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

Lupus IgA1 autoantibodies synergize with IgG to enhance plasmacytoid dendritic cell responses to RNA-containing immune complexes

Autoantibodies to nuclear antigens are hallmarks of systemic lupus erythematosus (SLE) where they contribute to pathogenesis. However, there remains a gap in our knowledge regarding how different isotypes of autoantibodies contribute to this autoimmune disease, including the production of the critical type I interferon (IFN) cytokines by plasmacytoid dendritic cells (pDCs) in response to immune complexes (ICs). We focused on IgA, which is the second-most prevalent isotype in serum and, along with IgG, is deposited in glomeruli in individuals with lupus nephritis. We show that individuals with SLE have serum IgA autoantibodies against most nuclear antigens, correlating with IgG against the same antigen. We investigated whether IgA autoantibodies against a major SLE autoantigen, Smith ribonucleoprotein (Sm/RNP), played a role in IC activation of pDCs. We found that pDCs expressed the IgA-specific Fc receptor, FcαR, and IgA1 autoantibodies synergized with IgG in RNA-containing ICs to generate robust primary blood pDC IFN-α responses in vitro. pDC responses to these ICs required both FcαR and FcγRIIa, showing synergy between these Fc receptors. Sm/RNP IC binding to and internalization by pDCs were greater when ICs contained both IgA1 and IgG. Circulating pDCs from individuals with SLE had higher binding of IgA1-containing ICs and higher expression of FcαR than pDCs from healthy control individuals. Although pDC FcαR expression correlated with the blood IFN-stimulated gene signature in SLE, Toll-like receptor 7 agonists, but not IFN-α, up-regulated pDC FcαR expression in vitro. Together, we show a mechanism by which IgA1 autoantibodies contribute to SLE pathogenesis.

Multifaceted roles of APOE in Alzheimer disease

For the past three decades, apolipoprotein E (APOE) has been known as the single greatest genetic modulator of sporadic Alzheimer disease (AD) risk, influencing both the average age of onset and the lifetime risk of developing AD. The APOEε4 allele significantly increases AD risk, whereas the ε2 allele is protective relative to the most common ε3 allele. However, large differences in effect size exist across ethnoracial groups that are likely to depend on both global genetic ancestry and local genetic ancestry, as well as gene-environment interactions. Although early studies linked APOE to amyloid-β - one of the two culprit aggregation-prone proteins that define AD - in the past decade, mounting work has associated APOE with other neurodegenerative proteinopathies and broader ageing-related brain changes, such as neuroinflammation, energy metabolism failure, loss of myelin integrity and increased blood-brain barrier permeability, with potential implications for longevity and resilience to pathological protein aggregates. Novel mouse models and other technological advances have also enabled a number of therapeutic approaches aimed at either attenuating the APOEε4-linked increased AD risk or enhancing the APOEε2-linked AD protection. This Review summarizes this progress and highlights areas for future research towards the development of APOE-directed therapeutics.

Reversible Chemical Modification of Antibody Effector Function Mitigates Unwanted Systemic Immune Activation

Antibody effector functions including antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP) are mediated through the interaction of the antibody Fc region with Fcγ receptors present on immune cells. Several approaches have been used to modulate antibody Fc-Fcγ interactions with the goal of driving an effective antitumor immune response, including Fc point mutations and glycan modifications. However, robust antibody-Fcγ engagement and immune cell binding of Fc-enhanced antibodies in the periphery can lead to the unwanted induction of systemic cytokine release and other dose-limiting infusion-related reactions. Creating a balance between effective engagement of Fcγ receptors that can induce antitumor activity without incurring systemic immune activation is an ongoing challenge in the field of antibody and immuno-oncology therapeutics. Herein, we describe a method for the reversible chemical modulation of antibody-Fcγ interactions using simple poly(ethylene glycol) (PEG) linkers conjugated to antibody interchain disulfides with maleimide attachments. This method enables dosing of a therapeutic with muted Fcγ engagement that is restored in vivo in a time-dependent manner. The technology was applied to an effector function enhanced agonist CD40 antibody, SEA-CD40, and experiments demonstrate significant reductions in Fc-induced immune activation in vitro and in mice and nonhuman primates despite showing retained efficacy and improved pharmacokinetics compared to the parent antibody. We foresee that this simple, modular system can be rapidly applied to antibodies that suffer from systemic immune activation due to peripheral FcγR binding immediately upon infusion.

Development of a Time-Resolved Fluorescence Resonance Energy Transfer ultra-high throughput screening assay for targeting SYK and FCER1G interaction

The spleen tyrosine kinase (SYK) and high affinity immunoglobulin epsilon receptor subunit gamma (FCER1G) interaction has a major role in the normal innate and adaptive immune responses, but dysregulation of this interaction is implicated in several human diseases, including autoimmune disorders, hematological malignancies, and Alzheimer's Disease. Development of small molecule chemical probes could aid in studying this pathway both in normal and aberrant contexts. Herein, we describe the miniaturization of a time-resolved fluorescence resonance energy transfer (TR-FRET) assay to measure the interaction between SYK and FCER1G in a 1536-well ultrahigh throughput screening (uHTS) format. The assay utilizes the His-SH2 domains of SYK, which are indirectly labeled with anti-His-terbium to serve as TR-FRET donor and a FITC-conjugated phosphorylated ITAM domain peptide of FCER1G to serve as acceptor. We have optimized the assay into 384-well HTS format and further miniaturized the assay into a 1536-well uHTS format. Robust assay performance has been achieved with a Z' factor > 0.8 and signal-to-background (S/B) ratio > 15. The utilization of this uHTS TR-FRET assay for compound screening has been validated by a pilot screening of 2,036 FDA-approved and bioactive compounds library. Several primary hits have been identified from the pilot uHTS. One compound, hematoxylin, was confirmed to disrupt the SYK/FECR1G interaction in an orthogonal protein-protein interaction assay. Thus, our optimized and miniaturized uHTS assay could be applied to future scaling up of a screening campaign to identify small molecule inhibitors targeting the SYK and FCER1G interaction.

Development of SYK NanoBRET Cellular Target Engagement Assays for Gain-of-Function Variants

Spleen tyrosine kinase (SYK) is a non-receptor tyrosine kinase that is activated by phosphorylation events downstream of FcR, B-cell and T-cell receptors, integrins, and C-type lectin receptors. When the tandem Src homology 2 (SH2) domains of SYK bind to phosphorylated immunoreceptor tyrosine-based activation motifs (pITAMs) contained within these immunoreceptors, or when SYK is phosphorylated in interdomain regions A and B, SYK is activated. SYK gain-of-function (GoF) variants were previously identified in six patients that had higher levels of phosphorylated SYK and phosphorylated downstream proteins JNK and ERK. Furthermore, the increased SYK activation resulted in the clinical manifestation of immune dysregulation, organ inflammation, and a predisposition for lymphoma. The knowledge that the SYK GoF variants have enhanced activity was leveraged to develop a SYK NanoBRET cellular target engagement assay in intact live cells with constructs for the SYK GoF variants. Herein, we developed a potent SYK-targeted NanoBRET tracer using a SYK donated chemical probe, MRL-SYKi, that enabled a NanoBRET cellular target engagement assay for SYK GoF variants, SYK(S550Y), SYK(S550F), and SYK(P342T). We determined that ATP-competitive SYK inhibitors bind potently to these SYK variants in intact live cells. Additionally, we demonstrated that MRL-SYKi can effectively reduce the catalytic activity of SYK variants, and the phosphorylation levels of SYK(S550Y) in an epithelial cell line (SW480) stably expressing SYK(S550Y).

NOD2 activation enhances macrophage Fcγ receptor function and may increase the efficacy of antibody therapy

Introduction

Therapeutic antibodies have become a major strategy to treat oncologic diseases. For chronic lymphocytic leukemia, antibodies against CD20 are used to target and elicit cytotoxic responses against malignant B cells. However, efficacy is often compromised due to a suppressive microenvironment that interferes with cellular immune responses. To overcome this suppression, agonists of pattern recognition receptors have been studied which promote direct cytotoxicity or elicit anti-tumoral immune responses. NOD2 is an intracellular pattern recognition receptor that participates in the detection of peptidoglycan, a key component of bacterial cell walls. This detection then mediates the activation of multiple signaling pathways in myeloid cells. Although several NOD2 agonists are being used worldwide, the potential benefit of these agents in the context of antibody therapy has not been explored.

Methods

Primary cells from healthy-donor volunteers (PBMCs, monocytes) or CLL patients (monocytes) were treated with versus without the NOD2 agonist L18-MDP, then antibody-mediated responses were assessed. In vivo, the Eµ-TCL1 mouse model of CLL was used to test the effects of L18-MDP treatment alone and in combination with anti-CD20 antibody.

Results

Treatment of peripheral blood mononuclear cells with L18-MDP led to activation of monocytes from both healthy donors and CLL patients. In addition, there was an upregulation of activating FcγR in monocytes and a subsequent increase in antibody-mediated phagocytosis. This effect required the NF-κB and p38 signaling pathways. Treatment with L18-MDP plus anti-CD20 antibody in the Eµ-TCL model of CLL led to a significant reduction of CLL load, as well as to phenotypic changes in splenic monocytes and macrophages.

Conclusions

Taken together, these results suggest that NOD2 agonists help overturn the suppression of myeloid cells, and may improve the efficacy of antibody therapy for CLL.

PET imaging of Aspergillus infection using Zirconium-89 labeled anti-β-glucan antibody fragments

PURPOSE

Invasive fungal diseases, such as pulmonary aspergillosis, are common life-threatening infections in immunocompromised patients and effective treatment is often hampered by delays in timely and specific diagnosis. Fungal-specific molecular imaging ligands can provide non-invasive readouts of deep-seated fungal pathologies. In this study, the utility of antibodies and antibody fragments (Fab) targeting β-glucans in the fungal cell wall to detect Aspergillus infections was evaluated both in vitro and in preclinical mouse models.

METHODS

The binding characteristics of two commercially available β-glucan antibody clones and their respective antigen-binding Fabs were tested using biolayer interferometry (BLI) assays and immunofluorescence staining. In vivo binding of the Zirconium-89 labeled antibodies/Fabs to fungal pathogens was then evaluated using PET/CT imaging in mouse models of fungal infection, bacterial infection and sterile inflammation.

RESULTS

One of the evaluated antibodies (HA-βG-Ab) and its Fab (HA-βG-Fab) bound to β-glucans with high affinity (KD = 0.056 & 21.5 nM respectively). Binding to the fungal cell wall was validated by immunofluorescence staining and in vitro binding assays. ImmunoPET imaging with intact antibodies however showed slow clearance and high background signal as well as nonspecific accumulation in sites of infection/inflammation. Conversely, specific binding of [89Zr]Zr-DFO-HA-βG-Fab to sites of fungal infection was observed when compared to the isotype control Fab and was significantly higher in fungal infection than in bacterial infection or sterile inflammation.

CONCLUSIONS

[89Zr]Zr-DFO-HA-βG-Fab can be used to detect fungal infections in vivo. Targeting distinct components of the fungal cell wall is a viable approach to developing fungal-specific PET tracers.

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

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

Genome-wide association studies for diarrhoea outcomes identified genomic regions affecting resistance to a severe enteropathy in suckling rabbits

Selection and breeding strategies to improve resistance to enteropathies are essential to reaching the sustainability of the rabbit production systems. However, disease heterogeneity (having only as major visible symptom diarrhoea) and low disease heritability are two barriers for the implementation of these strategies. Diarrhoea condition can affect rabbits at different life stages, starting from the suckling period, with large negative economic impacts. In this study, from a commercial population of suckling rabbits (derived from 133 litters) that experienced an outbreak of enteropathy, we first selected a few animals that died with severe symptoms of diarrhoea and characterized their microbiota, using 16S rRNA gene sequencing data. Clostridium genus was consistently present in all affected specimens. In addition, with the aim to identify genetic markers in the rabbit genome that could be used as selection tools, we performed genome-wide association studies for symptoms of diarrhoea in the same commercial rabbit population. These studies were also complemented with FST analyses between the same groups of rabbits. A total of 332 suckling rabbits (151 with severe symptoms of diarrhoea, 42 with mild symptoms and 129 without any symptoms till the weaning period), derived from 45 different litters (a subset of the 133 litters) were genotyped with the Affymetrix Axiom OrcunSNP Array. In both genomic approaches, rabbits within litters were paired to constitute two groups (susceptible and resistant, including the mildly affected in one or the other group) and run case and control genome-wide association analyses. Genomic heritability estimated in the designed experimental structure integrated in a commercial breeding scheme was 0.19-0.21 (s.e. 0.09-0.10). A total of eight genomic regions on rabbit chromosome 2 (OCU2), OCU3, OCU7, OCU12, OCU13, OCU16 and in an unassembled scaffold had significant single nucleotide polymorphisms (SNPs) and/or markers that trespassed the FST percentile distribution. Among these regions, three main peaks of SNPs were identified on OCU12, OCU13 and OCU16. The QTL region on OCU13 encompasses several genes that encode members of a family of immunoglobulin Fc receptors (FCER1G, FCRLA, FCRLB and FCGR2A) involved in the immune innate system, which might be important candidate genes for this pathogenic condition. The results obtained in this study demonstrated that resistance to an enteropathy occurring in suckling rabbits is in part genetically determined and can be dissected at the genomic level, providing DNA markers that could be used in breeding programmes to increase resistance to enteropathies in meat rabbits.

Identification of PPARG as key gene to link coronary atherosclerosis disease and rheumatoid arthritis via microarray data analysis

BACKGROUND

Inflammation is the common pathogenesis of coronary atherosclerosis disease (CAD) and rheumatoid arthritis (RA). Although it is established that RA increases the risk of CAD, the underlining mechanism remained indefinite. This study seeks to explore the molecular mechanisms of RA linked CAD and identify potential target gene for early prediction of CAD in RA patients.

MATERIALS AND METHODS

The study utilized five raw datasets: GSE55235, GSE55457, GSE12021 for RA patients, and GSE42148 and GSE20680 for CAD patients. Gene Set Enrichment Analysis (GSEA) was used to investigate common signaling pathways associated with RA and CAD. Then, weighted gene co-expression network analysis (WGCNA) was performed on RA and CAD training datasets to identify gene modules related to single-sample GSEA (ssGSEA) scores. Overlapping module genes and differentially expressed genes (DEGs) were considered as co-susceptible genes for both diseases. Three hub genes were screened using a protein-protein interaction (PPI) network analysis via Cytoscape plug-ins. The signaling pathways, immune infiltration, and transcription factors associated with these hub genes were analyzed to explore the underlying mechanism connecting both diseases. Immunohistochemistry and qRT-PCR were conducted to validate the expression of the key candidate gene, PPARG, in macrophages of synovial tissue and arterial walls from RA and CAD patients.

RESULTS

The study found that Fc-gamma receptor-mediated endocytosis is a common signaling pathway for both RA and CAD. A total of 25 genes were screened by WGCNA and DEGs, which are involved in inflammation-related ligand-receptor interactions, cytoskeleton, and endocytosis signaling pathways. The principal component analysis(PCA) and support vector machine (SVM) and receiver-operator characteristic (ROC) analysis demonstrate that 25 DEGs can effectively distinguish RA and CAD groups from normal groups. Three hub genes TUBB2A, FKBP5, and PPARG were further identified by the Cytoscape software. Both FKBP5 and PPARG were downregulated in synovial tissue of RA and upregulated in the peripheral blood of CAD patients and differential mRNAexpreesion between normal and disease groups in both diseases were validated by qRT-PCR.Association of PPARG with monocyte was demonstrated across both training and validation datasets in CAD. PPARG expression is observed in control synovial epithelial cells and foamy macrophages of arterial walls, but was decreased in synovial epithelium of RA patients. Its expression in foamy macrophages of atherosclerotic vascular walls exhibits a positive correlation (r = 0.6276, p = 0.0002) with CD68.

CONCLUSION

Our findings suggest that PPARG may serve as a potentially predictive marker for CAD in RA patients, which provides new insights into the molecular mechanism underling RA linked CAD.

Lupus IgA1 autoantibodies synergize with IgG to enhance pDC responses to RNA-containing immune complexes

Autoantibodies to nuclear antigens are hallmarks of the autoimmune disease systemic lupus erythematosus (SLE) where they contribute to pathogenesis. However, there remains a gap in our knowledge regarding how different isotypes of autoantibodies contribute to disease, including the production of the critical type I interferon (IFN) cytokines by plasmacytoid dendritic cells (pDCs) in response to immune complexes (ICs). We focused on IgA, which is the second most prevalent isotype in serum, and along with IgG is deposited in glomeruli in lupus nephritis. Here, we show that individuals with SLE have IgA autoantibodies against most nuclear antigens, correlating with IgG against the same antigen. We investigated whether IgA autoantibodies against a major SLE autoantigen, Smith ribonucleoproteins (Sm/RNPs), play a role in IC activation of pDCs. We found that pDCs express the IgA-specific Fc receptor, FcαR, and there was a striking ability of IgA1 autoantibodies to synergize with IgG in RNA-containing ICs to generate robust pDC IFNα responses. pDC responses to these ICs required both FcαR and FcγRIIa, showing a potent synergy between these Fc receptors. Sm/RNP IC binding to and internalization by pDCs were greater when ICs contained both IgA1 and IgG. pDCs from individuals with SLE had higher binding of IgA1-containing ICs and higher expression of FcαR than pDCs from healthy control individuals. Whereas pDC FcαR expression correlated with blood ISG signature in SLE, TLR7 agonists, but not IFNα, upregulated pDC FcαR expression in vitro. Together, we show a new mechanism by which IgA1 autoantibodies contribute to SLE pathogenesis.

Identification of miRNAs that target Fcγ receptor-mediated phagocytosis during macrophage activation syndrome

Macrophage activation syndrome (MAS) is a life-threatening complication of systemic juvenile arthritis, accompanied by cytokine storm and hemophagocytosis. In addition, COVID-19-related hyperinflammation shares clinical features of MAS. Mechanisms that activate macrophages in MAS remain unclear. Here, we identify the role of miRNA in increased phagocytosis and interleukin-12 (IL-12) production by macrophages in a murine model of MAS. MAS significantly increased F4/80+ macrophages and phagocytosis in the mouse liver. Gene expression profile revealed the induction of Fcγ receptor-mediated phagocytosis (FGRP) and IL-12 production in the liver. Phagocytosis pathways such as High-affinity IgE receptor is known as Fc epsilon RI -signaling and pattern recognition receptors involved in the recognition of bacteria and viruses and phagosome formation were also significantly upregulated. In MAS, miR-136-5p and miR-501-3p targeted and caused increased expression of Fcgr3, Fcgr4, and Fcgr1 genes in FGRP pathway and consequent increase in phagocytosis by macrophages, whereas miR-129-1-3p and miR-150-3p targeted and induced Il-12. Transcriptome analysis of patients with MAS revealed the upregulation of FGRP and FCGR gene expression. A target analysis of gene expression data from a patient with MAS discovered that miR-136-5p targets FCGR2A and FCGR3A/3B, the human orthologs of mouse Fcgr3 and Fcgr4, and miR-501-3p targets FCGR1A, the human ortholog of mouse Fcgr1. Together, we demonstrate the novel role of miRNAs during MAS pathogenesis, thereby suggesting miRNA mimic-based therapy to control the hyperactivation of macrophages in patients with MAS as well as use overexpression of FCGR genes as a marker for MAS classification.

In Vivo mRNA CAR T Cell Engineering via Targeted Ionizable Lipid Nanoparticles with Extrahepatic Tropism

With six therapies approved by the Food and Drug Association, chimeric antigen receptor (CAR) T cells have reshaped cancer immunotherapy. However, these therapies rely on ex vivo viral transduction to induce permanent CAR expression in T cells, which contributes to high production costs and long-term side effects. Thus, this work aims to develop an in vivo CAR T cell engineering platform to streamline production while using mRNA to induce transient, tunable CAR expression. Specifically, an ionizable lipid nanoparticle (LNP) is utilized as these platforms have demonstrated clinical success in nucleic acid delivery. Though LNPs often accumulate in the liver, the LNP platform used here achieves extrahepatic transfection with enhanced delivery to the spleen, and it is further modified via antibody conjugation (Ab-LNPs) to target pan-T cell markers. The in vivo evaluation of these Ab-LNPs confirms that targeting is necessary for potent T cell transfection. When using these Ab-LNPs for the delivery of CAR mRNA, antibody and dose-dependent CAR expression and cytokine release are observed along with B cell depletion of up to 90%. In all, this work conjugates antibodies to LNPs with extrahepatic tropism, evaluates pan-T cell markers, and develops Ab-LNPs capable of generating functional CAR T cells in vivo.

Dissecting the Ability of Siglecs To Antagonize Fcγ Receptors

Fcγ receptors (FcγRs) play key roles in the effector function of IgG, but their inappropriate activation plays a role in several disease etiologies. Therefore, it is critical to better understand how FcγRs are regulated. Numerous studies suggest that sialic acid-binding immunoglobulin-type lectins (Siglecs), a family of immunomodulatory receptors, modulate FcγR activity; however, it is unclear of the circumstances in which Siglecs can antagonize FcγRs and which Siglecs have this ability. Using liposomes displaying selective ligands to coengage FcγRs with a specific Siglec, we explore the ability of Siglec-3, Siglec-5, Siglec-7, and Siglec-9 to antagonize signaling downstream of FcγRs. We demonstrate that Siglec-3 and Siglec-9 can fully inhibit FcγR activation in U937 cells when coengaged with FcγRs. Cells expressing Siglec mutants reveal differential roles for the immunomodulatory tyrosine-based inhibitory motif (ITIM) and immunomodulatory tyrosine-based switch motif (ITSM) in this inhibition. Imaging flow cytometry enabled visualization of SHP-1 recruitment to Siglec-3 in an ITIM-dependent manner, while SHP-2 recruitment is more ITSM-dependent. Conversely, both cytosolic motifs of Siglec-9 contribute to SHP-1/2 recruitment. Siglec-7 poorly antagonizes FcγR activation for two reasons: masking by cis ligands and differences in its ITIM and ITSM. A chimera of the Siglec-3 extracellular domains and Siglec-5 cytosolic tail strongly inhibits FcγR when coengaged, providing evidence that Siglec-5 is more like Siglec-3 and Siglec-9 in its ability to antagonize FcγRs. Additionally, Siglec-3 and Siglec-9 inhibited FcγRs when coengaged by cells displaying ligands for both the Siglec and FcγRs. These results suggest a role for Siglecs in mediating FcγR inhibition in the context of an immunological synapse, which has important relevance to the effectiveness of immunotherapies.

Characterization of covalent inhibitors that disrupt the interaction between the tandem SH2 domains of SYK and FCER1G phospho-ITAM

RNA sequencing and genetic data support spleen tyrosine kinase (SYK) and high affinity immunoglobulin epsilon receptor subunit gamma (FCER1G) as putative targets to be modulated for Alzheimer's disease (AD) therapy. FCER1G is a component of Fc receptor complexes that contain an immunoreceptor tyrosine-based activation motif (ITAM). SYK interacts with the Fc receptor by binding to doubly phosphorylated ITAM (p-ITAM) via its two tandem SH2 domains (SYK-tSH2). Interaction of the FCER1G p-ITAM with SYK-tSH2 enables SYK activation via phosphorylation. Since SYK activation is reported to exacerbate AD pathology, we hypothesized that disruption of this interaction would be beneficial for AD patients. Herein, we developed biochemical and biophysical assays to enable the discovery of small molecules that perturb the interaction between the FCER1G p-ITAM and SYK-tSH2. We identified two distinct chemotypes using a high-throughput screen (HTS) and orthogonally assessed their binding. Both chemotypes covalently modify SYK-tSH2 and inhibit its interaction with FCER1G p-ITAM, however, these compounds lack selectivity and this limits their utility as chemical tools.

Epigenetic control of inflammation in Atopic Dermatitis

Atopic dermatitis (AD), also known as atopic eczema, is a common but also complex chronic, itchy skin condition with underlying inflammation of the skin. This skin ailment is prevalent worldwide and affects people of all ages, particularly children below five years of age. The itching and resulting rashes in AD patients are often the result of inflammatory signals, thus necessitating a closer look at the inflammation-regulating mechanisms for putative relief, care and therapy. Several chemical- as well as genetically-induced animal models have established the importance of targeting pro-inflammatory AD microenvironment. Epigenetic mechanisms are gaining attention towards a better understanding of the onset as well as the progression of inflammation. Several physiological processes with implications in pathophysiology of AD, such as, barrier dysfunction either due to reduced filaggrin / human β-defensins or altered microbiome, reprograming of Fc receptors with resulting overexpression of high affinity IgE receptors, elevated eosinophil numbers or the elevated IL-22 production by CD4 + T cells have underlying epigenetic mechanisms that include differential promoter methylation and/or regulation by non-coding RNAs. Reversing these epigenetic changes has been verified to reduce inflammatory burden through altered secretion of cytokines IL-6, IL-4, IL-13, IL-17, IL-22 etc, with benefit against AD progression in experimental models. A thorough understanding of epigenetic remodeling of inflammation in AD has the potential of opening avenues for novel diagnostic, prognostic and therapeutic options.

Characterization of Large Immune Complexes with Size Exclusion Chromatography and Native Mass Spectrometry Supplemented with Gas Phase Ion Chemistry

Large immune complexes formed by the cross-linking of antibodies with polyvalent antigens play critical roles in modulating cell-mediated immunity. While both the size and the shape of immune complexes are important determinants in Fc receptor-mediated signaling responsible for phagocytosis, degranulation, and, in some instances, autoimmune pathologies, their characterization remains extremely challenging due to their large size and structural heterogeneity. We use native mass spectrometry (MS) supplemented with limited charge reduction in the gas phase to determine the stoichiometry of immune complexes formed by a bivalent (homodimeric) antigen, a 163 kDa aminopeptidase P2 (APP2), and a monoclonal antibody (mAb) to APP2. The observed (APP2·mAb)n complexes populate a wide range of stoichiometries (n = 1-4) with the largest detected species exceeding 1 MDa, although the gas-phase dissociation products are also evident in the mass spectra. While frequently considering a nuisance that complicates interpretation of native MS data, limited dissociation provides an additional dimension for characterization of the immune complex quaternary structure. APP2/mAb associations with identical composition but slightly different elution times in size exclusion chromatography exhibit notable differences in their spontaneous fragmentation profiles. The latter indicates the presence of both extended linear and cyclized (APP2·mAb)n configurations. The unique ability of MS to distinguish between such isomeric structures will be invaluable for a variety of applications where the biological effects of immune complexes are determined by their ability to assemble Fc receptor clusters of certain density on cell surfaces, such as platelet activation by clustering the low-affinity receptors FcγRIIa on their surface.

Therapeutic strategies in FcγIIA receptor-dependent thrombosis and thromboinflammation as seen in heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombocytopenia and thrombosis (VITT)

INTRODUCTION

Fcγ-receptors (FcγR) are membrane receptors expressed on a variety of immune cells, specialized in recognition of the Fc part of immunoglobulin G (IgG) antibodies. FcγRIIA-dependent platelet activation in platelet factor 4 (PF4) antibody-related disorders have gained major attention, when these antibodies were identified as the cause of the adverse vaccination event termed vaccine-induced immune thrombocytopenia and thrombosis (VITT) during the COVID-19 vaccination campaign. With the recognition of anti-PF4 antibodies as cause for severe spontaneous and sometimes recurrent thromboses independent of vaccination, their clinical relevance extended far beyond heparin-induced thrombocytopenia (HIT) and VITT.

AREAS COVERED

Patients developing these disorders show life-threatening thromboses, and the outcome is highly dependent on effective treatment. This narrative literature review summarizes treatment options for HIT and VITT that are currently available for clinical application and provides the perspective toward new developments.

EXPERT OPINION

Nearly all these novel approaches are based on in vitro, preclinical observations, or case reports with only limited implementation in clinical practice. The therapeutic potential of these approaches still needs to be proven in larger cohort studies to ensure treatment efficacy and long-term patient safety.

Effects of exercise on whole-blood transcriptome profile in children with overweight/obesity

BACKGROUND

The current knowledge about the molecular mechanisms underlying the health benefits of exercise is still limited, especially in childhood. We set out to investigate the effects of a 20-week exercise intervention on whole-blood transcriptome profile (RNA-seq) in children with overweight/obesity.

METHODS

Twenty-four children (10.21 ± 1.33 years, 46% girls) with overweight/obesity, were randomized to either a 20-week exercise program (intervention group; n = 10), or to a no-exercise control group (n = 14). Whole-blood transcriptome profile was analyzed using RNA-seq by STRT technique with GlobinLock technology.

RESULTS

Following the 20-week exercise intervention program, 161 genes were differentially expressed between the exercise and the control groups among boys, and 121 genes among girls (p-value <0.05), while after multiple correction, no significant difference between exercise and control groups persisted in gene expression profiles (FDR >0.05). Genes enriched in GO processes and molecular pathways showed different immune response in boys (antigen processing and presentation, infections, and T cell receptor complex) and in girls (Fc epsilon RI signaling pathway) (FDR <0.05).

CONCLUSION

These results suggest that 20-week exercise intervention program alters the molecular pathways involved in immune processes in children with overweight/obesity.

Nanoparticles targeting the intestinal Fc receptor enhance intestinal cellular trafficking of semaglutide

Semaglutide is the first oral glucagon-like peptide-1 (GLP-1) analog commercially available for the treatment of type 2 diabetes. In this work, semaglutide was incorporated into poly(lactic-co-glycolic acid)-poly(ethylene glycol) (PLGA-PEG) nanoparticles (NPs) to improve its delivery across the intestinal barrier. The nanocarriers were surface-decorated with either a peptide or an affibody that target the human neonatal Fc receptor (hFcRn), located on the luminal cell surface of the enterocytes. Both ligands were successfully conjugated with the PLGA-PEG via maleimide-thiol chemistry and thereafter, the functionalized polymers were used to produce semaglutide-loaded NPs. Monodisperse NPs with an average size of 170 nm, neutral surface charge and 3% of semaglutide loading were obtained. Both FcRn-targeted NPs exhibited improved interaction and association with Caco-2 cells (cells that endogenously express the hFcRn), compared to non-targeted NPs. Additionally, the uptake of FcRn-targeted NPs was also observed to occur in human intestinal organoids (HIOs) expressing hFcRn through microinjection into the lumen of HIOs, resulting in potential increase of semaglutide permeability for both ligand-functionalized nanocarriers. Herein, our study demonstrates valuable data and insights that the FcRn-targeted NPs has the capacity to promote intestinal absorption of therapeutic peptides.

Respiratory distress in SARS-CoV-2 exposed uninfected neonates followed in the COVID Outcomes in Mother-Infant Pairs (COMP) Study

Respiratory distress (RD) has been reported in SARS-CoV-2 exposed uninfected (SEU) term neonates. Prior studies suggest that prenatal exposure to Coronavirus Disease 19 (COVID-19) may activate an inflammatory cascade in the newborn airway. In this study, we examine the relationship between maternal COVID-19 vaccination and neonatal RD using a longitudinal cohort of mother-infant pairs in Los Angeles, CA. Two-hundred and twenty-one mothers with laboratory confirmed SARS-CoV-2 during pregnancy and 227 exposed fetuses are enrolled in our study. Maternal disease severity and neonatal RD variables were defined based on current accepted clinical criteria. To explore the multifactorial associations between maternal COVID-19 parameters and infant RD, we utilize a multivariable logistic regression model and a proteomic sub-analysis to propose a pathway for the development of RD following in utero exposure to SARS-CoV-2. Unusually high rates of RD are observed in SEU infants (17%). The odds ratio of RD is 3.06 (95% CI:1.08-10.21) in term neonates born to unvaccinated individuals versus those born to individuals vaccinated prior to maternal infection. Proteomic analysis reveals a robust inflammatory response associated with ciliary dysregulation and enhanced IgE production among SEU neonates with RD. Maternal vaccination against COVID-19 reduces the frequency of neonatal RD.

Understanding Fc function for rational vaccine design against pathogens

Antibodies represent the primary correlate of immunity following most clinically approved vaccines. However, their mechanisms of action vary from pathogen to pathogen, ranging from neutralization, to opsonophagocytosis, to cytotoxicity. Antibody functions are regulated both by antigen specificity (Fab domain) and by the interaction of their Fc domain with distinct types of Fc receptors (FcRs) present in immune cells. Increasing evidence highlights the critical nature of Fc:FcR interactions in controlling pathogen spread and limiting the disease state. Moreover, variation in Fc-receptor engagement during the course of infection has been demonstrated across a range of pathogens, and this can be further influenced by prior exposure(s)/immunizations, age, pregnancy, and underlying health conditions. Fc:FcR functional variation occurs at the level of antibody isotype and subclass selection as well as post-translational modification of antibodies that shape Fc:FcR-interactions. These factors collectively support a model whereby the immune system actively harnesses and directs Fc:FcR interactions to fight disease. By defining the precise humoral mechanisms that control infections, as well as understanding how these functions can be actively tuned, it may be possible to open new paths for improving existing or novel vaccines.

The many facets of immune-mediated thrombocytopenia: Principles of immunobiology and immunotherapy

Immune thrombocytopenia (ITP) is a rare autoimmune condition, due to peripheral platelet destruction through antibody-dependent cellular phagocytosis, complement-dependent cytotoxicity, cytotoxic T lymphocyte-mediated cytotoxicity, and megakaryopoiesis alteration. This condition may be idiopathic or triggered by drugs, vaccines, infections, cancers, autoimmune disorders and systemic diseases. Recent advances in our understanding of ITP immunobiology support the idea that other forms of thrombocytopenia, for instance, occurring after immunotherapy or cellular therapies, may share a common pathophysiology with possible therapeutic implications. If a decent pipeline of old and new agents is currently deployed for classical ITP, in other more complex immune-mediated thrombocytopenic disorders, clinical management is less harmonized and would deserve further prospective investigations. Here, we seek to provide a fresh overview of pathophysiology and current therapeutical algorithms for adult patients affected by this disorder with specific insights into poorly codified scenarios, including refractory ITP and post-immunotherapy/cellular therapy immune-mediated thrombocytopenia.

A Interacting Model: How TRIM21 Orchestrates with Proteins in Intracellular Immunity

Tripartite motif-containing protein 21 (TRIM21), identified as both a cytosolic E3 ubiquitin ligase and FcR (Fragment crystallizable receptor), primarily interacts with proteins via its PRY/SPRY domains and promotes their proteasomal degradation to regulate intracellular immunity. But how TRIM21 involves in intracellular immunity still lacks systematical understanding. Herein, it is probed into the TRIM21-related literature and raises an interacting model about how TRIM21 orchestrates proteins in cytosol. In this novel model, TRIM21 generally interacts with miscellaneous protein in intracellular immunity in two ways: For one, TRIM21 solely plays as an E3, ubiquitylating a glut of proteins that contain specific interferon-regulatory factor, nuclear transcription factor kappaB, virus sensors and others, and involving inflammatory responses. For another, TRIM21 serves as both E3 and specific FcR that detects antibody-complexes and facilitates antibody destroying target proteins. Correspondingly delineated as Fc-independent signaling and Fc-dependent signaling in this review, how TRIM21's interactions contribute to intracellular immunity, expecting to provide a systematical understanding of this important protein and invest enlightenment for further research on the pathogenesis of related diseases and its prospective application is elaborated.

Spatial Transcriptomics Resolve an Emphysema-Specific Lymphoid Follicle B Cell Signature in Chronic Obstructive Pulmonary Disease

Rationale: Within chronic obstructive pulmonary disease (COPD), emphysema is characterized by a significant yet partially understood B cell immune component. Objectives: To characterize the transcriptomic signatures from lymphoid follicles (LFs) in ever-smokers without COPD and patients with COPD with varying degrees of emphysema. Methods: Lung sections from 40 patients with COPD and ever-smokers were used for LF proteomic and transcriptomic spatial profiling. Formalin- and O.C.T.-fixed lung samples obtained from biopsies or lung explants were assessed for LF presence. Emphysema measurements were obtained from clinical chest computed tomographic scans. High-confidence transcriptional target intersection analyses were conducted to resolve emphysema-induced transcriptional networks. Measurements and Main Results: Overall, 115 LFs from ever-smokers and Global Initiative for Chronic Obstructive Lung Disease (GOLD) 1-2 and GOLD 3-4 patients were analyzed. No LFs were found in never-smokers. Differential gene expression analysis revealed significantly increased expression of LF assembly and B cell marker genes in subjects with severe emphysema. High-confidence transcriptional analysis revealed activation of an abnormal B cell activity signature in LFs (q-value = 2.56E-111). LFs from patients with GOLD 1-2 COPD with emphysema showed significantly increased expression of genes associated with antigen presentation, inflammation, and B cell activation and proliferation. LFs from patients with GOLD 1-2 COPD without emphysema showed an antiinflammatory profile. The extent of centrilobular emphysema was significantly associated with genes involved in B cell maturation and antibody production. Protein-RNA network analysis showed that LFs in emphysema have a unique signature skewed toward chronic B cell activation. Conclusions: An off-targeted B cell activation within LFs is associated with autoimmune-mediated emphysema pathogenesis.

Intracellular Pathogens: Infection, Immunity, and Intervention

Intracellular pathogens comprise a diverse group of pathogens that all share a required location in a host cell to infect, survive, and replicate. Intracellular location allows pathogens to hide from host immune responses, avoid competition with other pathogens, mediate host cellular functions, replicate safely, and cause infection that is difficult to target with therapeutics. All intracellular pathogens have varying routes of infiltration into host cells and different host cell preferences. For example, bacteria Mycobacterium tuberculosis chooses to invade antigen-presenting cells, which allows them to moderate host antigen presentation to memory cells, whereas rabies virus prefers to invade neurons because they have pre-existing innate immunity protection systems. Regardless of the pathway that each intracellular pathogen follows, all share the capacity to cause disease if they succeed in entering host cells. Here, we give an overview of selected intracellular pathogens and infections they cause, immune responses they induce, and intervention strategies used to treat and control them.

Cell-based production of Fc-GlcNAc and Fc-alpha-2,6 sialyl glycan enriched antibody with improved effector functions through glycosylation pathway engineering

Glycosylation of antibody plays an important role in Fc-mediated killing of tumor cells and virus-infected cells through effector functions such as antibody-dependent cellular cytotoxicity (ADCC), antibody dependent cell-mediated phagocytosis (ADCP) and vaccinal effect. Previous studies showed that therapeutical humanized antibodies with α2-6 sialyl complex type (SCT) glycan attached to Fc-Asn297 exhibited optimal binding to the Fc receptors on effector cells associated with ADCC, ADCP and vaccinal effect. However, the production of antibodies with homogeneous Fc-SCT needs multiple in vitro enzymatic and purification steps. In this study, we report two different approaches to shorten the processes to produce SCT-enriched antibodies. First, we expressed a bacterial endoglycosidase in GNT1-KO EXPI293 cells to trim all N -glycans to mono-GlcNAc glycoforms for in vitro transglycosylation to generate homogeneous SCT antibody. Second, we engineered the glycosylation pathway of HEK293 cells through knockout of the undesired glycosyltransferases and expression of the desired glycosyltransferases to produce SCT enriched antibodies with similar binding affinity to Fc receptors and ADCC activity to homogenous SCT antibody.

An immunomodulatory role of Fc receptor γ chain independent of FcγR ligation by IgG in acute neuroinflammation triggered by MPTP intoxication

Aberrant microglial activation is a prominent feature of neuroinflammation, which is implicated in the pathogenesis of neurological disorders. Fc receptor common γ-chain (FcRγ), one of the two immunoreceptor tyrosine-based activation motif-bearing adaptor proteins, is abundantly expressed in microglia. It couples with different receptors, such as receptors for the Fc portion of IgG. In this study, we observed increased FcRγ expression along with increased IgG-binding during acute neuroinflammation triggered by MPTP intoxication, where adaptive immune responses should not be involved. Notably, FcRγ was expressed not only in the cell membrane but also in the cytoplasm in the activated microglia. FcRγ deficiency exacerbated microglial activation, pro-inflammatory factor upregulation, nigral dopaminergic neuronal loss and motor deficits, implicating a beneficial role of FcRγ in this model. Blockade of Fcγ receptor ligation by IgG in mice by Endoglycosidase S treatment, a bacterial endo-β-N-acetylglucosaminidase cleaving specifically the Asn297-linked glycan of IgG, or by using the mice deficient in mature B cells (muMT) with IgG production defects, did not show similar phenotypes to those observed in FcRγ-deficient mice, indicating that the beneficial effect mediated by FcRγ did not depend on FcγR ligation by IgG. Further, FcRγ knockout aggravated the expression and activation of STAT1 in microglia, suggesting FcRγ modulated neuroinflammation by dampening STAT1 signaling. Collectively, these results revealed that FcRγ-associated receptors could function as negative regulators of neuroinflammation and dopaminergic neurodegeneration.

Neutrophils in Inflammatory Diseases: Unraveling the Impact of Their Derived Molecules and Heterogeneity

Inflammatory diseases involve numerous disorders and medical conditions defined by an insufficient level of self-tolerance. These diseases evolve over the course of a multi-step process through which environmental variables play a crucial role in the emergence of aberrant innate and adaptive immunological responses. According to experimental data accumulated over the past decade, neutrophils play a significant role as effector cells in innate immunity. However, neutrophils are also involved in the progression of numerous diseases through participation in the onset and maintenance of immune-mediated dysregulation by releasing neutrophil-derived molecules and forming neutrophil extracellular traps, ultimately causing destruction of tissues. Additionally, neutrophils have a wide variety of functional heterogeneity with adverse effects on inflammatory diseases. However, the complicated role of neutrophil biology and its heterogeneity in inflammatory diseases remains unclear. Moreover, neutrophils are considered an intriguing target of interventional therapies due to their multifaceted role in a number of diseases. Several approaches have been developed to therapeutically target neutrophils, involving strategies to improve neutrophil function, with various compounds and inhibitors currently undergoing clinical trials, although challenges and contradictions in the field persist. This review outlines the current literature on roles of neutrophils, neutrophil-derived molecules, and neutrophil heterogeneity in the pathogenesis of autoimmune and inflammatory diseases with potential future therapeutic strategies.

Biomimetic Systems Involving Macrophages and Their Potential for Targeted Drug Delivery

The concept of targeted drug delivery can be described in terms of the drug systems' ability to mimic the biological objects' property to localize to target cells or tissues. For example, drug delivery systems based on red blood cells or mimicking some of their useful features, such as long circulation in stealth mode, have been known for decades. On the contrary, therapeutic strategies based on macrophages have gained very limited attention until recently. Here, we review two biomimetic strategies associated with macrophages that can be used to develop new therapeutic modalities: first, the mimicry of certain types of macrophages (i.e., the use of macrophages, including tumor-associated or macrophage-derived particles as a carrier for the targeted delivery of therapeutic agents); second, the mimicry of ligands, naturally absorbed by macrophages (i.e., the use of therapeutic agents specifically targeted at macrophages). We discuss the potential applications of biomimetic systems involving macrophages for new advancements in the treatment of infections, inflammatory diseases, and cancer.

Serum immunoglobulin and the threshold of Fc receptor-mediated immune activation

Antibodies can mediate immune recruitment or clearance of immune complexes through the interaction of their Fc domain with cellular Fc receptors. Clustering of antibodies is a key step in generating sufficient avidity for efficacious receptor recognition. However, Fc receptors may be saturated with prevailing, endogenous serum immunoglobulin and this raises the threshold by which cellular receptors can be productively engaged. Here, we review the factors controlling serum IgG levels in both healthy and disease states, and discuss how the presence of endogenous IgG is encoded into the functional activation thresholds for low- and high-affinity Fc receptors. We discuss the circumstances where antibody engineering can help overcome these physiological limitations of therapeutic antibodies. Finally, we discuss how the pharmacological control of Fc receptor saturation by endogenous IgG is emerging as a feasible mechanism for the enhancement of antibody therapeutics.

Anti-phospholipid autoantibodies in human diseases

Anti-phospholipid autoantibodies are a group of antibodies that can specifically bind to anionic phospholipids and phospholipid protein complexes. Recent studies have reported elevated serum anti-phospholipid autoantibody levels in patients with antiphospholipid syndrome, systemic lupus erythematosus, rheumatoid arthritis, metabolic disorders, malaria, SARS-CoV-2 infection, obstetric diseases and cardiovascular diseases. However, the underlying mechanisms of anti-phospholipid autoantibodies in disease pathogenesis remain largely unclear. Emerging evidence indicate that anti-phospholipid autoantibodies modulate NETs formation, monocyte activation, blockade of apoptotic cell phagocytosis in macrophages, complement activation, dendritic cell activation and vascular endothelial cell activation. Herein, we provide an update on recent advances in elucidating the effector mechanisms of anti-phospholipid autoantibodies in the pathogenesis of various diseases, which may facilitate the development of potential therapeutic targets for the treatment of anti-phospholipid autoantibody-related disorders.

Genetic analysis of potential biomarkers and therapeutic targets in age-related hearing loss

Age-related hearing loss (ARHL) or presbycusis is the phenomenon of hearing loss due to the aging of auditory organs with age. It seriously affects the cognitive function and quality of life of the elderly. This study is based on comprehensive bioinformatic and machine learning methods to identify the critical genes of ARHL and explore its therapy targets and pathological mechanisms. The ARHL and normal samples were from GSE49543 datasets of the Gene Expression Omnibus (GEO) database. Weighted gene co-expression network analysis (WGCNA) was applied to obtain significant modules. The Limma R-package was used to identify differentially expressed genes (DEGs). The 15 common genes of the practical module and DEGs were screened. Functional enrichment analysis suggested that these genes were mainly associated with inflammation, immune response, and infection. Cytoscape software created the protein-protein interaction (PPI) layouts and cytoHubba, support vector machine-recursive feature elimination (SVM-RFE), and random forests (RF) algorithms screened hub genes. After validating the hub gene expressions in GSE6045 and GSE154833 datasets, Clec4n, Mpeg1, and Fcgr3 are highly expressed in ARHL and have higher diagnostic efficacy for ARHL, so they were identified as hub genes. In conclusion, Clec4n, Mpeg1, and Fcgr3 play essential roles in developing ARHL, and they might become vital targets in ARHL diagnosis and anti-inflammatory therapy.

IgG and insulin enhance endocytosis in THP-1 cells via activation of phosphatidylinositol 3-kinase (PI3K)

Extracellular substances, including membrane-impermeable nutrients, are taken up by cells via endocytosis. Endocytosis is also an important pathway for antigen uptake by antigen-presenting cells such as monocytes, macrophages, dendritic cells, and B cells. In this study, we investigated the regulatory mechanism of endocytosis in THP-1 cells, a monocytic leukemia cell line. We analyzed the effect of IgG and insulin, which are abundant in the serum and play important roles in immunity and metabolism, respectively, on the endocytic activity in THP-1 cells. The results indicated that IgG and insulin enhance pinocytosis and phagocytosis via activation of phosphatidylinositol 3-kinase (PI3K). Our results suggest that IgG and insulin contribute to the maintenance of endocytic activity and are important for antigen presentation and nutrient uptake.

Exploring molecular interactions of potential inhibitors against the spleen tyrosine kinase implicated in autoimmune disorders via virtual screening and molecular dynamics simulations

The spleen tyrosine kinase (Syk) plays a pivotal role in immune cells' signal transduction mechanism. While fostamatinib, an FDA-approved Syk inhibitor, is currently used to treat immune thrombocytopenia, the search for improved Syk-targeted medications to treat autoimmune diseases is still underway. Herein, we screened 38,493 compounds against Syk and selected eight leads based on the docking score and ADMET properties, and performed 3× 200 ns long molecular dynamics simulations of the apo and Syk-ligand complexes. We considered R406, the active component of fostamatinib, as a control. The molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) calculations demonstrated the lead1 (Δ G b i n d  = -30.35 kcal/mol) exhibited a similar binding free energy as the control (Δ G b i n d = -29.82 kcal/mol). The Syk stabilizing effect of lead1 was also indicated in its network features, sampling space, and residual correlation motion analysis. We further generated 100 structural analogues of lead1 using deep learning, and one of the analogues displayed a better binding free energy (Δ G b i n d = -47.58 kcal/mol) compared to the control or lead1, facilitated by more favourable van der Waals interactions and lesser binding-opposing net polar forces. This analogue may be further exploited to develop effective therapeutics against Syk-associated diseases after validation in vitro and in vivo.

Platelet-derived circulating soluble P-selectin is sufficient to induce hematopoietic stem cell mobilization

BACKGROUND

Granulocyte colony-stimulating factor (G-CSF)-mediated mobilization of hematopoietic stem cells (HSCs) is a well-established method to prepare HSCs for transplantation nowadays. A sufficient number of HSCs is critical for successful HSC transplantation. However, approximately 2-6% of healthy stem cell donors are G-CSF-poor mobilizers for unknown reasons; thus increasing the uncertainties of HSC transplantation. The mechanism underlining G-CSF-mediated HSC mobilization remains elusive, so detailed mechanisms and an enhanced HSC mobilization strategy are urgently needed. Evidence suggests that P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1) are one of the cell-cell adhesion ligand-receptor pairs for HSCs to keep contacting bone marrow (BM) stromal cells before being mobilized into circulation. This study hypothesized that blockage of PSGL-1 and P-selectin may disrupt HSC-stromal cell interaction and facilitate HSC mobilization.

METHODS

The plasma levels of soluble P-selectin (sP-sel) before and after G-CSF administration in humans and male C57BL/6J mice were analyzed using enzyme-linked immunosorbent assay. Male mice with P-selectin deficiency (Selp-/-) were further employed to investigate whether P-selectin is essential for G-CSF-induced HSC mobilization and determine which cell lineage is sP-sel derived from. Finally, wild-type mice were injected with either G-CSF or recombinant sP-sel to investigate whether sP-sel alone is sufficient for inducing HSC mobilization and whether it accomplishes this by binding to HSCs and disrupting their interaction with stromal cells in the BM.

RESULTS

A significant increase in plasma sP-sel levels was observed in humans and mice following G-CSF administration. Treatments of G-CSF induced a decrease in the level of HSC mobilization in Selp-/- mice compared with the wild-type (Selp+/+) controls. Additionally, the transfer of platelets derived from wild-type mice can ameliorate the defected HSC mobilization in the Selp-/- recipients. G-CSF induces the release of sP-sel from platelets, which is sufficient to mobilize BM HSCs into the circulation of mice by disrupting the PSGL-1 and P-selectin interaction between HSCs and stromal cells. These results collectively suggested that P-selectin is a critical factor for G-CSF-induced HSC mobilization.

CONCLUSIONS

sP-sel was identified as a novel endogenous HSC-mobilizing agent. sP-sel injections achieved a relatively faster and more convenient regimen to mobilize HSCs in mice than G-CSF. These findings may serve as a reference for developing and optimizing human HSC mobilization in the future.

Coexpression analysis of lncRNAs and mRNAs identifies potential regulatory long noncoding RNAs involved in the inflammatory effects of lipopolysaccharide on bovine mammary epithelial cells

BACKGROUND

The infection of bovine mammary glands by pathogenic microorganisms not only causes animal distress but also greatly limits the development of the dairy industry and animal husbandry. A deeper understanding of the host's initial response to infection may increase the accuracy of selecting drug-resistant animals or facilitate the development of new preventive or therapeutic intervention strategies. In addition to their functions of milk synthesis and secretion, bovine mammary epithelial cells (BMECs) play an irreplaceable role in the innate immune response. To better understand this process, the current study identified differentially expressed long noncoding lncRNAs (DE lncRNAs) and mRNAs (DE mRNAs) in BMECs exposed to Escherichia coli lipopolysaccharide (LPS) and further explored the functions and interactions of these lncRNAs and mRNAs.

RESULTS

In this study, transcriptome analysis was performed by RNA sequencing (RNA-seq), and the functions of the DE mRNAs and DE lncRNAs were predicted by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. Next, we constructed a modulation network to gain a deeper understanding of the interactions and roles of these lncRNAs and mRNAs in the context of LPS-induced inflammation. A total of 231 DE lncRNAs and 892 DE mRNAs were identified. Functional enrichment analysis revealed that pathways related to inflammation and the immune response were markedly enriched in the DE genes. In addition, research results have shown that cell death mechanisms, such as necroptosis and pyroptosis, may play key roles in LPS-induced inflammation.

CONCLUSIONS

In summary, the current study identified DE lncRNAs and mRNAs and predicted the signaling pathways and biological processes involved in the inflammatory response of BMECs that might become candidate therapeutic and prognostic targets for mastitis. This study also revealed several possible pathogenic mechanisms of mastitis.

Emerging roles for ITAM and ITIM receptor signaling in microglial biology and Alzheimer's disease-related amyloidosis

Microglia are critical responders to amyloid beta (Aβ) plaques in Alzheimer's disease (AD). Therefore, the therapeutic targeting of microglia in AD is of high clinical interest. While previous investigation has focused on the innate immune receptors governing microglial functions in response to Aβ plaques, how microglial innate immune responses are regulated is not well understood. Interestingly, many of these microglial innate immune receptors contain unique cytoplasmic motifs, termed immunoreceptor tyrosine-based activating and inhibitory motifs (ITAM/ITIM), that are commonly known to regulate immune activation and inhibition in the periphery. In this review, we summarize the diverse functions employed by microglia in response to Aβ plaques and also discuss the innate immune receptors and intracellular signaling players that guide these functions. Specifically, we focus on the role of ITAM and ITIM signaling cascades in regulating microglia innate immune responses. A better understanding of how microglial innate immune responses are regulated in AD may provide novel therapeutic avenues to tune the microglial innate immune response in AD pathology.

FcγRIIB expression increases during primary biliary cholangitis

Primary biliary cholangitis (PBC) is a severe disease with unknown aetiology and poor prognosis owing to ineffective treatment. B-cell antibodies play a regulatory role during immune responses; therefore, their role in PBC should not be overlooked. Fcγ receptors (FcγRs) of IgG and cell surface glycoproteins play an important role in autoimmune and infectious disease prevention. In this study, 60 patients with PBC and 35 healthy controls (HCs) were recruited. The number of B cells and the expression of the FcγRIIB on the peripheral blood mononuclear cells of patients with PBC were evaluated using FACS. The concentrations of soluble FcγRs were determined using ELISA, and intrahepatic FcγRIIB and CD19 expressions in patients with PBC were visualised using IHC. FcγRIIB expression in B cells was significantly higher in patients with PBC than in HCs (P < 0.0001). The soluble FcγRIIB levels in the plasma were higher in patients with PBC than in HCs (P = 0.0009). Notably, these levels were reduced by treatment with ursodeoxycholic acid (P = 0.0236). CD19 and FcγRIIB expression increased in the liver of patients with PBC relative to that in HCs. These findings can provide new insights into PBC pathogenesis and can aid the future development of treatment strategies.

Function-structure approach reveals novel insights on the interplay of Immunoglobulin G 1 proteoforms and Fc gamma receptor IIa allotypes

Human Fc gamma receptor IIa (FcγRIIa) or CD32a has two major allotypes with a single amino acid difference at position 131 (histidine or arginine). Differences in FcγRIIa allotypes are known to impact immunological responses such as the clinical outcome of therapeutic monoclonal antibodies (mAbs). FcγRIIa is involved in antibody-dependent cellular phagocytosis (ADCP), which is an important contributor to the mechanism-of-action of mAbs by driving phagocytic clearance of cancer cells. Hence, understanding the impact of individual mAb proteoforms on the binding to FcγRIIa, and its different allotypes, is crucial for defining meaningful critical quality attributes (CQAs). Here, we report a function-structure based approach guided by novel FcγRIIa affinity chromatography-mass spectrometry (AC-MS) assays to assess individual IgG1 proteoforms. This allowed to unravel allotype-specific differences of IgG1 proteoforms on FcγRIIa binding. FcγRIIa AC-MS confirmed and refined structure-function relationships of IgG1 glycoform interactions. For example, the positive impact of afucosylation was higher than galactosylation for FcγRIIa Arg compared to FcγRIIa His. Moreover, we observed FcγRIIa allotype-opposing and IgG1 proteoform integrity-dependent differences in the binding response of stress-induced IgG1 proteoforms comprising asparagine 325 deamidation. The FcγRIIa-allotype dependent binding differences resolved by AC-MS were in line with functional ADCP-surrogate bioassay models. The molecular basis of the observed allotype specificity and proteoform selectivity upon asparagine 325 deamidation was elucidated using molecular dynamics. The observed differences were attributed to the contributions of an inter-molecular salt bridge between IgG1 and FcγRIIa Arg and the contribution of an intra-molecular hydrophobic pocket in IgG1. Our work highlights the unprecedented structural and functional resolution of AC-MS approaches along with predictive biological significance of observed affinity differences within relevant cell-based methods. This makes FcγRIIa AC-MS an invaluable tool to streamline the CQA assessment of therapeutic mAbs.

Proteomic analysis of signaling pathways modulated by FABP5 in macrophages

Background

While acute inflammation serves essential functions in maintaining tissue homeostasis, chronic inflammation is causally linked to many diseases. Macrophages are a major cell-type that orchestrates inflammatory processes. During inflammation, macrophages undergo polarization and activation, thereby mobilizing pro-inflammatory and anti-inflammatory transcriptional programs that regulate ensuing macrophage functions. Fatty acid binding protein 5 (FABP5) is a lipid chaperone that is highly expressed in macrophages. FABP5 deletion is implicated in driving macrophages towards an anti-inflammatory phenotype, yet the signaling pathways regulated by macrophage FABP5 have not been systematically profiled. Herein, we leveraged proteomic and phosphoproteomic approaches to characterize pathways modulated by FABP5 in M1 and M2 polarized bone marrow derived macrophages (BMDMs).

Results

Stable isotope labeling by amino acids (SILAC) based analysis of M1 and M2 polarized wild-type (WT) and FABP5 knockout (KO) BMDMs revealed numerous differentially regulated proteins and phosphoproteins. FABP5 deletion impacted several downstream pathways associated with inflammation, cytokine production, oxidative stress, and kinase activity. Kinase enrichment analysis based on phosphorylated sites revealed key kinases, including members of the GRK family, that were altered in FABP5 KO BMDMs. Reactive oxygen species (ROS) levels were elevated in M1 polarized KO macrophages, consistent with the differential protein expression profiles.

Conclusions

This study represents a comprehensive characterization of the impact of FABP5 deletion upon the proteomic and phosphoproteomic landscape of M1 and M2 polarized BMDMs. Loss of FABP5 altered multiple pathways implicated in inflammatory responses and macrophage function. This work provides a foundation for future studies seeking to investigate the therapeutic potential of FABP5 inhibition in pathophysiological states resulting from dysregulated inflammatory signaling.

Dynamics of inflammatory responses after SARS-CoV-2 infection by vaccination status in the USA: a prospective cohort study

BACKGROUND

Cytokines and chemokines play a critical role in the response to infection and vaccination. We aimed to assess the longitudinal association of COVID-19 vaccination with cytokine and chemokine concentrations and trajectories among people with SARS-CoV-2 infection.

METHODS

In this longitudinal, prospective cohort study, blood samples were used from participants enrolled in a multi-centre randomised trial assessing the efficacy of convalescent plasma therapy for ambulatory COVID-19. The trial was conducted in 23 outpatient sites in the USA. In this study, participants (aged ≥18 years) were restricted to those with COVID-19 before vaccination or with breakthrough infections who had blood samples and symptom data collected at screening (pre-transfusion), day 14, and day 90 visits. Associations between COVID-19 vaccination status and concentrations of 21 cytokines and chemokines (measured using multiplexed sandwich immunoassays) were examined using multivariate linear mixed-effects regression models, adjusted for age, sex, BMI, hypertension, diabetes, trial group, and COVID-19 waves (pre-alpha or alpha and delta).

FINDINGS

Between June 29, 2020, and Sept 30, 2021, 882 participants recently infected with SARS-CoV-2 were enrolled, of whom 506 (57%) were female and 376 (43%) were male. 688 (78%) of 882 participants were unvaccinated, 55 (6%) were partly vaccinated, and 139 (16%) were fully vaccinated at baseline. After adjusting for confounders, geometric mean concentrations of interleukin (IL)-2RA, IL-7, IL-8, IL-15, IL-29 (interferon-λ), inducible protein-10, monocyte chemoattractant protein-1, and tumour necrosis factor-α were significantly lower among the fully vaccinated group than in the unvaccinated group at screening. On day 90, fully vaccinated participants had approximately 20% lower geometric mean concentrations of IL-7, IL-8, and vascular endothelial growth factor-A than unvaccinated participants. Cytokine and chemokine concentrations decreased over time in the fully and partly vaccinated groups and unvaccinated group. Log10 cytokine and chemokine concentrations decreased faster among participants in the unvaccinated group than in other groups, but their geometric mean concentrations were generally higher than fully vaccinated participants at 90 days. Days since full vaccination and type of vaccine received were not correlated with cytokine and chemokine concentrations.

INTERPRETATION

Initially and during recovery from symptomatic COVID-19, fully vaccinated participants had lower concentrations of inflammatory markers than unvaccinated participants suggesting vaccination is associated with short-term and long-term reduction in inflammation, which could in part explain the reduced disease severity and mortality in vaccinated individuals.

FUNDING

US Department of Defense, National Institutes of Health, Bloomberg Philanthropies, State of Maryland, Mental Wellness Foundation, Moriah Fund, Octapharma, HealthNetwork Foundation, and the Shear Family Foundation.

AutoCore: A network-based definition of the core module of human autoimmunity and autoinflammation

Although research on rare autoimmune and autoinflammatory diseases has enabled definition of nonredundant regulators of homeostasis in human immunity, because of the single gene-single disease nature of many of these diseases, contributing factors were mostly unveiled in sequential and noncoordinated individual studies. We used a network-based approach for integrating a set of 186 inborn errors of immunity with predominant autoimmunity/autoinflammation into a comprehensive map of human immune dysregulation, which we termed "AutoCore." The AutoCore is located centrally within the interactome of all protein-protein interactions, connecting and pinpointing multidisease markers for a range of common, polygenic autoimmune/autoinflammatory diseases. The AutoCore can be subdivided into 19 endotypes that correspond to molecularly and phenotypically cohesive disease subgroups, providing a molecular mechanism-based disease classification and rationale toward systematic targeting for therapeutic purposes. Our study provides a proof of concept for using network-based methods to systematically investigate the molecular relationships between individual rare diseases and address a range of conceptual, diagnostic, and therapeutic challenges.

The interplay between PEGylated nanoparticles and blood immune system

During the last two decades, an increasing number of reports have pointed out that the immunogenicity of polyethylene glycol (PEG) may trigger accelerated blood clearance (ABC) and hypersensitivity reaction (HSR) to PEGylated nanoparticles, which could make PEG modification counterproductive. These phenomena would be detrimental to the efficacy of the load and even life-threatening to patients. Consequently, further elucidation of the interplay between PEGylated nanoparticles and the blood immune system will be beneficial to developing and applying related formulations. Many groups have worked to unveil the relevance of structural factors, dosing schedule, and other factors to the ABC phenomenon and hypersensitivity reaction. Interestingly, the results of some reports seem to be difficult to interpret or contradict with other reports. In this review, we summarize the physiological mechanisms of PEG-specific immune response. Moreover, we speculate on the potential relationship between the induction phase and the effectuation phase to explain the divergent results in published reports. In addition, the role of nanoparticle-associated factors is discussed based on the classification of the action phase. This review may help researchers to develop PEGylated nanoparticles to avoid unfavorable immune responses based on the underlying mechanism.

Downregulated APOD and FCGR2A correlates with immune infiltration and lipid-induced symptoms of irritable bowel syndrome

Fat intake is among the most significant triggers for symptom development in patients with irritable bowel syndrome (IBS). Nevertheless, long-term restriction in fatty foods ingestion may lead to nutritional inadequacies. This study aimed to identify the crucial genes involved in lipid-induced gastrointestinal symptoms, contributing to helping IBS patients regulate fat. The clinical characteristics of the subjects were collected by questionnaire investigation and analyzed using multivariate logistic regression. Differentially expressed genes (DEG) and signaling pathways were analyzed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. ImmuInfiltration and CIBERSORT packages evaluated small intestine immune cell infiltration. Random forest and SVM-RFE algorithms were used to select hub genes. A receiver operating characteristic curve was used to access the diagnostic significance of each hub gene. Gene Set Enrichment Analysis (GSEA) was performed to identify hub genes' molecular processes in IBS development after lipid infusion. IBS patients' risk, severity, and quality of life increased with fat intake. In total, 116 robust DEGs were identified in IBS patients after lipid infusion using the GSE166869 dataset and were mainly clustered in the immune and inflammatory pathways. IBS patients had greater Neutrophils, CD4+ T cells, and M1 Macrophages than healthy controls. Furthermore, infiltration levels of Neutrophils and resting memory CD4+ T cells were inversely related to the expression of hub genes (IGKV1D-43, IGKV1-12, APOD, FCGR2A and IGKV2-29). After lipid infusion, GSEA results of each hub gene indicated the relevance of proinflammatory pathways in IBS pathogenesis. After verification, only APOD and FCGR2A were stably downregulated in small intestinal mucosa and plasma of IBS patients. The area under the curve of APOD combined with FCGR2A expression was 0.9. APOD and FCGR2A may be promising biomarkers for IBS diagnosis and lipid-sensitive IBS patients. Their potential roles in the immune microenvironment of the small intestinal mucosa may provide a vital clue to IBS precision therapy.

Characterization of covalent inhibitors that disrupt the interaction between the tandem SH2 domains of SYK and FCER1G phospho-ITAM

RNA sequencing and genetic data support spleen tyrosine kinase (SYK) and high affinity immunoglobulin epsilon receptor subunit gamma (FCER1G) as putative targets to be modulated for Alzheimer's disease (AD) therapy. FCER1G is a component of Fc receptor complexes that contain an immunoreceptor tyrosine-based activation motif (ITAM). SYK interacts with the Fc receptor by binding to doubly phosphorylated ITAM (p-ITAM) via its two tandem SH2 domains (SYK-tSH2). Interaction of the FCER1G p-ITAM with SYK-tSH2 enables SYK activation via phosphorylation. Since SYK activation is reported to exacerbate AD pathology, we hypothesized that disruption of this interaction would be beneficial for AD patients. Herein, we developed biochemical and biophysical assays to enable the discovery of small molecules that perturb the interaction between the FCER1G p-ITAM and SYK-tSH2. We identified two distinct chemotypes using a high-throughput screen (HTS) and orthogonally assessed their binding. Both chemotypes covalently modify SYK-tSH2 and inhibit its interaction with FCER1G p-ITAM.

Fc receptors act as innate immune receptors during infection?

Innate immunity constitutes the first nonspecific immunological line of defense against infection. In this response, a variety of mechanisms are activated: the complement system, phagocytosis, and the inflammatory response. Then, adaptive immunity is activated. Major opsonization mediators during infections are immunoglobulins (Igs), the function of which is mediated through Fc receptors (FcRs). However, in addition to their role in adaptive immunity, FcRs have been shown to play a role in innate immunity by interacting directly with bacteria in the absence of their natural ligands (Igs). Additionally, it has been hypothesized that during the early phase of bacterial infection, FcRs play a protective role via innate immune functions mediated through direct recognition of bacteria, and as the infection progresses to later phases, FcRs exhibit their established function as receptors in adaptive immunity. This review provides detailed insight into the potential role of FcRs as innate immune mediators of the host defense against bacterial infection independent of opsonins.

A Review: Understanding Molecular Mechanisms of Antibody-Dependent Enhancement in Viral Infections

Antibody Dependent Enhancement (ADE) of an infection has been of interest in the investigation of many viruses. It is associated with the severity of the infection. ADE is mediated by non-neutralizing antibodies, antibodies at sub-neutralizing concentrations, or cross-reactive non-neutralizing antibodies. Treatments like plasma therapy, B cell immunizations, and antibody therapies may trigger ADE. It is seen as an impediment to vaccine development as well. In viruses including the Dengue virus (DENV), severe acute respiratory syndrome (SARS) virus, Middle East respiratory syndrome (MERS) virus, human immunodeficiency virus (HIV), Ebola virus, Zika virus, and influenza virus, the likely mechanisms of ADE are postulated and described. ADE improves the likelihood of productively infecting cells that are expressing the complement receptor or the Fc receptor (FcR) rather than the viral receptors. ADE occurs when the FcR, particularly the Fc gamma receptor, and/or complement system, particularly Complement 1q (C1q), allow the entry of the virus-antibody complex into the cell. Moreover, ADE alters the innate immune pathways to escape from lysis, promoting viral replication inside the cell that produces viral particles. This review discusses the involvement of FcR and the downstream immunomodulatory pathways in ADE, the complement system, and innate antiviral signaling pathways modification in ADE and its impact on facilitating viral replication. Additionally, we have outlined the modes of ADE in the cases of different viruses reported until now.

The presence of activating IgG Fc receptors in macrophages aggravates the development of experimental abdominal aortic aneurysm

INTRODUCTION

Abdominal aortic aneurysm (AAA) is a multifactorial, degenerative disease characterized by progressive aortic dilation and chronic activation of inflammation, proteolytic activity, and oxidative stress in the aortic wall. The immune response triggered by antibodies against antigens present in the vascular wall participates in the formation and progression of AAA through mechanisms not completely understood. This work analyses the function of specific IgG receptors (FcγR), especially those expressed by monocytes/macrophages, in the development of experimental AAA.

METHODS

In the elastase-induced AAA model, the abdominal aortas from wildtype and FcγR deficient mice with/without macrophage adoptive transfer were analysed by histology and quantitative PCR. In vitro, mouse macrophages were transfected with RNA interference of FcγRIV/CD16.2 or treated with Syk kinase inhibitor before stimulation with IgG immune complexes.

RESULTS

Macrophage adoptive transfer in FcγR deficient mice increased the susceptibility to AAA development. Mice receiving macrophages with functional FcγR exhibited higher aortic diameter increase, higher content of macrophages and B lymphocytes, and upregulated expression of chemokine CCL2, cytokines (TNF-α and IL-17), metalloproteinase MMP2, prooxidant enzyme NADPH oxidase-2, and the isoforms FcγRIII/CD16 and FcγRIV/CD16.2. In vitro, both FcγRIV/CD16.2 gene silencing and Syk inhibition reduced cytokines and reactive oxygen species production induced by immune complexes in macrophages.

CONCLUSIONS

Activation of macrophage FcγR contributes to AAA development by inducing mediators of inflammation, proteolysis, and oxidative stress. Modulation of FcγR or effector molecules may represent a potential target for AAA treatment.