Immune complex/Ig negatively regulate TLR4-triggered inflammatory response in macrophages through Fc gamma RIIb-dependent PGE2 production

Catecholamines Attenuate LPS-Induced Inflammation through β2 Adrenergic Receptor Activation- and PKA Phosphorylation-Mediated TLR4 Downregulation in Macrophages

Inflammation is a tightly regulated process involving immune receptor recognition, immune cell migration, inflammatory mediator secretion, and pathogen elimination, all essential for combating infection and restoring damaged tissue. However, excessive inflammatory responses drive various human diseases. The autonomic nervous system (ANS) is known to regulate inflammatory responses; however, the detailed mechanisms underlying this regulation remain incompletely understood. Herein, we aimed to study the anti-inflammatory effects and mechanism of action of the ANS in RAW264.7 cells. Quantitative PCR and immunoblotting assays were used to assess lipopolysaccharide (LPS)-induced tumor necrosis factor α (TNFα) expression. The anti-inflammatory effects of catecholamines (adrenaline, noradrenaline, and dopamine) and acetylcholine were examined in LPS-treated cells to identify the receptors involved. Catecholamines inhibited LPS-induced TNFα expression by activating the β2 adrenergic receptor (β2-AR). β2-AR activation in turn downregulated the expression of Toll-like receptor 4 (TLR4) by stimulating protein kinase A (PKA) phosphorylation, resulting in the suppression of TNFα levels. Collectively, our findings reveal a novel mechanism underlying the inhibitory effect of catecholamines on LPS-induced inflammatory responses, whereby β2-AR activation and PKA phosphorylation downregulate TLR4 expression in macrophages. These findings could provide valuable insights for the treatment of inflammatory diseases and anti-inflammatory drug development.

A Cross-Sectional Exploratory Study of Cardiovascular Risk Biomarkers in Non-Obese Women with and without Polycystic Ovary Syndrome: Association with Vitamin D

Vitamin D is proposed to have a protective effect against cardiovascular disease, though the mechanism is unclear. Vitamin D deficiency is common in polycystic ovary syndrome (PCOS), where it is strongly related to obesity, insulin resistance (IR) and risk of cardiovascular disease. To determine if the inherent pathophysiology of PCOS or vitamin D levels are linked to dysregulation of cardiovascular risk proteins (CVRPs), a study in non-obese women with PCOS and without IR was undertaken. Our hypothesis was that the levels of vitamin D3 and its active metabolite would be associated with CVRPs comparably in women with and without PCOS. In women with PCOS (n = 29) and controls (n = 29), 54 CVRPs were determined by Slow Off-rate Modified Aptamer (SOMA)-scan plasma protein measurement and correlated to 25-hydroxyvitamin D3 (25(OH)D3) and the active 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) measured by gold standard isotope-dilution liquid chromatography tandem mass spectrometry. Women with PCOS had comparable IR and systemic inflammation (normal C-reactive protein) to control women, though had higher free androgen index and anti-Mullerian hormone levels. 25(OH)D3 and 1,25(OH)2D3 levels did not differ between groups. Nine CVRPs were higher in PCOS (p < 0.05) (Galectin-9, Brother of CDO, C-motif chemokine 3, Interleukin-18 receptor-1, Thrombopoietin, Interleukin-1 receptor antagonist protein, Programmed cell death 1 ligand-2, Low-affinity immunoglobulin gamma Fc-region receptor II-b and human growth hormone), whilst 45 CVRPs did not differ. 25(OH)D3 correlated with five CVRPs in PCOS and one in controls (p < 0.05). Despite the women with PCOS not exhibiting overt systemic inflammation, 9 of 54 CVRPs were elevated, all relating to inflammation, and 5 of these correlated with 25(OH)D3, suggesting an ongoing underlying inflammatory process in PCOS even in the absence of obesity/IR.

Unveiling the hidden role of the interaction between CD36 and FcγRIIb: implications for autoimmune disorders

BACKGROUND

The role of the scavenger receptor CD36 in cell metabolism and the immune response has been investigated mainly in macrophages, dendritic cells, and T cells. However, its involvement in B cells has not been comprehensively examined.

METHODS

To investigate the function of CD36 in B cells, we exposed Cd36fl/flMB1cre mice, which lack CD36 specifically in B cells, to apoptotic cells to trigger an autoimmune response. To validate the proteins that interact with CD36 in primary B cells, we conducted mass spectrometry analysis following anti-CD36 immunoprecipitation. Immunofluorescence and co-immunoprecipitation were used to confirm the protein interactions.

RESULTS

The data revealed that mice lacking CD36 in B cells exhibited a reduction in germinal center B cells and anti-DNA antibodies in vivo. Mass spectrometry analysis identified 30 potential candidates that potentially interact with CD36. Furthermore, the interaction between CD36 and the inhibitory Fc receptor FcγRIIb was first discovered by mass spectrometry and confirmed through immunofluorescence and co-immunoprecipitation techniques. Finally, deletion of FcγRIIb in mice led to decreased expression of CD36 in marginal zone B cells, germinal center B cells, and plasma cells.

CONCLUSIONS

Our data indicate that CD36 in B cells is a critical regulator of autoimmunity. The interaction of CD36-FcγRIIb has the potential to serve as a therapeutic target for the treatment of autoimmune disorders.

Cutting edges and therapeutic opportunities on tumor-associated macrophages in lung cancer

Lung cancer is a disease with remarkable heterogeneity. A deep understanding of the tumor microenvironment (TME) offers potential therapeutic strategies against this malignant disease. More and more attention has been paid to the roles of macrophages in the TME. This article briefly summarizes the origin of macrophages, the mutual regulation between anti-tumoral immunity and pro-tumoral statuses derived from macrophage polarization, and the therapeutic opportunities targeting alternately activated macrophages (AAM)-type macrophage polarization. Among them, cellular components including T cells, as well as acellular components represented by IL-4 and IL-13 are key regulators driving the polarization of AAM macrophages. Novel treatments targeting macrophage-associated mechanisms are mainly divided into small molecule inhibitors, monoclonal antibodies, and other therapies to re-acclimate AMM macrophages. Finally, we paid special attention to an immunosuppressive subgroup of macrophages with T cell immunoglobulin and mucin domain-3 (TIM-3) expression. Based on cellular interactions with cancer cells, TIM3+ macrophages facilitate the proliferation and progression of cancer cells, yet this process exposes targets blocking the ligand-receptor recognition. To sum up, this is a systematic review on the mechanism of tumor-associated macrophages (TAM) polarization, therapeutic strategies and the biological functions of Tim-3 positive macrophages that aims to provide new insights into the pathogenesis and treatment of lung cancer.

Tumor-associated macrophages in tumor progression and the role of traditional Chinese medicine in regulating TAMs to enhance antitumor effects

Purpose

To emphasize the importance of tumor-associated macrophages (TAMs) in tumor immunity and to describe the ways in which extracts from Traditional Chinese Medicine (TCM) achieve tumor therapy by modulating macrophages.

Significance

By summarizing these available data, this review focused on TAMs and TCM and can build the foundation for future research on antitumor therapeutics.

Methods

In this review, we summarized the key functions of TAMs in cancer development and overviewed literature on TCM targeting TAMs together with other immune cells aiming to enhance antitumor immunity.

Conclusions

With an indispensable role in antitumor immunity, TAMs contribute to tumor progression, migration, invasion, angiogenesis, lymphangiogenesis, and immunosuppressive microenvironment. In recent years, TCM has gradually gained attention as a potential antitumor adjunctive therapy in preclinical and clinical trials. TCM is also a regulator of cytokine secretion and cell surface molecule expression in balancing the tumor microenvironment (TME), especially macrophage activation and polarization. Therefore, it is believed that TCM could serve as modifiers with immunomodulatory capability.

Cyclic Attractors Are Critical for Macrophage Differentiation, Heterogeneity, and Plasticity

Adaptability, heterogeneity, and plasticity are the hallmarks of macrophages. How these complex properties emerge from the molecular interactions is an open question. Thus, in this study we propose an actualized regulatory network of cytokines, signaling pathways, and transcription factors to survey the differentiation, heterogeneity, and plasticity of macrophages. The network recovers attractors, which in regulatory networks correspond to cell types, that correspond to M0, M1, M2a, M2b, M2c, M2d, M2-like, and IL-6 producing cells, including multiple cyclic attractors that are stable to perturbations. These cyclic attractors reproduce experimental observations and show that oscillations result from the structure of the network. We also study the effect of the environment in the differentiation and plasticity of macrophages, showing that the observed heterogeneity in macrophage populations is a result of the regulatory network and its interaction with the micro-environment. The macrophage regulatory network gives a mechanistic explanation to the heterogeneity and plasticity of macrophages seen in vivo and in vitro, and offers insights into the mechanism that allows the immune system to react to a complex dynamic environment.

Aberrant FcγRIIb and FcγRIII expression on monocytes from patients with Behçet's disease

Behçet's disease (BD) patients have abnormal FcγR polymorphisms, the implication of which remains elusive. We examined FcγRIIb expression on neutrophils, monocytes, B cells, natural killer cells, dendritic cells and T cells, and FcγRI and FcγRIII expression on monocytes in BD patients and healthy controls using flow cytometry. We further stimulated monocytes with IgG and (or) lipopolysaccharide (LPS) and measured IL-6 and TNF-α production by enzyme-linked immunosorbent assay. We found that BD monocytes expressed a lower level of FcγRIIb and a higher level of FcγRIII, which were correlated with erythrocyte sedimentation rate and C-reactive protein and were rescued after treatment. Furthermore, LPS- and IgG-stimulated BD monocytes produced higher levels of IL-6 and TNF-α than HC monocytes. In summary, we found that BD monocytes downregulated FcγRIIb expression and upregulated FcγRIII expression, which were correlated with disease activity and potentially contributed to monocyte hyperactivation in BD.

Synergistic Activation of Toll-Like and NOD Receptors by Complementary Antigens as Facilitators of Autoimmune Disease: Review, Model and Novel Predictions

Persistent activation of toll-like receptors (TLR) and nucleotide-binding oligomerization domain-containing proteins (NOD) in the innate immune system is one necessary driver of autoimmune disease (AD), but its mechanism remains obscure. This study compares and contrasts TLR and NOD activation profiles for four AD (autoimmune myocarditis, myasthenia gravis, multiple sclerosis and rheumatoid arthritis) and their animal models. The failure of current AD theories to explain the disparate TLR/NOD profiles in AD is reviewed and a novel model is presented that explains innate immune support of persistent chronic inflammation in terms of unique combinations of complementary AD-specific antigens stimulating synergistic TLRs and/or NODs. The potential explanatory power of the model is explored through testable, novel predictions concerning TLR- and NOD-related AD animal models and therapies.

Macrophage metabolic reprogramming presents a therapeutic target in lupus nephritis

IgG antibodies cause inflammation and organ damage in autoimmune diseases such as systemic lupus erythematosus (SLE). We investigated the metabolic profile of macrophages isolated from inflamed tissues in immune complex (IC)-associated diseases, including SLE and rheumatoid arthritis, and following IgG Fcγ receptor cross-linking. We found that human and mouse macrophages undergo a switch to glycolysis in response to IgG IC stimulation, mirroring macrophage metabolic changes in inflamed tissue in vivo. This metabolic reprogramming was required to generate a number of proinflammatory mediators, including IL-1β, and was dependent on mTOR and hypoxia-inducible factor (HIF)1α. Inhibition of glycolysis, or genetic depletion of HIF1α, attenuated IgG IC-induced activation of macrophages in vitro, including primary human kidney macrophages. In vivo, glycolysis inhibition led to a reduction in kidney macrophage IL-1β and reduced neutrophil recruitment in a murine model of antibody-mediated nephritis. Together, our data reveal the molecular mechanisms underpinning FcγR-mediated metabolic reprogramming in macrophages and suggest a therapeutic strategy for autoantibody-induced inflammation, including lupus nephritis.

THP-1 cells increase TNF-α production upon LPS + soluble human IgG co-stimulation supporting evidence for TLR4 and Fcγ receptors crosstalk

The lipopolysaccharide (LPS) of Gram-negative bacteria is recognized on human monocytes and macrophages by TLR4 and MD2 and induces the production of inflammatory cytokines; the LPS + IgG complexes co-stimulation increases the cytokine production, mediated by the Fc-γRIIa (CD32a). We stimulated human CD14 + monocytes or THP-1 cells with LPS or LPS + soluble human IgG (sIgG) and TNF-α transcription and production, assessed RT-qPCR, ELISA, or flow cytometry, was enhanced by 30% upon LPS + sIgG compared to LPS stimulation. LPS + sIgG co-stimulation affected the NF-κB pathway (p65 phosphorylation and nucleus translocation, and IkB- α degradation). The biochemical inhibition of IRAK 1/4 and Syk kinases suppressed the enhancer effect of LPS + sIgG on TNF- α production, suggesting the involvement of both MyD88 dependent and independent pathways. Our results suggest that during LPS activation, sIgG may participate in a TLR4 - Fc-γR crosstalk.

Ubiquitin E3 Ligase Pellino-1 Inhibits IL-10-mediated M2c Polarization of Macrophages, Thereby Suppressing Tumor Growth

Pellino-1 is a ubiquitin (Ub) E3 ligase that plays a role in M1, but not M2a polarization of macrophages. However, it is unknown whether Pellino-1 regulates IL-10-mediated M2c polarization of macrophages. Here, we found that Pellino-1 attenuated tumor growth by inhibiting M2c polarization of macrophages. Upon IL-10 stimulation, Pellino-1-deificient bone marrow-derived macrophages (BMDMs) showed higher expression of M2c markers, but not M2a, and M2b markers than wild-type (WT) BMDMs, indicating that Pellino-1 inhibits M2c polarization of macrophages. Pellino-1-deficient BMDMs exhibited a defect in mitochondria respiration, but enhancement of glycolysis during M2c polarization. During M2c polarization of macrophages, Pellino-1 increased STAT1 phosphorylation via K63-linked ubiquitination of IL-1 receptor associated kinase 1 (IRAK1). Furthermore, Lysm-CrePellino-1 ^fl/fl mice showed enhancement of tumor growth via regulating M2c polarization of tumor-associated macrophages. These results demonstrate that Pellino-1 inhibits IL-10-induced M2c macrophage polarization via K63-linked ubiquitination of IRAK1 and activation of STAT1, thereby inhibiting tumor growth in vivo.

IgG and Fcγ Receptors in Intestinal Immunity and Inflammation

Fcγ receptors (FcγR) are cell surface glycoproteins that mediate cellular effector functions of immunoglobulin G (IgG) antibodies. Genetic variation in FcγR genes can influence susceptibility to a variety of antibody-mediated autoimmune and inflammatory disorders, including systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). More recently, however, genetic studies have implicated altered FcγR signaling in the pathogenesis of inflammatory bowel disease (IBD), a condition classically associated with dysregulated innate and T cell immunity. Specifically, a variant of the activating receptor, FcγRIIA, with low affinity for IgG, confers protection against the development of ulcerative colitis, a subset of IBD, leading to a re-evaluation of the role of IgG and FcγRs in gastrointestinal tract immunity, an organ system traditionally associated with IgA. In this review, we summarize our current understanding of IgG and FcγR function at this unique host-environment interface, from the pathogenesis of colitis and defense against enteropathogens, its contribution to maternal-fetal cross-talk and susceptibility to cancer. Finally, we discuss the therapeutic implications of this information, both in terms of how FcγR signaling pathways may be targeted for the treatment of IBD and how FcγR engagement may influence the efficacy of therapeutic monoclonal antibodies in IBD.

Gene Regulatory Network Modeling of Macrophage Differentiation Corroborates the Continuum Hypothesis of Polarization States

Macrophages derived from monocyte precursors undergo specific polarization processes which are influenced by the local tissue environment: classically activated (M1) macrophages, with a pro-inflammatory activity and a role of effector cells in Th1 cellular immune responses, and alternatively activated (M2) macrophages, with anti-inflammatory functions and involved in immunosuppression and tissue repair. At least three different subsets of M2 macrophages, namely, M2a, M2b, and M2c, are characterized in the literature based on their eliciting signals. The activation and polarization of macrophages is achieved through many, often intertwined, signaling pathways. To describe the logical relationships among the genes involved in macrophage polarization, we used a computational modeling methodology, namely, logical (Boolean) modeling of gene regulation. We integrated experimental data and knowledge available in the literature to construct a logical network model for the gene regulation driving macrophage polarization to the M1, M2a, M2b, and M2c phenotypes. Using the software GINsim and BoolNet, we analyzed the network dynamics under different conditions and perturbations to understand how they affect cell polarization. Dynamic simulations of the network model, enacting the most relevant biological conditions, showed coherence with the observed behavior of in vivo macrophages. The model could correctly reproduce the polarization toward the four main phenotypes as well as to several hybrid phenotypes, which are known to be experimentally associated to physiological and pathological conditions. We surmise that shifts among different phenotypes in the model mimic the hypothetical continuum of macrophage polarization, with M1 and M2 being the extremes of an uninterrupted sequence of states. Furthermore, model simulations suggest that anti-inflammatory macrophages are resilient to shift back to the pro-inflammatory phenotype.

Notch signaling regulates the responses of lipopolysaccharide-stimulated macrophages in the presence of immune complexes

Macrophages exhibit diverse effector phenotypes depending on the stimuli and their microenvironment. Classically activated macrophages are primed with interferon (IFN)γ and stimulated with pathogen-associated molecular patterns. They produce inflammatory mediators and inflammatory cytokines, such as IL-12. In the presence of immune complexes (ICs), activated macrophages have decreased IL-12 production and increased IL-10 production and presumably act as regulatory macrophages. Notch signaling has been shown to regulate the effector functions of classically activated macrophages. In this study, we investigated whether Notch signaling is active in lipopolysaccharide (LPS)-stimulated macrophages in the presence of ICs. LPS/IC stimulation increased the level of cleaved Notch1 in murine macrophages, while IC stimulation alone did not. Delta-like 4, but not Jagged1, was responsible for generating cleaved Notch1. The activation of Notch signaling by LPS/ICs depended upon NF-κB and MEK/Erk pathway activation. Macrophages with the targeted deletion of Rbpj, which encodes a DNA-binding protein central to canonical Notch signaling, produced significantly less IL-10 upon LPS/IC stimulation. A similar impact on IL-10 production was observed when Notch signaling was inhibited with a gamma-secretase inhibitor (GSI). Defects in NF-κB p50 nuclear localization were observed in GSI-treated macrophages and in Rbpj^-/- macrophages, suggesting cross-regulation between the Notch and NF-κB pathways. Transcriptomic analysis revealed that Notch signaling regulates the transcription of genes involved in the cell cycle, macrophage activation, leukocyte migration and cytokine production in LPS/IC-stimulated macrophages. Taken together, these results suggest that the Notch signaling pathway plays an important role in regulating the functions of macrophages activated by LPS and ICs.

Implications of macrophage polarization in autoimmunity

Macrophages are extremely heterogeneous and plastic cells with an important role not only in physiological conditions, but also during inflammation (both for initiation and resolution). In the early 1990s, two different phenotypes of macrophages were described: one of them called classically activated (or inflammatory) macrophages (M1) and the other alternatively activated (or wound-healing) macrophages (M2). Currently, it is known that functional polarization of macrophages into only two groups is an over-simplified description of macrophage heterogeneity and plasticity; indeed, it is necessary to consider a continuum of functional states. Overall, the current available data indicate that macrophage polarization is a multifactorial process in which a huge number of factors can be involved producing different activation scenarios. Once a macrophage adopts a phenotype, it still retains the ability to continue changing in response to new environmental influences. The reversibility of polarization has a critical therapeutic value, especially in diseases in which an M1/M2 imbalance plays a pathogenic role. In this review, we assess the high plasticity of macrophages and their potential to be exploited to reduce chronic/detrimental inflammation. On the whole, the evidence detailed in this review underscores macrophage polarization as a target of interest for immunotherapy.

IgG Immunocomplexes Sensitize Human Monocytes for Inflammatory Hyperactivity via Transcriptomic and Epigenetic Reprogramming in Rheumatoid Arthritis

Prevalence of circulating immunocomplexes (ICs) strongly correlates with rheumatoid arthritis (RA) in humans. Deposits of IgG-ICs are abundant in affected joints of patients, yet molecular mechanisms for the pathogenic roles of such ICs are not fully understood. In this study, we present evidence that IgG-ICs precipitated from RA sera sensitized human monocytes for a long-lasting inflammatory functional state, characterized by a strong TNF-α response to cellular proteins representing damage-associated molecular patterns and microbe-derived pathogen-associated molecular patterns. Importantly, plate-coated human IgG (a mimic of deposited IC without Ag restriction) exhibited a similarly robust ability of monocyte sensitization in vitro. The plate-coated human IgG-induced functional programming is accompanied by transcriptomic and epigenetic modification of various inflammatory cytokines and negative regulator genes. Moreover, macrophages freshly isolated from synovia of patients with RA, but not sera-negative arthropathy, displayed a signature gene expression profile highly similar to that of IC-sensitized human monocytes, indicative of historical priming events by IgG-ICs in vivo. Thus, the ability of IgG-ICs to drive sustainable functional sensitization/reprogramming of monocytes and macrophages toward inflammation may render them key players in the development of RA.

Infective Larvae of Brugia malayi Induce Polarization of Host Macrophages that Helps in Immune Evasion

Filarial parasites suppress, divert, or polarize the host immune response to aid their survival. However, mechanisms that govern the polarization of host MΦs during early filarial infection are not completely understood. In this study, we infected BALB/c mice with infective larvae stage-3 of Brugia malayi (Bm-L3) and studied their effect on the polarization of splenic MΦs. Results showed that MΦs displayed M2-phenotype by day 3 p.i. characterized by upregulated IL-4, but reduced IL-12 and Prostaglandin-D2 secretion. Increased arginase activity, higher arginase-1 but reduced NOS2 expression and poor phagocytic and antigen processing capacity was also observed. M2 MΦs supported T-cell proliferation and characteristically upregulated p-ERK but downregulated NF-κB-p65 and NF-κB-p50/105. Notably, Bm-L3 synergized with host regulatory T-cells (Tregs) and polarized M2 MΦs to regulatory MΦs (Mregs) by day 7 p.i., which secreted copious amounts of IL-10 and prostaglandin-E2. Mregs also showed upregulated expression levels of MHC-II, CD80, and CD86 and exhibited increased antigen-processing capacity but displayed impaired activation of NF-κB-p65 and NF-κB-p50/105. Neutralization of Tregs by anti-GITR + anti-CD25 antibodies checked the polarization of M2 MΦs to Mregs, decreased accumulation of regulatory B cells and inflammatory monocytes, and reduced secretion of IL-10, but enhanced IL-4 production and percentages of eosinophils, which led to Bm-L3 killing. In summary, we report hitherto undocumented effects of early Bm-L3 infection on the polarization of splenic MΦs and show how infective larvae deftly utilize the functional plasticity of host MΦs to establish themselves inside the host.

IL4 (interleukin 4) induces autophagy in B cells leading to exacerbated asthma

Allergic asthma is a common airway inflammatory disease in which B cells play important roles through IgE production and antigen presentation. SNP (single nucleotide polymorphism) analysis showed that Atg (autophagy-related) allele mutations are involved in asthma. It has been demonstrated that macroautophagy/autophagy is essential for B cell survival, plasma cell differentiation and immunological memory maintenance. However, whether B cell autophagy participates in asthma pathogenesis remains to be investigated. In this report, we found that autophagy was enhanced in pulmonary B cells from asthma-prone mice. Autophagy deficiency in B cells led to attenuated immunopathological symptoms in asthma-prone mice. Further investigation showed that IL4 (interleukin 4), a key effector Th2 cytokine in allergic asthma, was critical for autophagy induction in B cells both in vivo and in vitro, which further sustained B cell survival and enhanced antigen presentation by B cells. Moreover, IL4-induced autophagy depended on JAK signaling via an MTOR-independent, PtdIns3K-dependent pathway. Together, our data indicate that B cell autophagy aggravates experimental asthma through multiple mechanisms.

Immune complex negatively regulates toll-like receptor 3-triggered tumour necrosis factor α production in B cells

Inappropriate activation of toll-like receptor 3 (TLR3) has been implicated in the pathogenesis of autoimmune diseases, so the negative regulation of TLR3-triggered immune response has received increasing attention. Nonpathogenic immune complex (IC) has been used as treatment for many inflammatory and autoimmune diseases. However, the role of IC in the regulation of TLR3-triggered immune responses and the underlying mechanisms need to be investigated. In this study we demonstrate that IC or intravenous immunoglobulin (Ig) stimulation of B cells attenuates polyinosinic:polycytidylic acid (poly I:C)-induced CD40 expression; IC, but not Ig, can significantly inhibit poly I:C-induced pro-inflammatory tumour necrosis factor α (TNF-α) production by B cells. Moreover, IC/Ig stimulation does not alter the expression of TLR3 in B cells. Further experiments suggest that receptor for the Fc portion of IgGIIb (FcγRIIb) is involved in the suppressive effect of IC on TLR3-mediated TNF-α production, but not CD40 expression. Thus, we provide a new means of negative regulation of TLR3-triggered immune responses in B cells via FcγRIIb, and we provide a new mechanistic explanation of the therapeutic effect of nonpathogenic IC on inflammatory or autoimmune diseases.

FcγRIIb attenuates TLR4‑mediated NF‑κB signaling in B cells

Toll‑like receptors (TLRs) serve a vital role in activating the innate immune system by sensing conserved microbial products. Fc γ receptor IIb (FcγRIIb), the inhibitory Fc receptor, exerts its immune regulatory functions by binding to the immunoglobulin G Fc domain. Although the individual roles of TLRs and FcγRIIb have been studied intensively, the cross‑talk between FcγRIIb and TLR4 on B cells remains unknown. The present study demonstrated that FcγRIIb ligation by the immune complex (IC) attenuated the TLR4‑triggered nuclear factor (NF)‑κΒ activation, and decreased the release of interleukin (IL)‑6 from B cells, via enhancing LYN proto‑oncogene (Lyn) phosphorylation. In addition, IC treatment protected mice from lethal endotoxic shock. Accordingly, IC decreased the LPS‑induced serum levels of IL‑6, as well as intracellular IL‑6 production in B cells in vivo. However, these protective and inhibitory effects of IC were not observed in FcγRIIb‑/‑ mice. In conclusion, the present data demonstrated that FcγRIIb inhibited TLR4 signaling in B cells by activating Lyn phosphorylation and by inhibiting NF‑κΒ signaling. The present study elucidated the mechanism associated with the TLR4 and FcγRIIb cross‑talk in B cells.

Extraordinarily potent proinflammatory properties of lactoferrin-containing immunocomplexes against human monocytes and macrophages

Lactoferrin (LTF), an important first line defense molecule against infection, is a common target for humoral autoimmune reactions in humans. Since LTF is a multifunctional protein capable of activating innate immune cells via various surface receptors, we hypothesized that LTF-containing immune complexes (ICs) (LTF-ICs), likely formed in patients with high titer anti-LTF autoantibodies, could possess unique monocyte/macrophage-activating properties compared with other ICs. ELISA analysis on serum samples from rheumatoid arthritis (RA) patients (n = 80) and healthy controls (n = 35) for anti-LTF autoantibodies confirmed a positive correlation between circulating LTF-specific IgG and RA. ICs between human LTF and LTF-specific IgG purified from patient sera or immunized rabbits and mice, but not control ICs, LTF or Abs alone, elicited strong production of TNF-α and IL-1β by freshly fractionated human peripheral blood monocytes and monocytes-derived macrophages. Furthermore, LTF-ICs utilized both membrane-anchored CD14 and CD32a (FcγRIIa) to trigger monocyte activation in an internalization-, Toll-like receptor (TLR)4- and TLR9-dependent manner, and also that LTF-IC-induced cytokine production was blocked by specific inhibitors of caspase-1, NF-κB and MAPK. These results uncover a possible pathway for LTF-ICs perpetuating local inflammation and contributing to the pathogenesis of autoimmune diseases by triggering activation of infiltrating monocytes or tissue macrophages in vivo.

Oxidized Low-Density Lipoprotein Immune Complex Priming of the Nlrp3 Inflammasome Involves TLR and FcγR Cooperation and Is Dependent on CARD9

Oxidized low-density lipoprotein (oxLDL) is known to activate inflammatory responses in a variety of cells, especially macrophages and dendritic cells. Interestingly, much of the oxLDL in circulation is complexed to Abs, and these resulting immune complexes (ICs) are a prominent feature of chronic inflammatory disease, such as atherosclerosis, type-2 diabetes, systemic lupus erythematosus, and rheumatoid arthritis. Levels of oxLDL ICs often correlate with disease severity, and studies demonstrated that oxLDL ICs elicit potent inflammatory responses in macrophages. In this article, we show that bone marrow-derived dendritic cells (BMDCs) incubated with oxLDL ICs for 24 h secrete significantly more IL-1β compared with BMDCs treated with free oxLDL, whereas there was no difference in levels of TNF-α or IL-6. Treatment of BMDCs with oxLDL ICs increased expression of inflammasome-related genes Il1a, Il1b, and Nlrp3, and pretreatment with a caspase 1 inhibitor decreased IL-1β secretion in response to oxLDL ICs. This inflammasome priming was due to oxLDL IC signaling via multiple receptors, because inhibition of CD36, TLR4, and FcγR significantly decreased IL-1β secretion in response to oxLDL ICs. Signaling through these receptors converged on the adaptor protein CARD9, a component of the CARD9-Bcl10-MALT1 signalosome complex involved in NF-κB translocation. Finally, oxLDL IC-mediated IL-1β production resulted in increased Th17 polarization and cytokine secretion. Collectively, these data demonstrate that oxLDL ICs induce inflammasome activation through a separate and more robust mechanism than oxLDL alone and that these ICs may be immunomodulatory in chronic disease and not just biomarkers of severity.

FcγRIIB and autoimmunity

Autoimmune diseases are characterized by adaptive immune responses against self-antigens, including humoral responses resulting in the production of autoantibodies. Autoantibodies generate inflammation by activating complement and engaging Fcγ receptors (FcγRs). The inhibitory receptor FcγRIIB plays a central role in regulating the generation of autoantibodies and their effector functions, which include activation of innate immune cells and the cellular arm of the adaptive immune system, via effects on antigen presentation to CD4 T cells. Polymorphisms in FcγRIIB have been associated with susceptibility to autoimmunity but protection against infections in humans and mice. In the last few years, new mechanisms by which FcγRIIB controls the adaptive immune response have been described. Notably, FcγRIIB has been shown to regulate germinal center B cells and dendritic cell migration, with potential impact on the development of autoimmune diseases. Recent work has also highlighted the implication of FcγRIIB on the regulation of the innate immune system, via inhibition of Toll-like receptor- and complement receptor-mediated activation. This review will provide an update on the role of FcγRIIB in adaptive immune responses in autoimmunity, and then focus on their emerging function in innate immunity.

Immune complex negatively regulates Toll-like receptor 9-mediated immune responses in B cells through the inhibitory Fc-gamma receptor IIb

Because inappropriate activation of Toll-like receptor 9 (TLR9) may induce pathological damage, negative regulation of the TLR9-triggered immune response has attracted considerable attention. Nonpathogenic immune complex (IC) has been demonstrated to have beneficial therapeutic effects in some kinds of autoimmune diseases. However, the role of IC in the regulation of TLR9-triggered immune responses and the underlying mechanisms remain unclear. In this study, it was demonstrated that IC stimulation of B cells not only suppresses CpG-oligodeoxynucleotide (CpG-ODN)-induced pro-inflammatory IL-6 and IgM κ production, but also attenuates CD40 and CD80 expression. Furthermore, our results suggest that the receptor for the Fc portion of IgG (FcγR) IIb is involved in the suppressive effect of IC on TLR9-mediated CD40, CD80 and IL-6 expression. Finally, it was found that IC down-regulates TLR9 expression in CpG-ODN activated B cells. Our results provide an outline of a new pathway for the negative regulation of TLR9-triggered immune responses in B cells via FcγRIIb. A new mechanistic explanation of the therapeutic effect of nonpathogenic IC on inflammatory and autoimmune diseases is also provided.

Functional Role of FcγRIIB in the Regulation of Mesenchymal Stem Cell Function

Mesenchymal stem cells (MSCs) derived from bone marrow are plural-potent stem cells with immune regulatory functions. We aimed to evaluate role of FcγRIIB in the regulation of bone marrow-derived MSC function. MSCs were prepared from mouse bone marrow derived from wild-type (WT) or FcγRIIB-deficient (FcγRIIB-/-) mice. MSCs were co-cultured with bone marrow-derived dendritic cells (BMDCs), and BMDC maturation and function were evaluated by flow cytometric analysis and carboxyfluorescein succinimidyl ester-labeled OT-II T-cell addition. An acute asthma model was established by aeresol ovalbumin challenge in mice. Mice received WT or FcγRIIB-/- MSC therapy. Lung function was evaluated by histological examination and cytokine production measurement. mRNA and protein expression levels of target genes were examined by real-time quantitative polymerase chain reactionor western blotting. We found that MSCs derived from bone marrow exhibit a high level of FcγRIIB expression. FcγRIIB deficiency impaired the suppressive function of MSCs, as FcγRIIB deficiency efficiently reversed the inhibitory effect of MSCs on BMDC maturation and function. Additionally, FcγRIIB-/-MSCs were less potent at suppressing asthma in model mice, possibly through reduced expression of Smad2, Smad3, Cox-2, and prostaglandin E2 in FcγRIIB-/-MSCs. FcγRIIB might play an essential role in regulating the inhibitory effects of MSCs derived from bone marrow.

Divergence of the response induced by xenogenic immunization in the sepsis survival of rats

We have previously described that boosted natural xenoantibodies in rats cross-react to bacteria by targeting carbohydrate antigens. This type of immunization is associated with reduced survival after cecal ligation and puncture (CLP). In the present study, we investigated further this phenomenon by immunizing Lewis rats with three intraperitoneal injections, every other day, of hamster blood compared to saline-injected control animals. One day after the last injection, CLP was performed to produce a low-grade sepsis. Induction of xenoantibodies was associated with a reduction in animal survival after CLP relative to controls (45% vs. 90%, p<0.01). No bacterial blood load was observed after CLP in this model either with or without xenoantibody enhancement, indicating that the augmented mortality was not mediated by a direct effect of boosted xenoantibodies over blood bacteria. Nevertheless, the xenoimmunization produced a systemic inflammatory response in all rats. Additionally, a lack of weight gain at the time of CLP was present in animals that died after the procedure, which was not observed in surviving rats and controls. The cytokine profile at the time of CLP in animals that died after the procedure was characterized by an increase in the serum level of several cytokines, particularly adipokines. In contrast, the cytokine profile at CLP of xenoimmunized rats that survived the procedure was characterized by a reduction in the level of cytokines. In conclusion, this study failed to show a direct effect of boosted xenoantibodies over blood bacterial isolates as cause for the decreased survival after CLP. However, it evidenced that non-infectious systemic inflammation may lead to a pattern of augmented cytokines, particularly adipokines, which impairs survival after subsequent CLP. Therefore, the profile of cytokines existing before the infectious insult appears more crucial than that resulting from the condition for the outcome of sepsis.

Control of cytokine production by human fc gamma receptors: implications for pathogen defense and autoimmunity

Control of cytokine production by immune cells is pivotal for counteracting infections via orchestration of local and systemic inflammation. Although their contribution has long been underexposed, it has recently become clear that human Fc gamma receptors (FcγRs), which are receptors for the Fc region of immunoglobulin G (IgG) antibodies, play a critical role in this process by controlling tissue- and pathogen-specific cytokine production. Whereas individual stimulation of FcγRs does not evoke cytokine production, FcγRs cell-type specifically interact with various other receptors for selective amplification or inhibition of particular cytokines, thereby tailoring cytokine responses to the immunological context. The physiological function of FcγR-mediated control of cytokine production is to counteract infections with various classes of pathogens. Upon IgG opsonization, pathogens are simultaneously recognized by FcγRs as well as by various pathogen-sensing receptors, leading to the induction of pathogen class-specific immune responses. However, when erroneously activated, the same mechanism also contributes to the development of autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus. In this review, we discuss control of cytokine production as a novel function of FcγRs in human innate immune cells in the context of homeostasis, infection, and autoimmunity and address the possibilities for future therapeutic exploitation.

Calcium/calmodulin-dependent protein kinase II regulates cyclooxygenase-2 expression and prostaglandin E2 production by activating cAMP-response element-binding protein in rat peritoneal macrophages

Prostaglandin E2 (PGE2 ) is an important inducer of inflammation, which is also closely linked to the progress of tumours. In macrophages, PGE2 production is regulated by arachidonic acid release and cyclooxygenase-2 (COX-2) expression. In the present study, we found that COX-2 expression can be achieved by activating Ca(2+) /Calmodulin (CaM)-dependent protein kinase II (CaMKII) and cAMP-response element-binding protein (CREB) in rat peritoneal macrophages. Our results indicated that lipopolysaccharide and PMA could elicit the transient increase of the concentration of intracellular free calcium ions ([Ca(2+) ]i ), which induced activation of CaMKs with the presence of CaM. The subtype of CaMKs, CaMKII, then triggered the activation of CREB, which elevated COX-2 expression and PGE2 production in a chronological order. These results suggested that Ca(2+) /CaM-dependent CaMKII plays an important role in mediating COX-2 expression and PGE2 production by activating CREB in macrophages. The study also provides more useful information to clarify the mechanism of calcium regulation of PGE2 production, which plays an essential role in inflammation and cancers.

Dendritic cells and macrophages in the kidney: a spectrum of good and evil

Renal dendritic cells (DCs) and macrophages represent a constitutive, extensive and contiguous network of innate immune cells that provide sentinel and immune-intelligence activity; they induce and regulate inflammatory responses to freely filtered antigenic material and protect the kidney from infection. Tissue-resident or infiltrating DCs and macrophages are key factors in the initiation and propagation of renal disease, as well as essential contributors to subsequent tissue regeneration, regardless of the aetiological and pathogenetic mechanisms. The identification, and functional and phenotypic distinction of these cell types is complex and incompletely understood, and the same is true of their interplay and relationships with effector and regulatory cells of the adaptive immune system. In this Review, we discuss the common and distinct characteristics of DCs and macrophages, as well as key advances that have identified the renal-specific functions of these important phagocytic, antigen-presenting cells, and their roles in potentiating or mitigating intrinsic kidney disease. We also identify remaining issues that are of priority for further investigation, and highlight the prospects for translational and therapeutic application of the knowledge acquired.

Fc gamma receptor IIb on GM-CSF macrophages controls immune complex mediated inhibition of inflammatory signals

BACKGROUND

In rheumatoid arthritis (RA) macrophages play a major role in amplifying synovial inflammation. Important activating signals are those induced by Toll-like receptor (TLR) ligands and by activated T cells. The balance between activating and inhibitory Fc gamma receptors (FcγRs) on macrophages might be crucial in modulating these inflammatory responses. The purpose of this study was to determine FcγR expression on pro- and anti-inflammatory macrophages (gmMφ and mMφ, respectively) and identify functional consequences on immune complex uptake and macrophage activation.

METHODS

Human monocytes were isolated and differentiated into gmMφ and mMφ. A full FcγR characterization of both macrophage subtypes was performed and uptake of fluorescent immune complexes (ICs) was determined. FcγRIIb isoforms were determined by qPCR. Macrophages were stimulated via different TLRs or cytokine activated T cells in the presence or absence of ICs and cytokine production was determined. Blocking studies were performed to look into the pathways involved.

RESULTS

mMφ expressed high levels of the activating FcγRIIa and FcγRIII and low levels of the inhibitory FcγRIIb, while the FcγR balance on gmMφ was shifted towards the inhibitory FcγRIIb. This was accompanied by a clear increase in FcγRIIb1 mRNA expression in gmMφ. This resulted in higher IC uptake by mMφ compared to gmMφ. Furthermore, FcγR-mediated stimulation of gmMφ inhibited TLR2, 3, 4 and 7/8 mediated cytokine production via FcγRIIb and PI3K signaling. In addition, gmMφ but not mMφ produced TNFα upon co-culture with cytokine activated T cells, which was reduced by IC binding to FcγRIIb. The latter was dependent on PI3K signaling and COX2.

CONCLUSIONS

FcγR expression patterns on gmMφ and mMφ are significantly different, which translates in clear functional differences further substantiating FcγRIIb as an interesting target for inflammation control in RA and other autoimmune/inflammatory diseases.

Targeting the Fc receptor in autoimmune disease

INTRODUCTION

The Fc receptors (FcRs) and their interactions with immunoglobulin and innate immune opsonins, such as C-reactive protein, are key players in humoral and cellular immune responses. As the effector mechanism for some therapeutic monoclonal antibodies, and often a contributor to the pathogenesis and progression of autoimmunity, FcRs are promising targets for treating autoimmune diseases.

AREAS COVERED

This review discusses the nature of different FcRs and the various mechanisms of their involvement in initiating and modulating immunocyte functions and their biological consequences. It describes a range of current strategies in targeting FcRs and manipulating their interaction with specific ligands, while presenting the pros and cons of these approaches. This review also discusses potential new strategies including regulation of FcR expression and receptor crosstalk.

EXPERT OPINION

FcRs are appealing targets in the treatment of inflammatory autoimmune diseases. However, there are still knowledge limitations and technical challenges, the most important being a better understanding of the individual roles of each of the FcRs and enhancement of the specificity in targeting particular cell types and specific FcRs.

Inflammatory response of macrophages in infection

BACKGROUND

Macrophages are widely-distributed innate immune cells playing diverse roles in various physiological and pathological processes. The primary function of macrophages is to phagocytize and clear invading pathogens.

DATA SOURCES

A systematic search of PubMed was performed to identify relevant studies in English language literature using the key words such as macrophage and inflammation. A total of 122 articles related to inflammatory response of macrophages in infection were systematically reviewed.

RESULTS

The inflammatory responses of macrophages triggered by infection comprise four interrelated phases: recognition of pathogen-associated molecular patterns by pattern-recognition receptors expressed on/in macrophages; enrichment of quantity of macrophages in local infected tissue by recruitment of circulating monocytes and/or in situ proliferation; macrophage-mediation of microbicidal activity and conversion to anti-inflammatory phenotype to terminate anti-infectious response and to promote tissue repair. Complicated regulation of macrophage activation at molecular level recognized in the past decade is also reviewed, including intracellular multiple signaling molecules, membrane molecules, microRNAs and even epigenetic-associated molecules.

CONCLUSION

The inflammatory response of macrophages in infection is an orderly and complicated process under elaborate regulation at molecular level.

Fc gamma receptors in respiratory syncytial virus infections: implications for innate immunity

RSV infections are a major burden in infants less than 3 months of age. Newborns and infants express a distinct immune system that is largely dependent on innate immunity and passive immunity from maternal antibodies. Antibodies can regulate immune responses against viruses through interaction with Fc gamma receptors leading to enhancement or neutralization of viral infections. The mechanisms underlying the immunomodulatory effect of Fc gamma receptors on viral infections have yet to be elucidated in infants. Herein, we will discuss current knowledge of the effects of antibodies and Fc gamma receptors on infant innate immunity to RSV. A better understanding of the pathogenesis of RSV infections in young infants may provide insight into novel therapeutic strategies such as vaccination.

Amelioration of murine passive immune thrombocytopenia by IVIg and a therapeutic monoclonal CD44 antibody does not require the Myd88 signaling pathway

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by a low platelet count and the production of anti-platelet antibodies. The majority of ITP patients have antibodies to platelet integrin α_IIbβ₃ (GPIIbIIIa) which can direct platelet phagocytosis by macrophages. One effective treatment for patients with ITP is intravenous immunoglobulin (IVIg) which rapidly reverses thrombocytopenia. The exact mechanism of IVIg action in human patients is unclear, although in mouse models of passive ITP, IVIg can rapidly increase platelet counts in the absence of adaptive immunity. Another antibody therapeutic that can similarly increase platelet counts independent of adaptive immunity are CD44 antibodies. Toll-like receptors (TLRs) are pattern recognition receptors which play a central role in helping direct the innate immune system. Dendritic cells, which are notable for their expression of TLRs, have been directly implicated in IVIg function as an initiator cell, while CD44 can associate with TLR2 and TLR4. We therefore questioned whether IVIg, or the therapeutic CD44 antibody KM114, mediate their ameliorative effects in a manner dependent upon normal TLR function. Here, we demonstrate that the TLR4 agonist LPS does not inhibit IVIg or KM114 amelioration of antibody-induced thrombocytopenia, and that these therapeutics do not ameliorate LPS-induced thrombocytopenia. IVIg was able to significantly ameliorate murine ITP in C3H/HeJ mice which have defective TLR4. All known murine TLRs except TLR3 utilize the Myd88 adapter protein to drive TLR signaling. Employing Myd88 deficient mice, we found that both IVIg and KM114 ameliorate murine ITP in Myd88 deficient mice to the same extent as normal mice. Thus both IVIg and anti-CD44 antibody can mediate their ameliorative effects in murine passive ITP independent of the Myd88 signaling pathway. These data help shed light on the mechanism of action of IVIg and KM114 in the amelioration of murine ITP.

Expression of complement components and regulators by different subtypes of bone marrow-derived macrophages

Under inflammatory conditions, macrophages can differentiate into different functional subtypes. We show that bone marrow-derived macrophages constitutively express different levels of various complement-related genes. The relative expression levels are C1qb > Crry > CFH > C3 > C1r > CFB > DAF1 > CD59a > C2 > C1INH > C1s > C4. Upon activation, the expression of C1r, C1s, C3, C2, CFB, and C1INH was up-regulated, and CFH, CD59a, and DAF1, down-regulated in M1 (induced by interferon-γ + lipopolysaccharides (LPS)) and M2b (induced by immune complex + LPS) macrophages. The expression of C4 and CFH was slightly up-regulated in interleukin (IL)-10-induced M2c macrophages. Complement gene expression in IL-4-induced M2a macrophages was weakly down-regulated as compared to resting M0 macrophages. Higher levels of C3, C1INH, and CFB but lower levels of CFH expression in M1 and M2b macrophage suggests that they may be involved in the alternative pathway of complement activation during inflammation.

Regulatory dendritic cells program B cells to differentiate into CD19hiFcγIIbhi regulatory B cells through IFN-β and CD40L

Regulatory dendritic cells (DCs) play important roles in the induction of peripheral tolerance and control of adaptive immune response. Our previous studies demonstrate that splenic stroma can drive mature DCs to proliferate and further differentiate into a unique subset of CD11b(hi)Ia(low) regulatory DCs, which could inhibit T-cell response, program generation of immunosuppressive memory CD4 T cells. However, the effect of regulatory DCs on B-cell function remains unclear. Here, we report that regulatory DCs can induce splenic B cells to differentiate into a distinct subtype of IL-10-producing regulatory B cells with unique phenotype CD19(hi)FcγIIb(hi). CD19(hi)FcγIIb(hi) B cells inhibit CD4 T-cell response via IL-10. CD19(hi)FcγIIb(hi) B cells have enhanced phagocytic capacity compared with conventional CD19(+) B cells, and FcγRIIb mediates the uptake of immune complex by CD19(hi)FcγIIb(hi) B cells. We found that regulatory DC-derived IFN-β and CD40 ligand are responsible for the differentiation of CD19(hi)FcγIIb(hi) B cells. Furthermore, an in vivo counterpart of CD19(hi)FcγIIb(hi) B cells in the spleen and lymph nodes with similar phenotype and regulatory function has been identified. Our results demonstrate a new manner for regulatory DCs to down-regulate immune response by, at least partially, programming B cells into regulatory B cells.

Innate and adaptive immune responses during acute M. tuberculosis infection in adult household contacts in Kampala, Uganda

Contacts of active pulmonary tuberculosis (TB) patients are at risk for Mycobacterium tuberculosis (MTB) infection. Because most infections are controlled, studies during MTB infection provide insight into protective immunity. We compared immune responses of adult household contacts that did and did not convert the tuberculin skin test (TST). Innate and adaptive immune responses were measured by whole blood assay. Responses of TST converters (TSTC) were compared with persistently TST negative contacts (PTST-) and contacts who were TST+ at baseline (TST+). TLR-2, TLR-4, and IFN-γR responses to IFN-γ did not differ between the groups, nor did γδ T cell responses. T cell responses to MTB antigens differed markedly among TSTC, PTST-, and TST+ contacts. Thus, no differences in innate responses were found among the three household contact groups. However, adaptive T cell responses to MTB antigens did differ before and during MTB infection among PTST-, TSTC, and TST+ contacts.

CD83-stimulated monocytes suppress T-cell immune responses through production of prostaglandin E2

CD83 is commonly known as a specific marker for mature dendritic cells. It has been shown to be important for CD4(+) T-cell development in the thymus. However, its function in the peripheral immune system remains enigmatic. Here, we show that CD83 inhibits proliferation and production of IL-2 and IFN-γ by T cells, and the inhibitory effect of CD83 is mediated by monocytes. Prostaglandin E2 (PGE(2)), but not IL-10 or TGF-β, was up-regulated specifically by CD83 in monocytes. Consistent with high levels of PGE(2), expression of COX-2 also was increased upon CD83 treatment. NF-κB activation also is required for induction of PGE(2) by CD83. Finally, application of the COX-2-selective inhibitor NS-398 fully prevented CD83-triggered inhibition of T-cell responses. Our study establishes an immune-regulatory mechanism by CD83 via stimulation of PGE(2) production in monocytes.

Do regulatory antibodies offer an alternative mechanism to explain the hygiene hypothesis?

The 'hygiene hypothesis', or lack of microbial and parasite exposure during early life, is postulated as an explanation for the recent increase in autoimmune and allergic diseases in developed countries. The favored mechanism is that microbial and parasite-derived products interact directly with pathogen recognition receptors to subvert proinflammatory signaling via T regulatory cells, thereby inducing anti-inflammatory effects and control of autoimmune disease. Parasites, such as helminths, are considered to have a major role in the induction of immune regulatory mechanisms among children living in developing countries. Invoking Occam's razor, we believe we can select an alternative mechanism to explain the hygiene hypothesis, based on antibody-mediated inhibition of immune responses that may more simply explain the available evidence.

Preparations of intravenous immunoglobulins diminish the number and proinflammatory response of CD14+CD16++ monocytes in common variable immunodeficiency (CVID) patients

We have studied the effect of intravenous immunoglobulins (IVIG) on monocyte subpopulations and cytokine production in patients with CVID. The absolute number of CD14(+)CD16(++) monocytes decreased on average 2.5-fold 4h after IVIG and after 20h returned to the baseline. The cytokine level in the supernatants of peripheral blood mononuclear cells (PBMC) after ex vivo LPS stimulation demonstrated the >2-fold decrease in TNF production 4h after IVIG. The TNF expression, which is higher in the CD14(+)CD16(++) monocytes, was decreased in these cells by IVIG in 4/7 CVID cases. In vitro exposure of the healthy individuals' monocytes to the IVIG preparation resulted in reduced TNF production, which was overcome by blockade of the FcγRIIB in the CD14(+)CD16(++) CD32B(high) monocytes. Our data suggest that reduction in the number of CD14(+)CD16(++) monocytes and the blockade of their cytokine production via triggering CD32B can contribute to the anti-inflammatory action of IVIG.

Macrophage plasticity and interaction with lymphocyte subsets: cancer as a paradigm

Plasticity is a hallmark of cells of the myelomonocytic lineage. In response to innate recognition or signals from lymphocyte subsets, mononuclear phagocytes undergo adaptive responses. Shaping of monocyte-macrophage function is an essential component of resistance to pathogens, tissue damage and repair. The orchestration of myelomonocytic cell function is a key element that links inflammation and cancer and provides a paradigm for macrophage plasticity and function. A better understanding of the molecular basis of myelomonocytic cell plasticity will open new vistas in immunopathology and therapeutic intervention.

FcgammaRIIB in autoimmunity and infection: evolutionary and therapeutic implications

FcgammaRIIB is the only inhibitory Fc receptor. It controls many aspects of immune and inflammatory responses, and variation in the gene encoding this protein has long been associated with susceptibility to autoimmune disease, particularly systemic lupus erythematosus (SLE). FcgammaRIIB is also involved in the complex regulation of defence against infection. A loss-of-function polymorphism in FcgammaRIIB protects against severe malaria, the investigation of which is beginning to clarify the evolutionary pressures that drive ethnic variation in autoimmunity. Our increased understanding of the function of FcgammaRIIB also has potentially far-reaching therapeutic implications, being involved in the mechanism of action of intravenous immunoglobulin, controlling the efficacy of monoclonal antibody therapy and providing a direct therapeutic target.

Maternal immunization with ovalbumin prevents neonatal allergy development and up-regulates inhibitory receptor Fc gamma RIIB expression on B cells

BACKGROUND

Preconception allergen immunization prevents neonatal allergen sensitization in mice by a complex interaction between regulatory cells/factors and antibodies. The present study assessed the influence of maternal immunization with ovalbumin (OVA) on the immune response of 3 day-old and 3 week-old offspring immunized or non-immunized with OVA and evaluated the effect of IgG treatment during fetal development or neonatal period.

RESULTS

Maternal immunization with OVA showed increased levels of Fc gamma RIIb expression in splenic B cells of neonates, which were maintained for up to 3 weeks and not affected by additional postnatal OVA immunization. Maternal immunization also exerted a down-modulatory effect on both IL-4 and IFN-gamma-secreting T cells and IL-4 and IL-12- secreting B cells. Furthermore, immunized neonates from immunized mothers showed a marked inhibition of antigen-specific IgE Ab production and lowered Th2/Th1 cytokine levels, whereas displaying enhanced Fc gamma RIIb expression on B cells. These offspring also showed reduced antigen-specific proliferative response and lowered B cell responsiveness. Moreover, in vitro evaluation revealed an impairment of B cell activation upon engagement of B cell antigen receptor by IgG from OVA-immunized mice. Finally, in vivo IgG transference during pregnancy or breastfeeding revealed that maternal Ab transference was able to increase regulatory cytokines, such as IL-10, in the prenatal stage; yet only the postnatal treatment prevented neonatal sensitization. None of the IgG treatments induced immunological changes in the offspring, as it was observed for those from OVA-immunized mothers.

CONCLUSION

Maternal immunization upregulates the inhibitory Fc gamma RIIb expression on offspring B cells, avoiding skewed Th2 response and development of allergy. These findings contribute to the advancement of prophylactic strategies to prevent allergic diseases in early life.

FcgammaRIIb inhibits allergic lung inflammation in a murine model of allergic asthma

Allergic asthma is characterized by airway eosinophilia, increased mucin production and allergen-specific IgE. Fc gamma receptor IIb (FcγRIIb), an inhibitory IgG receptor, has recently emerged as a negative regulator of allergic diseases like anaphylaxis and allergic rhinitis. However, no studies to date have evaluated its role in allergic asthma. Our main objective was to study the role of FcγRIIb in allergic lung inflammation. We used a murine model of allergic airway inflammation. Inflammation was quantified by BAL inflammatory cells and airway mucin production. FcγRIIb expression was measured by qPCR and flow cytometry and the cytokines were quantified by ELISA. Compared to wild type animals, FcγRIIb deficient mice mount a vigorous allergic lung inflammation characterized by increased bronchoalveolar lavage fluid cellularity, eosinophilia and mucin content upon ragweed extract (RWE) challenge. RWE challenge in sensitized mice upregulated FcγRIIb in the lungs. Disruption of IFN-γ gene abrogated this upregulation. Treatment of naïve mice with the Th1-inducing agent CpG DNA increased FcγRIIb expression in the lungs. Furthermore, treatment of sensitized mice with CpG DNA prior to RWE challenge induced greater upregulation of FcγRIIb than RWE challenge alone. These observations indicated that RWE challenge upregulated FcγRIIb in the lungs by IFN-γ- and Th1-dependent mechanisms. RWE challenge upregulated FcγRIIb on pulmonary CD14+/MHC II+ mononuclear cells and CD11c+ cells. FcγRIIb deficient mice also exhibited an exaggerated RWE-specific IgE response upon sensitization when compared to wild type mice. We propose that FcγRIIb physiologically regulates allergic airway inflammation by two mechanisms: 1) allergen challenge mediates upregulation of FcγRIIb on pulmonary CD14+/MHC II+ mononuclear cells and CD11c+ cells by an IFN-γ dependent mechanism; and 2) by attenuating the allergen specific IgE response during sensitization. Thus, stimulating FcγRIIb may be a therapeutic strategy in allergic airway disorders.