Mouse Mast Cell Protease Research Articles

Ingestion of Casein Hydrolysate Induces Oral Tolerance and Suppresses Subsequent Epicutaneous Sensitization and Development of Anaphylaxis Reaction to Casein in Mice

Background: Casein is the most dominant causal allergen in cow’s milk allergy (CMA). Casein hydrolysates are frequently applied in infant formulas for children with a risk or history of CMA. However, there is limited information on the oral tolerance-inducing ability of casein hydrolysates. Objectives: The aim of this study was to investigate whether the ingestion of casein hydrolysate induces tolerance to casein, ultimately preventing subsequent epicutaneous sensitization and development of an anaphylaxis reaction. Methods: BALB/c mice were orally administered casein or a casein hydrolysate (CNH) via the drinking water and were then epicutaneously sensitized by repeated exposure of casein on tape-stripped skin. Sensitization was assessed by basophil activation tests, the serum levels of casein-specific antibodies, and cytokine production from casein-stimulated spleen and mesenteric lymph node (MLN) cells. Occurrence of an anaphylaxis reaction was evaluated by measuring rectal temperature and the plasma level of mouse mast cell protease-1 (mMCP-1) after oral casein challenges. The T cell population in the spleen and MLN was assessed by flow cytometry. Intestinal mast cells and basophils were analyzed histologically. Results: Sensitization and anaphylaxis reaction to casein were significantly suppressed in casein- or CNH-fed mice compared to controls. Prior ingestion of casein or CNH had no effect on the population of regulatory T cells and activated T cells in lymphoid tissues. Intestinal basophils increased by the epicutaneous sensitization of casein, which was suppressed in casein- or CNH-fed mice. Although the increase in the plasma level of mMCP-1 after oral challenge was suppressed in casein- or CNH-fed mice, there was no change in the number of intestinal mast cells. Conclusion: Prior ingestion of casein or CNH induced oral tolerance and suppressed subsequent epicutaneous sensitization and development of systemic anaphylaxis to casein.

Mast Cells Augment Neuroinflammation and Neurodegeneration

Activated glial cells, and neurons express several proinflammatory mediators that are implicated in neuroinflammation and neurodegeneration in neurodegenerative diseases including Parkinson's disease (PD), Alzheimer's disease (AD) and Multiple sclerosis (MS). Mast cells are immune and inflammatory cells that are implicated in neuroinflammation by releasing several prestored and newly synthesized multifunctional cytokines, chemokines and neurotoxic mediators. Protease activated receptor‐2 (PAR‐2) expression is increased in neuroinflammatory conditions. PD is characterized by neurodegeneration of dopaminergic neurons in the brain. Here, we have investigated how mast cells can contribute to neuroinflammation, and to the pathogenesis of PD. We demonstrate that inflammatory mediators such as interleukin‐1beta (IL‐1β), tumor necrosis factor‐alpha (TNF‐α) and the chemokine (C‐C motif) ligand 2 (CCL2) were lower in the brains of mast cell deficient (MC‐KO) mice and glia maturation factor‐deficient (GMF‐KO) mice when compared to wild type mice brains after acute 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) administration. Further, we found that reconstitution of mast cells in MC‐KO mice increases neuroinflammation in the MPTP‐injected mice brains as compared to the MC‐KO brains without mast cell reconstitution. Our immunofluorescence staining revealed that the PAR‐2 expression is increased in MPTP‐injected mice brains as compared to control wild type mice brains without MPTP administration. We also show significantly increased PAR‐2 expression in the cultured primary mouse astrocytes and neurons incubated with 1‐methyl‐4‐phenylpyridinium (MPP+), inflammatory protein GMF, mouse mast cell protease‐6 (MMCP‐6), and MMCP‐7. We conclude that mast cells augment neuroinflammation and neurodegeneration in neurodegenerative diseases including PD and inhibition of mast cell activation could be a therapeutic option in neuroinflammatory and neurodegenerative disorders.Support or Funding InformationThis work was supported by Veteran Affairs Merit Award I01BX002477 and National Institutes of Health Grants AG048205 & NS073670 to Prof. Asgar ZaheerThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Mouse mast cell protease 4 suppresses scar formation after traumatic spinal cord injury

Spinal cord injury (SCI) triggers the formation of a glial and fibrotic scar, which creates a major barrier for neuroregenerative processes. Previous findings indicate that mast cells (MCs) protect the spinal cord after mechanical damage by suppressing detrimental inflammatory processes via mouse mast cell protease 4 (mMCP4), a MC-specific chymase. In addition to these immunomodulatory properties, mMCP4 also plays an important role in tissue remodeling and extracellular matrix degradation. Therefore, we have investigated the effects of mMCP4 on the scarring response after SCI. We demonstrate that the decrease in locomotor performance in mMCP4−/− mice is correlated with excessive scar formation at the lesion. The expression of axon-growth inhibitory chondroitin sulfate proteoglycans was dramatically increased in the perilesional area in mMCP4−/− mice compared to wild type mice. Moreover, the fibronectin-, laminin-, and collagen IV-positive scar was significantly enlarged in mMCP4−/− mice at the lesion center. A degradation assay revealed that mMCP4 directly cleaves collagen IV in vitro. On the gene expression level, neurocan and GFAP were significantly higher in the mMCP4−/− group at day 2 and day 28 after injury respectively. In contrast, the expression of fibronectin and collagen IV was reduced in mMCP4−/− mice compared to WT mice at day 7 after SCI. In conclusion, our data show that mMCP4 modulates scar development after SCI by altering the gene and protein expression patterns of key scar factors in vivo. Therefore, we suggest a new mechanism via which endogenous mMCP4 can improve recovery after SCI.

High dietary fat intake induces a microbiota signature that promotes food allergy

Diet-induced obesity and food allergies increase in tandem, but a potential cause-and-effect relationship between these diseases of affluence remains to be tested. We sought to test the role of high dietary fat intake, diet-induced obesity, and associated changes in gut microbial community structure on food allergy pathogenesis. Mice were fed a high-fat diet (HFD) for 12weeks before food allergen sensitization on an atopic dermatitis-like skin lesion, followed by intragastric allergen challenge to induce experimental food allergy. Germ-free animals were colonized with a signature HFD or lean microbiota for 8weeks before induction of food allergy. Food-induced allergic responses were quantified by using a clinical allergy score, serum IgE levels, serum mouse mast cell protease 1 concentrations, and type 2 cytokine responses. Accumulation of intestinal mast cells was examined by using flow cytometry and chloroacetate esterase tissue staining. Changes in the gut microbial community structure were assessed by using high-throughput 16S ribosomal DNA gene sequencing. HFD-induced obesity potentiates food-induced allergic responses associated with dysregulated intestinal effector mast cell responses, increased intestinal permeability, and gut dysbiosis. An HFD-associated microbiome was transmissible to germ-free mice, with the gut microbial community structure of recipients segregating according to the microbiota input source. Independent of an obese state, an HFD-associated gut microbiome was sufficient to confer enhanced susceptibility to food allergy. These findings identify HFD-induced microbial alterations as risk factors for experimental food allergy and uncouple a pathogenic role of an HFD-associated microbiome from obesity. Postdieting microbiome alterations caused by overindulgence of dietary fat might increase susceptibility to food allergy.

Deficiency of mouse mast cell protease 4 mitigates cardiac dysfunctions in mice after myocardium infarction

Mouse mast cell protease-4 (mMCP4) is a chymase that has been implicated in cardiovascular diseases, including myocardial infarction (MI). This study tested a direct role of mMCP4 in mouse post-MI cardiac dysfunction and myocardial remodeling. Immunoblot and immunofluorescent double staining demonstrated mMCP4 expression in cardiomyocytes from the infarct zone from mouse heart at 28 day post-MI. At this time point, mMCP4-deficient Mcpt4−/− mice showed no difference in survival from wild-type (WT) control mice, yet demonstrated smaller infarct size, improved cardiac functions, reduced macrophage content but increased T-cell accumulation in the infarct region compared with those of WT littermates. mMCP4-deficiency also reduced cardiomyocyte apoptosis and expression of TGF-β1, p-Smad2, and p-Smad3 in the infarct region, but did not affect collagen deposition or α-smooth muscle actin expression in the same area. Gelatin gel zymography and immunoblot analysis revealed reduced activities of matrix metalloproteinases and expression of cysteinyl cathepsins in the myocardium, macrophages, and T cells from Mcpt4−/− mice. Immunoblot analysis also found reduced p-Smad2 and p-Smad3 in the myocardium from Mcpt4−/− mice, yet fibroblasts from Mcpt4−/− mice showed comparable levels of p-Smad2 and p-Smad3 to those of WT fibroblasts. Flow cytometry, immunoblot analysis, and immunofluorescent staining demonstrated that mMCP4-deficiency reduced the expression of proapoptotic cathepsins in cardiomyocytes and protected cardiomyocytes from H2O2-induced apoptosis. This study established a role of mMCP4 in mouse post-MI dysfunction by regulating myocardial protease expression and cardiomyocyte death without significant impact on myocardial fibrosis or survival post-MI in mice.

Shuang-Huang-Lian Attenuates Airway Hyperresponsiveness and Inflammation in a Shrimp Protein-Induced Murine Asthma Model.

Shuang-Huang-Lian (SHL), an herbal formula of traditional Chinese medicine, is clinically used for bronchial asthma treatment. Our previous study found that SHL prevented basophil activation to suppress Th2 immunity and stabilized mast cells through activating its mitochondrial calcium uniporter. Sporadic clinical reports that SHL was used for the treatment of bronchial asthma can be found. Thus, in this study, we systematically investigated the effects of SHL on asthmatic responses using a shrimp protein (SP)- induced mouse model. SHL significantly inhibited airway inspiratory and expiratory resistance, and histological studies suggested it reduced thickness of airway smooth muscle and infiltration of inflammation cells. It also could alleviate eosinophilic airway inflammation (EAI), including reducing the number of eosinophils and decreasing eotaxin and eosinophil peroxidase levels in the bronchoalveolar lavage fluid (BALF). Further studies indicated that SHL suppressed SP-elevated mouse mast cell protease-1 and IgE levels, prevented Th2 differentiation in mediastinal lymph nodes, and lowered Th2 cytokine (e.g., IL-4, IL-5, and IL-13) production in BALF. In conclusion, SHL attenuates airway hyperresponsiveness and EAI mainly via the inhibition of mast cell activation and Th2 immunity, which may help to elucidate the underlying mechanism of SHL on asthma treatment and support its clinical use.

Mice co-administrated with partially hydrolysed whey proteins and prebiotic fibre mixtures show allergen-specific tolerance and a modulated gut microbiota.

Non-breastfed infants at-risk of allergy are recommended to use a hydrolysed formula before the age of 6 months. The addition of prebiotics to this formula may reduce the allergy development in these infants, but clinical evidence is still inconclusive. This study evaluates (1) whether the exposure duration to different prebiotics alongside a partially hydrolysed whey protein (pHP) influences its' effectiveness to prevent allergy development and (2) whether the gut microbiota plays a role in this process. Mice orally sensitised with whey and/or cholera toxin were orally treated for six days before sensitization with phosphate buffered saline, whey or pHP to potentially induce tolerance. Two groups received an oligosaccharide diet only from day -7 until -2 (GFshort and GFAshort) whereas two other groups received their diets from day -15 until 37 (GFlong and GFAlong). On day 35, mice underwent an intradermal whey challenge, and the acute allergic skin response, shock score, and body temperatures were measured. At day 37, mice received whey orally and serum mouse mast cell protease-1, SLPI and whey-specific antibodies were assessed. Faecal samples were taken at day -15, -8 and 34. Feeding mice pHP alone during tolerance induction did not reduce ear swelling. The tolerance inducing mechanisms seem to vary according to the oligosaccharide-composition. GFshort, GFlong, and GFAlong reduced the allergic skin response, whereas GFAshort was not potent enough. However, in the treatment groups, the dominant Lactobacillus species decreased, being replaced by Bacteroidales family S24-7 members. In addition, the relative abundance of Prevotella was significantly higher in the GFlong, GFAshort and GFAlong groups. Co-administration of oligosaccharides and pHP can induce immunological tolerance in mice, although tolerance induction was strongest in the animals that were fed oligosaccharides during the entire protocol. Some microbial changes coincided with tolerance induction, however, a specific mechanism could not be determined based on these data.

Glia Maturation Factor and Mast Cell-Dependent Expression of Inflammatory Mediators and Proteinase Activated Receptor-2 in Neuroinflammation.

Parkinson's disease (PD) is characterized by the presence of inflammation-mediated dopaminergic neurodegeneration in the substantia nigra. Inflammatory mediators from activated microglia, astrocytes, neurons, T-cells and mast cells mediate neuroinflammation and neurodegeneration. Administration of neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induces PD like motor deficits in rodents. 1-methyl-4-phenylpyridinium (MPP+), a toxic metabolite of MPTP activates glial cells, neurons and mast cells to release neuroinflammatory mediators. Glia maturation factor (GMF), mast cells and proteinase activated receptor-2 (PAR-2) are implicated in neuroinflammation. Alpha-synuclein which induces neurodegeneration increases PAR-2 expression in the brain. However, the exact mechanisms are not yet understood. In this study, we quantified inflammatory mediators in the brains of MPTP-administered wild type (Wt), GMF-knockout (GMF-KO), and mast cell knockout (MC-KO) mice. Additionally, we analyzed the effect of MPP+, GMF, and mast cell proteases on PAR-2 expression in astrocytes and neurons in vitro. Results show that the levels of interleukin-1beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and the chemokine (C-C motif) ligand 2 (CCL2) were lesser in the brains of GMF-KO mice and MC-KO mice when compared to Wt mice brain after MPTP administration. Incubation of astrocytes and neurons with MPP+, GMF, and mouse mast cell protease-6 (MMCP-6) and MMCP-7 increased the expression of PAR-2. Our studies show that the absence of mast cells and GMF reduce the expression of neuroinflammatory mediators in the brain. We conclude that GMF along with mast cell interactions with glial cells and neurons during neuroinflammation can be explored as a new therapeutic target for PD and other neuroinflammatory disorders.

Mouse Mast Cell Protease 4 Deletion Protects Heart Function and Survival After Permanent Myocardial Infarction.

Chymase, a mast cell serine protease involved in the generation of multiple cardiovascular factors, such as angiotensin II and endothelin-1 (ET-1), is elevated and participates in tissue degeneration after permanent myocardial infarction (PMI). Anesthetized 4-month old male wild-type (WT) C57BL/6J mice and mouse mast cell protease-4 knockout (mMCP-4 KO) congeners were subjected to ligation of the left anterior descending (LAD) coronary artery. A group of mice was then subjected to Kaplan-Meier 28-day survival analysis. In another group of mice, 18F-fluorodeoxyglucose positron emission tomography (PET) was performed to evaluate heart function and the infarcted zone 3 days post-PMI surgery. Cardiac morphology following PMI was evaluated on formalin-fixed heart slices and glycoproteomic analysis was performed using mass spectrometry. Finally, cardiac and lung tissue content of immunoreactive ET-1 was determined. PMI caused 60% mortality in WT mice, due to left ventricular wall rupture, and 7% in mMCP-4 KO mice. Cardiac PET analysis revealed a significant reduction in left ventricular volume (systolic and diastolic) and preserved the ejection fraction in mMCP-4 KO compared to WT animals. The infarcted area, apoptotic signaling and wall remodeling were significantly decreased in mMCP-4 KO mice compared to their WT congeners, while collagen deposition was increased. Glycoproteomic analysis showed an increase in apolipoprotein A1, an established chymase substrate in mMCP-4 KO mice compared to WT mice post-PMI. ET-1 levels were increased in the lungs of WT, but not mMCP-4 KO mice, 24 h post-PMI. Thus, the genetic deletion of mMCP-4 improved survival and heart function post-PMI.

Oral exposure to the free amino acid glycine inhibits the acute allergic response in a model of cow's milk allergy in mice

The conditionally essential amino acid glycine functions as inhibitory neurotransmitter in the mammalian central nervous system. Moreover, it has been shown to act as an anti-inflammatory compound in animal models of ischemic perfusion, post-operative inflammation, periodontal disease, arthritis and obesity. Glycine acts by binding to a glycine-gated chloride channel, which has been demonstrated on neurons and immune cells, including macrophages, polymorphonuclear neutrophils and lymphocytes. The present study aims to evaluate the effect of glycine on allergy development in a cow's milk allergy model. To this end, C3H/HeOuJ female mice were supplemented with glycine by oral gavage (50 or 100 mg/mouse) 4 hours prior to sensitization with cow's milk whey protein, using cholera toxin as adjuvant. Acute allergic skin responses and anaphylaxis were assessed after intradermal allergen challenge in the ears. Mouse mast cell protease-1 (mMCP-1) and whey specific IgE levels were detected in blood collected 30 minutes after an oral allergen challenge. Jejunum was dissected and evaluated for the presence of mMCP-1-positive cells by immunohistochemistry. Intake of glycine significantly inhibited allergy development in a concentration dependent manner as indicated by a reduction in; acute allergic skin response, anaphylaxis, serum mMCP-1 and serum levels of whey specific IgE. In addition, in-vitro experiments using rat basophilic leukemia cells (RBL), showed that free glycine inhibited cytokine release but not cellular degranulation. These findings support the hypothesis that the onset of cow's milk allergy is prevented by the oral intake of the amino acid glycine. An adequate intake of glycine might be important in the improvement of tolerance against whey allergy or protection against (whey-induced) allergy development.

Mast Cell Proteases Activate Astrocytes and Glia-Neurons and Release Interleukin-33 by Activating p38 and ERK1/2 MAPKs and NF-κB

Inflammatory mediators released from activated microglia, astrocytes, neurons, and mast cells mediate neuroinflammation. Parkinson's disease (PD) is characterized by inflammation-dependent dopaminergic neurodegeneration in substantia nigra. 1-Methyl-4-phenylpyridinium (MPP+), a metabolite of parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), induces inflammatory mediators' release from brain cells and mast cells. Brain cells' interaction with mast cells is implicated in neuroinflammation. However, the exact mechanisms involved are not yet clearly understood. Mouse fetal brain-derived cultured primary astrocytes and glia-neurons were incubated with mouse mast cell protease-6 (MMCP-6) and MMCP-7, and mouse bone marrow-derived mast cells (BMMCs) were incubated with MPP+ and brain protein glia maturation factor (GMF). Interleukin-33 (IL-33) released from these cells was quantitated by enzyme-linked immunosorbent assay. Both MMCP-6 and MMCP-7 induced IL-33 release from astrocytes and glia-neurons. MPP+ and GMF were used as a positive control-induced IL-33 and reactive oxygen species expression in mast cells. Mast cell proteases and MPP+ activate p38 and extracellular signal-regulated kinases 1/2 (ERK1/2), mitogen-activated protein kinases (MAPKs), and transcription factor nuclear factor-kappa B (NF-κB) in astrocytes, glia-neurons, or mast cells. Addition of BMMCs from wt mice and transduction with adeno-GMF show higher chemokine (C-C motif) ligand 2 (CCL2) release. MPP+ activated glial cells and reduced microtubule-associated protein 2 (MAP-2) expression indicating neurodegeneration. IL-33 expression increased in the midbrain and striatum of PD brains as compared with age- and sex-matched control subjects. Glial cells and neurons interact with mast cells and accelerate neuroinflammation and these interactions can be explored as a new therapeutic target to treat PD.

Mast Cell Proteases Activate Glia‐Neurons and Release Interleukin‐33 by Activating MAPKs

Parkinson's disease (PD) is characterized by inflammation‐dependent dopaminergic neurodegeneration in the substantia nigra in the brain. Inflammatory mediators released from activated microglia, astrocytes, neurons, T‐cells and mast cells mediate neuroinflammation and neurodegeneration in the brain. 1‐methyl‐4‐phenylpyridinium (MPP+), a toxic metabolite of the parkinsonian neurotoxin 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induces the release of inflammatory mediators from glial cells, neurons and inflammatory cells including mast cells. Mast cells play an important role in neuroinflammation and neurodegeneration. Mast cell proteases are implicated in neuroinflammation. However, the exact mechanism involved in this process is not yet clearly understood. In the present study, mouse bone marrow‐derived mast cells (BMMCs) and mouse fetal brain‐derived glia/neurons and astrocytes were incubated with MPP+, mouse mast cell protease‐6 (MMCP‐6) and MMCP‐7 in vitro. Inflammatory cytokine interleukin‐33 (IL‐33) released from these cells was quantitated by enzyme‐linked immunosorbent assay. MMCP‐6 or MMCP‐7 stimulates astrocyte and glia/neurons to release significantly more IL‐33 as compared with untreated control cells. MPP+ also induced IL‐33 release from mouse mast cells and glia‐neurons. Our results show that mast cell proteases and MPP+ activate mitogen‐activated protein kinases (MAPKs) p38 and extracellular signal–regulated kinases1/2 (ERK1/2) and release IL‐33 from these cells. We suggest that mast cell interaction with glial cells and neurons during neuroinflammation can be explored as a new therapeutic target for PD and other neuroinflammatory conditions.Support or Funding InformationThis work was supported by Veteran Affairs Merit Award I01BX002477 and National Institutes of Health Grants AG048205.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Loss of Histamine Signaling Reduces Biliary and Hepatic Damage, Mast Cell Migration and Tumor Formation in 52 wk Old Multidrug Resistance‐2 Knockout Mice

BackgroundPrimary sclerosing cholangitis (PSC) is characterized by biliary damage and liver fibrosis. The multidrug resistance‐2 gene knockout (Mdr2−/−) mouse (i) develops cholestasis; (ii) mimics some characteristics of human PSC; and (iii) develops hepatocellular cancer (HCC) within one year. We have demonstrated that depletion of the l‐histidine decarboxylase/histamine (HDC/HA) axis using 12 week old HDC/Mdr2 double knockout (DKO) mice results in decreased (i) hepatic damage; (ii) mast cell (MC) infiltration and activation; (iii) biliary proliferation; (iv) inflammation and (v) liver fibrosis when compared to Mdr2−/− mice. The aim of our study was to evaluate the effects of the loss of the HDC/HA axis on biliary and hepatic damage, MC infiltration/activation and tumor formation in older Mdr2−/− and DKO mice.Method52 week old homozygous DKO mice and aged matched Mdr2−/− mice were utilized. Livers were evaluated for tumor formation and lobular damage by H&E staining. In total liver we evaluated: (i) HDC/histamine receptor (HR) expression by qPCR, (ii) MC infiltration by staining for mouse mast cell protease‐1, (iii) MC activation by qPCR for chymase, tryptase and c‐Kit expression, (iv) ductular reaction by CK‐19 and Ki67 immunohistochemistry and (v) biliary senescence by SA‐β‐galactosiadse activity and staining for p16, p18, p21 and p53. Changes in liver fibrosis were evaluated by Sirius red staining in liver sections, and staining for α‐SMA and collagen‐1a. Hepatic stellate cell (HSC) activation was determined by immunofluorescence and qPCR for SYP‐9. Inflammation was evaluated by staining for IL‐6, TNF‐α and F4/80. HA serum levels were measured by EIA. In livers and tumors (when present), we evaluated angiogenesis by VEGF and vWF gene expression.ResultsLoss of the HDC/HA axis in 52 week old DKO mice resulted in little to no tumor formation compared to age‐matched Mdr2−/− mice, which displayed large HCC tumors. The HDC/HA/HR axis and MC infiltration/activation were reduced in DKO mice compared to age‐matched Mdr2−/− mice. Infiltrating MCs were found near bile ducts. Ductular reaction, biliary senescence and hepatic fibrosis were increased in Mdr2−/− mice, but were reduced in DKO mice. Furthermore, angiogenesis and inflammation were all reduced in DKO when compared to age‐matched Mdr2−/− mice.ConclusionOur data demonstrates that depletion of the HDC/HA axis blunts tumor growth and progression in Mdr2−/− mice, which is coupled with reduced biliary and hepatic damage, and MC infiltration/activation. The HDC/HA axis may be a critical therapeutic target for patients with cholestasis or liver cancer.Support or Funding InformationNIH NIDDK R01, VA MeritThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

How do basophils contribute to Th2 cell differentiation and allergic responses?

Basophils and mast cells share some features, including basophilic granules in the cytoplasm, cell surface expression of the high-affinity IgE receptor and release of chemical mediators such as histamine. Because of this similarity and their minority status, basophils had often been erroneously considered as minor relatives or blood-circulating precursors of tissue-resident mast cells, and therefore long been neglected or underestimated in immunological studies. Taking advantage of newly developed tools, such as basophil-depleting antibodies and engineered mice deficient for only basophils, recent studies have identified previously unappreciated roles for basophils, distinct from those played by mast cells, in allergic responses, protective immunity against parasitic infections and regulation of other immune cells. In this review, we focus on two topics that we presented and discussed in the 46th Annual Meeting of the Japanese Society for Immunology held in Sendai in December 2017. The first topic is the function of basophils as antigen-presenting cells for driving Th2 cell differentiation. We demonstrated that basophils produce few or no MHC class II (MHC-II) proteins by themselves although they can acquire peptide-MHC-II complexes from dendritic cells through trogocytosis, and present them and provide IL-4 to naive CD4 T cells, promoting Th2 cell differentiation. The second topic is the basophil-specific effector molecules involved in allergic responses. Among mouse mast cell proteases (mMCPs), mMCP-8 and mMCP-11 are expressed almost exclusively by basophils. Analyses in vitro and in vivo revealed that both proteases can induce leukocyte migration through distinct mechanisms, contributing to the development of basophil-dependent allergic inflammation.

Shuang-Huang-Lian injection induces an immediate hypersensitivity reaction via C5a but not IgE

Among traditional Chinese medicine injections, intravenous Shuang-Huang-Lian (IV-SHL) has the highest incidence of injection-induced immediate hypersensitivity reactions (IHRs). The precise mechanisms of IV-SHL-induced IHRs remain ambiguous. In this study, we investigated the mechanisms of SHL injection (SHLI)-induced IHRs. Our data showed that serum total IgE and mouse mast cell protease 1 (MMCP1) levels were higher in the SHLI antiserum; however, these effects of SHLI disappeared in the antibiotic-treated mice. SHLI caused intraplantar vasopermeability and shock during the first local or systemic injection. SHLI-induced nonallergic IHRs were attributed to its intermediate fraction F2 (the extract of Lonicerae Japonicae Flos and Fructus forsythiae), and could be blocked by antagonists for histamine or C5a, rather than PAF or C3a. Eight constituents of F2 were able to directly activate C5 to promote local vasopermeability at the mg/mL level. In conclusion, SHLI-induced IHRs are not mediated by IgE. SHLI or its F2 can directly activate blood C5. Subsequently, C5a is likely to provoke histamine release from its effector cells (e.g., mast cells and basophils), indicating that histamine is a principal effector of IHRs induced by SHLI.

Skin inflammation exacerbates food allergy symptoms in epicutaneously sensitized mice.

Cutaneous exposure to food antigen through impaired skin barrier has been shown to induce epicutaneous sensitization, thereby causing IgE-mediated food allergies. We examined whether skin barrier impairment following epicutaneous sensitization exacerbates food allergies. BALB/c mice were epicutaneously sensitized by repeated application of ovalbumin (OVA) to MC903-pretreated ear skin for 48hours weekly and then intragastrically challenged with OVA. After the first oral challenge, the skin barrier was disrupted with topical application of MC903 or by tape-stripping. Mice were monitored for changes in body temperature and the occurrence of diarrhea after undergoing the second oral challenge. Serum levels of mouse mast cell protease-1 (mmcp1) and OVA-specific IgE, IgG1, IgG2a antibodies and OVA-specific IgA levels in intestinal lavage fluid were measured by ELISA. Tissue accumulation of eosinophils was determined histologically. Epicutaneously sensitized mice developed anaphylaxis after intragastric challenge, as evidenced by diarrhea, decreased body temperature, and increased serum mmcp1 levels. Skin barrier disruption by MC903 treatment or tape-stripping exacerbated allergic reactions induced by oral challenge. MC903 treatment increased serum baseline and postchallenge mmcp1 levels. Topical pretreatment with dexamethasone alleviated allergic reactions that were exacerbated by MC903 treatment. Even after eliminating exposure to the antigen, inflammation from skin barrier disruption can exacerbate the severity of food allergy symptoms. Serum baseline mmcp1 levels might be an effective marker for predicting the severity of antigen-induced allergic symptoms.

Mast cell heterogeneity underlies different manifestations of food allergy in mice.

Food can trigger a diverse array of symptoms in food allergic individuals from isolated local symptoms affecting skin or gut to multi-system severe reactions (systemic anaphylaxis). Although we know that gastrointestinal and systemic manifestations of food allergy are mediated by tissue mast cells (MCs), it is not clear why allergen exposure by the oral route can result in such distinct clinical manifestations. Our aim was to assess the contribution of mast cell subsets to different manifestations of food allergy. We used two common models of IgE-mediated food allergy, one resulting in systemic anaphylaxis and the other resulting in acute gastrointestinal symptoms, to study the immune basis of allergic reactions. We used responders and non-responders in each model system, as well as naïve controls to identify the association of mast cell activation with clinical reactivity rather than sensitization. Systemic anaphylaxis was uniquely associated with activation of connective tissue mast cells (identified by release of mouse mast cell protease (MMCP) -7 into the serum) and release of histamine, while activation of mucosal mast cells (identified by release of MMCP-1 in the serum) did not correlate with symptoms. Gastrointestinal manifestations of food allergy were associated with an increase of MMCP-1-expressing mast cells in the intestine, and evidence of both mucosal and connective tissue mast cell activation. The data presented in this paper demonstrates that mast cell heterogeneity is an important contributor to manifestations of food allergy, and identifies the connective tissue mast cell subset as key in the development of severe systemic anaphylaxis.

Mouse mast cells and mast cell proteases do not play a significant role in acute tissue injury pain induced by formalin.

Subcutaneous formalin injections are used as a model for tissue injury-induced pain where formalin induces pain and inflammation indirectly by crosslinking proteins and directly through activation of the transient receptor potential A1 receptor on primary afferents. Activation of primary afferents leads to both central and peripheral release of neurotransmitters. Mast cells are found in close proximity to peripheral sensory nerve endings and express receptors for neurotransmitters released by the primary afferents, contributing to the neuro/immune interface. Mast cell proteases are found in large quantities within mast cell granules and are released continuously in small amounts and upon mast cell activation. They have a wide repertoire of proposed substrates, including Substance P and calcitonin gene-related peptide, but knowledge of their in vivo function is limited. We evaluated the role of mouse mast cell proteases (mMCPs) in tissue injury pain responses induced by formalin, using transgenic mice lacking either mMCP4, mMCP6, or carboxypeptidase A3 (CPA3), or mast cells in their entirety. Further, we investigated the role of mast cells in heat hypersensitivity following a nerve growth factor injection. No statistical difference was observed between the respective mast cell protease knockout lines and wild-type controls in the formalin test. Mast cell deficiency did not have an effect on formalin-induced nociceptive responses nor nerve growth factor-induced heat hypersensitivity. Our data thus show that mMCP4, mMCP6, and CPA3 as well as mast cells as a whole, do not play a significant role in the pain responses associated with acute tissue injury and inflammation in the formalin test. Our data also indicate that mast cells are not essential to heat hypersensitivity induced by nerve growth factor.

Iron-induced chelation alleviates the potential allergenicity of ovotransferrin in a BALB/c mouse model

Ovotransferrin (OVT) is one of the main egg allergens with 2 iron-binding sites. Several studies have demonstrated that iron-chelation decreased the allergenicity of milk allergen and birch pollen allergens. Therefore, we hypothesized that iron-chelation could also reduce the allergenicity of OVT. Apo-OVT (iron-free OVT, the natural state in egg white) and Holo-OVT (iron-chelated OVT) were prepared, and the allergenicity of them were assessed and compared using a BALB/c mouse model as well as dendritic cells (DCs) based on antigen uptake. Mice were orally sensitized with Apo-OVT or Holo-OVT using cholera toxin as adjuvant. Clinical signs of allergy, morphological structure of jejunum, specific antibody levels, mast cell protease-1 (mMCP-1) concentrations, cytokines and antigen uptake by DCs were determined after the mice were challenged with Apo-OVT or Holo-OVT. Results showed that both Apo-OVT and Holo-OVT induced intestinal allergy, but no systematic allergic symbols were observed. Serum levels of mouse mast cell protease-1 (mMCP-1) and specific IgE in Apo-OVT group were lower than in control group, and no significant difference between Apo-OVT group and Holo-OVT group (P>.05). The levels of OVT-specific IgG and IgG1, as well as the Th-1 cytokine interferon gamma and Th2-type cytokine interleukin-13 in Holo-OVT sensitized mice were significantly decreased compared to Apo-OVT group (P<.05), while no significant difference with control group (P>.05). However, DCs took in less Apo-OVT than Holo-OVT. Overall, iron-induced chelation could alleviate the potential allergenicity of OVT in vivo.

Mechanism underlying the suppressor activity of retinoic acid on IL4-induced IgE synthesis and its physiological implication

The present study extends an earlier report that retinoic acid (RA) down-regulates IgE Ab synthesis in vitro. Here, we show the suppressive activity of RA on IgE production in vivo and its underlying mechanisms. We found that RA down-regulated IgE class switching recombination (CSR) mainly through RA receptor α (RARα). Additionally, RA inhibited histone acetylation of germ-line ε (GL ε) promoter, leading to suppression of IgE CSR. Consistently, serum IgE levels were substantially elevated in vitamin A-deficient (VAD) mice and this was more dramatic in VAD-lecithin:retinol acyltransferase deficient (LRAT−/−) mice. Further, serum mouse mast cell protease-1 (mMCP-1) level was elevated while frequency of intestinal regulatory T cells (Tregs) were diminished in VAD LRAT−/− mice, reflecting that deprivation of RA leads to allergic immune response. Taken together, our results reveal that RA has an IgE-repressive activity in vivo, which may ameliorate IgE-mediated allergic disease.