Release Of Mast Cell-derived Mediators Research Articles

Increased expression of formyl peptide receptor-1 by basophils from patients with mastocytosis

BackgroundSymptoms in patients with systemic mastocytosis (SM) are associated with an increase in mast cell burden and release of mast cell-derived mediators. The most frequent presentation of SM is indolent (ISM), with moderate symptoms and prognosis. Basophil numbers in these patients are generally normal. However, when examining basophil activation in patients with ISM, we noted an abnormal response to N-formylmethione-leucyl-phenylalanine (fMLP). ObjectiveTo compare basophil responsiveness to fMLP and anti-IgE in healthy volunteers and patients with ISM and relate findings to fMLP receptor (FPR) expression. MethodsBasophils isolated from peripheral blood of fifteen patients with ISM and fourteen healthy volunteers were stimulated with fMLP or anti-IgE. CD63 expression to assess basophil activation and expression of FPRs were assessed by flow cytometry. ResultsBaseline expression of CD63 on basophils was similar between healthy volunteers and patients with ISM. fMLP induced higher expression of CD63 on basophils from patients with ISM, while responses to anti-IgE were similar between groups. Basophils from patients with ISM also had higher fMLP1 receptor (FPR1) expression, while FPR2 and FPR3 were not detected. fMLP blocked the binding of anti-FPR1 antibody to FPR1, consistent with the conclusion that fMLP signals through FPR1. ConclusionsFMLP-induced basophil activation is higher in patients with ISM which is associated with an increase in FPR1 expression. Further investigation is needed to determine why FPR1 expression is elevated, whether such expression might serve as an additional surrogate marker in the diagnosis of ISM, and whether enhanced responses of basophils to fMPL might have some relationship to unexplained episodes of mediator release.

IL-6 is required for protective immune responses against early filarial infection

IL-6 has a wide range of biological activities that includes anti- and pro-inflammatory aspects. In this study, we investigated the role of IL-6 in immune responses to the rodent filarial nematode Litomosoides sigmodontis, a model for human filarial infections. IL-6−/− mice had a significantly increased worm burden after natural infection compared with wild type controls at early time points p.i. Given that the worm burden in IL-6−/− mice was already increased at the time point the infective larvae reached the pleural cavity, immune responses that may facilitate the migration from the site of infection (skin) via the lymphatics to the pleural cavity were analysed. Increased vascular permeability may facilitate larval migration, but blocking of histamine receptors had no effect on worm burden and vascular permeability was similar between IL-6−/− mice and wild type controls. In contrast, blocking mast cell degranulation reduced the worm burden in IL-6−/− mice partially, suggesting that release of mast cell-derived mediators improves larval migration to some degree. Protective immune responses within the skin were involved, as bypassing the skin barrier by inoculating infective L3s subcutaneously resulted in a comparable worm recovery in both mouse strains. Analysis of the cellular composition by flow cytometry and PCR array in the skin after exposure to filarial extract or L3s, respectively, indicate that the absence of IL-6 results in a delayed recruitment of neutrophils and macrophages to the site of initial infection. These results demonstrate that IL-6 is essentially involved in protective immune responses within the skin that impair migration of infective L3s.

Premature Collagen Fibril Formation, Fibroblast-Mast Cell Interactions and Mast Cell-Mediated Phagocytosis of Collagen in Keloids

Keloids are benign hyper-proliferative growths of fibrous tissue where increased fibroblast activity results in abnormal collagen deposition. Excessive inflammation is a characteristic feature of keloids, but little is known about the underlying ultrastructural features of keloids related to collagen processing, fibril and fiber formation, the interaction between fibroblasts and associated collagen fibers and mast cells. In this study, the ultrastructure of the dermis of keloid patients was evaluated using light and transmission electron microscopy techniques. Abnormal intracellular premature collagen fibril formation was observed. Phagocytosis of collagen fibrils by mast cells was a common ultrastructural feature of keloid tissue as was a close or direct association between fibroblasts and mast cells. Based on these findings and recent advances in knowledge related to collagen synthesis, fibril formation and processing, we hypothesize that keloid formation is primarily due to abnormal collagen synthesis where the consequent accumulation of collagen fibers causes increased mast cell recruitment and collagen phagocytosis. Subsequent release of mast cell-derived mediators then promotes further collagen synthesis. The observation of early formation in keloid tissue of premature insoluble collagen fibrils supports previous studies that enzymes such as procollagen C-proteinase are important early therapeutic targets.

Plasma contact system activation drives anaphylaxis in severe mast cell–mediated allergic reactions

Anaphylaxis is an acute, potentially lethal, multisystem syndrome resulting from the sudden release of mast cell-derived mediators into the circulation. We report here that a plasma protease cascade, the factor XII-driven contact system, critically contributes to the pathogenesis of anaphylaxis in both murine models and human subjects. Deficiency in or pharmacologic inhibition of factor XII, plasma kallikrein, high-molecular-weight kininogen, or the bradykinin B2 receptor, but not the B1 receptor, largely attenuated allergen/IgE-mediated mast cell hyperresponsiveness in mice. Reconstitutions of factor XII null mice with human factor XII restored susceptibility for allergen/IgE-mediated hypotension. Activated mast cells systemically released heparin, which provided a negatively charged surface for factor XII autoactivation. Activated factor XII generates plasma kallikrein, which proteolyzes kininogen, leading to the liberation of bradykinin. We evaluated the contact system in patients with anaphylaxis. In all 10 plasma samples immunoblotting revealed activation of factor XII, plasma kallikrein, and kininogen during the acute phase of anaphylaxis but not at basal conditions or in healthy control subjects. The severity of anaphylaxis was associated with mast cell degranulation, increased plasma heparin levels, the intensity of contact system activation, and bradykinin formation. In summary, the data collectively show a role of the contact system in patients with anaphylaxis and support the hypothesis that targeting bradykinin generation and signaling provides a novel and alternative treatment strategy for anaphylactic attacks.

Mastocytosis presenting as cardiac emergency

Mastocytosis is characterised by clonal proliferation of mast cells in the skin and in various internal organs, and by symptoms related to an acute release of mast cell-derived mediators. In 20-30% of patients, mastocytosis occurs without the typical skin lesions of urticaria pigmentosa that are usually the first clinical sign of the disease. In these patients, anaphylaxis is often the presenting sign of the disease. We report three cases in which a cardiac emergency (cardiac arrest or ventricular fibrillation) was the first clinical manifestation of anaphylaxis associated with systemic mastocytosis. All patients were men, none of them had previous episodes of anaphylaxis or other mediator-related symptoms, and none had major pre-existing cardiovascular condition. An eliciting factor was identified in one case (a wasp sting), but one was found in the other two. Elevation of the serum tryptase suggested a mastocytosis, which was confirmed by bone marrow biopsy. This case series demonstrates that cardiovascular emergencies may be presenting signs of mastocytosis, and that elevation of serum tryptase after an acute cardiac event, if confirmed under basal conditions, may be useful for diagnosing this disease.

Double-masked, randomized, placebo-controlled clinical study of the mast cell-stabilizing effects of treatment with olopatadine in the conjunctival allergen challenge model in humans

Objective: The purpose of this study was to assess the effects of olopatadine on the release of mast cell-derived mediators after conjunctival allergen challenge (CAC) in humans. Methods: This was a double-masked, randomized, placebo-controlled clinical trial. Subjects with a clinical history of seasonal allergic conjunctivitis (but no current symptoms or treatment at baseline) were studied. At visit 1, subjects underwent bilateral CAC with increasing doses of allergen every 15 minutes until a significant clinical reaction was obtained, then were evaluated at 15 minutes and 5 hours after CAC. At visit 2 (2 weeks later), subjects were rechallenged to confirm the allergic response. Subjects exhibiting positive reactions at both visits (at both 15 minutes and 5 hours) were randomized and instructed to treat 1 eye with olopatadine and the contralateral eye with placebo (commercially available artificial tears) in a double-masked fashion twice daily for the 5 days immediately preceding visit 3. At visit 3, bilateral CAC was performed with the same dose as at visit 2. Itching and redness were recorded. Tear cytology for inflammatory cell counts (ie, neutrophils, eosinophils, and lymphocytes) was carried out using precolored slides, and cell numbers were counted at 400x magnification. Tear histamine was assessed using radioimmunoassay histamine measurement. Intercellular adhesion molecule (ICAM)-1/CD54 monoclonal antibody was used for immunohistochemical staining of conjunctival epithelial cells obtained by impression cytology.

Mediator release in local heat urticaria

We described the sixteenth reported case of local heat urticaria, in a 59-yr-old woman with erythema and angioedema upon contact with hot water or outdoor heat exposure. Immersing her hand in 39° to 40° C heated water resulted in an erythematous, angioedematous response sharply demarcated by the line of immersion and was associated with immediate increases in histamine concentration (18 to 135 ng/ml) and high molecular weight neutrophil chemotactic activity (two to five times prechallenge levels) in venous blood draining the challenge site. We suggest that the local heat urticarial response in this woman was a form of physical urticaria associated with release of mast cell-derived mediators, akin to cold and cholinergic urticaria.