Fc gamma receptor-TLR cross-talk elicits pro-inflammatory cytokine production by human M2 macrophages

Potential different immune phenotypes of macrophages in oral lichen planus by integrating immunofluorescence double staining and single-cell RNA sequencing

Background/purpose

Oral lichen planus (OLP) is a chronic inflammatory disease with obscure etiopathogenesis. Macrophages play an important role in interaction between innate and adaptive immunity. This study aimed to investigate the macrophage phenotypes and obtain more comprehensive gene characteristics of macrophages in OLP.

Materials and methods

Double cluster of differentiation (CD) 68/CD86 and CD68/CD206 immunofluorescence staining was conducted in 11 biopsy-proven OLP tissue samples and 5 health control (HC) to represent M1 and M2 macrophages, respectively. The number of positively stained cells was manually counted, and the density was calculated. Furtherly, OLP single-cell dataset GSE211630 was downloaded from Gene Expression Omnibus. Gene characteristics and functional analysis of the macrophages were elucidated.

Results

In the OLP group, the densities of M1 (P < 0.001), M2 macrophages (P < 0.001) and M1/M2 ratio (P = 0.001) were significantly higher than those in HC group. Single-cell RNA sequencing revealed that proportions of CXCL10 macrophages (P = 0.003), IL1B/MMP19 macrophages (P < 0.001) were increased in OLP tissues compared with those in HC. Macrophages in OLP tissues had a stronger ability to cell chemotaxis, positive regulation of cell adhesion and antigen processing and presentation. Functional analysis revealed macrophages in OLP tissues could interact with multiple immune cells, and multiple signaling pathways were associated with macrophages in OLP.

Conclusion

A pro-inflammatory status of macrophages with different gene characteristics was found in the microenvironment of OLP by integrating immunofluorescence double staining and single-cell RNA sequencing, which provided a potential target for clinical treatment of OLP.

Age-associated changes in innate and adaptive immunity: role of the gut microbiota

Aging is generally regarded as an irreversible process, and its intricate relationship with the immune system has garnered significant attention due to its profound implications for the health and well-being of the aging population. As people age, a multitude of alterations occur within the immune system, affecting both innate and adaptive immunity. In the realm of innate immunity, aging brings about changes in the number and function of various immune cells, including neutrophils, monocytes, and macrophages. Additionally, certain immune pathways, like the cGAS-STING, become activated. These alterations can potentially result in telomere damage, the disruption of cytokine signaling, and impaired recognition of pathogens. The adaptive immune system, too, undergoes a myriad of changes as age advances. These include shifts in the number, frequency, subtype, and function of T cells and B cells. Furthermore, the human gut microbiota undergoes dynamic changes as a part of the aging process. Notably, the interplay between immune changes and gut microbiota highlights the gut's role in modulating immune responses and maintaining immune homeostasis. The gut microbiota of centenarians exhibits characteristics akin to those found in young individuals, setting it apart from the microbiota observed in typical elderly individuals. This review delves into the current understanding of how aging impacts the immune system and suggests potential strategies for reversing aging through interventions in immune factors.

Testosterone and estradiol reduce inflammation of human macrophages induced by anti-SARS-CoV-2 IgG

COVID-19, the disease caused by SARS-CoV-2, particularly causes severe inflammatory disease in elderly, obese, and male patients. Since both aging and obesity are associated with decreased testosterone and estradiol expression, we hypothesized that decreased hormone levels contribute to excessive inflammation in the context of COVID-19. Previously, we and others have shown that hyperinflammation in severe COVID-19 patients is induced by the production of pathogenic anti-spike IgG antibodies that activate alveolar macrophages. Therefore, we developed an in vitro assay in which we stimulated human macrophages with viral stimuli, anti-spike IgG immune complexes, and different sex hormones. Treatment with levels of testosterone reflecting young adults led to a significant reduction in TNF and IFN-γ production by human macrophages. In addition, estradiol significantly attenuated the production of a very broad panel of cytokines, including TNF, IL-1β, IL-6, IL-10, and IFN-γ. Both testosterone and estradiol reduced the expression of Fc gamma receptors IIa and III, the two main receptors responsible for anti-spike IgG-induced inflammation. Combined, these findings indicate that sex hormones reduce the inflammatory response of human alveolar macrophages to specific COVID-19-associated stimuli, thereby providing a potential immunological mechanism for the development of severe COVID-19 in both older male and female patients.

Mechanisms of antibody-dependent enhancement of infectious disease

Antibody-dependent enhancement (ADE) of infectious disease is a phenomenon whereby host antibodies increase the severity of an infection. It is well established in viral infections but ADE also has an underappreciated role during bacterial, fungal and parasitic infections. ADE can occur during both primary infections and re-infections with the same or a related pathogen; therefore, understanding the underlying mechanisms of ADE is critical for understanding the pathogenesis and progression of many infectious diseases. Here, we review the four distinct mechanisms by which antibodies increase disease severity during an infection. We discuss the most established mechanistic explanation for ADE, where cross-reactive, disease-enhancing antibodies bound to pathogens interact with Fc receptors, thereby enhancing pathogen entry or replication, ultimately increasing the total pathogen load. Additionally, we explore how some pathogenic antibodies can shield bacteria from complement-dependent killing, thereby enhancing bacterial survival. We interrogate the molecular mechanisms by which antibodies can amplify inflammation to drive severe disease, even in the absence of increased pathogen replication. We also examine emerging roles for autoantibodies in enhancing the pathogenesis of infectious diseases. Finally, we discuss how we can leverage these insights to improve vaccine design and future treatments for infectious diseases.

Enantiomer-Dependent Supramolecular Immunosuppressive Modulation for Tissue Reconstruction

Modulating the properties of biomaterials in terms of the host immune response is critical for tissue repair and regeneration. However, it is unclear how the preference for the cellular microenvironment manipulates the chiral immune responses under physiological or pathological conditions. Here, we reported that in vivo and in vitro oligopeptide immunosuppressive modulation was achieved by manipulation of macrophage polarization using chiral tetrapeptide (Ac-FFFK-OH, marked as FFFK) supramolecular polymers. The results suggested that chiral FFFK nanofibers can serve as a defense mechanism in the restoration of tissue homeostasis by upregulating macrophage M2 polarization via the Src-STAT6 axis. More importantly, transiently acting STAT6, insufficient to induce a sustained polarization program, then passes the baton to EGR2, thereby continuously maintaining the M2 polarization program. It is worth noting that the L-chirality exhibits a more potent effect in inducing macrophage M2 polarization than does the D-chirality, leading to enhanced tissue reconstruction. These findings elucidate the crucial molecular signals that mediate chirality-dependent supramolecular immunosuppression in damaged tissues while also providing an effective chiral supramolecular strategy for regulating macrophage M2 polarization and promoting tissue injury repair based on the self-assembling chiral peptide design.

Pyrogenic and inflammatory mediators are produced by polarized M1 and M2 macrophages activated with D-dimer and SARS-CoV-2 spike immune complexes

Lung macrophages are the first line of defense against invading respiratory pathogens including SARS-CoV-2, yet activation of macrophage in the lungs can lead to hyperinflammatory immune response seen in severe COVID-19. Here we used human M1 and M2 polarized macrophages as a surrogate model of inflammatory and regulatory macrophages and explored whether immune complexes (IC) containing spike-specific IgG can trigger aberrant cytokine responses in macrophages in the lungs and associated lymph nodes. We show that IC of SARS-CoV-2 recombinant S protein coated with spike-specific monoclonal antibody induced production of Prostaglandin E2 (PGE2) in non-polarized (M0) and in M1 and M2-type polarized human macrophages only in the presence of D-dimer (DD), a fibrinogen degradation product, associated with coagulopathy in COVID-19. Importantly, an increase in PGE2 was also observed in macrophages activated with DD and IC of SARS-CoV-2 pseudovirions coated with plasma from hospitalized COVID-19 patients but not from healthy subjects. Overall, the levels of PGE2 in macrophages activated with DD and IC were as follows: M1≫M2>M0 and correlated with the levels of spike binding antibodies and not with neutralizing antibody titers. All three macrophage subsets produced similar levels of IL-6 following activation with DD+IC, however TNFα, IL-1β, and IL-10 cytokines were produced by M2 macrophages only. Our study suggests that high titers of spike or virion containing IC in the presence of coagulation byproducts (DD) can promote inflammatory response in macrophages in the lungs and associated lymph nodes and contribute to severe COVID-19.

Intestinal homeostasis in the gut-lung-kidney axis: a prospective therapeutic target in immune-related chronic kidney diseases

In recent years, the role of intestinal homeostasis in health has received increasing interest, significantly improving our understanding of the complex pathophysiological interactions of the gut with other organs. Microbiota dysbiosis, impaired intestinal barrier, and aberrant intestinal immunity appear to contribute to the pathogenesis of immune-related chronic kidney diseases (CKD). Meanwhile, the relationship between the pathological changes in the respiratory tract (e.g., infection, fibrosis, granuloma) and immune-related CKD cannot be ignored. The present review aimed to elucidate the new underlying mechanism of immune-related CKD. The lungs may affect kidney function through intestinal mediation. Communication is believed to exist between the gut and lung microbiota across long physiological distances. Following the inhalation of various pathogenic factors (e.g., particulate matter 2.5 mum or less in diameter, pathogen) in the air through the mouth and nose, considering the anatomical connection between the nasopharynx and lungs, gut microbiome regulates oxidative stress and inflammatory states in the lungs and kidneys. Meanwhile, the intestine participates in the differentiation of T cells and promotes the migration of various immune cells to specific organs. This better explain the occurrence and progression of CKD caused by upper respiratory tract precursor infection and suggests the relationship between the lungs and kidney complications in some autoimmune diseases (e.g., anti-neutrophil cytoplasm antibodies -associated vasculitis, systemic lupus erythematosus). CKD can also affect the progression of lung diseases (e.g., acute respiratory distress syndrome and chronic obstructive pulmonary disease). We conclude that damage to the gut barrier appears to contribute to the development of immune-related CKD through gut-lung-kidney interplay, leading us to establish the gut-lung-kidney axis hypothesis. Further, we discuss possible therapeutic interventions and targets. For example, using prebiotics, probiotics, and laxatives (e.g., Rhubarb officinale) to regulate the gut ecology to alleviate oxidative stress, as well as improve the local immune system of the intestine and immune communication with the lungs and kidneys.

Positive and negative regulation of the Fcγ receptor-stimulating activity of RNA-containing immune complexes by RNase

The U1RNP complex, Ro/SSA, and La/SSB are major RNA-containing autoantigens. Immune complexes (ICs) composed of RNA-containing autoantigens and autoantibodies are suspected to be involved in the pathogenesis of some systemic autoimmune diseases. Therefore, RNase treatment, which degrades RNA in ICs, has been tested in clinical trials as a potential therapeutic agent. However, no studies to our knowledge have specifically evaluated the effect of RNase treatment on the Fcγ receptor-stimulating (FcγR-stimulating) activity of RNA-containing ICs. In this study, using a reporter system that specifically detects FcγR-stimulating capacity, we investigated the effect of RNase treatment on the FcγR-stimulating activity of RNA-containing ICs composed of autoantigens and autoantibodies from patients with systemic autoimmune diseases such as systemic lupus erythematosus. We found that RNase enhanced the FcγR-stimulating activity of Ro/SSA- and La/SSB-containing ICs, but attenuated that of the U1RNP complex-containing ICs. RNase decreased autoantibody binding to the U1RNP complex, but increased autoantibody binding to Ro/SSA and La/SSB. Our results suggest that RNase enhances FcγR activation by promoting the formation of ICs containing Ro/SSA or La/SSB. Our study provides insights into the pathophysiology of autoimmune diseases involving anti-Ro/SSA and anti-La/SSB autoantibodies, and into the therapeutic application of RNase treatment for systemic autoimmune diseases.

B cell treatment promotes a neuroprotective microenvironment after traumatic brain injury through reciprocal immunomodulation with infiltrating peripheral myeloid cells

Traumatic brain injury (TBI) remains a major cause of death and severe disability worldwide. We found previously that treatment with exogenous naïve B cells was associated with structural and functional neuroprotection after TBI. Here, we used a mouse model of unilateral controlled cortical contusion TBI to investigate cellular mechanisms of immunomodulation associated with intraparenchymal delivery of mature naïve B lymphocytes at the time of injury. Exogenous B cells showed a complex time-dependent response in the injury microenvironment, including significantly increased expression of IL-10, IL-35, and TGFβ, but also IL-2, IL-6, and TNFα. After 10 days in situ, B cell subsets expressing IL-10 or TGFβ dominated. Immune infiltration into the injury predominantly comprised myeloid cells, and B cell treatment did not alter overall numbers of infiltrating cells. In the presence of B cells, significantly more infiltrating myeloid cells produced IL-10, TGFβ, and IL-35, and fewer produced TNFα, interferon-γ and IL-6 as compared to controls, up to 2 months post-TBI. B cell treatment significantly increased the proportion of CD206+ infiltrating monocytes/macrophages and reduced the relative proportion of activated microglia starting at 4 days and up to 2 months post-injury. Ablation of peripheral monocytes with clodronate liposomes showed that infiltrating peripheral monocytes/macrophages are required for inducing the regulatory phenotype in exogenous B cells. Reciprocally, B cells specifically reduced the expression of inflammatory cytokines in infiltrating Ly6C+ monocytes/macrophages. These data support the hypothesis that peripheral myeloid cells, particularly infiltrating monocyte/macrophages, are key mediators of the neuroprotective immunomodulatory effects observed after B cell treatment.

Synovial monocytes contribute to chronic inflammation in childhood-onset arthritis via IL-6/STAT signalling and cell-cell interactions

Introduction

Monocytes are key effector cells in inflammatory processes. We and others have previously shown that synovial monocytes in childhood-onset arthritis are activated. However, very little is known about how they contribute to disease and attain their pathological features. Therefore, we set out to investigate the functional alterations of synovial monocytes in childhood-onset arthritis, how they acquire this phenotype, and whether these mechanisms could be used to tailorize treatment.

Methods

The function of synovial monocytes was analysed by assays believed to reflect key pathological events, such as T-cell activation-, efferocytosis- and cytokine production assays using flow cytometry in untreated oligoarticular juvenile idiopathic arthritis (oJIA) patients (n=33). The effect of synovial fluid on healthy monocytes was investigated through mass spectrometry and functional assays. To characterize pathways induced by synovial fluid, we utilized broad-spectrum phosphorylation assays and flow cytometry, as well as inhibitors to block specific pathways. Additional effects on monocytes were studied through co-cultures with fibroblast-like synoviocytes or migration in transwell systems.

Results

Synovial monocytes display functional alterations with inflammatory and regulatory features, e.g., increased ability to induce T-cell activation, resistance to cytokine production following activation with LPS and increased efferocytosis. In vitro, synovial fluid from patients induced the regulatory features in healthy monocytes, such as resistance to cytokine production and increased efferocytosis. IL-6/JAK/STAT signalling was identified as the main pathway induced by synovial fluid, which also was responsible for a majority of the induced features. The magnitude of synovial IL-6 driven activation in monocytes was reflected in circulating cytokine levels, reflecting two groups of low vs. high local and systemic inflammation. Remaining features, such as an increased ability to induce T-cell activation and markers of antigen presentation, could be induced by cell-cell interactions, specifically via co-culture with fibroblast-like synoviocytes.

Conclusions

Synovial monocytes in childhood-onset arthritis are functionally affected and contribute to chronic inflammation, e.g., via promoting adaptive immune responses. These data support a role of monocytes in the pathogenesis of oJIA and highlight a group of patients more likely to benefit from targeting the IL-6/JAK/STAT axis to restore synovial homeostasis.

IgA2 immune complexes selectively promote inflammation by human CD103+ dendritic cells

While immunoglobulin A (IgA) is well known for its neutralizing and anti-inflammatory function, it is becoming increasingly clear that IgA can also induce human inflammatory responses by various different immune cells. Yet, little is known about the relative role of induction of inflammation by the two IgA subclasses i.e. IgA1, most prominent subclass in circulation, and IgA2, most prominent subclass in the lower intestine. Here, we set out to study the inflammatory function of IgA subclasses on different human myeloid immune cell subsets, including monocytes, and in vitro differentiated macrophages and intestinal CD103+ dendritic cells (DCs). While individual stimulation with IgA immune complexes only induced limited inflammatory responses by human immune cells, both IgA subclasses strongly amplified pro-inflammatory cytokine production upon co-stimulation with Toll-like receptor (TLR) ligands such as Pam3CSK4, PGN, and LPS. Strikingly, while IgA1 induced slightly higher or similar levels of pro-inflammatory cytokines by monocytes and macrophages, respectively, IgA2 induced substantially more inflammation than IgA1 by CD103+ DCs. In addition to pro-inflammatory cytokine proteins, IgA2 also induced higher mRNA expression levels, indicating that amplification of pro-inflammatory cytokine production is at least partially regulated at the level of gene transcription. Interestingly, cytokine amplification by IgA1 was almost completely dependent on Fc alpha receptor I (FcαRI), whilst blocking this receptor only partially reduced cytokine induction by IgA2. In addition, IgA2-induced amplification of pro-inflammatory cytokines was less dependent on signaling through the kinases Syk, PI3K, and TBK1/IKKϵ. Combined, these findings indicate that IgA2 immune complexes, which are most abundantly expressed in the lower intestine, particularly promote inflammation by human CD103+ intestinal DCs. This may serve an important physiological function upon infection, by enabling inflammatory responses by this otherwise tolerogenic DC subset. Since various inflammatory disorders are characterized by disturbances in IgA subclass balance, this may also play a role in the induction or exacerbation of chronic intestinal inflammation.

Influence of Lenvatinib on the Functional Reprogramming of Peripheral Myeloid Cells in the Context of Non-Medullary Thyroid Carcinoma

Lenvatinib is a multitarget tyrosine kinase inhibitor (TKI) approved for the treatment of several types of cancers, including metastatic differentiated thyroid cancer (DTC). The intended targets include VEGFR 1-3, FGFR 1-4, PDGFRα, RET, and KIT signaling pathways, but drug resistance inevitably develops and a complete cure is very rare. Recent data has revealed that most of the TKIs have additional 'off-target' immunological effects, which might contribute to a protective antitumor immune response; however, human cellular data are lacking regarding Lenvatinib-mediated immunomodulation in DTC. Here, we investigated in ex vivo models the impact of Lenvatinib on the function of immune cells in healthy volunteers. We found that monocytes and macrophages were particularly susceptible to Lenvatinib, while neutrophiles and lymphocytes were less affected. In tumor-immune cell co-culture experiments, Lenvatinib exerted a broad inhibitory effect on the proinflammatory response in TC-induced macrophages. Interestingly, Lenvatinib-treated cells had decreased cellular M2 membrane markers, whereas they secreted a significantly higher level of the anti-inflammatory cytokine IL-10 upon LPS stimulation. In addition, prolonged exposure to Lenvatinib impaired macrophages survival and phenotypical differentiation, which was accompanied by remarkable morphological changes and suppressed cellular metabolic activity. These effects were mediated by myeloid cell-intrinsic mechanisms which are independent of Lenvatinib's on-target activity. Finally, using specific inhibitors, we argue that dual effects on p38 MAPK and Syk pathways are likely the underlying mechanism of the off-target immunological effects we observed in this study. Collectively, our data show the immunomodulatory properties of Lenvatinib on human monocytes. These insights could be harnessed for the future design of novel treatment strategies involving a combination of Lenvatinib with other immunotherapeutic agents.

The BNT162b2 mRNA SARS-CoV-2 vaccine induces transient afucosylated IgG1 in naive but not in antigen-experienced vaccinees

BACKGROUND

Afucosylated IgG1 responses have only been found against membrane-embedded epitopes, including anti-S in SARS-CoV-2 infections. These responses, intrinsically protective through enhanced FcγRIIIa binding, can also trigger exacerbated pro-inflammatory responses in severe COVID-19. We investigated if the BNT162b2 SARS-CoV-2 mRNA also induced afucosylated IgG responses.

METHODS

Blood from vaccinees during the first vaccination wave was collected. Liquid chromatography-Mass spectrometry (LC-MS) was used to study anti-S IgG1 Fc glycoprofiles. Responsiveness of alveolar-like macrophages to produce proinflammatory cytokines in presence of sera and antigen was tested. Antigen-specific B cells were characterized and glycosyltransferase levels were investigated by Fluorescence-Activated Cell Sorting (FACS).

FINDINGS

Initial transient afucosylated anti-S IgG1 responses were found in naive vaccinees, but not in antigen-experienced ones. All vaccinees had increased galactosylated and sialylated anti-S IgG1. Both naive and antigen-experienced vaccinees showed relatively low macrophage activation potential, as expected, due to the low antibody levels for naive individuals with afucosylated IgG1, and low afucosylation levels for antigen-experienced individuals with high levels of anti-S. Afucosylation levels correlated with FUT8 expression in antigen-specific plasma cells in naive individuals. Interestingly, low fucosylation of anti-S IgG1 upon seroconversion correlated with high anti-S IgG levels after the second dose.

INTERPRETATION

Here, we show that BNT162b2 mRNA vaccination induces transient afucosylated anti-S IgG1 responses in naive individuals. This observation warrants further studies to elucidate the clinical context in which potent afucosylated responses would be preferred.

FUNDING

LSBR1721, 1908; ZonMW10430012010021, 09150161910033, 10430012010008; DFG398859914, 400912066, 390884018; PMI; DOI4-Nr. 3; H2020-MSCA-ITN 721815.

Obesity Exacerbates Lupus Activity in Fc Gamma Receptor IIb Deficient Lupus Mice Partly through Saturated Fatty Acid-Induced Gut Barrier Defect and Systemic Inflammation

The prevalence of obesity is increasing, and the coexistence of obesity and systemic lupus erythematosus (lupus) is possible. A high-fat diet (HFD) was orally administered for 6 months in female 8-week-old Fc gamma receptor IIb deficient (FcgRIIb-/-) lupus or age and gender-matched wild-type (WT) mice. Lupus nephritis (anti-dsDNA, proteinuria, and increased creatinine), gut barrier defect (fluorescein isothiocyanate dextran), serum lipopolysaccharide (LPS), serum interleukin (IL)-6, liver injury (alanine transaminase), organ fibrosis (liver and kidney pathology), spleen apoptosis (activated caspase 3), and aorta thickness (but not weight gain and lipid profiles) were more prominent in HFD-administered FcgRIIb-/- mice than the obese WT, without injury in regular diet-administered mice (both FcgRIIb-/- and WT). In parallel, combined palmitic acid (PA; a saturated fatty acid) with LPS (PA + LPS) induced higher tumor necrotic factor-α, IL-6, and IL-10 in the supernatant, inflammatory genes (inducible nitric oxide synthase and IL-1β), reactive oxygen species (dihydroethidium), and glycolysis with reduced mitochondrial activity (extracellular flux analysis) when compared with the activation by each molecule alone in both FcgRIIb-/- and WT macrophages. However, the alterations of these parameters were more prominent in PA + LPS-administered FcgRIIb-/- than in the WT cells. In conclusion, obesity accelerated inflammation in FcgRIIb-/- mice, partly due to the more potent responses from the loss of inhibitory FcgRIIb against PA + LPS with obesity-induced gut barrier defect.

Spatial Organization of Dectin-1 and TLR2 during Synergistic Crosstalk Revealed by Super-resolution Imaging

Innate immune cells recognize and elicit responses against pathogens by integrating signals from different types of cell-surface receptors. How the receptors interact in the membrane to enable their signaling crosstalk is poorly understood. Here, we reveal the nanoscale organization of TLR2 and Dectin-1, a receptor pair known to cooperate in regulating antifungal immunity, through their synergistic signaling crosstalk at macrophage cell membranes. Using super-resolution single-molecule localization microscopy, we show that discrete noncolocalized nanoclusters of Dectin-1 and TLR2 are partially overlapped during their synergistic crosstalk. Compared to when one type of receptor is activated alone, the simultaneous activation of Dectin-1 and TLR2 leads to a higher percentage of both receptors being activated by their specific ligands and consequently an increased level of tyrosine phosphorylation. Our results depict, in nanoscale detail, how Dectin-1 and TLR2 achieve synergistic signaling through the spatial organization of their receptor nanoclusters.

Heterogeneity in IgG-CD16 signaling in infectious disease outcomes

In this review, we discuss how IgG antibodies can modulate inflammatory signaling during viral infections with a focus on CD16a-mediated functions. We describe the structural heterogeneity of IgG antibody ligands, including subclass and glycosylation that impact binding by and downstream activity of CD16a, as well as the heterogeneity of CD16a itself, including allele and expression density. While inflammation is a mechanism required for immune homeostasis and resolution of acute infections, we focus here on two infectious diseases that are driven by pathogenic inflammatory responses during infection. Specifically, we review and discuss the evolving body of literature showing that afucosylated IgG immune complex signaling through CD16a contributes to the overwhelming inflammatory response that is central to the pathogenesis of severe forms of dengue disease and coronavirus disease 2019 (COVID-19).

Gut Barrier Damage and Gut Translocation of Pathogen Molecules in Lupus, an Impact of Innate Immunity (Macrophages and Neutrophils) in Autoimmune Disease

The gut barrier is a single cell layer that separates gut micro-organisms from the host, and gut permeability defects result in the translocation of microbial molecules from the gut into the blood. Despite the silent clinical manifestation, gut translocation of microbial molecules can induce systemic inflammation that might be an endogenous exacerbating factor of systemic lupus erythematosus. In contrast, circulatory immune-complex deposition and the effect of medications on the gut, an organ with an extremely large surface area, of patients with active lupus might cause gut translocation of microbial molecules, which worsens lupus severity. Likewise, the imbalance of gut microbiota may initiate lupus and/or interfere with gut integrity which results in microbial translocation and lupus exacerbation. Moreover, immune hyper-responsiveness of innate immune cells (macrophages and neutrophils) is demonstrated in a lupus model from the loss of inhibitory Fc gamma receptor IIb (FcgRIIb), which induces prominent responses through the cross-link between activating-FcgRs and innate immune receptors. The immune hyper-responsiveness can cause cell death, especially apoptosis and neutrophil extracellular traps (NETosis), which possibly exacerbates lupus, partly through the enhanced exposure of the self-antigens. Leaky gut monitoring and treatments (such as probiotics) might be beneficial in lupus. Here, we discuss the current information on leaky gut in lupus.

In Vitro Model of Human Skeletal Muscle Tissue for the Study of Resident Macrophages and Stem Cells

Simple Summary

The skeletal muscle of younger adults has a remarkable regenerative capacity, which substantially declines with age. Despite many interspecies differences, animals have been used to study new treatments to promote muscle regeneration in humans. This study reports a novel human experimental model using human skeletal muscle tissue of older adults that was extracted during surgical procedures. We describe an optimal procedure for maintaining human skeletal muscle tissue under experimental conditions for 11 days. This experimental model allows the investigation of resident macrophages and stem cells, which mediate muscle regeneration.

Abstract

Findings from studies of muscle regeneration can significantly contribute to the treatment of age-related loss of skeletal muscle mass, which may predispose older adults to severe morbidities. We established a human experimental model using excised skeletal muscle tissues from reconstructive surgeries in eight older adults. Muscle samples from each participant were preserved immediately or maintained in agarose medium for the following 5, 9, or 11 days. Immunofluorescence analyses of the structural proteins, actin and desmin, confirmed the integrity of muscle fibers over 11 days of maintenance. Similarly, the numbers of CD80-positive M1 and CD163-positive M2 macrophages were stable over 11 days in vitro. However, the numbers of PAX7-positive satellite cells and MYOD-positive myoblasts changed in opposite ways, suggesting that satellite cells partially differentiated in vitro. Further experiments revealed that stimulation with unsaturated fatty acid C18[2]c (linoleic acid) increased resident M1 macrophages and satellite cells specifically. Thus, the use of human skeletal muscle tissue in vitro provides a direct experimental approach to study the regulation of muscle tissue regeneration by macrophages and stem cells and their responses to therapeutic compounds.

D-dimer and CoV-2 spike-immune complexes contribute to the production of PGE2 and proinflammatory cytokines in monocytes

An overreactive inflammatory response and coagulopathy are observed in patients with severe form of COVID-19. Since increased levels of D-dimer (DD) are associated with coagulopathy in COVID-19, we explored whether DD contributes to the aberrant cytokine responses. Here we show that treatment of healthy human monocytes with DD induced a dose dependent increase in production of pyrogenic mediator, Prostaglandin E2 (PGE2) and inflammatory cytokines, IL-6 and IL-8. The DD-induced PGE2 and inflammatory cytokines were enhanced significantly by co-treatment with immune complexes (IC) of SARS CoV-2 recombinant S protein or of pseudovirus containing SARS CoV-2 S protein (PVCoV-2) coated with spike-specific chimeric monoclonal antibody (MAb) containing mouse variable and human Fc regions. The production of PGE2 and cytokines in monocytes activated with DD and ICs was sensitive to the inhibitors of β2 integrin and FcγRIIa, and to the inhibitors of calcium signaling, Mitogen-Activated Protein Kinase (MAPK) pathway, and tyrosine-protein kinase. Importantly, strong increase in PGE2 and in IL-6/IL-8/IL-1β cytokines was observed in monocytes activated with DD in the presence of IC of PVCoV-2 coated with plasma from hospitalized COVID-19 patients but not from healthy donors. The IC of PVCoV-2 with convalescent plasma induced much lower levels of PGE2 and cytokines compared with plasma from hospitalized COVID-19 patients. PGE2 and IL-6/IL-8 cytokines produced in monocytes activated with plasma-containing IC, correlated well with the levels of spike binding antibodies and not with neutralizing antibody titers. Our study suggests that a combination of high levels of DD and high titers of spike-binding antibodies that can form IC with SARS CoV-2 viral particles might accelerate the inflammatory status of lung infiltrating monocytes leading to increased lung pathology in patients with severe form of COVID-19.

Folate Receptor Beta for Macrophage Imaging in Rheumatoid Arthritis

Non-invasive imaging modalities constitute an increasingly important tool in diagnostic and therapy response monitoring of patients with autoimmune diseases, including rheumatoid arthritis (RA). In particular, macrophage imaging with positron emission tomography (PET) using novel radiotracers based on differential expression of plasma membrane proteins and functioning of cellular processes may be suited for this. Over the past decade, selective expression of folate receptor β (FRβ), a glycosylphosphatidylinositol-anchored plasma membrane protein, on myeloid cells has emerged as an attractive target for macrophage imaging by exploiting the high binding affinity of folate-based PET tracers. This work discusses molecular, biochemical and functional properties of FRβ, describes the preclinical development of a folate-PET tracer and the evaluation of this tracer in a translational model of arthritis for diagnostics and therapy-response monitoring, and finally the first clinical application of the folate-PET tracer in RA patients with active disease. Consequently, folate-based PET tracers hold great promise for macrophage imaging in a variety of (chronic) inflammatory (autoimmune) diseases beyond RA.

Leveraging Antibody, B Cell and Fc Receptor Interactions to Understand Heterogeneous Immune Responses in Tuberculosis

Despite over a century of research, Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), continues to kill 1.5 million people annually. Though less than 10% of infected individuals develop active disease, the specific host immune responses that lead to Mtb transmission and death, as well as those that are protective, are not yet fully defined. Recent immune correlative studies demonstrate that the spectrum of infection and disease is more heterogenous than has been classically defined. Moreover, emerging translational and animal model data attribute a diverse immune repertoire to TB outcomes. Thus, protective and detrimental immune responses to Mtb likely encompass a framework that is broader than T helper type 1 (Th1) immunity. Antibodies, Fc receptor interactions and B cells are underexplored host responses to Mtb. Poised at the interface of initial bacterial host interactions and in granulomatous lesions, antibodies and Fc receptors expressed on macrophages, neutrophils, dendritic cells, natural killer cells, T and B cells have the potential to influence local and systemic adaptive immune responses. Broadening the paradigm of protective immunity will offer new paths to improve diagnostics and vaccines to reduce the morbidity and mortality of TB.

Folate Receptor Expression by Human Monocyte-Derived Macrophage Subtypes and Effects of Corticosteroids

OBJECTIVE

Folate receptor beta (FR-β) has been used as a clinical marker and target in multiple inflammatory diseases, including osteoarthritis (OA) and rheumatoid arthritis (RA). However, the conditions under which FR-β⁺ macrophages arise remain unclear and could be affected by corticosteroids. Therefore, we studied FR-β expression in vitro in macrophage subtypes and determined their response to triamcinolone acetonide (TA), a clinically often-used corticosteroid.

DESIGN

Human monocyte-derived macrophages were differentiated to the known M0, M1, or M2 macrophage phenotypes. The phenotype and FR-β expression and plasticity of the macrophage subtypes were determined using flow cytometry, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and enzyme-linked immunosorbent assay (ELISA).

RESULTS

FR-β expression was low in granulocyte-macrophage colony-stimulating factor (GM-CSF)-generated (M1-like) macrophages and high in macrophage colony-stimulating factor (M-CSF)-generated (M0 and M2-like) macrophages. FR-β expression remained high once the M0 or M2 macrophages were stimulated with pro-inflammatory stimuli (interferon-γ plus lipopolysaccharide) to induce M1-like macrophages. On the contrary, anti-inflammatory TA treatment skewed GM-CSF macrophage differentiation toward an M2 and FR-β⁺ phenotype.

CONCLUSIONS

As corticosteroids skewed monocytes toward an FR-β-expressing, anti-inflammatory phenotype, even in an M1 priming GM-CSF environment, FR-β has potential as a biomarker to monitor success of treatment with corticosteroids. Without corticosteroid treatment, M-CSF alone induces high FR-β expression which remains high under pro-inflammatory conditions. This explains why pro-inflammatory FR-β⁺ macrophages (exposed to M-CSF) are observed in arthritis patients and correlate with disease severity.

Use of integrated metabolomics, transcriptomics, and signal protein profile to characterize the effector function and associated metabotype of polarized macrophage phenotypes

MΦs display remarkable plasticity and the ability to activate diverse responses to a host of intracellular and external stimuli. Despite extensive characterization of M1 MΦs and a broad set of M2 MΦs, comprehensive characterization of functional phenotype and associated metabotype driving this diverse MΦ activation remains. Herein, an ex vivo model was utilized to produce 6 MΦ functional phenotypes. Isolated CD14⁺ PBMCs were differentiated into resting M0 MΦs, and then polarized into M1 (IFN-γ/LPS), M2a (IL-4/IL-13), M2b (IC/LPS), M2c (IL-10), and M2d (IL-6/LIF) MΦs. The MΦs were profiled using a bioanalyte matrix of 4 cell surface markers, ∼50 secreted proteins, ∼800 expressed myeloid genes, and ∼450 identified metabolites relative to M0 MΦs. Signal protein and expressed gene profiles grouped the MΦs into inflammatory (M1 and M2b) and wound resolution (M2a, M2c, and M2d) phenotypes; however, each had a unique metabolic profile. While both M1 and M2b MΦs shared metabotype profiles consistent with an inflammatory signature; key differences were observed in the TCA cycle, FAO, and OXPHOS. Additionally, M2a, M2c, and M2d MΦs all profiled as tissue repair MΦs; however, metabotype differences were observed in multiple pathways including hexosamine, polyamine, and fatty acid metabolism. These metabolic and other key functional distinctions suggest phagocytic and proliferative functions for M2a MΦs, and angiogenesis and ECM assembly capabilities for M2b, M2c, and M2d MΦs. By integrating metabolomics into a systems analysis of MΦ phenotypes, we provide the most comprehensive map of MΦ diversity to date, along with the global metabolic shifts that correlate to MΦ functional plasticity in these phenotypes.

Prognostic and Predictive Value of BGN in Colon Cancer Outcomes and Response to Immunotherapy

Background

Colon cancer is one of the most frequent malignancies and causes high mortality worldwide. Exploring the tumor-immune interactions in the tumor microenvironment and identifying new prognostic and therapeutic biomarkers will assist in decoding the novel mechanism of tumor immunotherapy. BGN is a typical extracellular matrix protein that was previously validated as a signaling molecule regulating multiple processes of tumorigenesis. However, its role in tumor immunity requires further investigation.

Methods

The differentially expressed genes in three GEO datasets were analyzed, and BGN was identified as the target gene by intersection analysis of PPIs. The relevance between clinical outcomes and BGN expression levels was evaluated using data from the GEO database, TCGA and tissue microarray of colon cancer samples. Univariable and multivariable Cox regression models were conducted for identifying the risk factors correlated with clinical prognosis of colon cancer patients. Next, the association between BGN expression levels and the infiltration of immune cells as well as the process of the immune response was analyzed. Finally, we predicted the immunotherapeutic response rates in the subgroups of low and high BGN expression by TIS score, ImmuCellAI and TIDE algorithms.

Results

BGN expression demonstrated a statistically significant upregulation in colon cancer tissues than in normal tissues. Elevated BGN was associated with shorter overall survival as well as unfavorable clinicopathological features, including tumor size, serosa invasion and length of hospitalization. Mechanistically, pathway enrichment and functional analysis demonstrated that BGN was positively correlated with immune and stromal scores in the TME and primarily involved in the regulation of immune response. Further investigation revealed that BGN was strongly expressed in the immunosuppressive phenotype and tightly associated with the infiltration of multiple immune cells in colon cancer, especially M2 macrophages and induced Tregs. Finally, we demonstrated that high BGN expression presented a better immunotherapeutic response in colon cancer patients.

Conclusion

BGN is an encouraging predictor of diagnosis, prognosis and immunotherapeutic response in patients with colon cancer. Assessment of BGN expression represents a novel approach with great promise for identifying patients who may potentially benefit from immunotherapy.

Macrophage-Based Combination Therapies as a New Strategy for Cancer Immunotherapy

BACKGROUND

Cells of the immune system can inhibit tumor growth and progression; however, immune cells can also promote tumor cell growth, survival, and angiogenesis as a result of the immunosuppressive microenvironments. In the last decade, a growing number of new therapeutic strategies focused on reversing the immunosuppressive status of tumor microenvironments (TMEs), to reprogram the TME to be normal, and to further activate the antitumor functions of immune cells. Most of the "hot tumors" are encompassed with M2 macrophages promoting tumor growth, and the accumulation of M2 macrophages into tumor islets leads to poor prognosis in a wide variety of tumors.

SUMMARY

Therefore, how to uncover more immunosuppressive signals and to reverse the M2 tumor-associated macrophages (TAMs) to M1-type macrophages is essential for reversing the immunosuppressive state. Except for reeducation of TAMs in the cancer immunotherapy, macrophages as central effectors and regulators of the innate immune system have the capacity of phagocytosis and immune modulation in macrophage-based cell therapies.

KEY MESSAGES

We review the current macrophage-based cell therapies that use genetic engineering to augment macrophage functionalities with antitumor activity for the application of novel genetically engineered immune cell therapeutics. A combination of TAM reeducation and macrophage-based cell strategy may bring us closer to achieving the original goals of curing cancer. In this review, we describe the characteristics, immune status, and tumor immunotherapy strategies of macrophages to provide clues and evidences for future macrophage-based immune cell therapies.

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

Systemic autoimmune and inflammatory diseases have a complex and only partially known pathophysiology with various abnormalities involving all the components of the immune system. Among these components, antibodies, and especially autoantibodies are key elements contributing to autoimmunity. The interaction of antibody fragment crystallisable (Fc) and several distinct receptors, namely Fc receptors (FcRs), have gained much attention during the recent years, with possible major therapeutic perspectives for the future. The aim of this review is to comprehensively describe the known roles for FcRs (activating and inhibitory FcγRs, neonatal FcR [FcRn], FcαRI, FcεRs, Ro52/tripartite motif containing 21 [Ro52/TRIM21], FcδR, and the novel Fc receptor-like [FcRL] family) in systemic autoimmune and inflammatory disorders, namely rheumatoid arthritis, Sjögren's syndrome, systemic lupus erythematosus, systemic sclerosis, idiopathic inflammatory myopathies, mixed connective tissue disease, Crohn's disease, ulcerative colitis, immunoglobulin (Ig) A vasculitis, Behçet's disease, Kawasaki disease, IgG4-related disease, immune thrombocytopenia, autoimmune hemolytic anemia, antiphospholipid syndrome and heparin-induced thrombocytopenia.

Directing the Future Breakthroughs in Immunotherapy: The Importance of a Holistic Approach to the Tumour Microenvironment

Simple Summary

Immunotherapies have changed the way we treat cancer and, while some patients have benefitted greatly, there are still those that do not respond to therapy. Understanding why some patients respond to therapy and others do not is critical in developing new immunotherapeutic strategies. The increasing awareness of the importance of investigating the tumour in its entirety, including the surrounding tissue and role of various immune cells is helping to differentiate responders and non-responders. In addition, the resolution gained by the development of sophisticated bioinformatic technologies allows for a deeper understanding of the complex roles of individual cells in the tumour. This advancement will be critical for the development of novel therapies to treat cancer.

Abstract

Immunotherapy has revolutionised the treatment of cancers by exploiting the immune system to eliminate tumour cells. Despite the impressive response in a proportion of patients, clinical benefit has been limited thus far. A significant focus to date has been the identification of specific markers associated with response to immunotherapy. Unfortunately, the heterogeneity between patients and cancer types means identifying markers of response to therapy is inherently complex. There is a growing appreciation for the role of the tumour microenvironment (TME) in directing response to immunotherapy. The TME is highly heterogeneous and contains immune, stromal, vascular and tumour cells that all communicate and interact with one another to form solid tumours. This review analyses major cell populations present within the TME with a focus on their diverse and often contradictory roles in cancer and how this informs our understanding of immunotherapy. Furthermore, we discuss the role of integrated omics in providing a comprehensive view of the TME and demonstrate the potential of leveraging multi-omics to decipher the underlying mechanisms of anti-tumour immunity for the development of novel immunotherapeutic strategies.

SARS-CoV-2 Antibodies Mediate Complement and Cellular Driven Inflammation

The ongoing pandemic of coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to constitute a serious public health threat worldwide. Protective antibody-mediated viral neutralization in response to SARS-CoV-2 infection has been firmly characterized. Where the effects of the antibody response are generally considered to be beneficial, an important biological question regarding potential negative outcomes of a SARS-CoV-2 antibody response has yet to be answered. We determined the distribution of IgG subclasses and complement activation levels in plasma from convalescent individuals using in-house developed ELISAs. The IgG response towards SARS-CoV-2 receptor-binding domain (RBD) after natural infection appeared to be mainly driven by IgG1 and IgG3 subclasses, which are the main ligands for C1q mediated classical complement pathway activation. The deposition of the complement components C4b, C3bc, and TCC as a consequence of SARS-CoV-2 specific antibodies were depending primarily on the SARS-CoV-2 RBD and significantly correlated with both IgG levels and disease severity, indicating that individuals with high levels of IgG and/or severe disease, might have a more prominent complement activation during viral infection. Finally, freshly isolated monocytes and a monocyte cell line (THP-1) were used to address the cellular mediated inflammatory response as a consequence of Fc-gamma receptor engagement by SARS-CoV-2 specific antibodies. Monocytic Fc gamma receptor charging resulted in a significant rise in the secretion of the pro-inflammatory cytokine TNF-α. Our results indicate that SARS-CoV-2 antibodies might drive significant inflammatory responses through the classical complement pathway and via cellular immune-complex activation that could have negative consequences during COVID-19 disease. We found that increased classical complement activation was highly associated to COVID-19 disease severity. The combination of antibody-mediated complement activation and subsequent cellular priming could constitute a significant risk of exacerbating COVID-19 severity.

NK Cell-Dependent Antibody-Mediated Immunotherapy Is Improved In Vitro and In Vivo When Combined with Agonists for Toll-like Receptor 2 in Head and Neck Cancer Models

The immunosuppressive character of head and neck cancers may explain the relatively low response rates to antibody therapy targeting a tumor antigen, such as cetuximab, and anti-PD-1 checkpoint inhibition. Immunostimulatory agents that overcome tumor-derived inhibitory signals could augment therapeutic efficacy, thereby enhancing tumor elimination and improving patient survival. Here, we demonstrate that cetuximab treatment combined with immunostimulatory agonists for Toll-like receptor (TLR) 2 induces profound immune responses. Natural killer (NK) cells, isolated from healthy individuals or patients with head and neck cancer, harbored enhanced cytotoxic capacity and increased tumor-killing potential in vitro. Additionally, combination treatment increased the release of several pro-inflammatory cytokines and chemokines by NK cells. Tumor-bearing mice that received cetuximab and the TLR2 ligand Pam3CSK4 showed increased infiltration of immune cells into the tumors compared to mice that received cetuximab monotherapy, resulting in a significant delay in tumor growth or even complete tumor regression. Moreover, combination treatment resulted in improved overall survival in vivo. In conclusion, combining tumor-targeting antibody-based immunotherapy with TLR stimulation represents a promising treatment strategy to improve the clinical outcomes of cancer patients. This treatment could well be applied together with other therapeutic strategies such as anti-PD-(L)1 checkpoint inhibition to further overcome immunosuppression.

Monocytes Exposed to Immune Complexes Reduce pDC Type 1 Interferon Response to Vidutolimod

Vidutolimod, also known as CMP-001, is a virus-like particle composed of the Qβ bacteriophage coat protein encasing a TLR9 agonist. Vidutolimod injected intratumorally is showing promise in early phase clinical trials based on its ability to alter the tumor microenvironment and induce an anti-tumor immune response. We previously demonstrated that the in vivo efficacy of vidutolimod is dependent on the presence of anti-Qβ antibodies that enhance opsonization and uptake of vidutolimod by TLR9-expressing plasmacytoid dendritic cells (pDCs). Here, we evaluated the effect of immune complexes, including anti-Qβ-coated vidutolimod, on induction of Type 1 Interferon production by peripheral blood mononuclear cells in response to vidutolimod and soluble TLR9 agonists. Immune complexes, including but not limited to anti-Qβ-coated vidutolimod, indirectly suppressed TLR9-mediated Type 1 Interferon production by pDCs in a monocyte-dependent manner. These findings indicate that anti-Qβ-coated vidutolimod has effects in addition to those mediated by TLR9 that could have important clinical implications for understanding the mechanism of action of this exciting new approach to in situ immunization and cancer immunotherapy.

Macrophages: The Good, the Bad, and the Gluttony

Macrophages are dynamic cells that play critical roles in the induction and resolution of sterile inflammation. In this review, we will compile and interpret recent findings on the plasticity of macrophages and how these cells contribute to the development of non-infectious inflammatory diseases, with a particular focus on allergic and autoimmune disorders. The critical roles of macrophages in the resolution of inflammation will then be examined, emphasizing the ability of macrophages to clear apoptotic immune cells. Rheumatoid arthritis (RA) is a chronic autoimmune-driven spectrum of diseases where persistent inflammation results in synovial hyperplasia and excessive immune cell accumulation, leading to remodeling and reduced function in affected joints. Macrophages are central to the pathophysiology of RA, driving episodic cycles of chronic inflammation and tissue destruction. RA patients have increased numbers of active M1 polarized pro-inflammatory macrophages and few or inactive M2 type cells. This imbalance in macrophage homeostasis is a main contributor to pro-inflammatory mediators in RA, resulting in continual activation of immune and stromal populations and accelerated tissue remodeling. Modulation of macrophage phenotype and function remains a key therapeutic goal for the treatment of this disease. Intriguingly, therapeutic intervention with glucocorticoids or other DMARDs promotes the re-polarization of M1 macrophages to an anti-inflammatory M2 phenotype; this reprogramming is dependent on metabolic changes to promote phenotypic switching. Allergic asthma is associated with Th2-polarised airway inflammation, structural remodeling of the large airways, and airway hyperresponsiveness. Macrophage polarization has a profound impact on asthma pathogenesis, as the response to allergen exposure is regulated by an intricate interplay between local immune factors including cytokines, chemokines and danger signals from neighboring cells. In the Th2-polarized environment characteristic of allergic asthma, high levels of IL-4 produced by locally infiltrating innate lymphoid cells and helper T cells promote the acquisition of an alternatively activated M2a phenotype in macrophages, with myriad effects on the local immune response and airway structure. Targeting regulators of macrophage plasticity is currently being pursued in the treatment of allergic asthma and other allergic diseases. Macrophages promote the re-balancing of pro-inflammatory responses towards pro-resolution responses and are thus central to the success of an inflammatory response. It has long been established that apoptosis supports monocyte and macrophage recruitment to sites of inflammation, facilitating subsequent corpse clearance. This drives resolution responses and mediates a phenotypic switch in the polarity of macrophages. However, the role of apoptotic cell-derived extracellular vesicles (ACdEV) in the recruitment and control of macrophage phenotype has received remarkably little attention. ACdEV are powerful mediators of intercellular communication, carrying a wealth of lipid and protein mediators that may modulate macrophage phenotype, including a cargo of active immune-modulating enzymes. The impact of such interactions may result in repair or disease in different contexts. In this review, we will discuss the origin, characterization, and activity of macrophages in sterile inflammatory diseases and the underlying mechanisms of macrophage polarization via ACdEV and apoptotic cell clearance, in order to provide new insights into therapeutic strategies that could exploit the capabilities of these agile and responsive cells.

The regulation of macrophage polarization by hypoxia-PADI4 coordination in Rheumatoid arthritis

BACKGROUND

Hypoxia, a common feature of rheumatoid arthritis (RA), induces the over-expression of peptidyl arginine deiminase 4 (PADI4) in fibroblast-like synoviocytes (FLSs) and macrophages. However, the roles of PADI4 and its inducer hypoxia in the regulation of macrophage polarization remain unclear. This study aimed to investigate the role of hypoxia-PADI4 for macrophage polarization in RA patients.

METHODS

Synovial tissue (ST) and synovial fluid (SF) were collected from 3 OA patients and 6 RA patients. The distribution of M1 and M2 in ST and cytokines in SF were examined by immunohistochemical analysis and Bio-Plex immunoassays. THP-1 macrophages and BMDM polarization were determined under normoxic (21% oxygen) or hypoxic (3% oxygen) conditions. The effects of PADI4 on macrophages were determined by transfection of adenovirus vector-coated PADI4 (AdPADI4) and the use of PADI4 inhibitor. Finally, the roles of PADI4 in joint synovial lesions on macrophage polarization were investigated in collagen-induced arthritis (CIA) rats.

RESULTS

We found increased macrophage polarization of M1 and M2 in the RA ST, compared with OA ST. The ratio of M1/M2 for RA and OA was 1.633 ± 0.1443 and 2.544 ± 0.4429, respectively. The concentration of M1- and M2-type cytokines was higher in RA than that in OA patients. Hypoxia contributed to the increase of the gene and protein expression of M1 and M2 markers. M1- but not M2-type gene expression showed a positive relationship with PADI4 expressionwhile the level of expression of M2-type genes showed no significant difference. The degree of joint swelling and destruction was effectively alleviated, and the number of macrophages especially M1 decreased in CIA rats after down-regulating PADI4 expression.

CONCLUSION

Hypoxia is responsible for the co-polarization of M1 and M2. Hypoxia-associated PADI4 is responsible for M1 macrophage activation, implying that the inflammatory environment can be eased by decreasing PADI4 expression and improving the hypoxic environment.

Platelets release mitochondrial antigens in systemic lupus erythematosus

The accumulation of DNA and nuclear components in blood and their recognition by autoantibodies play a central role in the pathophysiology of systemic lupus erythematosus (SLE). Despite the efforts, the sources of circulating autoantigens in SLE are still unclear. Here, we show that in SLE, platelets release mitochondrial DNA, the majority of which is associated with the extracellular mitochondrial organelle. Mitochondrial release in patients with SLE correlates with platelet degranulation. This process requires the stimulation of platelet FcγRIIA, a receptor for immune complexes. Because mice lack FcγRIIA and murine platelets are completely devoid of receptor capable of binding IgG-containing immune complexes, we used transgenic mice expressing FcγRIIA for our in vivo investigations. FcγRIIA expression in lupus-prone mice led to the recruitment of platelets in kidneys and to the release of mitochondria in vivo. Using a reporter mouse with red fluorescent protein targeted to the mitochondrion, we confirmed platelets as a source of extracellular mitochondria driven by FcγRIIA and its cosignaling by the fibrinogen receptor α2bβ3 in vivo. These findings suggest that platelets might be a key source of mitochondrial antigens in SLE and might be a therapeutic target for treating SLE.

Spatial organization of FcγR and TLR2/1 on phagosome membranes differentially regulates their synergistic and inhibitory receptor crosstalk

Many innate immune receptors function collaboratively to detect and elicit immune responses to pathogens, but the physical mechanisms that govern the interaction and signaling crosstalk between the receptors are unclear. In this study, we report that the signaling crosstalk between Fc gamma receptor (FcγR) and Toll-like receptor (TLR)2/1 can be overall synergistic or inhibitory depending on the spatial proximity between the receptor pair on phagosome membranes. Using a geometric manipulation strategy, we physically altered the spatial distribution of FcγR and TLR2 on single phagosomes. We demonstrate that the signaling synergy between FcγR and TLR2/1 depends on the proximity of the receptors and decreases as spatial separation between them increases. However, the inhibitory effect from FcγRIIb on TLR2-dependent signaling is always present and independent of receptor proximity. The overall cell responses are an integration from these two mechanisms. This study presents quantitative evidence that the nanoscale proximity between FcγR and TLR2 functions as a key regulatory mechanism in their signaling crosstalk.

High titers and low fucosylation of early human anti-SARS-CoV-2 IgG promote inflammation by alveolar macrophages

Patients diagnosed with coronavirus disease 2019 (COVID-19) become critically ill primarily around the time of activation of the adaptive immune response. Here, we provide evidence that antibodies play a role in the worsening of disease at the time of seroconversion. We show that early-phase severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) spike protein-specific immunoglobulin G (IgG) in serum of critically ill COVID-19 patients induces excessive inflammatory responses by human alveolar macrophages. We identified that this excessive inflammatory response is dependent on two antibody features that are specific for patients with severe COVID-19. First, inflammation is driven by high titers of anti-spike IgG, a hallmark of severe disease. Second, we found that anti-spike IgG from patients with severe COVID-19 is intrinsically more proinflammatory because of different glycosylation, particularly low fucosylation, of the antibody Fc tail. Low fucosylation of anti-spike IgG was normalized in a few weeks after initial infection with SARS-CoV-2, indicating that the increased antibody-dependent inflammation mainly occurs at the time of seroconversion. We identified Fcγ receptor (FcγR) IIa and FcγRIII as the two primary IgG receptors that are responsible for the induction of key COVID-19-associated cytokines such as interleukin-6 and tumor necrosis factor. In addition, we show that anti-spike IgG-activated human macrophages can subsequently break pulmonary endothelial barrier integrity and induce microvascular thrombosis in vitro. Last, we demonstrate that the inflammatory response induced by anti-spike IgG can be specifically counteracted by fostamatinib, an FDA- and EMA-approved therapeutic small-molecule inhibitor of Syk kinase.

Physiological and Pathological Inflammation Induced by Antibodies and Pentraxins

Macrophages play a key role in induction of inflammatory responses. These inflammatory responses are mostly considered to be instigated by activation of pattern recognition receptors (PRRs) or cytokine receptors. However, recently it has become clear that also antibodies and pentraxins, which can both activate Fc receptors (FcRs), induce very powerful inflammatory responses by macrophages that can even be an order of magnitude greater than PRRs. While the physiological function of this antibody-dependent inflammation (ADI) is to counteract infections, undesired activation or over-activation of this mechanism will lead to pathology, as observed in a variety of disorders, including viral infections such as COVID-19, chronic inflammatory disorders such as Crohn's disease, and autoimmune diseases such as rheumatoid arthritis. In this review we discuss how physiological ADI provides host defense by inducing pathogen-specific immunity, and how erroneous activation of this mechanism leads to pathology. Moreover, we will provide an overview of the currently known signaling and metabolic pathways that underlie ADI, and how these can be targeted to counteract pathological inflammation.

The role of macrophages in anti-tumor immune responses: pathological significance and potential as therapeutic targets

Malignant tumors comprise various types of normal cells and tumor cells, and are infiltrated by large numbers of immune cells, including macrophages. The results of numerous studies on the function and significance of intratumoral macrophages (tumor-associated macrophages) suggest that these macrophages generally enhance tumor progression rather than act as anti-tumor immune agents. Although much remains unknown, in this review, we attempt to describe the role of macrophages in the tumor microenvironment, and discuss their potential mechanisms on the recent immunotherapy.

The prospects for targeting FcR as a novel therapeutic strategy in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by synovial membrane hyperplasia, infiltration of inflammatory cells and bone tissue destruction. Although there have been many measures taken for RA therapy in recent years, they are not sufficiently safe or effective. Thus, it is very important to develop new drugs and slow down damage to other healthy organs in the case of RA. Lately, immunoglobulin Fc receptors (FcRs), such as the IgG Fc receptor (FcγR), IgA Fc receptor (FcαR), and IgD Fc receptor (FcδR), have been found to be involved in inducing or suppressing arthritis. FcRs interacting with immune complexes (ICs) are a key factor in the etiopathogenesis of RA. Therefore, an increasing number of methodsfor the targeted treatment of RA with FcRs are emerging, such as recombinant soluble FcγRs, recombinant multimeric Fc fragments and monoclonal antibodies, and have been demonstrated to significantly improve RA symptoms. Simultaneously, certain kinases involved in the downstream signaling of FcRs can also be a target for the treatment of RA, such as Syk and Btk inhibitors. An overview of these FcRs is provided in this review, including a description of FcR-related functions, signaling pathways, and potential FcR-targeting molecules for RA therapy. To date, the initial results of those developed FcR-targeting molecules have been promising. With this, FcRs might offer a better alternative to RA medication. Additionally, further pharmacological characterization and a better understanding of the unique mechanisms of FcR-targeting molecules are necessary.

Macrophage activation on "phagocytic synapse" arrays: Spacing of nanoclustered ligands directs TLR1/2 signaling with an intrinsic limit

The activation of Toll-like receptor heterodimer 1/2 (TLR1/2) by microbial components plays a critical role in host immune responses against pathogens. TLR1/2 signaling is sensitive to the chemical structure of ligands, but its dependence on the spatial distribution of ligands on microbial surfaces remains unexplored. Here, we reveal the quantitative relationship between TLR1/2-triggered immune responses and the spacing of ligand clusters by designing an artificial "phagocytic synapse" nanoarray platform to mimic the cell-microbe interface. The ligand spacing dictates the proximity of receptor clusters on the cell surface and consequently the pro-inflammatory responses of macrophages. However, cell responses reach their maximum at small ligand spacings when the receptor nanoclusters become adjacent to one another. Our study demonstrates the feasibility of using spatially patterned ligands to modulate innate immunity. It shows that the receptor clusters of TLR1/2 act as a driver in integrating the spatial cues of ligands into cell-level activation events.

A High-Content Screen for Mucin-1-Reducing Compounds Identifies Fostamatinib as a Candidate for Rapid Repurposing for Acute Lung Injury

Drug repurposing has the advantage of identifying potential treatments on a shortened timescale. In response to the pandemic spread of SARS-CoV-2, we took advantage of a high-content screen of 3,713 compounds at different stages of clinical development to identify FDA-approved compounds that reduce mucin-1 (MUC1) protein abundance. Elevated MUC1 levels predict the development of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) and correlate with poor clinical outcomes. Our screen identifies fostamatinib (R788), an inhibitor of spleen tyrosine kinase (SYK) approved for the treatment of chronic immune thrombocytopenia, as a repurposing candidate for the treatment of ALI. In vivo, fostamatinib reduces MUC1 abundance in lung epithelial cells in a mouse model of ALI. In vitro, SYK inhibition by the active metabolite R406 promotes MUC1 removal from the cell surface. Our work suggests fostamatinib as a repurposing drug candidate for ALI.

IgG Subclasses Shape Cytokine Responses by Human Myeloid Immune Cells through Differential Metabolic Reprogramming

IgG Abs are crucial for various immune functions, including neutralization, phagocytosis, and Ab-dependent cellular cytotoxicity. In this study, we identified another function of IgG by showing that IgG immune complexes elicit distinct cytokine profiles by human myeloid immune cells, which are dependent on FcγR activation by the different IgG subclasses. Using monoclonal IgG subclasses with identical Ag specificity, our data demonstrate that the production of Th17-inducing cytokines, such as TNF, IL-1β, and IL-23, is particularly dependent on IgG2, whereas type I IFN responses are controlled by IgG3, and IgG1 is able to regulate both. In addition, we identified that subclass-specific cytokine production is orchestrated at the posttranscriptional level through distinct glycolytic reprogramming of human myeloid immune cells. Combined, these data identify that IgG subclasses provide pathogen- and cell type-specific immunity through differential metabolic reprogramming by FcγRs. These findings may be relevant for future design of Ab-related therapies in the context of infectious diseases, chronic inflammation, and cancer.

Mucosal IgG in inflammatory bowel disease - a question of (sub)class?

Immunoglobulins (Igs) form a cornerstone of mucosal immunity. In the gastrointestinal tract, secretory IgA and IgM bind to commensal microorganisms within the intestinal lumen to prevent them from breaching the intestinal epithelium - a process known as immune exclusion. In recent years, there has been renewed interest in the role of IgG in intestinal immunity, driven in part by a genetic association of an affinity-lowering variant of an IgG receptor, FcγRIIA, with protection from ulcerative colitis (UC), a subclass of inflammatory bowel disease (IBD). We recently demonstrated a role for IgG and Fcγ receptor signalling in driving pathogenic IL-1β production by colonic mononuclear phagocytes and the subsequent induction of a local type 17 response in UC. Here, we discuss the potential relevance of our observations to the other major subclass of IBD - Crohn's disease (CD) - where the genetic association with FCGR variants is less robust and consider how this may impact therapeutic interventions in these disease subsets.

Quantitative planar array screen of 1000 proteins uncovers novel urinary protein biomarkers of lupus nephritis

OBJECTIVE

The goal of these studies is to discover novel urinary biomarkers of lupus nephritis (LN).

METHODS

Urine from systemic lupus erythematosus (SLE) patients was interrogated for 1000 proteins using a novel, quantitative planar protein microarray. Hits were validated in an independent SLE cohort with inactive, active non-renal (ANR) and active renal (AR) patients, in a cohort with concurrent renal biopsies, and in a longitudinal cohort. Single-cell renal RNA sequencing data from LN kidneys were examined to deduce the cellular origin of each biomarker.

RESULTS

Screening of 1000 proteins revealed 64 proteins to be significantly elevated in SLE urine, of which 17 were ELISA validated in independent cohorts. Urine Angptl4 (area under the curve (AUC)=0.96), L-selectin (AUC=0.86), TPP1 (AUC=0.84), transforming growth factor-β1 (TGFβ1) (AUC=0.78), thrombospondin-1 (AUC=0.73), FOLR2 (AUC=0.72), platelet-derived growth factor receptor-β (AUC=0.67) and PRX2 (AUC=0.65) distinguished AR from ANR SLE, outperforming anti-dsDNA, C3 and C4, in terms of specificity, sensitivity and positive predictive value. In multivariate regression analysis, urine Angptl4, L-selectin, TPP1 and TGFβ1 were highly associated with disease activity, even after correction for demographic variables. In SLE patients with serial follow-up, urine L-selectin (followed by urine Angptl4 and TGFβ1) were best at tracking concurrent or pending disease flares. Importantly, several proteins elevated in LN urine were also expressed within the kidneys in LN, either within resident renal cells or infiltrating immune cells, based on single-cell RNA sequencing analysis.

CONCLUSION

Unbiased planar array screening of 1000 proteins has led to the discovery of urine Angptl4, L-selectin and TGFβ1 as potential biomarker candidates for tracking disease activity in LN.

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

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

IgG Immune Complexes Break Immune Tolerance of Human Microglia

Microglia are phagocytic cells involved in homeostasis of the brain and are key players in the pathogenesis of multiple sclerosis (MS). A hallmark of MS diagnosis is the presence of IgG Abs, which appear as oligoclonal bands in the cerebrospinal fluid. In this study, we demonstrate that myelin obtained post mortem from 8 out of 11 MS brain donors is bound by IgG Abs. Importantly, we show that IgG immune complexes strongly potentiate activation of primary human microglia by breaking their tolerance for microbial stimuli, such as LPS and Poly I:C, resulting in increased production of key proinflammatory cytokines, such as TNF and IL-1β. We identified FcγRI and FcγRIIa as the two main responsible IgG receptors for the breaking of immune tolerance of microglia. Combined, these data indicate that IgG immune complexes potentiate inflammation by human microglia, which may play an important role in MS-associated inflammation and the formation of demyelinating lesions.

Plasmodium sporozoites induce regulatory macrophages

Professional antigen-presenting cells (APCs), like macrophages (Mϕs) and dendritic cells (DCs), are central players in the induction of natural and vaccine-induced immunity to malaria, yet very little is known about the interaction of SPZ with human APCs. Intradermal delivery of whole-sporozoite vaccines reduces their effectivity, possibly due to dermal immunoregulatory effects. Therefore, understanding these interactions could prove pivotal to malaria vaccination. We investigated human APC responses to recombinant circumsporozoite protein (recCSP), SPZ and anti-CSP opsonized SPZ both in monocyte derived MoDCs and MoMϕs. Both MoDCs and MoMϕs readily took up recCSP but did not change phenotype or function upon doing so. SPZ are preferentially phagocytosed by MoMϕs instead of DCs and phagocytosis greatly increased after opsonization. Subsequently MoMϕs show increased surface marker expression of activation markers as well as tolerogenic markers such as Programmed Death-Ligand 1 (PD-L1). Additionally they show reduced motility, produce interleukin 10 and suppressed interferon gamma (IFNγ) production by antigen specific CD8⁺ T cells. Importantly, we investigated phenotypic responses to SPZ in primary dermal APCs isolated from human skin explants, which respond similarly to their monocyte-derived counterparts. These findings are a first step in enhancing our understanding of pre-erythrocytic natural immunity and the pitfalls of intradermal vaccination-induced immunity.

Malaria continues to be the deadliest parasitic disease worldwide, and an effective vaccine yielding sterile immunity does not yet exist. Attenuated parasites can induce sterile protection in both human and rodent models for malaria, but these vaccines need to be administered directly into the bloodstream in order to convey protection; administration via the skin results in a much-reduced efficacy. We hypothesized this is caused by an early immune regulation initiated at the first site of contact with the immune system: the skin. However, the human skin stage of malaria has not been investigated to date. We used human antigen presenting cells as well as whole human skin explants to investigate (dermal) immune responses and found that Plasmodium sporozoites are able to suppress immune responses by inducing regulatory macrophages. Our study provides new insights in the mechanism of early immune regulation exploited by Plasmodium parasites and can help to explain why intradermal vaccination using whole attenuated sporozoites results in reduced protection.

Fc Gamma Receptors and Their Role in Antigen Uptake, Presentation, and T Cell Activation

The cellular uptake, intracellular processing, and presentation of foreign antigen are crucial processes for eliciting an effective adaptive host response to the majority of pathogens. The effective recognition of antigen by T cells requires that it is first processed and then presented on MHC molecules that are expressed on other cells. A critical step leading to the presentation of antigen is delivering the foreign cargo to an intracellular compartment where the antigen can be processed and loaded onto MHC molecules. Fc-gamma receptors (FcγRs) recognize IgG-coated targets, such as opsonized pathogens or immune complexes (ICs). Cross-linking leads to internalization of the cargo with associated activation of down-stream signaling cascades. FcγRs vary in their affinity for IgG and intracellular trafficking, and therefore have an opportunity to regulate antigen presentation by controlling the shuttling and processing of their cargos. In this way, they critically influence physiological and pathophysiological adaptive immune cell functions. In this review, we will cover the contribution of FcγRs to antigen-presentation with a focus on the intracellular trafficking of IgG-ICs and the pathways that support this function. We will also discuss genetic evidence linking FcγR biology to immune cell activation and autoimmune processes as exemplified by systemic lupus erythematosus (SLE).

Macrophage Immunometabolism and Inflammaging: Roles of Mitochondrial Dysfunction, Cellular Senescence, CD38, and NAD

Aging is a complex process that involves dysfunction on multiple levels, all of which seem to converge on inflammation. Macrophages are intimately involved in initiating and resolving inflammation, and their dysregulation with age is a primary contributor to inflammaging—a state of chronic, low-grade inflammation that develops during aging. Among the age-related changes that occur to macrophages are a heightened state of basal inflammation and diminished or hyperactive inflammatory responses, which seem to be driven by metabolic-dependent epigenetic changes. In this review article we provide a brief overview of mitochondrial functions and age-related changes that occur to macrophages, with an emphasis on how the inflammaging environment, senescence, and NAD decline can affect their metabolism, promote dysregulation, and contribute to inflammaging and age-related pathologies.