Exogenous nitric oxide regulates the degranulation of human basophils and rat peritoneal mast cells

Neurotransmitter and neuropeptide regulation of mast cell function: a systematic review

The existence of the neural control of mast cell functions has long been proposed. Mast cells (MCs) are localized in association with the peripheral nervous system (PNS) and the brain, where they are closely aligned, anatomically and functionally, with neurons and neuronal processes throughout the body. They express receptors for and are regulated by various neurotransmitters, neuropeptides, and other neuromodulators. Consequently, modulation provided by these neurotransmitters and neuromodulators allows neural control of MC functions and involvement in the pathogenesis of mast cell–related disease states. Recently, the roles of individual neurotransmitters and neuropeptides in regulating mast cell actions have been investigated extensively. This review offers a systematic review of recent advances in our understanding of the contributions of neurotransmitters and neuropeptides to mast cell activation and the pathological implications of this regulation on mast cell–related disease states, though the full extent to which such control influences health and disease is still unclear, and a complete understanding of the mechanisms underlying the control is lacking. Future validation of animal and in vitro models also is needed, which incorporates the integration of microenvironment-specific influences and the complex, multifaceted cross-talk between mast cells and various neural signals. Moreover, new biological agents directed against neurotransmitter receptors on mast cells that can be used for therapeutic intervention need to be more specific, which will reduce their ability to support inflammatory responses and enhance their potential roles in protecting against mast cell–related pathogenesis.

The parasympathetic nervous system as a regulator of mast cell function

Often considered as the archetype of neuroimmune communication, much of our understanding of the bidirectional relationship between the nervous and immune systems has come from the study of mast cell-nerve interaction. Mast cells play a role in resistance to infection and are extensively involved in inflammation and subsequent tissue repair. Thus, the relationship between mast cells and neurons enables the involvement of peripheral and central nervous systems in the regulation of host defense mechanisms and inflammation. Recently, with the identification of the cholinergic anti-inflammatory pathway, there has been increased interest in the role of the parasympathetic nervous system in regulating immune responses. Classical neurotransmitters and neuropeptides released from cholinergic and inhibitory NANC neurons can modulate mast cell activity, and there is good evidence for the existence of parasympathetic nerve-mast cell functional units in the skin, lung, and intestine that have the potential to regulate a range of physiological processes.

Inducible nitric oxide synthase plays important roles in allergic reactions of pollinosis in mice sensitized with pollen allergy

To elucidate the possible involvement of nitric oxide (NO) derived from inducible NO-synthase (iNOS) in the pathogenesis of patients with allergic rhinitis, we analyzed changes in the frequency of sneezing, plasma levels of NO metabolites, α-melanocyte-stimulating hormone (MSH) and immunoglobulin E and tracheal expression of IgA and mast cell tryptase in control and iNOS^−/− mice. Eight-week-old control and iNOS^−/− male C57BL/6j mice were sensitized with Cry j I antigen. After the last intranasal challenge of antigen, changes in the frequency of sneezing and plasma levels of IgE, α-MSH and NO metabolites and tracheal expression of iNOS, IgA and mast cell tryptase were analyzed by ELISA and immunohistochemistry using specific antibodies. The sensitization of mice with Cry j I antigen increased plasma levels of NO metabolites, α-MSH and IgE and tracheal expression of iNOS, IgA and mast cell tryptase in control not but in iNOS^−/− mice. Administration of N^G-nitro-L-arginine methyl ester strongly inhibited all these changes occurred in control mice. These results indicate that the symptom of pollinosis including sneezing is enhanced by iNOS derived NO through activation of α-MSH-receptor containing mast cells enriched with tryptase.

Inhibition of anti-IgE mediated human mast cell activation by NO donors is dependent on their NO release kinetics

BACKGROUND AND PURPOSE

Although the mast cell is a source of nitric oxide (NO), the effect of NO on human mast cells has not been defined. This study investigated if exogenous NO could affect human mast cell activation.

EXPERIMENTAL APPROACH

Effects of different NO donors on immunoglobulin E (IgE)-dependent activation of human-cultured mast cells (HCMC) derived from precursors in buffy coat were investigated by measuring histamine release. Intracellular NO in HCMC was monitored with confocal microscopy using the fluorescent NO indicator 4-amino-5-methylamino-2', 7'-difluorofluorescein.

KEY RESULTS

Diethylamine NONOate (DEA/NO) and MAHMA NONOate (NOC-9), both have rapid NO release rates, only inhibited anti-IgE-induced histamine release when added to HCMC at the time of activation. NO donors with slower NO release kinetics were ineffective even after 30 min incubation. Confocal microscopy revealed that the effectiveness of NO donors was dependent on the availability of adequate NO inside HCMC during activation. The inhibitory action of DEA/NO was diminished by the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl but potentiated by the anti-oxidant, N-acetylcysteine (NAC). Furthermore, co-incubation with NAC allowed previously ineffective NO donors to suppress HCMC activation and thus suggested that NAC could increase the availability of NO from NO donors.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrated that NO was able to modulate human mast cell activation but only when enough NO was present at the time of cell activation. Our findings explain the controversy over the effectiveness of NO on mast cell degranulation and supports the possibility that NO donors could be beneficial for treating allergic inflammation.

What's in a name? eNOS and anaphylactic shock

In this issue of the JCI, a study by Cauwels and colleagues suggests a central role for eNOS, the endothelial isoform of nitric oxide synthase, as a mediator of anaphylaxis (see the related article beginning on page 2244). Why is an enzyme originally described as a physiological mediator of vascular homeostasis implicated in the spectacular vascular collapse that is characteristic of anaphylaxis? And is the eNOS involved in anaphylaxis necessarily exerting its effect solely in the vascular endothelium, or might this "endothelial enzyme" actually be playing a more fundamental role in an entirely different tissue? After all, what's in a name?

Whole-body periodic acceleration modifies experimental asthma in sheep

RATIONALE

Nitric oxide is released from vascular endothelium in response to increased pulsatile shear stress. Nitric oxide inhibits mast cell activation and is antiinflammatory and therefore might be protective in asthma.

OBJECTIVES

We determined if a noninvasive motion platform that imparts periodic sinusoidal inertial forces to the whole body along the spinal axis (pGz) causing release of endothelial nitric oxide modulates experimental asthma in sheep.

METHODS

Allergic sheep were untreated (control) or were treated with pGz alone or after receiving intravenously the nitric oxide synthase inhibitor N(w)-nitro-L-arginine methyl ester (L-NAME) before aerosol challenge with Ascaris suum, and the effect on antigen-induced airway responses was determined. Bronchoalveolar lavage cells obtained 6 h after antigen challenge were analyzed for nuclear factor-kappaB (NF-kappaB) activity in the respective groups.

RESULTS

pGz treatment for 1 h before antigen challenge reduced the early airway response and blocked the late airway response but did not prevent the antigen-induced airway hyperresponsiveness 24 h after challenge. Administration of L-NAME before pGz completely reversed this protection, whereas L-NAME alone did not affect the antigen-induced responses. NF-kappaB activity was 1.9- and 1.8-fold higher in the control and L-NAME + pGz groups, respectively, compared with pGz-treated animals. Extending the pGz treatment to twice daily for 3 d and then 1 h before antigen challenge blocked the early and late airway responses, the 24-h airway hyperresponsiveness, and the airway inflammatory cell response.

CONCLUSION

Whole-body pGz modulates allergen-induced airway responses in allergic sheep.

Role of nitric oxide in mast cells: controversies, current knowledge, and future applications

Mast cells (MC) are important effector cells in allergic disorders. Recently, the role of MC in innate and adaptive immunity is gaining prominence. Nitric oxide is an important signaling molecule and its production in mast cell has been reported widely. However, controversy exists about whether MC produce NO. This review addresses the role of NO in MC biology and the reasons behind the controversy and discusses effects of NO in regulation of MC phenotype and function.

Effects of cigarette smoke on degranulation and NO production by mast cells and epithelial cells

Exhaled nitric oxide (eNO) is decreased by cigarette smoking. The hypothesis that oxides of nitrogen (NO_X) in cigarette smoke solution (CSS) may exert a negative feedback mechanism upon NO release from epithelial (AEC, A549, and NHTBE) and basophilic cells (RBL-2H3) was tested in vitro. CSS inhibited both NO production and degranulation (measured as release of beta-hexosaminidase) in a dose-dependent manner from RBL-2H3 cells. Inhibition of NO production by CSS in AEC, A549, and NHTBE cells was also dose-dependent. In addition, CSS decreased expression of NOS mRNA and protein expression. The addition of NO inhibitors and scavengers did not, however, reverse the effects of CSS, nor did a NO donor (SNP) or nicotine mimic CSS. N-acetyl-cysteine, partially reversed the inhibition of beta-hexosaminidase release suggesting CSS may act via oxidative free radicals. Thus, some of the inhibitory effects of CSS appear to be via oxidative free radicals rather than a NO_X -related negative feedback.

Bronchoconstriction and endogenous nitric oxide in isolated lungs of spontaneously hypertensive rats

Bronchoconstrictor responses were measured in lungs isolated from spontaneously hypertensive (SHR) and normotensive rats, perfused via the airways. Lungs from SHRs were more responsive than lungs from normotensive rats to methacholine, 5-hydroxytryptamine (5-HT), arachidonic acid or prostaglandin H(2). The responses of SHR airways to methacholine or 5-HT were unaffected by pretreatment in vivo with an inhibitor of nitric oxide (NO) synthase, N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME, 30 mg kg(-1)), although responses in normotensive airways to methacholine, but not to 5-HT, were enhanced. Antigen challenge of isolated lungs from actively sensitized rats elicited bronchoconstriction, not different between strains. Pretreatment with L-NAME increased the response to antigen challenge only in normotensive lungs. Compound 48/80 induced bronchoconstriction in lungs from either strain, equally. These responses to compound 48/80 were unaffected by L-NAME pretreatment. Thus, SHR airways lack relaxing factors and degranulation of mast cells in SHR lungs was not affected by endogenous NO.

Expression, localization, and regulation of NOS in human mast cell lines: effects on leukotriene production

Nitric oxide (NO) is a potent radical produced by nitric oxide synthase (NOS) and has pleiotrophic activities in health and disease. As mast cells (MCs) play a central role in both homeostasis and pathology, we investigated NOS expression and NO production in human MC populations. Endothelial NOS (eNOS) was ubiquitously expressed in both human MC lines and skin-derived MCs, while neuronal NOS (nNOS) was variably expressed in the MC populations studied. The inducible (iNOS) isoform was not detected in human MCs. Both growth factor-independent (HMC-1) and -dependent (LAD 2) MC lines showed predominant nuclear eNOS protein localization, with weaker cytoplasmic expression. nNOS showed exclusive cytoplasmic localization in HMC-1. Activation with Ca(2+) ionophore (A23187) or IgE-anti-IgE induced eNOS phosphorylation and translocation to the nucleus and nuclear and cytoplasmic NO formation. eNOS colocalizes with the leukotriene (LT)-initiating enzyme 5-lipoxygenase (5-LO) in the MC nucleus. The NO donor, S-nitrosoglutathione (SNOG), inhibited, whereas the NOS inhibitor, N(G)-nitro-l-arginine methyl ester (L-NAME), potentiated LT release in a dose-dependent manner. Thus, human MC lines produce NO in both cytoplasmic and nuclear compartments, and endogenously produced NO can regulate LT production by MCs.

Nicorandil inhibits the release of TNFα from a lymphocyte cell line and peripheral blood lymphocytes

Modulation of cytokine release may be of interest in modulating inflammatory diseases. This study determined whether nicorandil, a potassium channel opener, and nitric oxide (NO) donor could inhibit the release of tumour necrosis factor alpha (TNFalpha) from lymphocytes. Nicorandil significantly and dose-dependently inhibited the TNFalpha release from a human Epstein Barr virus-transformed B lymphocyte cell line (EBV-B) and peripheral blood B and T lymphocytes. The inhibition was reversed by the addition of both potassium channel inhibitor glibenclamide and the guanylyl cyclase inhibitor 1H-(1,2,4) oxadiazolo (4,3) quinoxalin-1-one (ODQ). Other potassium channel openers, pinacidil, or the nicorandil analogue SG-209, however, failed to demonstrate inhibition of TNFalpha release. The NO scavenger haemoglobin was unable to reverse the nicorandil-induced TNFalpha inhibition, but in contrast to this, sodium nitroprusside (SNP) partially inhibited the release, which was reversed by haemoglobin. Nicorandil is able to inhibit TNFalpha release from lymphocytes, which requires the dual modes of both potassium channel opening and the nitrate moiety. Moreover, NO donation mechanism appears to be more dominant in the nicorandil inhibitory activity in lymphocytes.The dual mechanism involved in the inhibition of this cytokines may represent a novel therapeutical approach in the modulation of inflammatory disease.

Protective effect of dietary nitrate on experimental gastritis in rats

Nitrates have long been considered as harmful dietary components and judged responsible for deleterious effects on human health, leading to stringent regulations concerning their levels in food and water. However, recent studies demonstrate that dietary nitrate may have a major role in human health as a non-immune mechanism for host defence, through its metabolism to NO in the stomach. NO is a versatile molecule and although evidence exists showing that administration of low doses of exogenous NO protects against gastrointestinal inflammation, higher NO doses have been shown to exacerbate injury. So, the effect of an ingestion of nitrates in doses corresponding to a normal diet in human consumers on an experimental gastritis induced by iodoacetamide in rats was investigated. During gastritis one of the following compounds was given orally: water; KNO3; the NO donor sodium nitroprusside; the NO scavenger haemoglobin given with either water or KNO3. N(G)-nitro-l-arginine methyl ester (l-NAME), a non-specific NO synthase inhibitor, was administered with either water, iodoacetamide alone, or combined with KNO3. After killing, the stomach was resected and microscopic damage scores, myeloperoxidase and NO synthase activities were determined. Iodoacetamide-induced gastritis was significantly reduced by KNO3 administration, an effect which was reproduced by sodium nitroprusside and reversed by haemoglobin. l-NAME induced gastric mucosal damage in itself, and KNO3 did not prevent the gastritis induced by iodoacetamide associated with l-NAME. In conclusion, dietary nitrate exerts a protective effect against an experimental gastritis in rats by releasing NO in the stomach but such an effect requires the production of endogenous NO.

Carbon monoxide modulates the response of human basophils to FcepsilonRI stimulation through the heme oxygenase pathway

We report the effects of exogenous and endogenous carbon monoxide (CO) on the immunological activation of human basophils. Hemin (1-100 microM), a heme oxygenase substrate analogue, significantly increased the formation of bilirubin from partially purified human basophils, thus indicating that these cells express heme oxygenase. This effect was reversed by preincubating the cells for 30 min with Zn-protoporphyrin IX (100 microM), a heme oxygenase inhibitor. Hemin (100 microM) also decreased immunoglobulin G anti-Fcepsilon (anti-IgE)-induced activation of basophils, measured by the expression of a membrane granule-associated protein, identified as cluster differentiation protein 63 (CD63), and by histamine release. These effects were reversed by Zn-protoporphyrin IX (100 microM), by oxyhemoglobin (HbO(2)), a CO scavenger (100 microM), and by 1H-[1,2,4]oxadiazolo[4,3-a] quinoxalin-1-one (ODQ), an inhibitor of the soluble guanylyl cyclase (100 microM). Exposure of basophils to exogenous CO (10 microM for 30 min) also decreased their activation, while nitrogen (N(2)) was ineffective. HbO(2) and ODQ reversed the inhibition, reversing both membrane protein CD63 expression and histamine release to basal values. Both hemin and exogenous CO significantly raised cGMP levels in basophils and blunted the rise of calcium levels caused by immunological activation. This study suggests that CO increases cGMP formation, which in turn induces a fall in intracellular Ca(2+) concentration, thereby resulting in the inhibition of human basophil activation.

Nitric oxide: a regulator of mast cell activation and mast cell-mediated inflammation

Nitric oxide (NO) plays diverse roles in physiological and pathological processes. During immune and inflammatory responses, for example in asthma, NO is generated at relatively high and sustained levels by the inducible form of nitric oxide synthase (NOS-2). NOS-2 derived NO regulates the function, growth, death and survival of many immune and inflammatory cell types. In the case of mast cells, NO suppresses antigen-induced degranulation, mediator release, and cytokine expression. The action of NO on mast cells is time dependent, requiring several hours, and noncGMP mediated, most probably involving chemical modification of proteins. NO inhibits a number of mast cell-dependent inflammatory processes in vivo, including histamine mediated vasodilatation, vasopermeation and leucocyte-endothelial cell attachment. In human asthma and animal models of lung inflammation the role of NO is harder to define. However, although there are conflicting data, the balance of evidence favours a predominantly protective role for NO. Mimicking or targeting NO dependent pathways may prove to be a valuable therapeutic approach to mast cell mediated diseases.

Regulation of CD8 expression in mast cells by exogenous or endogenous nitric oxide

We recently reported a novel CD8 molecule on rat alveolar macrophages and peritoneal mast cells (PMC). However, little is known about the regulation of CD8 expression and function on these cells. We investigated the regulation of CD8 expression on PMC by NO, because NO can regulate inflammatory responses and also because anti-CD8 Ab stimulates inducible NO synthase and NO production by PMC and alveolar macrophages. Ligation of CD8alpha on PMC with Ab (OX8) induced CD8alpha mRNA expression after 3-6 h, and flow cytometry demonstrated that OX8 treatment increased CD8alpha protein expression compared with PMC treated with isotype control IgG1. To test whether NO mediates the up-regulation of CD8alpha, we used the NO donor S-nitrosoglutathione (500 microM) and NO synthase inhibitors (N(G)-monomethyl-L-arginine and N(G)-nitro-L-arginine methyl ester; 100 microM). S-nitrosoglutathione up-regulated both mRNA and protein expression of CD8alpha in PMC compared with that in sham-treated cells, while NO synthase inhibitors down-regulated OX8 Ab-induced CD8alpha expression. To investigate how NO regulates CD8 expression on PMC, we examined the cGMP-dependent pathway using 8-bromo-cGMP (2 mM) and the guanylate cyclase inhibitor, 1H-oxadiazoloquinoxalin-1-one (20 microM). 8-Bromo-cGMP up-regulated CD8 expression, whereas 1H-oxadiazoloquinoxalin-1-one down-regulated its expression. Thus, ligation of CD8 up-regulates CD8 expression on PMC, a response mediated at least in part by NO through a cGMP-dependent pathway. The significance of this up-regulation of CD8alpha on mast cells (MC) is unclear, but since ligation of CD8 on MC with OX8 Ab can alter gene expression and mediator secretion, up-regulation of CD8 may enhance the MC response to natural ligation of this novel form of CD8.

Role of nitric oxide in histamine release from human basophils and rat peritoneal mast cells

The effects of a range of nitric oxide (NO)-related compounds on histamine release from human basophils and rat peritoneal mast cells were studied. Basal and immunologic histamine releases from human basophils were not affected by N(omega)-nitro-L-arginine, N(omega)-nitro-L-arginine methyl ester, aminoguanidine or methylene blue (all inhibitors of NO production), sodium nitroprusside (an NO donor), L-arginine (a substrate for NO synthase) or D-arginine (the inactive enantiomer of L-arginine). In rat peritoneal mast cells, NO donors such as sodium nitroprusside, sodium nitrite and sodium nitrate, and lipopolysaccharide (an inducer of NO synthase) had little effect on basal histamine release, while 3-morpholino-sydnonimine (SIN-1, an NO donor), L-arginine and D-arginine increased this release by up to threefold. None of the inhibitors of NO production had any striking effect on histamine release induced by anti-rat immunoglobulin E (IgE), compound 48/80, sodium fluoride, phospholipase C, 1,2-dioctanoyl-sn-glycerol or ionophore A23187. However, haemoglobin was found to inhibit histamine release by anti-rat IgE or A23187 by ca. 40%. Alone of the NO donors, low concentrations of L-arginine produced a mild inhibition of histamine release induced by anti-IgE, compound 48/80 and A23187, but not other ligands, while sodium nitroprusside dose-dependently inhibited (by a maximum of ca. 30%) histamine release by anti-rat IgE, sodium fluoride or A23187. Stimulation with a variety of secretagogues or treatment with L-arginine, D-arginine, lipopolysaccharide, SIN-1 or sodium nitroprusside had no effect on NO production. Similarly, L-arginine, D-arginine or sodium nitroprusside did not change intracellular cGMP levels. On the basis of these results, it is suggested that NO does not play a significant role in the modulation of histamine release from human basophils or rat peritoneal mast cells. The effects of L-arginine, D-arginine and sodium nitroprusside may involve mechanisms unrelated to NO.

Mast cells and nitric oxide: control of production, mechanisms of response

Mast cells are involved in numerous activities ranging from control of the vasculature, to tissue injury and repair, allergic inflammation and host defences. They synthesize and secrete a variety of mediators, activating and modulating the functions of nearby cells and initiating complex physiological changes. Interestingly, NO produced by mast cells and/or other cells in the microenvironment appears to regulate these diverse roles. This review outlines some of the pathways central to the production of NO by mast cells and identifies many of the tightly controlled regulatory mechanisms involved. Several cofactors and regulatory elements are involved in NO production, and these act at transcriptional and post-translational sites. Their involvement in NO production will be outlined and the possibility that these pathways are critically important in mast cell functions will be discussed. The effects of NO on mast cell functions such as adhesion, activation and mediator secretion will be examined with a focus on molecular mechanisms by which NO modifies intracellular signalling pathways dependent or independent of cGMP and soluble guanylate cyclase. The possibility that NO regulates mast cell function through effects on selected ion channels will be discussed. Metabolic products of NO including peroxynitrite and other reactive species may be the critical elements that affect the actions of NO on mast cell functions. Further understanding of the actions of NO on mast cell activities may uncover novel strategies to modulate inflammatory conditions.

Mast cells as a source and target for nitric oxide

Mast cells (MC), which are tissue-resident cells found widely distributed in the body, are derived from primitive hematopoietic cells. MC produce a variety of biologically active substances such as histamine, proteases, lipid derivatives and numerous cytokines and chemokines in response to immunologic or non-immunologic stimuli. Of interest, it has been reported that rodent MC can also be a source of nitric oxide (NO) derivatives, that they synthesize spontaneously, or only after activation, depending on their subtype. This synthesis appears to be under the control of the expression of the inducible isoform of the nitric oxide synthase (iNOS) and of the constitutive neuronal NOS (nNOS). MC might thus be able to influence the survival and functions of other types of NO-sensitive cells in close vicinity. Apart from being a source of NO, MC can also be the target for NO and its derivatives. Indeed, survival and reactivity of rodent MC is influenced by NO derivatives produced by MC themselves or by other cellular elements in close contact with the MC in tissues. By contrast, the existence of such mechanisms of cross-talk between MC and NO remains poorly documented in humans. If evidence are supplied in favor of such relationship, pharmacological modulation by agents acting at the level of the NO pathway might be of interest in order to regulate the functions of MC in immunologic, neoplastic, inflammatory and other conditions.

Involvement of nitric oxide in pollen-induced biphasic nasal blockage in sensitised guinea pigs

We have developed a reproducible allergic rhinitis model showing biphasic nasal blockage on repetitive inhalation challenge with Japanese cedar pollen in sensitised guinea pigs. The role of nitric oxide (NO) in inducing nasal blockage was evaluated with this model. N(omega)-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase (NOS) inhibitor, intravenously administered before the challenge, significantly inhibited both early and late nasal blockage by approximately 80% and 50%, respectively. When L-NAME treatment was performed after the challenge, the late response was inhibited by approximately 70%. This inhibition was completely reversed by co-administration of L-arginine. However, aminoguanidine and L-N(6)-(1-iminoethyl)lysine, selective inhibitors of inducible NOS, negligibly influenced the degree of nasal blockage. Meanwhile, the alpha-adrenergic agonist, naphazoline, strongly suppressed both early and late nasal blockage. These results indicate that NO, likely produced by constitutive rather than inducible NOS, plays a major role in the occurrence of biphasic nasal blockage, primarily by inducing vasodilatation.

Course of Brugia malayi infection in C57BL/6J NOS2 +/+ and -/- mice

Previous results from our laboratory using pharmacological approaches suggested a role for nitric oxide (NO) in the host defense against the human filarial parasite, Brugia malayi. We sought to determine whether a complementary genetic approach, using mice homozygous for a targeted mutation in the gene encoding inducible nitric oxide-synthase (NOS2), would confirm our observation. We hypothesized that such mice would exhibit some deficit in their ability to clear B. malayi. Our data show that the course of infection in NOS2-/- mice is the same as in wild-type mice. Thus, peritoneal cellular responses to infection are similar in NOS2-/- and wild-type mice, with the exception that T cells form a higher percentage of total peritoneal cells in the former. We find virtually no serum IgE in NOS2-/- mice, suggesting a less robust Th2 response. In contrast, NOS2-/- mice demonstrate an early rise in IgG2a titers compared to B6 +/+ mice. Our data suggest that NO is not an obligate requirement for the elimination of B. malayi from the peritoneal cavities of mice.

The multipotential pseudoantigenicity of X-ray contrast media. Pseudoantigen excess may downregulate the release of hypotensive mediators

BACKGROUND

X-ray contrast media (CM) toxicity resembles IgE-antigen-based anaphylaxis, and CM-related histamine release has been demonstrated in vitro and in vivo. While nobody has succeeded in producing antibodies against injections of neat CM, the ability of CM to compete with a series of antigens against their respective antibodies has recently been demonstrated. However, there is a paradox, since the CM with the strongest antibody binding are nevertheless the least likely to provoke antigen-antibody-related mast cell/basophil release.

METHODS

Two strains of rats were subjected to (a) passive cutaneous anaphylaxis (PCA) studies in the presence of various concentrations of CM, (b) blood pressure (BP) tracings following bolus administrations of various prototypical CM and (c) BP tracings in ovalbumin (OVA)-sensitized rats, challenged with OVA plus CM, vs. OVA plus CM-equivalent saline.

RESULTS

In the PCA studies, and the OVA challenge studies, the CM appear to act in an antigen excess mode, limiting the potential of the OVA to elicit anaphylactic changes, as demonstrated by permeability studies or by BP levels. The bolus CM studies demonstrate that the more potent CM 'antigens' actually produce an increase in BP and the less potent CM 'antigens', a drop in BP. These changes can be related to the CM acting in an 'antigen' excess mode vs. an 'antigen' equivalent mode.

CONCLUSIONS

The CM have the potential to act in an 'antigen' excess or 'antigen'-equivalent mode. The potential to express an 'antigen'-excess mode in vivo, may be unique to CM because of the high concentrations injected.

Allergy and the gut

There have frequently been doubts as to the relevance of food allergy, in particular as far as the involvement of the intestinal tract is concerned. Several studies, however, have confirmed the existence of allergic reactions in the gut, with an estimated prevalence of about 1-2% in adults. Clinical symptoms are unspecific and include nausea, vomiting, abdominal pain, cramping and diarrhea. Intestinal mast cells, as well as intestinal eosinophils, have been shown to be involved in the pathogenesis of food-allergy-related enteropathy. In addition to classical IgE-dependent degranulation, further agonists have been demonstrated for mast cell activation, for example IL-4. The methods used to confirm the diagnosis of intestinal allergy are still insufficient. Until now, blinded oral challenge procedures with food antigens have been accepted as the 'gold standard' in diagnosing food allergy, although these tests have practical problems. Therefore, new test systems have been developed, such as endoscopic provocation tests, that may improve diagnostic procedures. Elimination diet still presents the main basis of therapy. Aspects to be focused on in the future are the role fo IgE-independent allergic mechanisms in intestinal allergy, the impact of cross-reactivity with other allergens and the relationship to other inflammatory bowel diseases such as Crohn's disease, ulcerative colitis, celiac disease and irritable bowel syndrome.

Presentation of IFN-gamma to nitric oxide-producing cells: a novel function for mast cells

We report that mast cells can bind and present IFN-gamma in a functionally active form to macrophages. Flow-cytometric analysis revealed that biotinylated IFN-gamma bound equally well to purified peritoneal mast cells from both IFN-gammaR knockout and wild-type mice, indicating a non-IFN-gammaR binding site. Purified peritoneal mast cells, loaded with IFN-gamma for 30 min and washed, were able to induce NO synthesis by peritoneal macrophages. This response required cell contact and expression of IFN-gammaR on the responding macrophages, but not the mast cells. Human HMC-1 mast cells were also able to present IFN-gamma to mouse macrophages. Enzyme treatment of mouse mast cells revealed that binding of IFN-gamma was predominantly to chondroitin sulfate B (dermatan sulfate). Binding of IFN-gamma to dermatan sulfate was confirmed by inhibition ELISA. This study demonstrates for the first time that mast cells can present IFN-gamma to other cells via glycosaminoglycans. Mast cells may act as a reservoir of surface-stored functionally active cytokines.