Mediators Of Immediate Hypersensitivity Reactions Research Articles

A role for inflammatory mediators in heterologous desensitization of CysLT1 receptor in human monocytes

Cysteinyl-leukotrienes (cysteinyl-LT) are rapidly generated at sites of inflammation and, in addition to their role in asthma, rhinitis, and other immune disorders, are increasingly regarded as significant inflammatory factors in cancer, gastrointestinal, cardiovascular diseases. We recently demonstrated that in monocyte/macrophage-like U937 cells, extracellular nucleotides heterologously desensitize CysLT(1) receptor (CysLT(1)R)-induced Ca(2+) transients. Given that monocytes express a number of other inflammatory and chemoattractant receptors, this study was aimed at characterizing transregulation between these different stimuli. We demonstrate that in U937 cells and in primary human monocytes, a series of inflammatory mediators activating G(i)-coupled receptor (FPR1, BLT(1)) desensitize CysLT(1)R-induced Ca(2+) response unidirectionally through activation of PKC. Conversely, PAF-R, exclusively coupled to G(q), cross-desensitizes CysLT(1)R without the apparent involvement of any kinase. Interestingly, G(s)-coupled receptors (beta(2)AR, H(1/2)R, EP(2/4)R) are also able to desensitize CysLT(1)R response through activation of PKA. Heterologous desensitization seems to affect mostly the G(i)-mediated signaling of the CysLT(1)R. The hierarchy of desensitization among agonists may be important for leukocyte signal processing at the site of inflammation. Considering that monocytes/macrophages are likely to be the major source of cysteinyl-LT in many immunological and inflammatory processes, shedding light on how their receptors are regulated will certainly help to better understand the role of these cells in orchestrating this complex network of integrated signals.

Histamine H4 antagonism: a therapy for chronic allergy?

Chronic inflammatory diseases such as bronchial asthma, allergic gastrointestinal disease, and atopic dermatitis are characterized by the selective recruitment and activation of distinct subtypes of leukocytes, particularly eosinophils, into the tissue from peripheral blood (Rothenberg, 1998). Eosinophils, along with mast cells, are postulated to play a key role in the pathophysiology of these chronic diseases. The striking accumulation of eosinophils in allergic disease has stimulated intense scientific examination leading to the discovery of numerous molecular mechanisms responsible for this process. Eosinophils, like all leukocytes, migrate from the vascular lumen, across the endothelial cell surface into the appropriate tissue sites. This elaborate mechanism, known as transendothelial migration, has been shown to be a highly orchestrated process (Springer, 1994). The migratory pathway, or chemotaxis, of the leukocyte is directly influenced by soluble molecules known as chemoattractants. These molecules reside along a tissue gradient, and bind to and activate G-protein coupled receptors (GPCRs) on the leukocyte cell surface. Several eosinophil chemoattractants have been extensively studied. Some of these molecules, the classical chemoattractants, include the complement cleavage fragments, leukotrienes and platelet-activating factor (PAF). These chemoattractants have been shown to stimulate the recruitment of a wide variety of leukocyte subtypes, and are therefore nonselective. In contrast, chemotactic cytokines (or chemokines) such as eotaxin-1, -2, -3, and monocyte chemoattractant protein (MCP)-4 are more selective for the recruitment of leukocytes associated with allergic inflammation, such as eosinophils, mast cells, and basophils.

THE CYSTEINYL LEUKOTRIENE D4 RECEPTOR ANTAGONIST MONTELUKAST FOR THE TREATMENT OF INTERSTITIAL CYSTITIS

The presence of leukotriene D4 receptors in human detrusor myocytes and increased urinary leukotriene E4 in patients with interstitial cystitis and detrusor mastocytosis imply a role for cysteinyl containing leukotrienes as proinflammatory mediators in this disease. We examined the efficacy of the cysteinyl leukotriene 1 receptor antagonist montelukast for treating patients with interstitial cystitis and detrusor mastocytosis. Ten women in whom interstitial cystitis was diagnosed according to National Institute of Diabetes and Digestive and Kidney Diseases criteria and who also had detrusor mastocytosis with a minimum of 28 mast cells per mm.2 muscle tissue were included in this study. Patients received a single dose of montelukast daily for 3 months. The efficacy of treatment was determined by 24-hour urinary frequency, nocturia and pain using visual analog scales. After 1 month of montelukast treatment there was a statistically significant decrease in 24-hour urinary frequency, nocturia and pain which persisted during the 3 months of treatment. After 3 months 24-hour urinary frequency had decreased from 17.4 to 12 voidings (p = 0.009), nocturia had decreased from 4.5 to 2.8 (p = 0.019) and pain had decreased from 46.8 to 19.6 mm. on a visual analog scale (p = 0.006). No side effects were observed during treatment. Montelukast treatment resulted in significant improvement in urinary frequency and pain. Its efficacy for decreasing urinary frequency and pain imply a role of leukotriene receptor antagonists for managing interstitial cystitis but further placebo controlled clinical studies are needed.

Induction and regulation of the IgE response.

Immunoglobulin E (IgE) is believed to be one of the major mediators of immediate hypersensitivity reactions that underlie atopic conditions such as urticaria, seasonal allergy, asthma and anaphylaxis. Factors that control IgE production are therefore essential to the pathogenesis of these important afflictions. But a complete understanding of this topic is lacking, while new data have raised questions regarding the precise role of IgE in atopic disease. Evolving concepts of IgE production and elimination are likely to clarify the importance of IgE in health and disease.

Regulation of leukotriene biosynthesis

Leukotrienes are products of arachidonic acid metabolism derived through the action of the 5-lipoxygenase enzyme pathway. Leukotriene B4 has been implicated as a mediator of inflammation through induction of leukocyte and lymphocyte activation. The cysteinyl leukotrienes are important mediators of immediate hypersensitivity reactions and initiate smooth muscle contraction. Regulation of the production of leukotrienes can be achieved either through the action of direct 5-lipoxygenase inhibitors or indirect leukotriene biosynthesis inhibitors which bind to 5-lipoxygenase activating protein. Leukotriene C4 synthase and leukotriene A4 hydrolase represent alternative enzymic targets within the biosynthetic cascade. Leukotriene receptor antagonists also have important therapeutic possibilities and in particular, leukotriene D4 receptor antagonists have shown utility in the treatment of human bronchial asthma.

Analyses of microvascular permeability in response to mediators of immediate hypersensitivity

Mediator-induced changes in microvascular permeability were studied in rodent skin. To monitor these changes, Evan's blue dye, iodinated rat albumin and IgG, and tritiated neutral dextran molecules having different molecular radii were used. After intradermal injections of serotonin, histamine, and bradykinin, the degree of radiolabeled tracer efflux was determined by measuring the extent of blueing and the level of radioactivity in skin biopsy specimens. Although the mediators varied in potency on a molar basis (serotonin > bradykinin > histamine), the efflux resulting from each was similar. Furthermore, kinetic studies revealed that each of these vasoactive agents caused a marked but transient increase in macromolecular permeability that lasted less than 30 minutes. To determine the pore size created and the effect of charge on the transudation of macromolecules into the interstitium, fractions of neutral [ 3H]dextrans with a known molecular size (average radii, 12 and 4.4 nm, respectively) were infused either singly or in combination with 125I-labeled rat albumin and/or IgG before intradermal injection of serotonin, histamine, bradykinin, or compound 48 80 . Regardless of the mediator used, no differences could be demonstrated in macromolecular efflux, as indicated by either the molecular size of the charge of the tracer used. Thus, all mediators of immediate hypersensitivity reactions that were studied produce venular gaps >12 nm in addition to displaying similar vasopermeable characteristics.

Enzymes involved in the biosynthesis of leukotriene B4

Ten years have elapsed since the discovery and structural elucidation of the leukotriene compounds (1-5). The leukotrienes constitute a group of potent biologically active arachidonic acid-derived metabolites which are implicated as mediators of immediate hypersensitivity reactions and inflammation. They were first discovered in leukocytes and were determined to contain a conjugated triene structure, thus the derivation of their name (6). The cysteinyl-containing leukotrienes (LTC,, LTD4, and LTE,),' which together make up the slow reacting substance of anaphylaxis, are synthesized primarily by eosinophils, mast cells, and macrophages. They stimulate contraction of various smooth muscle cells, promote bronchial mucous secretion, and induce extravasation of plasma proteins by increasing microvascular permeability. Leukotriene B, (LTB,), synthesized predominantly by neutrophils, is capable of stimulating circulating leukocytes to adhere to the vascular endothelium and induces extravasation and chemotaxis of polymorphonuclear leukocytes in nanomolar concentrations. At higher concentrations, LTBI induces polymorphonuclear leukocyte degranulation, superoxide generation, and can augment natural killer cell activity. Several reviews on the structure, biosynthesis, and biological actions of the leukotrienes have been written (7-13). It is the aim of the present review to concentrate on the advances made in recent years, primarily through molecular biology studies, on the reaction pathway leading to production of LTB,. 5-Lipoxygenase

Immediate hypersensitivity reactions in the guinea-pig conjunctiva: studies with a second-generation leukotriene D4 receptor antagonist, MK-571

The role of leukotriene D4 (LTD4) as a mediator of immediate hypersensitivity reactions in the guinea-pig conjunctiva was examined using a potent, second-generation LTD4 receptor antagonist, MK-571 (also known as L-660,711). The microvascular permeability changes in the guinea-pig conjunctiva following challenge with either LTD4 or antigen were measured through accumulation of intravenously administered 99mtechnetium-labeled albumin. Topical application of MK-571 (up to 2 h pretreatment) significantly inhibited the conjunctival responses to LTD4 (ED50 of 18-60 ng/eye) but not to histamine. The responses to a single topical antigen challenge in ovalbumin-sensitized guinea pigs were significantly inhibited (44%) by topical treatment with MK-571, in contrast to the lack of effect previously observed with prototypic antagonists. The inhibitory effects of MK-571 did not involve an action on conversion of [3H]LTC4 to LTD4 and LTE4. Following a second antigen challenge (24 h after the first), MK-571 inhibited the resultant permeability changes by 78%. Specific histamine H1 and H2 antagonists similarly inhibited the responses to the first and second challenges (63 and 74%, respectively). The present study suggests that LTD4 is involved in conjunctival hypersensitivity reactions and that potent LTD4 receptor antagonists may be of therapeutic value in the treatment of allergic conjunctivitis.

Mediators of Immediate Hypersensitivity Reactions

PATIENTS with immediate hypersensitivity reactions are commonly encountered by physicians in both primary care and various specialty practices. Such patients present a broad spectrum of illnesses, ranging in severity from mild urticaria or seasonal rhinitis to fatal anaphylactic shock. For many years the pathophysiology of these illnesses has been known to involve the release of inflammatory mediators by mast cells and basophils. Over the past 10 years, considerable progress has been made in elucidating the structure and function of these mediators. Thus, many of the signs and symptoms of allergic responses in humans can now be attributed to specific mast-cell . . .

Inhibition of IgE-mediated release of histamine and peptide leukotriene from human basophils and mast cells by forskolin

Forskolin, a diterpene compound isolated from the roots of Coleus forskohlii, activates adenylate cyclase in membranes from a variety of mammalian tissues. We found that forskolin (10 −7 to 3 × 10 −5 M) caused a concentration-related inhibition of IgE-mediated release of histamine and peptide leukotriene C 4 (LTC 4) from human basophils and lung mast cells. There was a significant linear correlation between the per cent inhibition of histamine and LTC 4 release from both cell types. However, in both systems forskolin exerted a significantly greater inhibitory effect on LTC 4 release than on histamine release. The concentration-response inhibition curve was paralleled by a forskolin-induced rise in cAMP levels in human leukocyte and mast cell preparations. The relationship between the effect of forskolin and the cAMP concentration was supported by the finding that forskolin inhibited the “first stage” of antigen-induced histamine release, but not the release caused by the Ca 2+ ionophore, A23187. Propranolol, a competitive β-receptor antagonist, did not block the inhibition of mediator release or the cAMP accumulation caused by forskolin. These data suggest that forskolin modulates the release of mediators of immediate hypersensitivity reactions via the activation of adenylate cyclase in human basophils and mast cells.

Immunopharmacology of Anaphylatoxin-Induced Bronchoconstrictor Responses

The complement anaphylatoxin peptides, C3a and C5a, are potential mediators of immediate hypersensitivity reactions, eliciting many of the same actions on isolated tissue and cell preparations as specific antigen. Instilled intratracheally in experimental animals, the peptides induce acute bronchospasms and are sometimes lethal. In vitro, they cause dose-dependent contraction of isolated lung tissue preparations, a response which correlates well with bronchospasms observed in vivo, and our current understanding of the cellular and molecular mechanisms of this action are reviewed here. C5a and its catabolic derivative, C5ades Arg, stimulate contraction of isolated guinea pig lung parenchymal strips in part by production of leukotrienes that constitute SRS-A, and by release of histamine. Leukotrienes in turn release thromboxane from lung tissue, and evidence indicates that at least part of the spasmogenic activity of these peptidolipids is mediated by this effect. C3a is considerably less potent than C5a in contracting lung tissues and appears to act primarily by causing the release of spasmogenic cyclooxygenase metabolites. Both peptides may additionally have direct action on contractile cells within the tissue. Platelet-activating factor (PAF), an unusual phospholipid mediator released from inflammatory cells stimulated with C5a and other agents, also contracts isolated lung parenchymal tissues. PAF stimulates release of significant quantities of thromboxane from guinea pig lung; however, indomethacin does not block contractile responses of the tissue. Recent evidence indicates that PAF may act on parasympathetic neurons in lung to release endogenous acetylcholine, and this action may be a major component of tissue responses to this mediator. Thus the complement anaphylatoxins stimulate release of many of the same mediators from lung tissues as are released by antigen challenge of sensitized tissue, and may, therefore, play an important role in the pathogenesis of allergic bronchospasms.

Inhibition of IgE-mediated histamine release from human basophils and mast cells by fenoterol.

Fenoterol, a beta 2-adrenergic agonist recently introduced to treat asthmatic disorders, inhibits antigen-induced histamine release from human basophil leukocytes and lung mast cells in a dose-dependent fashion. The dose-response inhibition curve is paralleled by a fenoterol-induced increase in the cAMP levels of human leukocyte preparations. The relationship between the effect of fenoterol and cAMP level is supported by the finding that the beta 2-adrenergic agonist only inhibits the first stage of antigen-induced histamine release and not the release caused by the Ca2+ ionophore, A23187. Propranolol, a competitive antagonist of beta 2-adrenergic receptor, blocks the inhibition of release and the cAMP accumulation caused by fenoterol. Finally, theophylline, a cAMP phosphodiesterase inhibitor, synergistically potentiates the inhibitory effect of fenoterol on histamine release and the accumulation of cAMP. These data suggest that fenoterol may modulate the in vivo release of the mediators of immediate hypersensitivity reactions via the activation of beta 2-adrenergic receptor linked to adenylate cyclase on human basophils and mast cells.

Pharmacological alteration of antigen-induced contraction of lung parenchymal strips isolated from the actively sensitized guinea pig

Several drugs, known to influence the action or formation of histamine and SRS-A, were examined for their abilities to alter antigen (ovalbumin)-induced contractions of guinea-pig isolated lung parenchymal strips. Cumulative dose-response effects of ovalbumin were obtained on paired parenchymal strips, one used as control and the other drug treated. When used alone, mepyramine, 10 −6 M, phenoxybenzamine, 3 × 10 −5 M and FPL55712, 10 −5 M, did not alter ovalbumin-induced contractions. 5,8,11,14-eicosatetraynoic acid (ETYA), 10 −4 M, produced a small (2.5-fold) rightward shift of the dose-response curves to ovalbumin and histamine. Indomethacin, 5 × 10 −6 M, produced a small increase in the maximum response to ovalbumin and a small (2-fold) rightward shift of the histamine dose-response curve. The effect of indomethacin on ovalbumin-induced contraction was not seen in the presence of phenoxybenzamine and may therefore be due to an increase in histamine release. Combination of indomethacin with FPL55712 or ETYA did not alter antigen-induced contractions. The effect of ETYA on the histamine dose-response curve was not seen in the presence of indomethacin. Combination of phenoxybenzamine with FPL55712 or ETYA caused a marked reduction of the maximum contractile response to ovalbumin. The effect of phenoxybenzamine and ETYA was not observed in the presence of indomethacin. The results suggest that the ability of ETYA to reduce antigen responses in the absence or presence of phenoxybenzamine as well as histamine-induced contraction is related to inhibition of contractile product(s) of cyclooxygenase metabolism of arachidonic acid. Even though substantial antagonism of antigen-induced contractions of guinea-pig parenchymal strips could only be achieved with a combination of drugs, the magnitude of the antagonism was not as large as observed in other pulmonary smooth muscle preparations. This may reflect the existence of other contractile mediators, different interactions between known mediators of immediate hypersensitivity reactions or relative insensitivity of parenchymal strips to effects of the drugs.

Leukotrienes: mediators of immediate hypersensitivity reactions and inflammation.

Arachidonic acid plays a central role in a biological control system where such oxygenated derivatives as prostaglandins, thromboxanes, and leukotrienes are mediators. The leukotrienes are formed by transformation of arachidonic acid into an unstable epoxide intermediate, leukotriene A4, which can be converted enzymatically by hydration to leukotriene B4, and by addition of glutathione to leukotriene C4. This last compound is metabolized to leukotrienes D4 and E4 by successive elimination of a gamma-glutamyl residue and glycine. Slow-reacting substance of anaphylaxis consists of leukotrienes C4, D4, and E4. The cysteinyl-containing leukotrienes are potent bronchoconstrictors, increase vascular permeability in postcapillary venules, and stimulate mucus secretion. Leukotriene B4 causes adhesion and chemotactic movement of leukocytes and stimulates aggregation, enzyme release, and generation of superoxide in neutrophils. Leukotrienes C4, D4, and E4, which are released from the lung tissue of asthmatic subjects exposed to specific allergens, seem to play a pathophysiological role in immediate hypersensitivity reactions. These leukotrienes, as well as leukotriene B4, have pro-inflammatory effects.

BL-5255 II: effects on release and smooth muscle activity of mediators of immediate hypersensitivity reactions.

BL-5255 inhibited release of preformed mediators from passively sensitized mast cells in the rat peritoneal cavity, chopped monkey lung or human lung tissue. The compound failed to block rat cutaneous reactions elicited by histamine or serotonin. It exhibited weak to no ability, depending on the mediator employed, to block contraction of isolated guinea pig ileum or tracheal tissue. At concentrations of 1 microM or greater, BL-5255 itself was contractile to the ileum but not to the quiescent or submaximally contracted trachea. The compound relaxed spontaneously contracting rabbit jejunum muscle but at doses not likely to be achieved in vivo. Phosphodiesterase activities in extracts of rat and human lung were inhibited at concentrations greater than those required to inhibit mediator release.

Allergy and immunology: an annotated bibliography of recent literature. Allergy and Immunology Committee, American College of Physicians.

Allergy and immunology: an annotated bibliography of recent literature. Allergy and Immunology Committee, American College of Physicians.

Leukotrienes are potent constrictors of human bronchi.

Slow reacting substance of anaphylaxis (SRS-A) is released by various stimuli, including immunological challenge, and has long been considered an important mediator of immediate hypersensitivity reactions, such as bronchoconstriction in allergic asthma. Recently, slow reacting substances from several tissues have been identified and characterized as members of a newly discovered group of substances, the leukotrienes. Leukotrienes are generated from arachidonic acid and other polyunsaturated fatty acids in a pathway initially involving a lipoxygenase-catalysed oxygenation at C-5 (Fig. 1). This differs from the synthesis of prostaglandins and thromboxanes, where the initial transformation of arachidonic acid is catalysed by a cyclo oxygenase (Fig. 1). Recently, leukotriene C4(LTC4:5(S)-hydroxy,6(R)-S-glutathionyl-7,9-trans, 11,14-cis-eicosatetraenoic acid) and D4(LTD4:5(S)-hydroxy,6(R)-S-cysteinyl-glycyl-7,9-trans,11,14-cis-eicosatetraenoic acid) were found to have biological effects in several bioassay systems, which are strikingly similar to those previously reported for impure extracts of SRS-A. Here we report the remarkable contractile activity of both LTC4 and LTD4 on isolated human bronchi, which further emphasizes the possibility that leukotrienes are potent mediators of bronchoconstriction in man.

Adenosine Receptor on Human Basophils: Modulation of Histamine Release

Adenosine, at physiologic concentrations, inhibits in vitro IgE-mediated human basophil histamine release in a dose-dependent fashion. The inhibition dose-response curve is paralleled by an adenosine-induced increase in cAMP levels of human leukocyte preparations. Further evidence that the adenosine effect is related to changes in cAMP levels is that the nucleoside inhibits only in the first stage of antigen-induced histamine release and fails to inhibit the release caused by ionophore A23187. A poorly metabolized derivative of adenosine, 2-chloroadenosine inhibits as effectively as adenosine; dipyridamole, which blocks adenosine uptake, does not impair the inhibition caused by adenosine. Finally, theophylline, which is a competitive antagonist of adenosine in human lymphocytes also blocks the inhibition of release caused by adenosine. These data suggest that adenosine acts via a specific cell-surface receptor linked to adenylate cyclase. It appears that the human basophil has a specific receptor for adenosine and that this nucleoside may modulate the in vivo release of the mediators of immediate hypersensitivity reactions.

Anaphylactic relase of a basophil kallikrein-like activity. II. A mediator of immediate hypersensitivity reactions.

This report describes the immune release of a new mediator from human peripheral leukocytes, a basophil kallikrein-like activity (BK-A). The release process is initiated by the interaction of antigen on anti-IgE with cell-bound IgE, and appears to be similar in mechanism to the relase of histamine and other mediators of the immediate hypersensitivity reaction. The dose-response relationships and kinetics of histamine and BK-A release from antigen-challenged peripheral leukocytes are similar. The relase of the BK-A is calcium and temperature dependent, requires metabolic energy, and is controlled by hormone-receptor interactions that influence the cellular level of cyclic AMP, as has been described for other mediators of immediate hypersensitivity reactions. The data indicate that the interaction of BK-A with human plasma kininogen, generates immunoreactive kinin. We conclude that the antigen-IgE interation leads to the release from human basophils of a new mediator, a basophil kallikrein-like activity which may well be a link between reactions of immediate hypersenstivitity and the plasma and/or tissue kinin-generating systems.

Chemical Mediators of Immediate Hypersensitivity Reactions

The investigation of the mast cell-basophil products has progressed from studies directed solely at implicating histamine or serotonin in allergic diseases to molecular definitions of pathways to target cell activation and mediator release. In addition, within the last several years the detection and molecular characterization of the many other mediators of immediate hypersensitivity have begun. This area should continue to prove a fruitful arena in the future. Identification of the physiologic importance of these mediators in the heaves syndrome or other potential equine allergic syndromes may contribute both to the basic understanding of the pathogenesis of allergy, as well as suggest possible avenues for control.