, anti-inflammatory, and immunomodulatory processes that are initiated upon engagement by the Fc domain. In this chapter, we discuss the mechanisms that regulate Fc domain binding to the various types of Fc receptors and provide an overview of the astonishing diversity of effector functions that are mediated through Fc-FcR interactions on myeloid cells. Lastly, we discuss the impact of FcR-mediated interactions in the context of IgG-mediated inflammation, autoimmunity, susceptibility to infection, and responsiveness to antibody-based therapeutics.

Fc Gamma Receptor IIA (CD32A) R131 Polymorphism as a Marker of Genetic Susceptibility to Sepsis

Sepsis is a devastating disease that can affect humans at any time between neonates and the elderly and is associated with mortality rates that range from 30 to 80%. Despite intensive efforts, its treatment has remained the same over the last few decades. Fc receptors regulate multiple immune responses and have been investigated in diverse complex diseases. FcγRIIA (CD32A) is an immunoreceptor, tyrosine-based activation motif-bearing receptor that binds immunoglobulin G and C-reactive protein, important opsonins in host defense. We conducted a study of 702 patients (184 healthy individuals, 171 non-infected critically ill patients, and 347 sepsis patients) to investigate if genetic polymorphisms in the CD32A coding region affect the risk of septic shock. All individuals were genotyped for a variant at position 131 of the FcγRIIA gene. We found that allele G, associated with the R131 genotype, was significantly more frequent in septic patients than in the other groups (p = 0.05). Our data indicate that FcγRIIA genotyping can be used as a marker of genetic susceptibility to sepsis.

FcGR genetic polymorphisms and the response to adalimumab in patients with rheumatoid arthritis

AIM

The aim of our study was to explore the potential of FcGR genetic polymorphisms as a predictor of adalimumab efficacy in rheumatoid arthritis (RA) patients.

MATERIALS & METHODS

The study population was composed of 302 Dutch RA patients receiving adalimumab therapy. The FcGR2A (R131>H; rs1801274) and FcGR3A (F158>V; rs396991) genetic variants were genotyped using the TaqMan(®) allelic discrimination technology. Treatment outcome was evaluated with the use of the 28-joint disease activity score criteria (DAS28) and good response and remission were classified according to European League Against Rheumatism (EULAR) criteria.

RESULTS

Comparing allelic frequencies between responders and nonresponders, the presence of the FcGR2A*R allele was associated with EULAR good response at 14 weeks (p = 0.017, odds ratio: 1.53, 95% CI: 1.08-2.17). No significant association was found for FcGR3A, with good response or remission. The combined effect of both FcGR2A and FcGR3A SNPs showed a trend for association with EULAR good response (p-value = 0.041, odds ratio: 1.38, 95% CI: 1.01-1.89).

CONCLUSION

Our results indicate that FcGR polymorphisms could be a determinant of adalimumab efficacy in RA patients. Original submitted 28 July 2014; Revision submitted 19 December 2014.

FcγR requirements leading to successful immunotherapy

Monoclonal antibody (mAb) immunotherapy is currently experiencing an unprecedented amount of success, delivering blockbuster sales for the pharmaceutical industry. Having experienced several false dawns and overcoming technical issues which limited progress, we are now entering a golden period where mAbs are becoming a mainstay of treatment regimes for diseases ranging from cancer to autoimmunity. In this review, we discuss how these mAbs are most likely working and focus in particular on the key receptors that they interact with to precipitate their therapeutic effects. Although their targets may vary, their engagement with Fcγ receptors (FcγRs) on numerous immune effector cells is almost universal, and here we review their roles in delivering successful immunotherapy.

Human FcR polymorphism and disease

Fc receptors play a central role in maintaining the homeostatic balance in the immune system. Our knowledge of the structure and function of these receptors and their naturally occurring polymorphisms, including single nucleotide polymorphisms and/or copy number variations, continues to expand. Through studies of their impact on human biology and clinical phenotype, the contributions of these variants to the pathogenesis, progression, and/or treatment outcome of many diseases that involve immunoglobulin have become evident. They affect susceptibility to bacterial and viral pathogens, constitute as risk factors for IgG or IgE mediated inflammatory diseases, and impact the development of many autoimmune conditions. In this chapter, we will provide an overview of these genetic variations in classical FcγRs, FcRLs, and other Fc receptors, as well as challenges in achieving an accurate and comprehensive understanding of the FcR polymorphisms and genomic architecture.

Fcγ receptor polymorphisms do not predict response to intravenous immunoglobulin in myasthenia gravis

We studied 63 patients with myasthenia gravis (MG) requiring treatment with intravenous immunoglobulin, to determine if polymorphisms within the FCγR2A (rs1801274), FCγR2B (rs1050501), FCγR3A (rs396991), and FCγR3B (NA1/NA2) genes are correlated with response to treatment. There was no significant difference in any of the polymorphisms studied between responders and nonresponders. Patients with the FCγR2B-232I/I polymorphism had higher disease severity measured by the quatitative myasthenia gravis score (QMGS). There was no difference in the distribution of the FCγR2B-232 polymorphisms between the patients and 90 healthy controls. The finding of greater disease severity in patients with the FCγR2B-232I/I polymorphism requires confirmation in a larger population of patients with myasthenia gravis.

Functional and clinical consequences of Fc receptor polymorphic and copy number variants

Receptors for immunoglobulins (Fc receptors) play a central role during an immune response, as they mediate the specific recognition of antigens of almost infinite diversity by leucocytes, thereby linking the humoral and cellular components of immunity. Indeed, engagement of Fc receptors by immunoglobulins initiates a range of immunoregulatory processes that might also play a role in disease pathogenesis. In the circulation, five main types of immunoglobulins (Ig) exist - namely IgG, IgA, IgE, IgM and IgD and receptors with the ability to recognize and bind to IgG (Fc gamma receptor family), IgE (Fc epsilon RI and CD23), IgA (CD89; Fc alpha/microR) and IgM (Fc alpha/microR) have been identified and characterized. However, it is astonishing that nearly all the known human Fc receptors display extensive genetic variation with clear implications for their function, thus representing a substantial genetic risk factor for the pathogenesis of a range of chronic inflammatory disorders.

Low-affinity Fcgamma receptors, autoimmunity and infection

Low-affinity Fcgamma receptors (FcgammaRs) mediate the effects of immunoglobulin G (IgG) antibodies on leukocytes, including recruitment to inflammatory lesions, phagocytosis, antibody-dependent cellular cytotoxicity, release of inflammatory mediators and regulation of B cell activation. These functions are an important part of the mammalian response to infection, but if deployed inappropriately can cause autoimmune disease. Although most FcgammaRs are activatory, there is also an inhibitory FcgammaR that, when bound to IgG immune complexes, is able to downregulate the effects of both the activatory FcgammaRs and the B cell receptor. This review discusses the role of the low-affinity FcgammaRs in a balanced immune response and how perturbations in FcgammaR function result in susceptibility to infection or autoimmunity.

Genetic factors in autoimmune myasthenia gravis

Autoimmune myasthenia gravis (MG) is a multifactorial disease, markedly influenced by genetic factors, even though it shows limited heritability. The clinically typical form of autoimmune MG with thymus hyperplasia shows the most reproducible genetic associations, especially with the A1-B8-DR3 (8.1) haplotype of the major histocompatibility complex (MHC). However, because of strong linkage disequilibrium, the causative polymorphism in this region is not known yet. Increasing the density of genetic markers has nevertheless recently revealed the complex, but highly significant contribution of this essential genetic region in controlling the disease phenotype and the quantitative expression of serum autoantibodies. The advances of the human genome program, the development of genotyping and sequencing tools with increasing throughput, and the availability of powerful statistical methods now make feasible the dissection of a complex genetic region, such as the MHC and beyond, the systematic search throughout the genome for variants influencing disease predisposition. The identification of such functional variants should provide new clues to the pathogenesis of MG, as recently illustrated by the study of a promoter polymorphism of the CHRNA1 locus, influencing its thymic expression and central tolerance, or of a coding variant of the PTPN22 intracellular phosphatase.

Inhibitory IgG receptor FcgammaRIIB fails to inhibit experimental autoimmune myasthenia gravis pathogenesis

Deficiency of the inhibitory FcgammaRIIB renders mice susceptible to autoimmune disorders characterized with cellular infiltration of target tissue. To analyze the role of FcgammaRIIB in an antibody-mediated autoimmune disease, experimental autoimmune myasthenia gravis (EAMG), FcgammaRIIB knockout (KO) and wild-type mice were immunized with acetylcholine receptor (AChR). In contrast with previous reports, FcgammaRIIB KO mice were mildly resistant to EAMG despite preserved anti-AChR antibody production and neuromuscular junction complement deposition capacity. EAMG resistance was associated with reduced lymph node cell IL-6 and IL-10 production and increased CD4(+)CD25(+) cell ratios in lymph nodes. Our data suggest that FcgammaRIIB promotes antibody-mediated autoimmunity.

CCR2-64I and CCR5Delta32 Polymorphisms in Korean Patients with Myasthenia Gravis

BACKGROUND AND PURPOSE

Chemokines participate in the regulation of immune and inflammatory responses by interacting with their receptors, which are primarily expressed on immune and inflammatory cells such as B- and T-lymphocytes and antigen-presenting cells. Chemokines and their receptors are therefore considered to mediate inflammation and tissue damage in autoimmune disorders. Chemokine receptor (CCR) genotypes were recently identified, and the importance of their genetic polymorphisms in some autoimmune and infectious disorders has been demonstrated. To define the roles of the polymorphism of the CCR2 gene at codon 64 (CCR2-64I) and the 32-bp deletion in the coding region of CCR5 (CCR5Delta32) in Korean patients with myasthenia gravis (MG), we compared these genotypes in MG cases and healthy controls and investigated the clinical features associated with these genotypes.

METHODS

One hundred and fifteen healthy controls (51 men and 64 women) and 109 MG patients (44 men and 65 women) from three University hospitals were included. We examined each patient for clinical features using electrophysiology tests, laboratory tests, and thymic pathology. The CCR2-64I and CCR5Delta32 polymorphisms were determined by the PCR-RFLP method.

RESULTS

We detected no difference in the frequencies of CCR2-64I polymorphism between MG patients and healthy controls. All of the MG patients and the healthy controls were homozygous for the wild-type CCR5 genotype. The results of electrophysiological tests and thymic pathologies were not influenced by the type of CCR2-64I polymorphism. However, the anti-acetylcholine-receptor (AChR) antibody titer was higher in the CCR2 G/G genotype (13.34+/-12.71 nmol/L) than in the CCR2 A/A genotype (5.83+/-2.56 nmol/L).

CONCLUSIONS

We found no evidence of an increased risk for MG associated with the CCR2-64I and CCR5Delta32 polymorphisms. However, the increased anti-AChR antibody titer in the patients with the CCR2 G/G genotype suggests that the CCR2 gene play a role in the pathophysiology of MG.