A. Dean Befus

Mast cell differentiation and heterogeneity

Major differences between mast cells from different tissues and species have been known for at least 20 years but have been rigorously studied only recently. A recent meeting focused on the ontogeny and differentiation of mast cells, their functional characteristics and the clinical and biological significance of their heterogeneity.

Prostaglandins inhibit inflammatory mediator release from rat mast cells

BACKGROUNDnMast cells have been implicated in the pathogenesis of gastric ulceration. It is possible that prostaglandins exert cytoprotective effects by inhibiting the release of proulcerogenic mediators from mast cells.nnnMETHODSnThe effects of three prostaglandins on the release of platelet-activating factor, tumor necrosis factor, and histamine from rat mast cells (peritoneal and intestinal mucosal) activated with calcium ionophore or antigen were assessed.nnnRESULTSnUpon stimulation with either agonist, intestinal mucosal and peritoneal mast cells released significant quantities of platelet-activating factor. Preincubation for 5 minutes with misoprostol, prostaglandin (PG)E2, 16,16-dimethyl PGE2, ketotifen, or PF-5901 concentration-dependently reduced ionophore-stimulated platelet-activating factor release; significant effects were observed with picomolar to nanomolar concentrations of the prostaglandins and micromolar concentrations of the other compounds. Tumor necrosis factor release from peritoneal and mucosal mast cells was also significantly inhibited by the prostaglandins in picomolar to nanomolar concentrations. Misoprostol and PGE2 at concentrations of 5-50 nmol/L significantly inhibited histamine release from peritoneal mast cells stimulated with ionophore but did not affect histamine release stimulated by antigen.nnnCONCLUSIONSnThese results show potent inhibitory effects of prostaglandins on the release of pro-ulcerogenic inflammatory mediators from mast cells. Such effects may contribute to the protective and anti-inflammatory effects of prostaglandins in the gastrointestinal tract and elsewhere.

Intestinal Immunity and Inflammation: Recent Progress

The previous sections illustrate that we are still defining (a) which sets of lymphoid cells are present in the intestine and which are not, (b) which sets are peculiar to the intestine, and (c) how the sets that are there function in the intestinal microenvironment. An understanding of the latter point is going to require knowledge of how these sets communicate with and regulate one another via cell surface molecules such as MHC class I and class II molecules, and via soluble mediators or lymphokines. The recent advances in various technologies make this a particularly exciting time in this field because the tools are now available to address and answer some of these basic and important questions in mucosal immunology. At the same time these advances hold great promise for our eventual understanding of chronic inflammatory diseases of the intestine. As was mentioned at the outset, the immune system has considerable power for both protection and destruction. It remains a puzzle how this latter potential is contained and controlled in the intestine of most individuals, such that they do not have inflammatory disease even in the setting of intense stimulation by substances, such as endotoxin, that are phlogistic elsewhere in the body. An answer to the question of why everyone does not have intestinal inflammation could provide new insights into the mechanisms involved in chronic intestinal inflammatory diseases. The recent advances just detailed, as well as others sure to come, suggest that it is only a matter of time before such questions are answered.

Extracts of mosquito salivary gland inhibit tumour necrosis factor alpha release from mast cells.

Extracts of salivary glands of the yellow fever mosquito Aedes aegypti inhibit tumour cell‐stimulated release of tumour necrosis factor alpha (TNFα) from rat mast cells, but do not inhibit antigen‐induced histamine secretion. This inhibitory activity for TNFα is found in salivary glands of female but not in male mosquitoes. This inhibition is not mediated by bacterial contamination (LPS), by calcitonin gene related peptide (CGRP), nerve growth factor (NGF), epidermal growth factor (EGF) or transforming growth factor β (TGFβ). The factor(s) has a molecular weight > 10 kDa and is neutralized by boiling for 10 min or heating at 56°C for 30 min. The modulation of this proinflammatory mediator, TNFα, produced by mast cells in sites of blood feeding may facilitate completion of the blood meal, and as reported for certain vector‐transmitted parasites, may enhance infectivity.

Platelet‐activating factor synthesis by peritoneal mast cells and its inhibition by two quinoline‐based compounds

1 Peritoneal mast cells from rat were co‐incubated in vitro in a platelet aggregometer cuvette with washed rabbit platelets. In response to stimulation with calcium ionophore (A23187; 1–5 μm), the mast cells released a substance which stimulated the platelets to aggregate. These concentrations of ionophore did not stimulate platelet aggregation in the absence of mast cells, nor affect the responsiveness of the platelets to aggregation induced by thrombin or PAF. Release of a PAF‐like substance was also observed in response to stimulation of the mast cells with antigen. 2 This pro‐aggregatory activity is attributable to the release of PAF by the mast cells, since the activity could be abolished by preincubating the platelets with a specific PAF receptor antagonist (WEB 2086; 10 μm). Furthermore, the platelet‐aggregating factor co‐migrated with PAF on thin‐layer chromatographs and could be abolished by incubation with phospholipase A2 (20 μg ml−1) or a specific antibody directed against PAF. 3 The release of PAF by peritoneal mast cells could be inhibited, in a concentration‐dependent manner, by PF‐5901 (IC50 of 3.9μm) or Wy‐50,295 (IC50 of 1.2μm), two structurally similar compounds with inhibitory effects on leukotriene synthesis, as well as leukotriene D4 (LTD4) receptor antagonist properties. 4 Inhibition of PAF synthesis was not observed when the mast cells were incubated with a structurally unrelated 5‐lipoxygenase inhibitor (A‐64077), a structurally dissimilar inhibitor of 5‐lipoxygenase activating protein (MK‐886) or with a structurally related LTD4 receptor antagonist (MK‐571) which lacks inhibitory effects on leukotriene synthesis, each at concentrations of up to 100 μm. 5 Neither PF‐5901 nor Wy‐50,295 (1 or 10 μm) significantly affected histamine release or prostaglandin D2 synthesis by peritoneal mast cells in response to calcium ionophore stimulation. 6 These results demonstrate the ability of a class of quinoline‐based compounds to inhibit PAF synthesis by peritoneal mast cells. This activity does not appear to be related to effects of these compounds on leukotriene synthesis or LTD4 receptors. The ability of these compounds to inhibit PAF synthesis may contribute to their anti‐inflammatory properties.

Modulation of Mast Cell Function in the Gastrointestinal Tract

Publisher Summary The immunologic and inflammatory responses in gastrointestinal tract involve a complex network among nerves, cells, and inflammatory mediators. Different immune cell types, such as lymphocytes, neutrophils, eosinophils, macrophages and mast cells, are present throughout the gastrointestinal tract and can produce a spectrum of mediators, which may be host protective or pathogenic. This chapter describes mast cells. Mast cell stimulation may lead to the release of various cytokine and macrophage inflammatory protein that are implicated in the inflammatory network. In addition, mast cells are a source of arachidonate metabolites, which are important inflammatory mediators in gastric ulceration as well as in IBD. Thus, given the role of mast cells in inflammation and their abundance and activation in gastrointestinal diseases, they appear to be potentially important therapeutic targets. Mast cell mediators can be separated into two categories: preformed and newly synthesized following activation. Preformed mediators can be divided into those that are soluble and can be found in the circulation after their secretion and those that are insoluble. Histamine, serotonin, rat mast cell protease II, tryptases (human), exoglycosidases, and chemotactic factors for neutrophils and eosinophils are highly soluble, whereas heparin, chondroitin sulfates, rat mast cell protease I, carboxy-peptidase, peroxidase, and superoxide dismutase are insoluble. The newly synthesized mediators include platelet activating factor (PAF), adenosine, arachidonate metabolites, and nitric oxide.

Platelet activating factor and systemic anaphylaxis in Nippostrongylus brasiliensis‐sensitized rats: differential effects of PAF antagonists

1 The effects of two platelet‐activating factor (PAF) antagonists, WEB 2086 and BN 52021, in reducing the changes in extravasation (Evans blue technique) and blood flow (radiolabelled microsphere method) to various organs and tissues following anaphylactic shock in the Nippostrongylus brasiliensis‐sensitized rat were investigated. 2 Both antagonists attenuated anaphylaxis‐induced increases in plasma protein leak in the trachea, stomach and small intestine, although they did not block extravasation in the colon and kidneys. 3 Anaphylaxis‐induced decreases in blood flow to the adrenals were effectively antagonized by WEB 2086, although this antagonist did not reverse blood flow decreases to any other tissues. BN 52021, on the other hand, did not alter anaphylaxis‐induced decreases in blood flow to the adrenals, but effectively prevented dramatic decreases in blood flow to the large and small bowel and spleen. 4 Anaphylactic shock produced marked reduction in blood pressure that was partly reversed by WEB 2086, whereas BN 52021 effectively blocked the decreases in cardiac output. 5 Thus, PAF is responsible for some of the haemodynamic and extravasation of protein changes associated with systemic anaphylaxis in the rat, although the differential inhibition observed with the two antagonists suggests that PAF alters vascular responsiveness through different mechanisms in selected tissues.

Vcsa1 gene peptides for the treatment of inflammatory and allergic reactions.

The recently emerged Vcsa1 gene is one member of the variable coding sequence (VCS) multigene family of Rattus norvegicus. This gene encodes the precursor prohormone SMR1 (submandibular rat-1), which on enzymatic processing gives rise to several 5 to 11 amino acid peptides that modulate a variety of physiological functions. The analgesic pentapeptide sialorphin and anti-inflammatory heptapeptide submandibular gland peptide-T (TDIFEGG) are the most intensively studied. Although the Vcsa1 gene and its protein product are unique to rats, TDIFEGG or a derivative acts on all species examined to date, including human cells, in functions related to allergic reactions and inflammation. In this review, the patent and academic literature on SMR1 and its natural peptides and their derivatives are reviewed for consideration of biological targets and relevance to the development of novel therapeutic agents. The VCS gene family is discussed and we speculate on possible human homologs of these potent anti-inflammatory rat-derived peptides. The biologically active peptide products of SMR1 are considered and the mechanism of action and structure-activity relationships of the anti-inflammatory submandibular gland peptide-T and its derivatives are discussed.

Modulation of Tumour Necrosis Factor-Alpha mRNA Levels by Interferons in Different Populations of Mast Cells

Tumour necrosis factor alpha (TNF-α) is a multipotent cytokine1 which can be produced by mast cells2 (MC). Given the regulatory roles of interferons (IFN) and the ability of IFN to potentiate TNF-α activity of macrophages3 we previously studied the effects of IFN on MC TNF-α activity.4 In contrast with effects on macrophages, IFN-α/β and IFN-γ inhibited TNF-α activity of mast cells. Thus, we analyzed the effects of IFN-α/β and IFN-γ on MC mRNA expression for TNF-α, high affinity immunoglobulin E receptor-alpha chain (FcERI-α chain), 2’5’ oligo adenylate synthetase (2’5’OAS) and β-actin.