Evidence Of Mast Cell Activation Research Articles

Incidence of perioperative hypersensitivity reactions: Asingle-center, prospective, US cohort experience.

A previous study, using administrative data, reported an incidence of perioperative anaphylaxis (POA) of 1:6537 procedures in the United States. We sought to determine the incidence of POA in a prospective US cohort. Adult participants undergoing a procedure at a single tertiary care center were studied prospectively between April 2018 and January 2022. Subinvestigators recorded vital signs and skin checks preoperatively, 15 minutes into induction, and hourly thereafter until 1 hour into the postoperative period. If participants developed an adverse reaction, additional variables were documented: causal agent(s) exposure, type of nonallergic adverse reaction, Sixth National Audit Project severity score, evidence of mast cell activation by serum acute and baseline tryptase pairing, Allergy consult, and causal agent identification. Among 939 procedures (mean age, 59.25± 14.78 years; 58% females; 87% White), there were 12 (1.3%) cases with an identified adverse reaction. Nine cases were classified as nonhypersensitivity adverse reactions (1%) and 3 as possible hypersensitivity reactions (0.3%); 1 case was classified as suspected perioperative hypersensitivity and 2 as POA (0.2%). Both POA cases were males, had previous procedures, had evidence of mast cell activation, had a Sixth National Audit Project score of 3, and were referred to Allergy for further evaluation. There were 9 participants who developed a nonhypersensitivity adverse reaction: relative overdose of anesthetic (n= 6), transient rash (n= 2), and isolated bronchospasm (n= 1). All transient rashes were observed during undraping protocol. In our prospective study, the incidence of POA is 1:470 procedures. Our study suggests that the incidence of POA may be higher than previously reported.

Seasonal and Lab Variation of Serum Tryptase

Mast cell activation syndrome (MCAS) is a non-clonal disease that requires evidence of mast cell activation at times of symptoms. An expert opinion panel established a consensus recommendation of an increase of 20% + 2 ng/ml above a patient’s baseline serum tryptase as diagnostic for this condition. However, there is little published data on natural variance of tryptase over time.

Crizanlizumab-Associated Painful Febrile Reaction in Sickle Cell Disease Patients

Background: P-selectin expressed on endothelium and platelets has been implicated in the pathophysiology of vaso-occlusive crises (VOCs) in sickle cell disease (SCD) patients. Crizanlizumab is a humanized monoclonal anti-P-selectin antibody approved by the FDA to reduce the frequency of VOCs. While severe adverse events (AEs) are rare, over 80% of patients most commonly have headache, back pain, nausea, or arthralgia; infusion-related reactions occurred in 3% according to the package insert. We report on 2 patients whose crizanlizumab-associated reactions help shed light on how to manage such events and possible mechanisms.Case reports: Case 1, a 48-year-old woman with hemoglobin SC disease, history of left shoulder replacement due to avascular necrosis and left knee avascular necrosis, pending surgical replacement. Given her frequent pain episodes, she was initiated on crizanlizumab after being intolerant to hydroxyurea (watery diarrhea). She received the first dose of crizanlizumab uneventfully, but at the end of her second infusion, she developed acute bilateral groin pain that radiated to both legs. She was eventually admitted to the hospital with a fever of 38-39°C without evidence of infection. She also received one unit of RBC transfusion for a drop in Hct from 32% to 25%. For her third infusion, we premedicated her with acetaminophen 650mg, diphenhydramine 50mg, ketorolac 1g along with concurrent IV hydration. She tolerated an initial infusion at 20ml/h for the first 15 minutes after which we ramped it up to the regular rate of 200ml/h. Within minutes of that rate increase, the patient developed chest pain and dyspnea, so infusion was stopped immediately. Blood samples taken right after the event revealed tryptase and IgE levels within normal limits, and she chose to discontinue the medication.Case 2, a 20-year-old woman with sickle cell anemia with frequent painful episodes despite hydroxyurea at 25mg/kg/day. The patient preferred to start crizanlizumab over increasing oral medication. She reported having had fever and chills at home after her first crizanlizumab infusion and improved with acetaminophen. About 10 minutes into her second infusion, she developed acute severe migratory pain in her back, moving to her lower limbs, associated with tachycardia. Infusion was immediately discontinued, and she was medicated with diphenhydramine 25mg and methylprednisolone 125mg with no improvement. She progressed with abdominal pain moving into her arms and needed meperidine 25mg and hydromorphone 1mg to achieve pain resolution. She completed the infusion successfully at 50% reduced rate but still reported subjective high fevers and chills again the next day, medicated with acetaminophen. She continues monthly infusions with a slower rate.Discussion: As of October 2020, Novartis (manufacturer of crizanlizumab) informed that, out of 3,500 patients, there have been 22 postmarketing reports of severe pain during or within 24 hours of the infusion. Seven cases reported complications, all of which resolved. Immediate hypersensitivity reactions to monoclonal antibodies can be a cytokine release syndrome, IgE-mediated, or IgG-mediated. One case report has suggested this may be a complement activation-related pseudoallergy (CARPA) as sC5b-9 was mildly elevated in a 17-year-old male patient who developed sudden and severe pain in his back, legs and head within 10 minutes of the infusion, despite having been premedicated with acetaminophen, later developing a fever and need for admission. Differently from that case, our patients developed severe pain with a second exposure of the drug, arguing in favor of an antibody-mediated process. We did not find evidence of mast cell activation or increased IgE production in our patient who needed to discontinue the medication. We therefore hypothesize that crizanlizumab-associated painful febrile reaction may be IgG-mediated. Premedication in our experience was unsuccessful, and symptomatic treatment with acetaminophen was appropriate, but slower infusion rates may prove useful for some patients.Conclusion: While rare, crizanlizumab-associated painful febrile reactions may be observed after a first uneventful infusion and are possibly IgG-mediated. Patients experiencing this reaction may require symptomatic treatment with acetaminophen despite premedication and can be tried on slower infusion rates. DisclosuresFertrin: Sanofi Genzyme: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Eosinophilic esophagitis.

Eosinophilic esophagitis (EoE) is defined by symptoms related to esophageal dysfunction, persistent esophageal eosinophilia, and exclusion of other etiologies that may be contributing to the condition. EoE is different from erosive esophagitis. In children, symptoms vary by age groups, such as feeding disorders in 2 year olds; vomiting in 8 year olds; and abdominal pain, dysphagia, and/or food impaction in adolescents. Most adults present with dysphagia, food impaction, heartburn, or chest pain. Common endoscopic features in adults with EoE include linear furrows (creases that orient longitudinally), mucosal rings (esophageal "trachealization"), small-caliber esophagus, white plaques or exudates (which are microabscesses of eosinophils), and strictures. Children often present with similar endoscopic features, yet one-third of pediatric patients with EoE have a normal result in an endoscopic examination. Histologic features of EoE include increased intramucosal eosinophils in the esophagus (≥15 eosinophils per high power field), without similar findings in the stomach or duodenum. There also may be eosinophilic microabscesses. In addition to evidence of mast cell activation, mucosa from patients with EoE have increased levels of interleukin 5; supporting eosinophilia; and upregulation of gene expression of eotaxin-3, a chemokine important in eosinophil migration. The majority of patients have evidence of either aeroallergen and/or food sensitization. Dietary therapy is considered first-line therapy for patients with EoE because it is inexpensive and effective, without requiring pharmacologic therapy. Removal of food antigens has been shown to improve symptoms in patients with EoE. Topical corticosteroids improve esophageal eosinophilia and symptoms, and have become the criterion standard of pharmacotherapy.

Assessment of Perigenital Sensitivity and Prostatic Mast Cell Activation in a Mouse Model of Neonatal Maternal Separation

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) has a lifetime prevalence of 14% and is the most common urological diagnosis for men under the age of 50, yet it is the least understood and studied chronic pelvic pain disorder. A significant subset of patients with chronic pelvic pain report having experienced early life stress or abuse, which can markedly affect the functioning and regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Mast cell activation, which has been shown to be increased in both urine and expressed prostatic secretions of CP/CPPS patients, is partially regulated by downstream activation of the HPA axis. Neonatal maternal separation (NMS) has been used for over two decades to study the outcomes of early life stress in rodent models, including changes in the HPA axis and visceral sensitivity. Here we provide a detailed protocol for using NMS as a preclinical model of CP/CPPS in male C57BL/6 mice. We describe the methodology for performing NMS, assessing perigenital mechanical allodynia, and histological evidence of mast cell activation. We also provide evidence that early psychological stress can have long-lasting effects on the male urogenital system in mice.

Assessment of Perigenital Sensitivity and Prostatic Mast Cell Activation in a Mouse Model of Neonatal Maternal Separation.

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) has a lifetime prevalence of 14% and is the most common urological diagnosis for men under the age of 50, yet it is the least understood and studied chronic pelvic pain disorder. A significant subset of patients with chronic pelvic pain report having experienced early life stress or abuse, which can markedly affect the functioning and regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Mast cell activation, which has been shown to be increased in both urine and expressed prostatic secretions of CP/CPPS patients, is partially regulated by downstream activation of the HPA axis. Neonatal maternal separation (NMS) has been used for over two decades to study the outcomes of early life stress in rodent models, including changes in the HPA axis and visceral sensitivity. Here we provide a detailed protocol for using NMS as a preclinical model of CP/CPPS in male C57BL/6 mice. We describe the methodology for performing NMS, assessing perigenital mechanical allodynia, and histological evidence of mast cell activation. We also provide evidence that early psychological stress can have long-lasting effects on the male urogenital system in mice.

Chapter 26: Eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is distinguished from gastroesophageal reflux disease (GERD) by persistent esophageal eosinophilia despite medical therapy with proton-pump inhibitors for 4-6 weeks. In children, symptoms vary by age groups such as feeding disorders in 2 year olds; vomiting in 8 year olds; and abdominal pain, dysphagia, and/or food impaction in adolescents. Most adults present with dysphagia, food impaction, heartburn or chest pain. Common endoscopic features in adults with EoE include linear furrows (creases that orient longitudinally), mucosal rings (esophageal "trachealization"), small-caliber esophagus, white plaques or exudates (which are microabscesses of eosinophils), and strictures. Children often present with similar endoscopic features, but one-third of pediatric patients with EoE have normal endoscopy. Histological features of EoE include increased intramucosal eosinophils in the esophagus (≥15 eosinophils/high-power field) without similar findings in the stomach or duodenum. There also may be eosinophilic microabscesses. In addition to evidence of mast cell activation, mucosa from patients with EoE have increased IL-5, supporting eosinophilia, and up-regulation of gene expression of eotaxin-3, a chemokine important in eosinophil migration. The majority of patients have evidence of either aeroallergen and/or food sensitization. An elemental/amino acid-based formula diet has shown to be effective in children but may not be well tolerated by adults because of taste and volume or high expense. Topical corticosteroids improve esophageal eosinophilia and symptoms and have become the "gold standard" of pharmacotherapy.

Exercise but not mannitol provocation increases urinary Clara cell protein (CC16) in elite swimmers

Elite swimmers have an increased risk of developing asthma, and exposure to chloramine is believed to be an important trigger factor. The aim of the present study was to explore pathophysiological mechanisms behind induced bronchoconstriction in swimmers exposed to chloramine, before and after swim exercise provocation as well as mannitol provocation. Urinary Clara cell protein (CC16) was used as a possible marker for epithelial stress. 101 elite aspiring swim athletes were investigated and urinary samples were collected before and 1h after completed exercise and mannitol challenge. CC16, 11β-prostaglandin (PG)F(2α) and leukotriene E(4) (LTE(4)) were measured. Urinary levels of CC16 were clearly increased after exercise challenge, while no reaction was seen after mannitol challenge. Similar to CC16, the level of 11β-PGF(2α) was increased after exercise challenge, but not after mannitol challenge, while LTE(4) was reduced after exercise. There was no significant difference in urinary response between those with a negative compared to positive challenge, but a tendency of increased baseline levels of 11β-PGF(2α) and LTE(4) in individuals with a positive mannitol challenge. The uniform increase of CC16 after swim exercise indicates that CC16 is of importance in epithelial stress, and may as such be an important pathogenic factor behind asthma development in swimmers. The changes seen in urinary levels of 11β-PGF(2α) and LTE(4) indicate a pathophysiological role in both mannitol and exercise challenge.

Mast cells in the promotion and limitation of chronic inflammation

Observations of increased numbers of mast cells at sites of chronic inflammation have been reported for over a hundred years. Light and electron microscopic evidence of mast cell activation at such sites, taken together with the known functions of the diverse mediators, cytokines, and growth factors that can be secreted by appropriately activated mast cells, have suggested a wide range of possible functions for mast cells in promoting (or suppressing) many features of chronic inflammation. Similarly, these and other lines of evidence have implicated mast cells in a variety of adaptive or pathological responses that are associated with persistent inflammation at the affected sites. Definitively characterizing the importance of mast cells in chronic inflammation in humans is difficult. However, mice that genetically lack mast cells, especially those which can undergo engraftment with wildtype or genetically altered mast cells, provide a means to investigate the importance of mast cells and specific mast cell functions or products in diverse models of chronic inflammation. Such work has confirmed that mast cells can significantly influence multiple features of chronic inflammatory responses, through diverse effects that can either promote or, perhaps more surprisingly, suppress aspects of these responses.

Hypertonicity of the challenge solution may increase the diagnostic accuracy of histamine challenge

There is significant overlap in the responsiveness to direct airway challenges, such as the histamine challenge, between asthmatic and non-asthmatic subjects, which decreases their accuracy in the diagnosis of asthma. To minimise this overlap, a new test, hypertonic histamine challenge, was developed. Fifteen healthy subjects, 16 subjects with steroid-naive asthma, and 16 asthmatic subjects undergoing inhaled corticosteroid treatment underwent inhalation challenges with hypertonic saline, isotonic histamine, and hypertonic histamine, using an ultrasonic nebuliser and 2-min tidal breathing method. The increase in histamine solution tonicity decreased the histamine PC20 values only in the steroid-naive asthmatic subjects (1.1 (0.5-2.7) vs. 0.5 (0.2-1.2) mg/ml, P = 0.047). Using 1mg/ml as the cut-off value, the sensitivity, specificity, and accuracy of the hypertonic histamine challenge to detect steroid-naive asthma was 81%, 100%, and 90%. The respective values for the isotonic histamine challenge were 56%, 100%, and 77%. Furthermore, there was a statistically significant difference in the hypertonic histamine PC20 between steroid-naive and steroid-treated asthmatic subjects, which could not be detected in the isotonic histamine PC20. The hypertonic histamine PC20 was highly repeatable, with a single determination 95% range of +/-1.35 doubling concentrations. The hypertonic histamine challenge was safe but provoked more cough and throat irritation than the other two challenges. In conclusion, compared with a conventional, isotonic histamine challenge, hypertonic histamine challenge may be more accurate in the diagnosis of asthma and also, more capable to detect the effects of inhaled corticosteroid treatment.

Ocular allergic disease.

This review will focus on recent advances in our understanding of the pathogenesis of allergic eye diseases. Common findings in acute allergic conjunctivitis (seasonal and perennial) and chronic allergic conjunctivitis (vernal keratoconjunctivitis, atopic keratoconjunctivitis, and giant papillary conjunctivitis) include evidence of mast cell activation and eosinophil attraction and activation. Cytokine levels found in tears, conjunctival impression cytology and biopsy specimens, and serum have been evaluated as markers of disease, and as targets of therapeutic intervention. Human conjunctival epithelial cells respond to tumor necrosis factor alpha, interleukin-1 beta, and interferon-gamma individually and in combination. Intracellular adhesion molecule-1 expression is upregulated by interleukin-1 beta and tumor necrosis factor alpha. Conjunctival epithelial cells release interleukin-8 in response to interleukin-1 beta and tumor necrosis factor alpha but not interferon-gamma. Supernatants from activated mast cells cause increased adhesion of eosinophils to conjunctival epithelium. Tear levels of tumor necrosis factor alpha were elevated in vernal keratoconjunctivitis patients compared with normal controls. T cell lines from chronic allergic eye disease patients showed inconsistent production of cytokines in atopic and vernal keratoconjunctivitis and low levels in giant papillary conjunctivitis. Vernal keratoconjunctivitis patients have differing levels of eosinophil cationic protein in their serum if they were serum specific immunoglobulin E positive compared to serum specific immunoglobulin E negative patients. Recent findings continue to expand our basic knowledge of mechanisms and differences between seasonal and perennial allergic conjunctivitis and atopic and vernal keratoconjunctivitis. Understanding the complex interactions and cross talk between cells, cytokines and other mediators is relevant for new therapeutic approaches directed at specific disease entities.

Evidence of mast cell activation and leukotriene release after mannitol inhalation.

The aim of this study was to investigate if mannitol inhalation, as a model of exercise-induced bronchoconstriction (EIB), causes mast cell activation and release of mediators of bronchoconstriction. Urinary excretion of previously identified mediators of EIB was investigated in association with mannitol-induced bronchoconstriction. Twelve asthmatic and nine nonasthmatic subjects inhaled mannitol and urine was collected 60 min before and for 90 min after challenge. The urinary concentrations of leukotriene (LT)E4, the prostaglandin (PG)D2 metabolite and the mast cell marker 9alpha,11beta-PGF2 were measured by enzyme immunoassay. N(tau)-methylhistamine was measured by radioimmunoassay. In asthmatic subjects, inhalation of a mean+/-SEM dose of 272+/-56 mg mannitol induced a reduction in forced expiratory volume in one second (FEV1) of 34.5+/-2.1%. This was associated with increases in urinary 9alpha,11beta-PGF2 (91.9+/-8.2 versus 66.9+/-6.6 ng x mmol creatinine(-1), peak versus baseline) and LTE4 (51.3+/-7.5 versus 32.9+/-4.7). In nonasthmatic subjects, the reduction in FEV1 was 1.0+/-0.5% after inhaling 635 mg of mannitol. Although smaller than in the asthmatics, significant increases of urinary 9alpha,11beta-PGF2 (68.4+/-6.9 versus 56.0+/-5.8 ng x mmol creatinine(-1)) and LTE4 (58.5+/-5.3 versus 43.0+/-3.3 ng x mmol creatinine(-1)) were observed in the nonasthmatic subjects. There was also a small increase in urinary excretion of N(tau)-methylhistamine in the nonasthmatics, but not in the asthmatics. The increased urinary levels of 9alpha,11beta-prostaglandin F2 support mast cell activation with release of mediators following inhalation of mannitol. Increased bronchial responsiveness to the released mediators could explain the exclusive bronchoconstriction in asthmatic subjects.

Evidence of mast-cell activation in a subset of patients with eosinophilic chronic obstructive pulmonary disease.

Although asthma has been viewed mainly as an eosinophilic disease, and chronic obstructive pulmonary disease (COPD) as a neutrophilic disease, recent studies have shown increased neutrophil counts in severe asthma and sputum eosinophilia in some COPD patients. In an attempt to further characterise these two syndromes according to pathology, the current authors have conducted a study of induced sputum in 15 subjects with COPD, 17 asthmatics, and 17 nonatopic healthy individuals. Sputum was analysed for cytology and levels of eosinophil cationic protein (ECP), albumin, tryptase and soluble intercellular adhesion molecule-1. The COPD subjects differed from the asthmatics as they had higher sputum neutrophil and lower columnar epithelial cell counts, but there were no differences in any soluble marker studied. When compared to control subjects, both the asthmatic and COPD subjects had raised eosinophil counts and ECP levels. In a subset of COPD subjects with sputum eosinophilia (>3% of total cells), significantly increased levels of tryptase were detected. In conclusion, although chronic obstructive pulmonary disease is a more neutrophilic disease than asthma, the two diseases are difficult to distinguish on the basis of sputum levels of the soluble markers traditionally associated with asthma. However, a subset of patients with chronic obstructive pulmonary disease with airway eosinophilia and mast-cell activation might represent a distinct pathological phenotype.

Absence of mast cell involvement in active systemic anaphylaxis in rats

This study investigates the role of mast cells in the hypotension induced by antigen-mediated anaphylaxis, compound 48/80 and dextran in mast cell-deficient white spotting (Ws/Ws) and normal wild type (+/+) rats. Rats were sensitized with 10 μg of intraperitoneal ovalbumin in saline or saline alone (sham-sensitized). Sensitized rats, both Ws/Ws and +/+ but not sham-sensitized rats, challenged intravenously with ovalbumin exhibited hypotensive responses. There was no evidence of mast cell activation in rat mesentery 20 min after intravenous antigen challenge in sensitized +/+ rats. Hypotension induced by intravenous injection of dextran (Dextran-162, 6%, 2 ml kg −1) or compound 48/80 (1 mg kg −1) occurred in +/+ rats, but not in Ws/Ws rats, and was inhibited by pretreatment with a combination of chlorpheniramine and cimetidine. Taken together, these data indicate that the hypotensive response induced by antigen-mediated anaphylaxis is independent of mast cell activation, whereas mast cell amines play the main role in the hypotensive response induced by dextran or compound 48/80.

Mast cell tryptase in dermal neurogenic inflammation.

Mast cell activation has been assumed to play a role in dermal neurogenic inflammation: C fibre-derived neuropeptides activating mast cells and releasing histamine, which in turn would activate C fibres. To test this hypothesis mast cell tryptase (MCT) was measured inside the axon reflex flare area. Axon reflexes were elicited by histamine or compound 48/80, a polyanionic mast cell-degranulating substance. The time course of plasma extravasation and release of histamine and MCT from dermal mast cells in neurogenic inflammation was measured in vivo by intradermal microdialysis in humans. Single hollow plasmapheresis fibres (pore cutoff size: 3000 kDa) were inserted intracutaneously at the volar forearm and perfused with Ringer's solution (4 microL/min) with one microdialysis fibre located at the planned stimulation site and a second inside the axon reflex area. Neurogenic inflammation was induced by intraprobe delivery of either histamine or the mast cell-degranulating agent compound 48/80. Mediator release was measured at the stimulation sites and inside the arising axon reflex flare area. Mast cell degranulation induced marked plasma protein extravasation (PPE 0.25 +/- 0.04-1.31 +/- 0.6 mg/mL; pre- and post-stimulation, mean +/- sem, n = 7) and release of histamine (2.0 +/- 0.9-38.7 +/- 1.4 ng/mL) and MCT (9.84 +/- 2.4-92.2 +/- 21.6 ng/mL). Interestingly, in addition to increasing PPE (0.33 +/- 0. 11-1.85 +/- 0.9 mg/mL), histamine also induced a slight but significant increase in MCT (11.3 +/- 3.0-12.4 +/- 2.3 ng/mL). No evidence for mast cell activation was observed inside the axon reflex areas, where PPE (0.34 +/- 0.03-0.25 +/- 0.02 mg/mL), histamine (1.64 +/- 0.5-1.46 +/- 0.4 ng/mL) and MCT concentration (11.6 +/- 3.1-7.6 +/- 1.7 ng/mL) gradually decreased. It is concluded that dermal neurogenic inflammation does not degranulate mast cells.

Evidence for mast cell activation during exercise-induced bronchoconstriction.

Controversy remains about the causative mediators in the bronchoconstrictive response to exercise in asthma. This study examined whether mast cell activation is a feature of exercise-induced bronchoconstriction by measuring urinary metabolites of mast cell mediators. Twelve nonsmoking subjects with mild asthma and a history of exercise-induced bronchoconstriction exercised on a stationary bicycle ergometer for 5 min at 80% maximum work load. Pulmonary function was monitored and urine was collected before and 30 and 90 min after the provocation. The urinary concentrations of the mast cell markers 9alpha,11beta-prostaglandin (PG)F2 and Ntau-methylhistamine, as well as leukotriene E4 (LTE4) were determined by immunoassay. Seven of the 12 subjects (responders) experienced bronchoconstriction (>15% fall in the forced expiratory volume in one second) following exercise, whereas the pulmonary function of the remaining five subjects (nonresponders) remained stable. The urinary excretion (mean+/-SE) of 9alpha,11beta-PGF2 in the responders increased significantly compared with the nonresponders at 30 (77.1+/-14.4 versus 37.2+/-5.6; p<0.05) and 90 min (79.3+/-8.6 versus 40.4+/-8.5, p<0.05) after exercise challenge. The urinary excretion of Ntau-methylhistamine and LTE4 was not significantly different between the two groups at 30 or 90 min after exercise. The findings represent the first documentation of increased urinary levels of 9alpha,11beta-prostaglandin F2 in adults following exercise challenge and provides clear evidence for mast cell activation during exercise-induced bronchoconstriction in asthmatics.

Carbachol-induced bladder mast cell activation: Augmentation by estradiol and implications for interstitial cystitis

Interstitial cystitis (IC) is a painful, sterile bladder disorder that occurs primarily in women, many of whom also experience allergies with symptoms that worsen perimenstrually. Increased numbers of activated bladder mast cells have recently been implicated in the pathophysiology of IC. These mast cells express high-affinity estrogen receptors and are located close to increased bladder nerves, many of which contain the neuropeptide substance P (SP). We therefore investigated whether the neurotransmitter acetylcholine (ACh) and SP could activate bladder mast cells and whether estradiol could influence this effect. Bladder pieces from male Sprague-Dawley rats were perfused with carbachol (the stable analogue of ACh), SP, or the mast cell secretagogue compound 48/80 (C48/80) with or without preincubation with beta-estradiol. The effect of carbachol was also investigated after pretreatment with the muscarinic antagonist atropine. Mast cell activation was assessed by release of 3H-serotonin and morphologic evidence of secretion by light and electron microscopy. Carbachol triggered rat bladder mast cell serotonin release in a dose-dependent manner, an effect increased by tissue pretreatment with estradiol and blocked by atropine. The effect of carbachol was accompanied by ultrastructural evidence of mast cell activation and was stronger than that obtained by either C48/ 80 or SP. Bladder mast cell activation is neurogenically mediated and augmented by estradiol, findings that could possibly explain the painful symptoms of IC and its prevalence in women, as well as the worsening of symptoms perimenstrually.

The anaphylaxis hypothesis of sudden infant death syndrome (SIDS): mast cell degranulation in cot death revealed by elevated concentrations of tryptase in serum.

A series of cases of sudden unexpected post-neonatal deaths from two centres in the UK have been investigated for evidence of mast cell activation using the biochemical markers tryptase and 9 alpha,11 beta-PGF2. Tryptase was selected as a possible marker because it is a component of mast cell secretory granules and, unlike histamine, it is not released from basophils. The prostaglandin 9 alpha,11 beta-PGF2 is an initial and pharmacologically active metabolite of PGD2, the major mast cell-derived cyclooxygenase product. This prostaglandin was chosen to serve as a marker of newly generated mediator release. In the study, unexplained infant deaths were associated with a higher concentration of tryptase in serum compared with cases of unexpected, but subsequently explained death. However, 9 alpha,11 beta-PGF2 was found to be an unsuitable post mortem marker in this situation. These results provide direct evidence that mast cell degranulation, possibly as a result of anaphylaxis, may be occurring around the time of death in some cases of cot death.

Reversible expansion of primate mast cell populations in vivo by stem cell factor.

Mast cell development in mice is critically regulated by stem cell factor (SCF), the term used here to designate a product of fibroblasts and other cell types that is a ligand for the tyrosine kinase receptor protein encoded by the proto-oncogene c-kit. However, the factors which regulate the size of mast cell populations in primates are poorly understood. Here we report that the subcutaneous administration of recombinant human SCF (rhSCF) to baboons (Papio cynocephalus) or cynomolgus monkeys (Macaca fascicularis) produced a striking expansion of mast cell populations in many anatomical sites, with numbers of mast cells in some organs of rhSCF-treated monkeys exceeding the corresponding values in control monkeys by more than 100-fold. Animals treated with rhSCF did not exhibit clinical evidence of mast cell activation, and discontinuation of treatment with rhSCF resulted in a rapid decline of mast cell numbers nearly to baseline levels. These findings are the first to demonstrate that a specific cytokine can regulate mast cell development in primates in vivo. They also provide the first evidence, in any mammalian species, to indicate that the cytokine-dependent expansion of tissue mast cell populations can be reversed when administration of the cytokine is discontinued.

Cellular Inflammation in Asthma: Neutral Proteases of Mast Cells

Atopy is a major risk factor for the development of asthma, and mast cells are the major effector cells of the immediate phase of allergic reactions. A variety of observations support the involvement of mast cells in asthma (table I). High numbers ofmast cells normally reside in the bronchial and alveolar walls, a few of which appear in the lumen (I). In asthmatic subjects, portions of the bronchial epithelium are shed, perhaps accounting for the modest increase in the numbers of luminal mast cells reported. Pulmonary mast cells respond to allergen in vivo as evidenced by increased concentrations of mast cell mediators in bronchoalveolar lavage fluid after inhalation of allergen by atopic subjects (2, 3). Furthermore, those atopic subjects with asthma show evidence for mast cell activation at baseline, when the only obvious pulmonary function abnormality is bronchial hyperreactivity (2). Finally, the hyperresponsiveness of atopic asthmatics to inhaled adenosine most likely occurs by the augmented release of preformed mediators from mast cells being activated concomitantly by other means (4-7). Whether this apparent state of mast cell activation in atopic asthma occurs through a classical IgE-allergen pathway or through other factors such as an imbalance in the ratio of histamine release factors and inhibiting factors is not known. The possibility of a more pervasive involvement of this cell type in asthma seems likely. Mast cells, when activated by allergen, release preformed mediators stored in secretory granules, which is typically accompanied by the synthesis and secretion 0 f lipid mediators and, possibly, eytokines (8). The predominant components that reside in the secretory granules of human mast cells include histamine, proteoglycan, either heparin or chondroitin sulfates, and neutral proteases. The neutral proteases include tryptase, chymase, carboxypeptidase (9), and a cathepsin-G-like enzyme (10). Tryptase resides in the secretory granules of all mast cells from the time granules first begin to form (11), whereas the others dwell in the granules of a subpopulation of mast cells. Those mast cells with tryptase alone are called MCT cells; those with all of the enzymes are called MCTe cells (12). Recently, five different cDNA molecules for human tryptase have been cloned and sequenced (13-15), and two genes for tryptase have been localized to chromosome 16. Whether more than one form of the catalytic enzyme exists and whether the cDNA products are distributed differently in different mast cell types are unknown at present. The possibility of additional forms of human chymase, analogous to the situation in rodents, also needs to be considered. The fact that these enzymes are selectively concentrated in mast cell secretory granules 518 should permit them to serve as indicators of mast cell activation and as markers of different types of mast cells. Also, their catalytic activities provide a mechanism for amplification of the phlogistic events observed in atopic disease. This discussion will focus on the neutral proteases of human mast cells as related to asthma.