Idiopathic anaphylaxis remains a perplexing disorder in which existing prophylactic therapy is inadequate. In this prospective study, we sought to determine whether patients with idiopathic anaphylaxis might have evidence for a clonal disorder of mast cells related to mastocytosis and for which novel targeted therapies might be considered. We report 12 patients with "idiopathic" anaphylaxis who did not exhibit either urticaria pigmentosa or the characteristic bone marrow biopsy finding of multifocal mast-cell aggregates observed in systemic mastocytosis. Of these 12 patients, 5 had evidence of 1 or more minor criteria for mastocytosis. C-KIT mutational analysis was positive for the 816D>V activating mutation in 3 of 3 patients in CD25 ؉ bone marrow cells where the analysis was performed. These results demonstrate the presence of an aberrant mast-cell population carrying clonal markers in a subset of patients diagnosed with "idiopathic" anaphylaxis, who may respond to inhibitors targeting mutated C-KIT. This intramural clinical trial was conducted in 2003 and 2004 and was registered at http:// clinicalcenter.nih.gov with a study number 03-I-0010. Since the study is now closed, it is no longer available online.

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The neurotransmitter serotonin (5-hydroxytryptamine (5-HT)) is implicated in enhancing inflammatory reactions of skin, lung, and gastrointestinal tract. To determine whether 5-HT acts, in part, through mast cells (MC), we first established that mouse bone marrow-derived MC (mBMMC) and human CD34+-derived MC (huMC) expressed mRNA for multiple 5-HT receptors. We next determined the effect of 5-HT on mouse and human MC degranulation, adhesion, and chemotaxis. We found no evidence that 5-HT degranulates MC or modulates IgE-dependent activation. 5-HT did induce mBMMC and huMC adherence to fibronectin; and immature and mature mBMMC and huMC migration. Chemotaxis was accompanied by actin polymerization. Using receptor antagonists and pertussis toxin, we identified 5-HT1A as the principal receptor mediating the effects of 5-HT on MC. mBMMC from the 5-HT1A receptor knockout mouse (5-HT1AR−/−) did not respond to 5-HT. 5-HT did induce accumulation of MC in the dermis of 5-HT1AR+/+ mice, but not in 5-HT1AR−/− mice. These studies are the first to demonstrate an effect of 5-HT on MC. Furthermore, both mouse and human MC respond to 5-HT through the 5-HT1A receptor. Our data are consistent with the conclusion that 5-HT promotes inflammation by increasing MC at the site of tissue injury.

Background-Mast cells (MCs) have a central role in the induction of allergic inflammation, such as seen in asthma, and contribute to the severity of certain autoimmune diseases, such as rheumatoid arthritis. The mast cell thus represents an important inflammatory cell, and one which has resisted therapeutic attempts to alter its role in disease.

Inhalation of crystalline silica results in pulmonary fibrosis and silicosis. It has been suggested that mast cells play a role in these conditions. How mast cells would influence pathology is unknown. We thus explored mast cell interactions with silica in vitro and in B6.CgKit W-sh mast cell-deficient mice. B6.Cg-Kit W-sh mice did not develop inflammation or significant collagen deposition after instillation of silica, while C57Bl/6 wild-type mice did have these findings. Given this supporting evidence of a role for mast cells in the development of silicosis, we examined the ability of silica to activate mouse bone marrow-derived mast cells (BMMC), including degranulation (␤-hexosaminidase release); production of reactive oxygen species (ROS) and inflammatory mediators; and the effects of silica on Fc⑀RI-dependent activation. Silica did not induce mast cell degranulation. However, TNF-␣, IL-13, monocyte chemotactic protein-1, protease activity, and production of ROS were dose-dependently increased after silica exposure, and production was enhanced after Fc⑀RI stimulation. This mast cell activation was inhibited by anti-inflammatory compounds. As silica mediates some effects in macrophages through scavenger receptors (SRs), we first determined that mast cells express scavenger receptors; then explored the involvement of SR-A and macrophage receptor with colleagenous structure (MARCO). Silica-induced ROS formation, apoptosis, and TNF-␣ production were reduced in BMMC obtained from SR-A, MARCO, and SR-A/MARCO knockout mice. These findings demonstrate that silica directs mast cell production of inflammatory mediators, in part through SRs, providing insight into critical events in the pathogenesis and potential therapeutic targets in silicosis. Keywords: B6.Cg-kitW-sh sash mouse; CD204; macrophage receptor with collagenous structure; mast cell; silicosis; SR-A Among environmental exposures that lead to pathologic changes in tissues is crystalline silica, which can result in occupational silicosis from inhalation of silica dusts in manufacturing, construction, farming, and mining operations. Silicosis, for which there is no effective treatment, leads to decreased pulmonary function and increased susceptibility to diseases of the respiratory tract (1, 2).Involvement of mast cells in silica-induced pulmonary inflammation has been suggested by two clinical observations. First, the number of mast cells within the lungs of individuals exposed to silica dust is increased (3). Second, an increase in mast cells staining for basic fibroblast growth factor located within silicotic nodules has been reported in lung sections obtained from patients with silicosis (4). Despite the suggestive CLINICAL RELEVANCEThis study demonstrates a role for mast cells in silicosis and is the first study to examine direct effects of silica on mast cell biology. It provides evidence that treatment of silicosis should explore mast cells as a potential therapeutic target.evidence for a role of mast cells in the development of silicosis, there are ...

Ionizing gamma radiation has several therapeutic indications including bone marrow transplantation and tumor ablation. Among immune cells, susceptibility of lymphocytes to gamma radiation is well known. However, there is little information on the effects of gamma radiation on mast cells, which are important in both innate and acquired immunity. Previous studies have suggested that mast cells may release histamine in response to high doses of gamma radiation, whereas other reports suggest that mast cells are relatively radioresistant. No strong link has been established between gamma radiation and its effect on mast cell survival and activation. We examined both human and murine mast cell survival and activation, including mechanisms related to innate and acquired immune responses following gamma radiation. Data revealed that human and murine mast cells were resistant to gamma radiation-induced cytotoxicity and, importantly, that irradiation did not directly induce β-hexosaminidase release. Instead, a transient attenuation of IgE-mediated β-hexosaminidase release and cytokine production was observed which appeared to be the result of reactive oxygen species formation after irradiation. Mast cells retained the ability to phagocytose Escherichia coli particles and respond to TLR ligands as measured by cytokine production after irradiation. In vivo, there was no decrease in mast cell numbers in skin of irradiated mice. Additionally, mast cells retained the ability to respond to Ag in vivo as measured by passive cutaneous anaphylaxis in mice after irradiation. Mast cells are thus resistant to the cytotoxic effects and alterations in function after irradiation and, despite a transient inhibition, ultimately respond to innate and acquired immune activation signals.

Background Mastocytosis is a clonal disorder associated with an increased mast cell burden. We have recently demonstrated the ability of human mast cells to express and be activated through multiple serotonin receptors; to synthesize and release serotonin; and that mastocytosis patients may have abnormal serotonin levels. As serotonin has been implicated in the genesis of clinical symptoms found in association with some chronic diseases, we have now determined the whole blood serotonin levels in 29 patients diagnosed with mastocytosis, and correlated these levels with multiple clinical and laboratory parameters. Materials and methods Patients with mastocytosis were categorized according to disease variant. Blood serotonin values were determined and correlated with values reported for normal subjects; and clinical and laboratory features of the disease. Results Total blood serotonin levels followed a bimodal distribution in line with our earlier report, unlike the normal distribution reported for normal individuals. Serotonin levels did not correlate with platelet numbers, liver function tests or serum tryptase levels. Patients with lower serotonin values had greater rates of fatigue (P = 0·0001), migraine headaches (P = 0·0028), psychiatric symptoms (P = 0·0001), diarrhoea (P = 0·0407), flushing (0·0085), and abdominal and bone pain (P = 0·0001). Conclusions Our study suggests that low blood serotonin levels help define a sub-group of patients with mastocytosis that are more likely to present with neurological and gastrointestinal complaints, and suggests that the use of pharmacologic agents that alter blood serotonin levels could be explored in selected patients.

Background: Mastocytosis is associated with a pathological increase in tissue mast cells. Associated skeletal problems include a decrease in bone density and pathological fractures. Methods: In order to explore the relationship between bone density and the severity of mastocytosis, 21 patients with mastocytosis who underwent dual-energy X-ray absorptiometry were entered into this study. Correlation coefficients were computed between Z-scores and demographic, clinical and laboratory data. Femoral neck Z-scores correlated with serum tryptase levels when all the patients were considered (p = 0.029). Results and Conclusion: Patients with less severe disease had significantly lower values at the L1–L4 spine (p = 0.046) and femoral neck (p = 0.029) Z-scores compared to patients with more severe disease. Most patients who had low Z-scores (between –1 and –2.5) were under 50 years of age, had less severe disease and had lower serum tryptase levels. A history of gastroesophageal reflux disease and a history of hypotensive episodes correlated with lower L1–L4 spine Z-scores (p < 0.05). Thus, patients with less severe disease and lower serum tryptase levels should in particular have their bone density determined with treatment appropriate to the findings.