Background-We compared cardiac mast cell (HHMC) density and the immunological and nonimmunological release of mediators from mast cells isolated from heart tissue of patients with idiopathic dilated (DCM) (nϭ24) and ischemic cardiomyopathy (ICM) (nϭ10) undergoing heart transplantation and from control subjects (nϭ10) without cardiovascular disease. Methods and Results-HHMC density in DCM (18.4Ϯ1.6 cells/mm 2 ) and ICM (18.4Ϯ1.5 cells/mm 2 ) was higher than that in control hearts (5.3Ϯ0.7 cells/mm 2 ; PϽ.01). The histamine and tryptase contents of DCM and ICM hearts were higher than those of control hearts. The histamine content of the hearts was correlated with mast cell density (r s ϭ.91; PϽ.001). Protein A/gold staining of heart tissue revealed stem cell factor (SCF), the principal growth, differentiating, and activating factor of human mast cells, in HHMC secretory granules. Histamine release from cardiac mast cells caused by immunological (anti-IgE and rhSCF) and nonimmunological stimuli (Ca 2ϩ ionophore A23187) was higher in patients with DCM and ICM compared with control subjects. Immunological activation of HHMC induced a significantly greater release of tryptase and LTC 4 in patients with DCM and ICM compared with control subjects. Conclusions-Histamine and tryptase content and mast cell density are higher in failing hearts than in control hearts. SCF, present in secretory granules of HHMC, might represent an autocrine factor sustaining mast cell hyperplasia in heart tissue in these patients. The increased local release of fibrogenic factors (eg, histamine, tryptase, and leukotriene C 4 ) might contribute to collagen accumulation in the hearts of patients with cardiomyopathy. 1 Mast cells are present in human heart tissue 2,3 and in adventia and intima of coronary arteries of patients with coronary artery disease. [4][5][6] Moreover, the in vitro immunological activation of human heart tissue with anti-IgE induces the release of histamine and prostaglandin D 2 . 7,8 The concentration of histamine and the density of mast cells are increased in the arteries of cardiac patients, 4,5,9 and coronary arteries from cardiac patients are hyperresponsive in vitro to histamine. 4 Furthermore, in vivo administration of histamine and other mast cell-derived mediators (peptide LTC 4 ) in humans causes significant cardiovascular effects. 10 -12 Finally, serum IgE levels are increased in patients with coronary artery disease. 13,14 Taken together, these observations raise the possibility that local activation of cardiac mast cells might contribute, through the release of vasoactive mediators, to certain cardiovascular diseases. 15,16 Fibrosis is a hallmark of failing hearts in DCM and ICM. 17 The cells and the mediators responsible for fibroblast proliferation and collagen accumulation in failing hearts in DCM and ICM are largely unknown. Mast cells are involved in many types of inflammation and repair processes and are found in increased numbers in fibrotic tissues. For example, increased mast cell density has be...

Objective. To examine the ultrastructure of human synovial mast cells in situ, to identify immunologic and nonimmunologic stimuli that activate these cells in vitro, and to quantify a number of preformed and de novo-synthesized mediators.Methods. We conducted an ultrastructural study of synovial mast cells in situ and performed immunoelectron microscopy localization of tryptase and chymase. Isolated synovial mast cells were analyzed biochemically, immunologically, and functionally in vitro and compared with cells from human lung, heart, and skin.Results. Ultrastructural study of synovial tissue revealed mast cells with homogeneously dense, scrolled, crystal, and mixed granules, and lipid bodies in the cytoplasm. A small percentage of mast cells showed evidence of degranulation. Immunoelectron microscopy demonstrated the subcellular localization of tryptase and chymase over granules of >90% of the mast cells, which were of the MC,, subtype. Isolated synovial mast cells released histamine in response to immunologic (anti-IgE and anti-Fcs receptor I [anti-FcsRI]) and nonimmunologic (substance P, recombinant human stem cell factor, and 48/80) stimuli, but did not respond to recombinant human C5a in vitro. Synovial mast cells differed from those isolated from other human tissues, in a variety of immunologic and biochemical features. There was a linear correlation between the percentage of histamine secretion and tryptase release (r = 0.79, P <

Eosinophilia in humans is associated with eosinophil infiltration and cardiac localization of eosinophil granule proteins. Eosinophil cationic proteins are responsible for cardiac disease in some patients with eosinophilia. We have investigated the in vitro effect of four eosinophil granule proteins: eosinophil cationic protein (ECP), major basic protein (MBP), eosinophil-derived neurotoxin (EDN) and eosinophil peroxidase (EPO), on mast cells isolated from human cardiac tissue (HHMC). ECP and, to a lesser extent MBP (0.3–3 μM), but not EDN and EPO, stimulated the release of histamine and tryptase from HHMC. This release reaction induced by ECP and MBP was Ca²⁺- and temperature-dependent and was abolished by preincubation with anti-ECP and anti-MBP, respectively. The activation of HHMC by ECP and MBP was abolished by preincubation with 2-deoxy-D-glucose and antimycin A. These data demonstrate that some eosinophil cationic proteins, ECP and MBP, are selective activators of HHMC, thus contributing to the cardiac lesions in patients with eosinophilia.

Mast cells and their chemical mediators play a role in cardiac and systemic anaphilaxis. Perivascular and cardiac mast cells have been implicated in the pathogenesis of coronary artery spasm, atherosclerosis, myocardial ischemia, and cardiomyopathy. Despite this, nothing is known about the immunological and biochemical characteristics of the human heart mast cell (HHMC). We have isolated and partially purified HHMC and compared them with mast cells isolated from lung (HLMC) and skin (HSMC) tissues. Cross-linking of the high-affinity receptor for IgE (Fc_ΕRI) by a polyclonal anti-Fc_Ε antibody caused the release of preformed (histamine and tryptase) and de novo synthesized mediators [peptide leukotriene C₄ (LTC₄) and prostaglandin D₂ (PGD₂)]. The tryptase content of HHMC (19.4 ± 1.5 µg/10⁶ cells) was lower than HSMC (33.4 ± 2.5 µg/10⁶ cells) and higher than HLMC (10.6 ± 1.9 µg/10⁶ cells). Maximal stimulation of HHMC with anti-IgE led to the release of LTC₄ (17.5 ± 5.1 µg/10⁶ mast cells) and PGD₂ (17.8 ± 5.0 µg/10⁶ mast cells, whereas HSMC synthesized more PGD2 (65.0 ± 6.8 µg/10⁶ mast cells) and much less LTC₄ (< 5 µg/10⁶ cells). Recombinant human C5a anaphylatoxin and protamine induced histamine release from HHMC and HSMC, but not from HLMC. Substance P and morphine selectively induced the release of histamine from HSMC, but not from HHMC and HLMC. Compound 48/80 caused histamine release from HSMC and HHMC, but not from HLMC. The pattern of mediators synthesized and the responsiveness of HHMC to different secretagogues appear unique providing strong evidence of human mast cell heterogeneity.

Objective. To evaluate the in vitro effects of 4 antiinflammatory and 5 immunosuppressive agents on the release of preformed and de novo‐synthesized mediators from human synovial mast cells (HSyMC) activated by immunologic and nonimmunologic stimuli. Methods. The effects of antiinflammatory and immunosuppressive agents were evaluated on the in vitro release of histamine and tryptase and the de novo synthesis of prostaglandin D2 (PGD2) and leukotriene C4 (LTC4) by HSyMC challenged with anti‐IgE and substance P. Results. Nimesulide, a sulfonanilide nonsteroidal antiinflammatory drug (NSAID) chemically unrelated to other acidic NSAIDs (such as acetylsalicylic acid [ASA], diclofenac, and piroxicam) inhibited in a concentration‐dependent manner the release of preformed (histamine and tryptase) mediators from HSyMC challenged with anti‐IgE. In contrast, diclofenac and piroxicam had little or no effect on HSyMC activated by anti‐IgE. ASA, diclofenac, piroxicam, and nimesulide caused a concentration‐dependent inhibition of IgE‐mediated PGD2 release from HSyMC. Nimesulide, but not diclofenac or piroxicam, also inhibited the de novo synthesis of LTC4 by HSyMC challenged with anti‐IgE. Nimesulide, diclofenac, and piroxicam had no effect on HSyMC activated by substance P. Cyclosporin A (CSA) inhibited histamine release from HSyMC challenged with anti‐IgE, whereas cyclosporin H (CSH) had no effect. FK‐506 also inhibited histamine release from HSyMC activated by anti‐IgE, whereas rapamycin had no effect. Neither CSA, CSH, FK‐506, nor rapamycin inhibited the release of histamine from HSyMC induced by substance P. Methotrexate had no effect on the release of mediators from these cells, whereas adenosine (R‐phenylisopropyl adenosine and 5‐N‐ethylcarboxamide adenosine) enhanced histamine release from immunologically activated HSyMC in a concentration‐dependent manner. Conclusion. Mast cells isolated from human synovia display 4 levels of pharmacologic heterogeneity with regard to 1) the inhibitory effects of 4 antiinflammatory drugs; 2) the capacity of different immunosuppressive drugs to exert antiinflammatory activity; 3) the inhibition of the release of different mediators; and 4) the capacity of antiinflammatory and immunosuppressive drugs to modulate HSyMC activated by different stimuli. This complexity of pharmacologic modulation of HSyMC in vitro might help explain the different activity of the compounds used to treat various pathophysiologic aspects of the inflammatory arthritides.