Intestinal mast cell–derived leukotrienes mediate the anaphylactic response to ingested antigens
INTRODUCTION
Food allergies are a growing medical problem in the industrialized world. In the most extreme cases, allergic reactions manifest as anaphylaxis, a life-threatening state of bronchoconstriction and hemodynamic collapse, which occurs when food antigens enter the bloodstream and activate immunoglobulin E (IgE)–primed mast cells throughout the body. This view has led to diverse models studying anaphylaxis through intravenous administration of food antigens; however, this perspective minimizes the importance of local exposure to food antigens in mucosal tissues in the gut.
RATIONALE
Mouse models of food allergy utilize repeated gastrointestinal administration of allergen, which increases anaphylactic responses to ingestion over time. This hypersensitive state is associated with an increase in the number of mucosal mast cells in the small intestine, and studies utilizing mice deficient in intestinal mast cell expansion suggest that this population is critical for food-induced anaphylaxis to occur. We used bulk and single-cell RNA sequencing, in vitro culture models, and flow cytometry to analyze intestinal mast cell biology and to identify factors governing oral anaphylaxis susceptibility and severity.
RESULTS
Intestinal mast cells expanded during experimental food allergy in a manner that required IgE-mediated stimulation of Fcε receptor 1 (FcεR1). These mast cells were largely found within the epithelium of the intestine. Intestinal mast cells localized to the epithelium were distinct from the connective tissue mast cells found throughout the body, as well as those found within the lamina propria of the intestine, because they expressed different integrins, had a reduced histamine synthetic capacity, and enhanced cysteinyl leukotriene production. Treatment of bone marrow–derived mast cells with transforming growth factor–β (TGFβ) in vitro induced changes to cell-surface markers and inflammatory mediators that were similar to those observed in mast cells isolated from the intestinal epithelium. Blocking αvβ6 integrin, which can liberate TGFβ, changed the expression of the integrins expressed by the epithelial mast cells in vivo.
We interrogated the role for cysteinyl leukotrienes in our food allergy model using mice that lacked expression of enzymes involved in leukotriene synthesis or where leukotriene receptors had been knocked out. The knockout mice were compared with wild-type controls after both groups had been administered allergen intragastrically or through intravenous injection. Mice deficient in arachidonate 5-lipoxygenase (aLOX5) or leukotriene C4 synthase (LTC4S) were protected from anaphylaxis resulting from intragastric challenge, whereas that induced by intravenous injection was unaltered. Genetic deficiency of cysteinyl leukotriene receptor 1 (CysLTR1) or CysLTR2 individually reduced intestinal mast cell expansion and mirrored this protection. However, only acute blockade of aLOX5, but not of CysLTR1 or CysLTR2, ameliorated responses to intragastric challenge without affecting local mast cell expansion.
CONCLUSION
Cysteinyl leukotrienes were required for anaphylaxis after gastrointestinal exposure to allergens, but not to systemic allergens. We propose that cysteinyl leukotrienes have dual functions in food allergy in mice by promoting mucosal mast cell expansion and by stimulating acute sensitization to oral anaphylaxis through signaling to epithelial cells, neurons, and group 2 innate lymphoid cells (ILC2s). Other conditions capable of driving leukotriene excess in the intestines or ILC2 activation may act as cofactors toward the development of severe anaphylactic responses to foods. Thus, local intestinal responses may be acutely targetable as a therapeutic strategy to prevent anaphylaxis in severely food-allergic individuals.
EDITOR’S SUMMARY
Cysteinyl leukotrienes (CysLTs) are inflammatory mediators implicated in allergic responses, particularly asthma. Two studies examined the role of CysLTs in the development of anaphylaxis in response to ingested food allergens in mice. Hoyt et al. found that CysLTs promoted the transport of intact food allergens from the gut lumen into the tissue. Mice that did not experience anaphylaxis had variants of DPEP1, an enzyme that metabolizes CysLTs, linked to augmented enzymatic activity. Batchel et al. found that when cells from the hematopoietic compartment could not synthesize CysLTs, mice had attenuated responses to ingested allergens. Mast cells within the intestinal epithelium could synthesize and respond to CysLTs. In both studies, blocking the synthesis of CysLTs using the drug zileuton before or concurrent with food-allergen exposure prevented the symptoms associated with anaphylaxis in mice.
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Nathaniel D Bachtel; Jaime L Cullen; Min Liu; Steven A Erickson; Vassily I Kutyavin; Darine W El-Naccache; Esther B Florsheim; Jaechul Lim; Zuri A Sullivan; Raiden Imaeda; Andrew Hudak; Cuiling Zhang; Ruslan Medzhitov
INTRODUCTION
Food allergies are a growing medical problem in the industrialized world. In the most extreme cases, allergic reactions manifest as anaphylaxis, a life-threatening state of bronchoconstriction and hemodynamic collapse, which occurs when food antigens enter the bloodstream and activate immunoglobulin E (IgE)–primed mast cells throughout the body. This view has led to diverse models studying anaphylaxis through intravenous administration of food antigens; however, this perspective minimizes the importance of local exposure to food antigens in mucosal tissues in the gut.
RATIONALE
Mouse models of food allergy utilize repeated gastrointestinal administration of allergen, which increases anaphylactic responses to ingestion over time. This hypersensitive state is associated with an increase in the number of mucosal mast cells in the small intestine, and studies utilizing mice deficient in intestinal mast cell expansion suggest that this population is critical for food-induced anaphylaxis to occur. We used bulk and single-cell RNA sequencing, in vitro culture models, and flow cytometry to analyze intestinal mast cell biology and to identify factors governing oral anaphylaxis susceptibility and severity.
RESULTS
Intestinal mast cells expanded during experimental food allergy in a manner that required IgE-mediated stimulation of Fcε receptor 1 (FcεR1). These mast cells were largely found within the epithelium of the intestine. Intestinal mast cells localized to the epithelium were distinct from the connective tissue mast cells found throughout the body, as well as those found within the lamina propria of the intestine, because they expressed different integrins, had a reduced histamine synthetic capacity, and enhanced cysteinyl leukotriene production. Treatment of bone marrow–derived mast cells with transforming growth factor–β (TGFβ) in vitro induced changes to cell-surface markers and inflammatory mediators that were similar to those observed in mast cells isolated from the intestinal epithelium. Blocking αvβ6 integrin, which can liberate TGFβ, changed the expression of the integrins expressed by the epithelial mast cells in vivo.
We interrogated the role for cysteinyl leukotrienes in our food allergy model using mice that lacked expression of enzymes involved in leukotriene synthesis or where leukotriene receptors had been knocked out. The knockout mice were compared with wild-type controls after both groups had been administered allergen intragastrically or through intravenous injection. Mice deficient in arachidonate 5-lipoxygenase (aLOX5) or leukotriene C4 synthase (LTC4S) were protected from anaphylaxis resulting from intragastric challenge, whereas that induced by intravenous injection was unaltered. Genetic deficiency of cysteinyl leukotriene receptor 1 (CysLTR1) or CysLTR2 individually reduced intestinal mast cell expansion and mirrored this protection. However, only acute blockade of aLOX5, but not of CysLTR1 or CysLTR2, ameliorated responses to intragastric challenge without affecting local mast cell expansion.
CONCLUSION
Cysteinyl leukotrienes were required for anaphylaxis after gastrointestinal exposure to allergens, but not to systemic allergens. We propose that cysteinyl leukotrienes have dual functions in food allergy in mice by promoting mucosal mast cell expansion and by stimulating acute sensitization to oral anaphylaxis through signaling to epithelial cells, neurons, and group 2 innate lymphoid cells (ILC2s). Other conditions capable of driving leukotriene excess in the intestines or ILC2 activation may act as cofactors toward the development of severe anaphylactic responses to foods. Thus, local intestinal responses may be acutely targetable as a therapeutic strategy to prevent anaphylaxis in severely food-allergic individuals.
EDITOR’S SUMMARY
Cysteinyl leukotrienes (CysLTs) are inflammatory mediators implicated in allergic responses, particularly asthma. Two studies examined the role of CysLTs in the development of anaphylaxis in response to ingested food allergens in mice. Hoyt et al. found that CysLTs promoted the transport of intact food allergens from the gut lumen into the tissue. Mice that did not experience anaphylaxis had variants of DPEP1, an enzyme that metabolizes CysLTs, linked to augmented enzymatic activity. Batchel et al. found that when cells from the hematopoietic compartment could not synthesize CysLTs, mice had attenuated responses to ingested allergens. Mast cells within the intestinal epithelium could synthesize and respond to CysLTs. In both studies, blocking the synthesis of CysLTs using the drug zileuton before or concurrent with food-allergen exposure prevented the symptoms associated with anaphylaxis in mice.
Web | PDF | Science | Paywall