Selective inhibition of the Fc epsilon RI-induced de novo synthesis of mediators by an inhibitory receptor

Anti-atopic dermatitis effects of dictamni cortex: Studies on in vitro and in vivo experimental models

BACKGROUND

Dictamni Cortex (DC), a Chinese herbal medicine with wind dispelling and itchiness relieving effects, is the most popular single herb prescribed for the treatment of atopic dermatitis (AD), as it is used in up to 12.68% of all herbal prescriptions for AD.

PURPOSE

The present study aimed to evaluate the anti-AD effect of Dictamni Cortex extract (DCE) and elucidate the underlying molecular mechanisms of its action using the 1-chloro-2,4-dinitrobenzene (DNCB)-induced AD-like mouse model and a relevant in vitro experimental model.

METHODS

Female Balb/c mice were sensitized with 200 μl 0.5% DNCB for three days. After sensitization, mice were challenged with 200 μl 1% DNCB on the same dorsal skin and also 20 μl 1% DNCB on each ear every 3 days, and orally administrated by gavage with DCE (0.6, 1.2 and 2.4 g/kg) daily from day 14 to day 29 for 16 consecutive days. At the end of experiment, the clinical scores for AD on the mice were calculated to evaluate the therapeutic effect of DCE; and serum, ears and dorsal skin of the mice were collected for mechanistic study. The anti-allergic activity of DCE was also evaluated using antigen-induced RBL-2H3 cell line. The release of selected cytokines, chemokines and β-hexosaminidase was measured to determine the anti-allergic activity of DCE. In addition, intracellular Ca²⁺ level, MAPKs and Lyn phosphorylations were further investigated to reveal its anti-allergic molecular mechanisms.

RESULTS

Our results demonstrated that DCE could markedly improve the AD-like symptoms in AD-like mice by inhibiting the mast cell infiltration, suppressing the production of Th2-associated cytokine (IL-4) and pro-inflammatory cytokines (TNF-α), and enhancing the protein expression of filaggrin through inhibition of the MAPKs and NF-κB pathways. Moreover, DCE suppressed mast cell degranulation through decreasing the intracellular Ca²⁺ level and inactivation of Lyn, Syk and PLCγs, suggesting DCE could regulate mast-cell-mediated allergic response.

CONCLUSION

Our experimental results unambiguously indicate that DCE possesses potent anti-allergic effect, and help place the application of DC for the treatment of AD on a scientific footing.

Recent advances in our understanding of mast cell activation - or should it be mast cell mediator disorders?

INTRODUCTION

An increasing number of patients present with multiple symptoms affecting many organs including the brain due to multiple mediators released by mast cells. These unique tissue immune cells are critical for allergic reactions triggered by immunoglobulin E (IgE), but are also stimulated (not activated) by immune, drug, environmental, food, infectious, and stress triggers, leading to secretion of multiple mediators often without histamine and tryptase. The presentation, diagnosis, and management of the spectrum of mast cell disorders are very confusing. As a result, neuropsychiatric symptoms have been left out, and diagnostic criteria made stricter excluding most patients. Areas covered: A literature search was performed on papers published between January 1990 and November 2018 using MEDLINE. Terms used were activation, antihistamines, atopy, autism, brain fog, heparin, KIT mutation, IgE, inflammation, IL-6, IL-31, IL-37, luteolin, mast cells, mastocytosis, mediators, mycotoxins, release, secretion, tetramethoxyluteolin, and tryptase. Expert opinion: Conditions associated with elevated serum or urine levels of any mast cell mediator, in the absence of comorbidities that could explain elevated levels, should be considered 'Mast Cell Mediator Disorders (MCMD).' Emphasis should be placed on the identification of unique mast cell mediators, and development of drugs or supplements that inhibit their release.

Probing the Antiallergic and Anti-inflammatory Activity of Biflavonoids and Dihydroflavonols from Dietes bicolor

Dietes bicolor (Iridaceae) is an ornamental plant used by African local healers to treat diarrhea and dysentery. A new dihydroflavonol, (2R,3R)-3,5,7-trihydroxy-8-methoxyflavanone (1); two known dihydroflavonols, trans-3-hydroxy-5-methoxy-6,7-methylenedioxyflavanone (2) and trans-3-hydroxy-5,7-dimethoxyflavanone (3); the known isoflavone orobol 7,3'-di-O-methyl ether (4); the known biflavones lanaroflavone (5), robustaflavone (6), and amentoflavone (7); and β-sitosterol (8) were isolated from the CH₂Cl₂ fraction of D. bicolor leaves. The extract showed potent activity in antiallergic and anti-inflammatory assays. The structures of the isolates were identified by spectroscopic and spectrometric methods. Compounds 6 and 7 (400 μM) exhibited antiallergic activity by inhibiting antigen-induced β-hexosaminidase release at 45.7% and 46.3%, respectively. Moreover, 6 and 7 exerted anti-inflammatory activity as demonstrated by the inhibition of superoxide anion generation with an IC₅₀ value of 1.0 μM as well as the inhibition of elastase release with IC₅₀ values of 0.45 and 0.75 μM, respectively. The anti-inflammatory activity was further explained by the virtual docking of the isolated compounds to the binding sites in the human neutrophil elastase (HNE) crystal structure using Discovery Studio 2.5. It was concluded that the biflavonoids bind directly to HNE and inhibit its enzymatic activity based on the CDOCKER algorithm. The data provided evidence for the potential use of D. bicolor against certain diseases related to allergy and inflammation.

Anti-inflammatory and anti-allergic effects and underlying mechanisms of Huang-Lian-Jie-Du extract: Implication for atopic dermatitis treatment

ETHNOPHARMACOLOGICAL RELEVANCE

Huang-Lian-Jie-Du Decoction (HLJDD), a well-known Chinese herbal formula recorded in the Tang dynasty, is composed of Coptidis rhizoma (Huang-Lian), Scutellariae radix (Huang-Qin), Phellodendri Chinensis cortex (Huang-Bai) and Gardenia fructus (Zhi-Zi). It has clinical efficacy of purging fire for removing toxin and is commonly used for the treatment of disease including Alzheimer's disease, stroke and gastrointestinal disorders. HLJDD is also frequently applied for the treatment of various skin diseases, such as atopic dermatitis (AD) and various types of eczema. The aim of this study is to investigate the anti-inflammatory and anti-allergic actions of Huang-Lian-Jie-Du ethanolic extract (HLJDE) and to elucidate underlying molecular mechanisms of action using relevant in vitro experimental models.

MATERIALS AND METHODS

The anti-inflammatory effects of HLJDE were investigated through evaluating the change of nitric oxide (NO) and the production of several cytokines and chemokines in lipopolysaccharide (LPS)-stimulated RAW264.7 cell line. Expression of mitogen-activated protein kinases (MAPKs), NF-κB p65 phosphorylation, inhibitor-κBα (IκBα) degradation were further investigated to elucidate its anti-inflammatory molecular mechanisms. Meanwhile, the anti-allergic activities of HLJDE was also evaluated using antigen-induced RBL-2H3 cell line. β-hexosaminidase and histamine release and selected cytokines and chemokines were measured to evaluate the anti-allergic activities of HLJDE. In addition, intracellular Ca(2+)level, MAPKs and Lyn phosphorylation were further investigated to reveal its anti-allergic molecular mechanisms.

RESULTS

HLJDE could significantly suppress the secretion of NO, IL-1β, IL-4, MCP-1 and GM-CSF in RAW264.7 cells in a dose-dependent manner. In addition, HLJDE also markedly reduced the phosphorylation of MAPKs, and inhibited the transcriptional activity of NF-κB and IκBα degradation. Furthermore, HLJDE exerted marked anti-allergic activity through inhibiting the release of β-hexosaminidase and histamine. The release of cytokines and chemokines (IL-4, TNF-α, MCP-1) from activated RBL-2H3 cells were also attenuated by pretreatment with HLJDE. The inhibitory effects on intracellular Ca(2+)level, and reduced phosphorylation of MAPKs and Lyn are believed to be the anti-allergic mechanisms.

CONCLUSIONS

HLJDE exerted significant anti-inflammatory and anti-allergic effects through suppressing the production of allergic and inflammatory mediators via the NF-κB and MAPKs inactivation and IκBα degradation in the LPS-stimulated RAW24.7 cells, inactivation of MAPKs and Lyn pathway in antigen-induced RBL-2H3 cells. The present study provides in vitro experimental evidence to support the use of HLJDE for the clinical treatment of AD.

Antiallergic activity of rosmarinic acid esters is modulated by hydrophobicity, and bulkiness of alkyl side chain

Methyl, propyl and hexyl esters of rosmarinic, caffeic and p-coumaric acids were tested for antiallergic activity, and rosmarinic acid propyl ester exhibited the greatest β-hexosaminidase release suppression (IC50, 23.7 μM). Quadratic correlations between pIC50 and cLogP (r(2) = 0.94, 0.98, and 1.00, respectively) were observed in each acid ester series. The antiallergic activity is modulated by hydrophobicity, and alkyl chain bulkiness.

Immunopharmacological modulation of mast cells

Mast cells produce a wide spectrum of mediators and they have been implicated in several physiopathological conditions (e.g. allergic reactions and certain tumors). Pharmacologic agents that modulate the release of mediators from mast cells has helped to elucidate the biochemical mechanisms by which immunological and non-immunological stimuli activate these cells. Furthermore, the study of surface receptors and signaling pathways associated with mast cell activation revealed novel pharmacologic targets. Thus, the development of pharmacologic agents based on this new wave of knowledge holds promise for the treatment of several mast cell-mediated disorders.

The inhibitory activity of atractylenolide Ш, a sesquiterpenoid, on IgE-mediated mast cell activation and passive cutaneous anaphylaxis (PCA)

ETHNOPHARMACOLOGICAL RELEVANCE

AT Ш, a sesquiterpenoid, is the major component of Atractylodes japonica Koidz that has been used as a traditional oriental medicine.

AIM OF THE STUDY

We investigated the anti-allergic activity of AT Ш and its mechanism of action.

MATERIALS AND METHODS

The released amount of β-hexosaminidase in mast cells, a key parameter of degranulation, was measured. Anti-allergic potential of AT Ш was evaluated using passive cutaneous anaphylaxis in vivo. The anti-allergic mechanism of AT Ш was investigated by immunoblotting analysis, RT-PCR and measurement of [Ca(2+)]i in mast cells.

RESULTS

AT Ш significantly inhibited IgE/Ag-mediated degranulation with an IC(50) value (36 ± 4 μM) in RBL-2H3 cells without affecting cell viability. It also suppressed IgE/Ag-mediated passive cutaneous anaphylaxis (PCA) response with an ED(50) value (65 ± 41 mg/kg) in vivo. AT Ш suppressed the production of interleukin (IL-4) and tumor necrosis factor (TNF)-alpha mRNAs more potent than the Src-family kinase inhibitor PP2 in RBL-2H3 cells at all concentrations. In order to elucidate the anti-allergic mechanisms of AT Ш in mast cells, we examined the activated levels of signaling molecules. AT Ш inhibited the phosphorylation of Lyn, Fyn, Syk, LAT, PLCγ, Gab2, Akt, p38, and JNK kinases expression. IgE/Ag-mediated [Ca(2+)]i elevation was significantly inhibited by AT Ш.

CONCLUSIONS

Our study suggests that AT Ш might be used as a therapeutic agent for allergic diseases.

Different inhibitory capacities of human and mouse KLRG1 are linked to distinct disulfide-mediated oligomerizations

The killer cell lectin-like receptor G1 (KLRG1) is a cadherin-binding inhibitory receptor expressed by NK and T cells in humans and mice. Although structural and ligand-binding properties of human (h) and mouse (m) KLRG1 are very similar, KLRG1-mediated inhibition under physiological conditions is only observed with human lymphocytes. Using a well-defined in vitro system, we demonstrate here that mKLRG1 exhibits a significantly lower inhibitory capacity compared with the human homolog. Biochemical analyses further showed that mKLRG1 formed monomers and disulfide-linked dimers, trimers, and tetramers whereas hKLRG1 was exclusively present as disulfide-linked dimer. Mutational analysis revealed a crucial role of Cys(62) present in the stalk region of mKLRG1 but not of hKLRG1 for oligomer formation. Strikingly, mimicking hKLRG1 by replacement of Cys(62) in mKLRG1 by glutamine prevented tri- and tetramer formation and increased the inhibitory capacity. Furthermore, mutated mKLRG1 molecules that were unable to form disulfide-linked dimers at all or at a decreased level lacked inhibitory activity. These data indicate that only dimeric KLRG1 entities exhibit potent inhibitory capacities. The lower inhibitory capacity of mKLRG1 compared with hKLRG1 can thus be rationalized by a decreased proportion of dimeric entities, which can be pinpointed to a single amino acid.

CD84 negatively regulates IgE high-affinity receptor signaling in human mast cells

CD84 is a self-binding receptor from the CD150 (or signaling lymphocyte activation molecule [SLAM]) family that is broadly expressed in hematopoietic cells. It has been described that the adaptors SLAM-associated protein (SAP) and EWS-FLI1-activated transcript 2 (EAT-2) are critical for CD150 family members' signaling and function. We observed that human mast cells express CD84 but lack SAP or EAT-2, that CD84 is tyrosine phosphorylated upon FcεRI engagement, and that the release of granule contents is reduced when FcεRI is coengaged with CD84 in LAD2 and human CD34(+)-derived mast cells. In addition, we observed that the release of IL-8 and GM-CSF was also reduced in FcεRI/CD84-costimulated cells as compared with FcεRI/Ig control. To understand how CD84 downregulates FcεRI-mediated function, we analyzed signaling pathways affected by CD84 in human mast cells. Our results showed that CD84 dampens FcεRI-mediated calcium mobilization after its co-cross-linking with the receptor. Furthermore, FcεRI-mediated Syk-linker for activation of T cells-phospholipase C-γ1 axis activity is downregulated after CD84 stimulation, compared with FcεRI/Ig control. The inhibitory kinase Fes phosphorylates mainly the inhibitory motif for CD84. Moreover, Fes, which has been described to become phosphorylated after substrate binding, also gets phosphorylated when coexpressed with CD84. Consistently, Fes was observed to be more phosphorylated after CD84 and FcεRI co-cross-linking. The phosphorylation of the protein phosphatase Src homology region 2 domain-containing phosphatase-1 also increases after CD84 and FcεRI coengagement. Taken together, our results show that CD84 is highly expressed in mast cells and that it contributes to the regulation of FcεRI signaling in SAP- and EAT-2-independent and Fes- and Src homology region 2 domain-containing phosphatase-1-dependent mechanisms.

Down-regulation of mast cell responses through ITIM containing inhibitory receptors

The multiple cell types that comprise the immune system provide an efficient defense system against invading pathogens and micro-organisms. In general, immune cells are activated for disparate functions, such as proliferation, production and release of mediators and chemotaxis, as a result of interactions between ligands and their matching immunoreceptors. This in turn leads to the recruitment and activation of a cascade of second messengers, via their regulators/adaptors, that determine the net effect of the initial response. However, activation of cells of the immune system must be tightly regulated by a finely tuned interplay between activation and inhibition to avoid excessive or inappropriate responsiveness and to maintain homeostasis. Loss of inhibitory signals may disrupt this balance, leading to various pathological processes such as allergic and auto-immune diseases. In this chapter, we will discuss down-regulating mechanisms of mast cells focusing on immunoreceptor tyrosine-based inhibition motifs (ITIM)-containing inhibitory receptors (IR).

Inhibitory C-type lectin receptors in myeloid cells

C-type lectin receptors encoded by the natural killer gene complex play critical roles in enabling NK cell discrimination between self and non-self. In recent years, additional genes at this locus have been identified with patterns of expression that extend to cells of the myeloid lineage where many of the encoded inhibitory receptors have equally important functions as regulators of immune homeostasis. In the present review we highlight the roles of some of these receptors including recent insights gained with regard to the identification of exogenous and endogenous ligands, mechanisms of cellular inhibition and activation, regulated expression within different cellular and immune contexts, as well as functions that include the regulation of bone homeostasis and involvement in autoimmunity.

The effects of omalizumab on IgE-induced cytokine synthesis by asthmatic airway smooth muscle cells

BACKGROUND

Human airway smooth muscle cells (ASMCs) express high- and low-affinity IgE receptors and respond to IgE, thereby contributing to airway inflammation.

OBJECTIVE

To determine whether anti-IgE antibodies (omalizumab) block the response of ASMCs to IgE in patients with asthma.

METHODS

Airway smooth muscle cells, isolated from the biopsy specimens of patients with asthma, patients with chronic obstructive pulmonary disease, and control participants (6 in each group), were stimulated with IgE with and without omalizumab treatment, and cytokine secretion was determined by enzyme-linked immunosorbent assay, and messenger RNA (mRNA) secretion by real-time polymerase chain reaction, over 24 hours. IgE receptor expression was determined by immunoblotting.

RESULTS

IgE-stimulated mRNA synthesis encoded for interleukin (IL) 6, IL-8, and tumor necrosis factor a in ASMCs via mitogen-activated protein kinases, extracellular signal-regulated kinase 1/2, or p38. The secretion of the respective cytokines increased significantly: IL-6, IL-8, and tumor necrosis factor a at 6 hours and IL-4 at 24 hours. Cytokine mRNA synthesis and protein secretion were inhibited by omalizumab in a dose-dependent manner. The expression of low- and high-affinity IgE receptors was not altered by omalizumab in ASMCs.

CONCLUSIONS

Omalizumab reduced IgE-stimulated synthesis and secretion of proinflammatory cytokines by human ASMCs. These findings imply a beneficial action of omalizumab in asthma therapy. This effect is not restricted to inflammatory cells; it also includes tissue-forming cells.

Regulation of the mast cell response to the type 1 Fc epsilon receptor

The type I Fc epsilon receptor (Fc epsilon RI) is one of the better understood members of its class and is central to the immunological activation of mast cells and basophils, the key players in immunoglobulin E (IgE)-dependent immediate hypersensitivity. This review provides background information on several distinct regulatory mechanisms controlling this receptor's stimulus-response coupling network. First, we review the current understanding of this network's operation, and then we focus on the inhibitory regulatory mechanisms. In particular, we discuss the different known cytosolic molecules (e.g. kinases, phosphatases, and adapters) as well as cell membrane proteins involved in negatively regulating the Fc epsilon RI-induced secretory responses. Knowledge of this field is developing at a fast rate, as new proteins endowed with regulatory functions are still being discovered. Our understanding of the complex networks by which these proteins exert regulation is limited. Although the scope of this review does not include addressing several important biochemical and biophysical aspects of the regulatory mechanisms, it does provide general insights into a central field in immunology.

New developments in FcepsilonRI regulation, function and inhibition

The high-affinity Fc receptor for IgE (FcepsilonRI), a multimeric immune receptor, is a crucial structure for IgE-mediated allergic reactions. In recent years, advances have been made in several important areas of the study of FcepsilonRI. The first area relates to FcepsilonRI-mediated biological responses that are antigen independent. The second area encompasses the biological relevance of the distinct signalling pathways that are activated by FcepsilonRI; and the third area relates to the accumulated evidence for the tight control of FcepsilonRI signalling through a broad array of inhibitory mechanisms, which are being developed into promising therapeutic approaches.

Heme oxygenase-1 inhibits cytokine production by activated mast cells

Heme oxygenase-1 (HO-1) is thought to contribute to host defense reactions against various stresses. In addition, recent reports have suggested that HO-1 modulates immunocyte activation and functions. HO-1 suppresses mast cell degranulation, but whether HO-1 suppresses cytokine synthesis as well is not yet known. We examined whether rat HO-1 cDNA transfected rat basophilic leukemia (RBL)-2H3 cells have altered cytokine production in response to stimulation with anti-ovalbumin (OA) serum/OA compared to Mock transfected RBL-2H3 cells. HO-1 inhibited anti-OA serum/OA-induced IL-3 and TNF-alpha production. Inhibition of HO-1 activity by Zn (II) protoporphyrin IX, a specific HO-1 inhibitor, prevented the suppression of TNF-alpha production. The cytokine inhibition by HO-1 was associated with selective suppression of the DNA-binding activity of AP-1 transcription factors. The suppression of mast cell cytokine production by HO-1 may be an important aspect of the processes that lead to resolution of allergic inflammation.