Sensitivity to intravenous injections of histamine and serotonin in inbred mouse strains

Intrinsic endothelial hyperresponsiveness to inflammatory mediators drives acute episodes in models of Clarkson disease

Clarkson disease, or monoclonal gammopathy-associated idiopathic systemic capillary leak syndrome (ISCLS), is a rare, relapsing-remitting disorder featuring the abrupt extravasation of fluids and proteins into peripheral tissues, which in turn leads to hypotensive shock, severe hemoconcentration, and hypoalbuminemia. The specific leakage factor(s) and pathways in ISCLS are unknown, and there is no effective treatment for acute flares. Here, we characterize an autonomous vascular endothelial defect in ISCLS that was recapitulated in patient-derived endothelial cells (ECs) in culture and in a mouse model of disease. ISCLS-derived ECs were functionally hyperresponsive to permeability-inducing factors like VEGF and histamine, in part due to increased endothelial nitric oxide synthase (eNOS) activity. eNOS blockade by administration of N(γ)-nitro-l-arginine methyl ester (l-NAME) ameliorated vascular leakage in an SJL/J mouse model of ISCLS induced by histamine or VEGF challenge. eNOS mislocalization and decreased protein phosphatase 2A (PP2A) expression may contribute to eNOS hyperactivation in ISCLS-derived ECs. Our findings provide mechanistic insights into microvascular barrier dysfunction in ISCLS and highlight a potential therapeutic approach.

Network-Based Functional Prediction Augments Genetic Association To Predict Candidate Genes for Histamine Hypersensitivity in Mice

Genetic mapping is a primary tool of genetics in model organisms; however, many quantitative trait loci (QTL) contain tens or hundreds of positional candidate genes. Prioritizing these genes for validation is often ad hoc and biased by previous findings. Here we present a technique for prioritizing positional candidates based on computationally inferred gene function. Our method uses machine learning with functional genomic networks, whose links encode functional associations among genes, to identify network-based signatures of functional association to a trait of interest. We demonstrate the method by functionally ranking positional candidates in a large locus on mouse Chr 6 (45.9 Mb to 127.8 Mb) associated with histamine hypersensitivity (Histh). Histh is characterized by systemic vascular leakage and edema in response to histamine challenge, which can lead to multiple organ failure and death. Although Histh risk is strongly influenced by genetics, little is known about its underlying molecular or genetic causes, due to genetic and physiological complexity of the trait. To dissect this complexity, we ranked genes in the Histh locus by predicting functional association with multiple Histh-related processes. We integrated these predictions with new single nucleotide polymorphism (SNP) association data derived from a survey of 23 inbred mouse strains and congenic mapping data. The top-ranked genes included Cxcl12, Ret, Cacna1c, and Cntn3, all of which had strong functional associations and were proximal to SNPs segregating with Histh. These results demonstrate the power of network-based computational methods to nominate highly plausible quantitative trait genes even in challenging cases involving large QTL and extreme trait complexity.

IgE antibodies, FcεRIα, and IgE-mediated local anaphylaxis can limit snake venom toxicity

BACKGROUND

Type 2 cytokine-related immune responses associated with development of antigen-specific IgE antibodies can contribute to pathology in patients with allergic diseases and to fatal anaphylaxis. However, recent findings in mice indicate that IgE also can enhance defense against honeybee venom.

OBJECTIVE

We tested whether IgE antibodies, IgE-dependent effector mechanisms, and a local anaphylactic reaction to an unrelated antigen can enhance defense against Russell viper venom (RVV) and determined whether such responses can be influenced by immunization protocol or mouse strain.

METHODS

We compared the resistance of RVV-immunized wild-type, IgE-deficient, and Fcer1a-deficient mice after injection of a potentially lethal dose of RVV.

RESULTS

A single prior exposure to RVV enhanced the ability of wild-type mice, but not mice lacking IgE or functional FcεRI, to survive challenge with a potentially lethal amount of RVV. Moreover, IgE-dependent local passive cutaneous anaphylaxis in response to challenge with an antigen not naturally present in RVV significantly enhanced resistance to the venom. Finally, we observed different effects on resistance to RVV or honeybee venom in BALB/c versus C57BL/6 mice that had received a second exposure to that venom before challenge with a high dose of that venom.

CONCLUSION

These observations illustrate the potential benefit of IgE-dependent effector mechanisms in acquired host defense against venoms. The extent to which type 2 immune responses against venoms can decrease pathology associated with envenomation seems to be influenced by the type of venom, the frequency of venom exposure, and the genetic background of the host.

The immunology of food allergy

Food allergies represent an increasingly prevalent human health problem, and therapeutic options remain limited, with avoidance being mainstay, despite its adverse effects on quality of life. A better understanding of the key immunological mechanisms involved in such responses likely will be vital for development of new therapies. This review outlines the current understanding of how the immune system is thought to contribute to prevention or development of food allergies. Drawing from animal studies, as well as clinical data when available, the importance of oral tolerance in sustaining immunological nonresponsiveness to food Ags, our current understanding of why oral tolerance may fail and sensitization may occur, and the knowledge of pathways that may lead to anaphylaxis and food allergy-associated responses are addressed.

Regulatory CD4+Foxp3+ T cells control the severity of anaphylaxis

OBJECTIVE

Anaphylaxis is a life-threatening outcome of immediate-type hypersensitivity to allergen, consecutive to mast cell degranulation by allergen-specific IgE. Regulatory T cells (Treg) can control allergic sensitization and mast cell degranulation, yet their clinical benefit on anaphylactic symptoms is poorly documented. Here we investigated whether Treg action during the effector arm of the allergic response alleviates anaphylaxis.

METHODS

We used a validated model of IgE-mediated passive systemic anaphylaxis, induced by intravenous challenge with DNP-HSA in mice passively sensitized with DNP-specific IgE. Anaphylaxis was monitored by the drop in body temperature as well as plasma histamine and serum mMCP1 levels. The role of Treg was analyzed using MHC class II-deficient (Aβ(°/°)) mice, treatment with anti-CD25 or anti-CD4 mAbs and conditional ablation of Foxp3(+) Treg in DEREG mice. Therapeutic efficacy of Treg was also evaluated by transfer experiments using FoxP3-eGFP knock-in mice.

RESULTS

Anaphylaxis did not occur in mast cell-deficient W/W(v) mutant mice and was only moderate and transient in mice deficient for histamine receptor-1. Defects in constitutive Treg, either genetic or induced by antibody or toxin treatment resulted in a more severe and/or sustained hypothermia, associated with a rise in serum mMCP1, but not histamine. Adoptive transfer of Foxp3(+) Treg from either naïve or DNP-sensitized donors similarly alleviated body temperature loss in Treg-deficient DEREG mice.

CONCLUSION

Constitutive Foxp3(+) Treg can control the symptomatic phase of mast cell and IgE-dependent anaphylaxis in mice. This might open up new therapeutic avenues using constitutive rather than Ag-specific Treg for inducing tolerance in allergic patients.

Mast cells are required for experimental oral allergen-induced diarrhea

Gastrointestinal allergic disorders represent a diverse spectrum of inflammatory diseases that are occurring with increasing incidence and severity. An essential question concerning these disorders is to determine the specific cells and mediators responsible for specific clinical manifestations. With this in mind, we developed a murine model of oral allergen-induced intestinal inflammation accompanied by strong Th2-associated humoral and cellular responses and focused on the immunopathogenesis of allergic diarrhea. Exposure of OVA/alum-sensitized mice to repeated doses of intragastric OVA induced genetically restricted, dose-dependent, acute diarrhea associated with increased intestinal permeability, eosinophilia, and mastocytosis. Mice developed limited systemic manifestations of anaphylaxis, even though they developed marked intestinal mucosal mast cell degranulation. Notably, experiments involving mast cell depletion (with anti-c-kit mAb), anti-IgE treatment, and Fc epsilon RI-deficient mice indicated a critical effector role for mast cells in mediating allergic diarrhea. Furthermore, allergic diarrhea was dependent upon synergistic signaling induced by serotonin and platelet-activating factor (PAF), but not histamine. These results demonstrate that oral allergen-induced diarrhea associated with experimental Th2 intestinal inflammation is largely mast cell, IgE, serotonin, and PAF dependent.

Ethanol-induced colitis prevents oral tolerance induction in mice

The gut mucosa is a major site of contact with antigens from food and microbiota. Usually, these daily contacts with natural antigens do not result in inflammatory reactions; instead they result in a state of systemic hyporesponsiveness named oral tolerance. Inflammatory bowel diseases (IBD) are associated with the breakdown of the immunoregulatory mechanisms that maintain oral tolerance. Several animal models of IBD/colitis are available. In mice, these include targeted disruptions of the genes encoding cytokines, T cell subsets or signaling proteins. Colitis can also be induced by intrarectal administration of chemical substances such as 2,4,6-trinitrobenzene sulfonic acid in 50% ethanol. We report here a novel model of colitis induced by intrarectal administration of 50% ethanol alone. Ethanol-treated mice develop an inflammatory reaction in the colon characterized by an intense inflammatory infiltrate in the mucosa and submucosa of the large intestine. They also present up-regulation of both interferon gamma (IFN-gamma) and interleukin-4 (IL-4) production by cecal lymph node and splenic cells. These results suggest a mixed type of inflammation as the substrate of the colitis. Interestingly, cells from mesenteric lymph nodes of ethanol-treated mice present an increase in IFN-gamma production and a decrease in IL-4 production indicating that the cytokine balance is altered throughout the gut mucosa. Moreover, induction of oral tolerance to ovalbumin is abolished in these animals, strongly suggesting that ethanol-induced colitis interferes with immunoregulatory mechanisms in the intestinal mucosa. This novel model of colitis resembles human IBD. It is easy to reproduce and may help us to understand the mechanisms involved in IBD pathogenesis.

Pathways of anaphylaxis in the mouse

BACKGROUND

Although anaphylaxis is classically mediated by IgE, FcepsilonRI, mast cells, and histamine, several rodent studies suggest that an alternative pathway involving IgG, FcgammaRIII, macrophages and platelets, and platelet-activating factor (PAF) may be more important in the anaphylactic response to antigen challenge.

OBJECTIVES

We sought to determine the relative roles of the classical and alternative pathways of anaphylaxis in a mouse model characterized by mastocytosis and a high level of antigen-specific IgE antibody.

METHODS

Wild-type, IgE-deficient, FcepsilonRI-deficient, and mast cell-deficient mice were immunized with goat anti-mouse IgD antibody, which induces mastocytosis and a large IgE and IgG anti-goat IgG response, and then challenged 14 days later with antigen (goat IgG) or rat anti-mouse IgE mAb. Specific vasoactive mediators, cell types, Ig isotypes, or Ig receptors were blocked or eliminated before challenge in some experiments. The severity of anaphylaxis was gauged by changes in body temperature, physical activity, and mortality.

RESULTS

Equal doses of antigen or anti-IgE mAb induced similar anaphylactic responses. Anti-IgE mAb-induced anaphylaxis was FcepsilonRI and mast cell dependent and mediated predominantly by histamine. In contrast, neither mast cells nor platelets appeared important for antigen-induced anaphylaxis, which was FcgammaRIII and macrophage dependent and mediated predominantly by PAF.

CONCLUSIONS

Antigen-induced anaphylaxis in the mouse proceeds primarily through the IgG, FcgammaRIII, macrophage, and PAF pathway, even in an experimental model that is characterized by strong mast cell and IgE responses. The presence of FcgammaRIII on human macrophages makes it possible that the IgG, FcgammaRIII, macrophage, and PAF pathway also contributes to human anaphylaxis.

Divalent hapten-induced intestinal anaphylaxis in the mouse enhances macromolecular uptake from the stomach

The capacity of the stomach to participate in anaphylaxis induced by the hapten N,N'-di-2,4,dinitrophenyllysine (di-DNP-lysine) was examined in BDF1 female mice immunized with dinitrophenylated Ascaris suum extract. Immunized animals underwent laparotomy and nontraumatic pyloric occlusion using a microvascular clamp. Following wound closure, animals were gavage-fed ovalbumin together with di-DNP-lysine. Other mice were subjected to systemic anaphylaxis by intravenous injection of di-DNP-lysine administered 1 min after gavage feeding of ovalbumin. The intravenous and intragastric administration of di-DNP-lysine led to a sixfold or greater increase in serum immunoreactive ovalbumin. Examination of 1-micron sections of gastric tissue from DNP-Asc-immunized and unimmunized mice showed an intact mucosal and submucosal architecture. A 75% increase in the number of mast cells below the muscularis mucosa was seen in immunized compared with unimmunized BDF1 mice. Gastric tissue sections from immunized mice challenged orally or intravenously with di-DNP-lysine showed compaction of erythrocytes in blood vessels, degranulation of mast cells, degenerative changes in the gastric epithelium, expulsion of mucus from gastric glands, and edema in the lamina propria. The present model may be useful for further defining the consequences of anaphylaxis on the development of immune responses to dietary antigens.