Mast Cell-nerve Interaction Research Articles

Mast Cell-Specific MRGPRX2: a Key Modulator of Neuro-Immune Interaction in Allergic Diseases.

Atopic dermatitis (AD) and allergic asthma are complex disorders with significant public health burden. This review provides an overview of the recent developments on Mas-related G protein-coupled receptor-X2 (MRGPRX2; mouse counterpart MrgprB2) as a potential candidate to target neuro-immune interaction in AD and allergic asthma. Domestic allergens directly activate sensory neurons to release substance P (SP), which induces mast cell degranulation via MrgprB2 and drives type 2 skin inflammation in AD. MRGPRX2 expression is upregulated in human lung mast cells and serum of asthmatic patients. Both SP and hemokinin-1 (HK-1 generated from macrophages, bronchial cells, and mast cells) cause degranulation of human mast cells via MRGPRX2. MrgprB2 contributes to mast cell-nerve interaction in the pathogenesis of AD. Furthermore, asthma severity is associated with increased MRGPRX2 expression in mast cells. Thus, MRGPRX2 could serve as a novel target for modulating AD and asthma.

1030 Role of mast cells in psoriasis associated-pruritus

Whilst a key role of mast cells in itch (pruritogenic pruritus) is well-established, the exact underlying mechanisms remain to be fully elucidated. Here, we have examined the role of mast cells in psoriasis-associated pruritus. By immunofluorescence microscopy we confirmed not only that lesional psoriasis skin showed increased mast cell numbers, degranulation activity and overall innervation, but also an increased density of PAR2-positive nerve fibres. Moreover, the proximity of visualized nerve fibres and mast cells was increased suggesting enhanced mast cell-nerve interaction. To characterized mast cell related-itch pathways, healthy human skin was exposed in vitro for 18 hours to known pruritogens which induce mast cell activation such as compound 48/80, substance P (SP), and the selective proteinase-activated receptor 2 (PAR2)-activating peptide, SLIGKV, to mimic conditions of itch and neurogenic skin inflammation and to compare the expression of itch-associated genes with unexposed skin. RNA-Seq with DESeq2 was used for analysis of transcript expression. In organ-cultured healthy human skin, TSLP transcripts were upregulated 1.65, 1.53, and 1.59 fold following stimulation with 100 μg/ml of compound 48/80, 2 μM of SP and 100 μM of SLIGKV, respectively. In addition, SP stimulation upregulated IL31RA and TLR7 gene expression 3.22 and 2.56 fold, respectively, whilst stimulation with SLIGKV also upregulated MRGPRX2, TRPA1, and IL2RA 1.56, 2.21, and 1.76 fold, respectively. The differences in itch-associated genes, other than TSLP, upregulated following stimulation of skin with compound 48/80, SP, and SLIGKV may suggest that SP and PAR-2 agonists could induce itch through multiple, distinct and synergistic signalling pathways. Furthermore, these findings indicate that SP stimulation increases the sensitivity of the skin to potent pruritogens, such as IL-31 or TLR7 ligands, by upregulating their receptors.

Mast cell-nerve interaction in the colon of Trypanosoma cruzi-infected individuals with chagasic megacolon.

Chagas disease is an infection caused by the parasite Trypanosoma cruzi that affects millions of people worldwide and is endemic in Latin America. Megacolon is the most frequent complication of the digestive chronic form and happens due to lesions of the enteric nervous system. The neuronal lesions seem to initiate in the acute phase and persist during the chronic phase, albeit the mechanisms involved in this process are still debated. Among the cells of the immune system possibly involved in this pathological process is the mast cell (MC) due to its well-known role in the bi-directional communication between the immune and nervous systems. Using ultrastructural analysis, we found an increased number of degranulated MCs in close proximity to nerve fibers in infected patients when compared with uninfected controls. We also immunostained MCs for the two pro-inflammatory molecules tryptase and chymase, the first being also important in neuronal death. The number of MCs immunostained for tryptase or chymase was increased in patients with megacolon, whereas increased tryptase staining was additionally observed in patients without megacolon. Moreover, we detected the expression of the tryptase receptor PAR2 in neurons of the enteric nervous system, which correlated to the tryptase staining results. Altogether, the data presented herein point to the participation of MCs on the denervation process that occurs in the development of T. cruzi-induced megacolon.

The parasympathetic nervous system as a regulator of mast cell function.

Often considered as the archetype of neuroimmune communication, much of our understanding of the bidirectional relationship between the nervous and immune systems has come from the study of mast cell-nerve interaction. Mast cells play a role in resistance to infection and are extensively involved in inflammation and subsequent tissue repair. Thus, the relationship between mast cells and neurons enables the involvement of peripheral and central nervous systems in the regulation of host defense mechanisms and inflammation. Recently, with the identification of the cholinergic anti-inflammatory pathway, there has been increased interest in the role of the parasympathetic nervous system in regulating immune responses. Classical neurotransmitters and neuropeptides released from cholinergic and inhibitory NANC neurons can modulate mast cell activity, and there is good evidence for the existence of parasympathetic nerve-mast cell functional units in the skin, lung, and intestine that have the potential to regulate a range of physiological processes.

Mast cells reduce survival of myenteric neurons in culture

Mast cell–nerve interactions play a key role in intestinal inflammation and irritable bowel disease. Loss of enteric neurons has been reported in inflammatory conditions but the contribution of mast cells in this event is unknown. To study neuronal survival and plasticity of myenteric neurons in contact with mast cells a co-culture system using myenteric neurons from rat small intestine and peritoneal mast cells was set up. Dissociated myenteric neurons were cultured for 4 days before addition of mast cells isolated by peritoneal lavage. Neuronal survival and expression of vasoactive intestinal peptide (VIP) and nitric oxide synthase (NOS) were studied by immunocytochemistry and neuronal cell counting. Myenteric neurons cultured without mast cells were used to study the rate of neuronal survival after the addition of various mast cell mediators, proteinase-activated receptor 2 (PAR 2) agonist, VIP or corticosteroid. A striking mast cell-induced neuronal cell death was found after co-culturing. It was counteracted by the addition of mast cell stabiliser doxantrazole, protease inhibitors, PAR 2 antagonist FSLLRY-amide, corticosteroid or VIP. In myenteric neurons cultured without mast cells the PAR 2 agonist SLIGRL-amide, prostaglandin D 2 and interleukin (IL) 6 reduced neuronal survival while histamine, serotonin, heparin, IL1β and tumour necrosis factor α had no effect; corticosteroid and VIP enhanced neuronal survival. The relative numbers of VIP-, but not NOS-expressing myenteric neurons increased after co-culturing. Mast cell-induced neuronal cell death is suggested to be mediated via PAR 2 activation, IL6 and prostaglandin D 2. Corticosteroid and VIP are neuroprotective and able to prevent cell death of myenteric neurons in co-culture.

Mast Cell–Nerve Interactions in Children With Functional Dyspepsia

Functional dyspepsia in childhood is commonly triggered by food allergen in sensitised individuals. We investigated the topography of eosinophils and mast cells in gastric antral lamina propria, the interaction of mast cell products with mucosal nerve fibres, and changes in gastric antral muscle slow wave activity in children with atopy and non-atopy-related functional dyspepsia. Open label study of gastric mucosal cow's milk challenge in 10 atopic and 6 nonatopic children (ages 2-12 years) investigated consecutively with gastroscopy for functional dyspepsia. Simultaneous surface electrogastrography and milk challenge were undertaken and laser scanning fluorescence microscopy used to examine the association of mast cell tryptase with mucosal nerves in the gastric mucosa before and after challenge. Eosinophils and mast cells within the lamina propria were increased in number in children with atopic functional dyspepsia and degranulated rapidly after cow's milk challenge in the atopic group. For degranulating eosinophils, median = 13.0% (interquartile range = 3.7-31.0) premilk versus 32.0% (12.0-42.0) after milk biopsies (P < 0.05); for degranulating mast cells, 5.35% (2.7-10.9) premilk biopsies versus 18.75% (12.9-22.1) after milk biopsies (P < 0.05). No such differences were seen in nonatopic patients. Mast cells were closely associated with mucosal nerve fibres and released tryptase, which colocalised with proteinase-activated receptors on mucosal nerve fibres. The gastric antral slow wave became abnormal within 2 minutes of antigen challenge in atopics with an increase in dominant frequency instability coefficient (P < 0.005), decrease in 3 cycles per minute myoelectrical activity (P < 0.01), and increase in bradygastria (P < 0.01). Early-onset neuroimmune interactions induced by cow's milk in the gastric mucosa of atopic children are associated with rapid disturbance of gastric myoelectrical activity and dyspeptic symptoms.

Effect of Substance P on Histamine Secretion from Gut Mucosa in Inflammatory Bowel Disease

Background: Mast cell hyperplasia in the gut is a feature of inflammatory bowel disease (IBD), but the role of mast cells in this disease is still unclear. Since mast cell-nerve interactions might have some impact on intestinal inflammation, the present study investigated whether the neuropeptide substance P causes histamine secretion from human gut mucosal mast cells. Methods: Four hundred and eighteen colorectal endoscopic samples from 20 patients with IBD and 10 controls were studied. Colorectal biopsy samples were cultured in an oxygenated medium for spontaneous histamine release or were stimulated with substance P, anti-human immunoglobulin E, and a combination of substance P and anti-human immunoglobulin E. Histamine release was measured using a highly sensitive and specific radioimmunoassay. Results: Substance P failed to induce mast cell activation in histologically normal mucosa from controls. In contrast, mucosal specimens taken from inflamed IBD tissue or from uninvolved Crohn disease tissue showed a considerably enhanced rate of histamine secretion towards substance P, alone or in combination with anti-IgE. Unaffected mucosa with ulcerative colitis appeared insensitive towards substance P. Conclusions: The neuropeptide substance P was shown to preferentially enhance mucosal mast cell mediator secretion in active IBD. Thus, it appears likely that mast cell-nerve interactions are involved in as yet uninvestigated neurovegetative histamine-releasing processes of the gut in IBD.

Immunohistochemical localization of mast cells and mast cell-nerve interactions in oral lichen planus.

Mast cell mediators are likely to be involved in at least some aspects of the immunopathogenesis of oral lichen planus (OLP). The aim of this project was to map mast cell populations in OLP and identify possible sites of mast cell-nerve interactions. Monoclonal antibodies specific for tryptase and neurofilaments were used to identify mast cells and nerves respectively in an immunohistochemical study of OLP (n = 25) and normal oral buccal mucosa (NOBM) (n = 13) using a double-labelling protocol. Data analysis used paired t-test, multiway analysis of variance and Wilcoxon rank tests. Morphometric analyses showed the greatest mast cell density in the most superficial of the three depth layers examined in OLP, an increase of 130% compared with NOBM. Mast cells associated with neurofilaments ranged from 21.9% in OLP to 10.2% in NOBM. Mean epithelial thickness was significantly lower in OLP (P < 0.001) but without a strong correlation with mast cell density. Increased mast cell and mast cell-nerve interactions in OLP suggest both a controlling role over the lesional cell populations and a secondary role to the immune response once this becomes established.

Immunomodulation of Epithelium

Many studies have provided evidence that the immune system is a key regulatory system of intestinal function. The interaction of immune cells with the gut epithelium plays an important role in host defence, acting to eliminate pathogens, antigens and other noxious material from the lumen of the gastrointestinal tract. During inflammatory conditions of the gut, the mucosa becomes packed with immune cells in close proximity to the enterocytes. Mediators released from these cells have profound effects on epithelial functions. The two main functions of the intestinal epithelium are to transport nutrients, ions and water, and to act as a barrier to prevent unimpeded uptake of antigenic material and microbes from the lumen. Both these functions are altered by immune reactions in response to various stimuli. Topics discussed include mast cells and epithelial function; mast cell-nerve interaction; mast cell activation; neutrophils, eosinophils and macrophages; T cells; and prostaglandins and immune cell activation.

Neurophysiology of mast cell-nerve interactions in the airways.

The sensitized guinea pig was employed as a model to study the effect of immunological activation of resident mast cells on neuronal activity in the airways. The trachea was isolated with the vagus nerves and vagal sensory ganglia intact. Using conventional electrophysiological recording techniques, we noted that antigenic stimulation led to an increase in the sensitivity of sensory nerve endings located in the airway wall. Moreover, previous work has revealed that antigen challenge potentiates action-potential-driven tachykinin release from afferent fibers in the guinea pig isolated airway. Anatomical and electrophysiological studies indicate that tachykinin-containing sensory fibers directly innervate the local parasympathetic ganglion neurons in the airway. Therefore, antigen-induced increases in the excitability of sensory fibers in the airways can increase parasympathetic tone in the airway by increasing central and peripheral reflex arcs. In addition, we have found that antigen stimulation has direct effects on the excitability of the parasympathetic ganglion neurons. Considered together, the data demonstrate that increased vagal sensory and parasympathetic activity may be a consequence of the allergic reaction in the airways.

Ionizing radiation reduces neurally evoked electrolyte transport in rat ileum through a mast cell-dependent mechanism

Background/Aims: Mechanisms of neuroimmune regulation of intestinal electrolyte transport under pathophysiological conditions are unclear. This study investigated the effect of ionizing radiation on ileal electrolyte transport. Methods: Rats were exposed to 10 Gy γ-radiation and were killed 2, 24, and 48 hours later. Ileal segments were either mounted in Ussing chambers and exposed to electrical field stimulation, prostaglandin E2, leukotriene D4, or theophylline, or they were assayed for biochemical indices of inflammation. Other segments were processed for routine histological screening, mast cell counts, or immunohistochemical analysis of the distribution of vasoactive intestinal polypeptide or substance P immunoreactivity. Results: Basal short-circuit current was unchanged 2, 24, or 48 hours postirradiation. However, there was a reduction of tissue responsiveness to electrical field stimulation, prostaglandin E2, and theophylline but not to leukotriene D4. Decreased responsiveness at 2-hours postirradiation was blocked by pretreatment with the H1 antagonist pyrilamine. Tissue myeloperoxidase activity and 5-hydroxytryptamine content were not altered post-irradiation, but tissue histamine and mucosal mast cells were significantly reduced at 24 and 48 hours. There were no significant changes in villus-crypt architecture until 48 hours postirradiation. There was no significant alteration in the distribution of immunoreactive vasoactive intestinal polypeptide or substance P. Conclusions: Ionizing radiation reduced the transport response to neural stimulation. The effect correlated temporally with decreased mast cells and histamine, suggesting a functional role for previously reported mast cell-nerve interactions.

Evidence of a neurogenic component during IgE-mediated inflammation in mouse skin

IgE-mediated inflammation was measured in mouse footpads that lacked sciatic innervation. Mice were passively sensitized with a monoclonal antibody, IgE anti-dinitrophenol, or were immunized for specific IgE production. Antigen-induced swelling in the denervated footpads was reduced 23–39% when compared to sham or untreated controls. Reduced IgE-mediated swelling responses were attributed to the loss of a mast cell-nerve interaction and not to blood vessel sensitivity to vasoamines. Furthermore, electrical stimulation of the distal segment of the sciatic nerve completely restored IgE-mediated inflammation. These data provide in vivo evidence that peripheral nerves participate in cutaneous IgE-mediated swelling reactions with the net effect of increasing inflammation.