Eructations From Eosinophils

Abstract

See “A randomized double-blind placebo-controlled trial of fluticasone propionate for pediatric eosinophilic esophagitis” by Konikoff MR, Noel R, Blanchard C, Kirby C, Jameson SC, Buckmeier B, Akers R, Cohen MB, Collins MH, Assa’ad AH, Aceves SS, Putnam PE, and Rothenberg ME on page 1381 and “Eosinophilic bowel disease controlled by the BB rat-derived lymphopenia/Gimap5 gene” by Cousins L, Graham M, Tooze R, Carter C, Miller JR, Powrie FM, MacPherson GG, and Butcher GW on page 1475.The last decade brought changes in the eosinophil’s image as it transitioned from an overlooked, innocent bystander hidden within mucosal biopsies to an unmistakable, culpable marker of gastrointestinal diseases. In that light, a large body of literature associates mucosal eosinophilia with food allergies. In clinical practice, the mere presence of eosinophils in intestinal biopsies prompts an almost automatic diagnosis of food allergic enteropathy. Although this may be the case for many patients, the indiscriminant assignment of eosinophils to one disease is unfortunate; mucosal eosinophilia is associated with an increasingly broad differential diagnosis that includes infections, hypereosinophilic syndrome, inflammatory bowel disease, allergic enteropathy, collagen vascular disease, hypersensitivity reactions, peptic disease, and eosinophilic gastrointestinal diseases (EGIDs).EGIDs are a group of diseases (eosinophilic esophagitis, eosinophilic gastritis, eosinophilic gastroenteritis, eosinophilic colitis) characterized by gastrointestinal symptoms and mucosal eosinophilia.1Rothenberg M.E. Eosinophilic gastrointestinal disorders (EGID).J Allergy Clin Immunol. 2004; 113 (quiz 29): 11-28Abstract Full Text Full Text PDF PubMed Scopus (695) Google Scholar Although the etiology of these diseases is uncertain, many patients respond to nutritional management suggesting food as an inciting factor. Of these clinical subtypes, eosinophilic esophagitis (EE) is the best described; recent case reports and translational studies provide detailed analyses of this interesting group of patients characterized by chronic gastroesophageal reflux disease-like symptoms, which are unresponsive to acid blockade and esophageal biopsies that demonstrate intense epithelial eosinophilia.2Fox V.L. Nurko S. Furuta G.T. Eosinophilic esophagitis: it’s not just kid’s stuff.Gastrointest Endosc. 2002; 56: 260-270Abstract Full Text Full Text PDF PubMed Scopus (267) Google Scholar Patients with EE often are sensitive to food products and most respond to elimination or elemental diets. Those who are unresponsive or who are unable to comply with nutritional management typically improve with systemic or topical corticosteroids. Presently, the decision to treat patients with EE is often driven by the association of EE with esophageal strictures; this is guided by attempts to relieve symptoms and the incidence of long-term complications is still unknown.Limitations of our knowledge regarding eosinophil’s impact on the gut relates to the inadequate number of peripheral eosinophils for study, lack of commercially available reagents, limited animal models, and scarcity of affected human tissues. Few investigators have determined mechanisms of intestinal eosinophilia, but those who have are providing interesting results. Gut eosinophilia has been studied in animal models of infection, hapten-induced injury, allergen exposure, and genetic modeling. Allergen-induced models utilizing knock-out and transgenic mice demonstrated that interleukin (IL)-5 and eotaxin-3 play central roles in esophageal eosinophilia; eotaxin-1 is critical to eosinophilia of the stomach and small bowel.3Blanchard C. Wang N. Stringer K.F. Mishra A. Fulkerson P.C. Abonia J.P. Jameson S.C. Kirby C. Konikoff M.R. Collins M.H. Cohen M.B. Akers R. Hogan S.P. Assa’ad A.H. Putnam P.E. Aronow B.J. Rothenberg M.E. Eotaxin-3 and a uniquely conserved gene-expression profile in eosinophilic esophagitis.J Clin Invest. 2006; 116: 536-547Crossref PubMed Scopus (696) Google Scholar, 4Hogan S. Mishra A. Brandt E. Royalty M. Pope S. Zimmerman N. Foster P. Rothenberg M. A pathological function for eotaxin and eosinophils in eosinophilic gastrointestinal inflammation.Nat Immunol. 2001; 2: 353-360Crossref PubMed Scopus (275) Google Scholar, 5Mishra A. Hogan S.P. Brandt E.B. Rothenberg M.E. IL-5 promotes eosinophil trafficking to the esophagus.J Immunol. 2002; 168: 2464-2469PubMed Google Scholar The recent landmark translational study by Blanchard et al3Blanchard C. Wang N. Stringer K.F. Mishra A. Fulkerson P.C. Abonia J.P. Jameson S.C. Kirby C. Konikoff M.R. Collins M.H. Cohen M.B. Akers R. Hogan S.P. Assa’ad A.H. Putnam P.E. Aronow B.J. Rothenberg M.E. Eotaxin-3 and a uniquely conserved gene-expression profile in eosinophilic esophagitis.J Clin Invest. 2006; 116: 536-547Crossref PubMed Scopus (696) Google Scholar used a combination of microarray analysis of human esophageal tissues and murine systems to establish an EE signature panel of genes. Translational studies identified IL-5 and tumor necrosis factor-α in the affected epithelium of patients with EE.6Gupta S.K. Fitzgerald J.F. Kondratyuk T. HogenEsch H. Cytokine expression in normal and inflamed esophageal mucosa: a study into the pathogenesis of allergic eosinophilic esophagitis.J Pediatr Gastroenterol Nutr. 2006; 42: 22-26Crossref PubMed Scopus (151) Google Scholar, 7Straumann A. Kristl J. Conus S. Vassina E. Spichtin H.P. Beglinger C. Simon H.U. Cytokine expression in healthy and inflamed mucosa: probing the role of eosinophils in the digestive tract.Inflamm Bowel Dis. 2005; 11: 720-726Crossref PubMed Scopus (113) Google ScholarAlthough this emerging literature brings increased clinical awareness, no consensus diagnostic criteria for EE have yet been proposed. In fact, only recently have normal values for mucosal eosinophilia been published.8DeBrosse C.W. Case J.W. Putnam P.E. Collins M.H. Rothenberg M.E. Quantity and distribution of eosinophils in the gastrointestinal tract of children.Pediatr Dev Pathol. 2006; 9: 210-218Crossref PubMed Scopus (213) Google Scholar To address this problem, the North American Society of Pediatric Gastroenterology, Hepatology, and Nutrition organized The First International Gastrointestinal Eosinophil Research Symposium on October 17–18, 2006. Results of this symposium yielded practical clinical guidelines and a feasible research agenda in which we can begin to address important issues focusing on eosinophilia of the gut.In that light, this issue of Gastroenterology provides us with 2 exciting studies that emphasize the importance of chronic eosinophilic inflammation. In the first study, Cousins et al.9Cousins L. Graham M. Tooze R. Carter C. Miller J.R. Powrie F.M. MacPherson G.G. Butcher G.W. Eosinophilic bowel disease controlled by the BB rat-derived lymphpeina/GIMP5 gene.Gastroenterology. 2006; 131: 1475-1485Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar made the novel observation that the BioBreeding (BB) rat, characterized by lymphopenia secondary to GTPase of the immunity-associated protein family (GIMAP5) deficiency, developed progressive systemic and intestinal eosinophilia. Previously, this group and others utilized this model to investigate diabetes mellitus. In specific pathogen-free environments, animals developed significant body wasting by 20 weeks that progressed to include intestinal bloating and then death by 50 weeks. Necropsy revealed massively distended small and large bowels and histologic specimens identified intense eosinophilia of the lamina propria with preservation of villous structure. The esophagus and stomach were unaffected.Features identified here provide a novel model system to determine mechanisms of systemic and mucosal eosinophilia. Eosinophilia was dependent on the lyp gene that encodes for GIMAP5, a molecule thought to be responsible for, among other things, lymphocyte apoptosis and T-cell survival. To date, little is known about the impact of GIMAP5 on eosinophils. Other features of this model system included splenomegaly and enlargement of the mesenteric, but not peripheral, lymph nodes. A significant reduction in CD4+, CD8+, and natural killer T (NKT) cells compared with controls was observed. T- and B-cell functions were preserved and overall they carried a Th2 phenotype with significant increases in IL-4, -5, and -13 RNA levels and serum immunoglobulin (Ig) E. Finally, lyp animals in germ-free conditions were found to have an intestinal autoantibody; at 2–3 months of age, BB rat serum IgG bound to intestinal cells that resembled fibroblasts. IgG did not bind to other tissues including lung, spleen, and thymus, and this antibody appeared before histopathologic abnormalities were seen. This novel model system may help to determine mechanisms of systemic and mucosal gut eosinophilia.In the second article, Konikoff et al.10Konikoff M.R. Noel R.J. Blanchard C. Kirby C. Jameson S.C. Buckmeier B. Akers R. Cohen M.B. Collins M.H. Assa’ad A. Aceves S.S. Putnam P.E. Rothenberg M.E. A randomized, double-blind, placebo-controlled trial of fluticasone propionate for pediatric eosinophilic esophagitis.Gastroenterology. 2006; 131: 1381-1391Abstract Full Text Full Text PDF PubMed Scopus (513) Google Scholar determined the efficacy of gavaged fluticasone propionate (FP) for the treatment of EE.10Konikoff M.R. Noel R.J. Blanchard C. Kirby C. Jameson S.C. Buckmeier B. Akers R. Cohen M.B. Collins M.H. Assa’ad A. Aceves S.S. Putnam P.E. Rothenberg M.E. A randomized, double-blind, placebo-controlled trial of fluticasone propionate for pediatric eosinophilic esophagitis.Gastroenterology. 2006; 131: 1381-1391Abstract Full Text Full Text PDF PubMed Scopus (513) Google Scholar Previous investigators have shown the clinical impact of topical steroids in the treatment of EE, but none have performed a placebo-controlled trial.11Faubion Jr, W.A. Perrault J. Burgart L.J. Zein N.N. Clawson M. Freese D.K. Treatment of eosinophilic esophagitis with inhaled corticosteroids.J Pediatr Gastroenterol Nutr. 1998; 27: 90-93Crossref PubMed Scopus (288) Google Scholar, 12Noel R.J. Putnam P.E. Collins M.H. Assa’ad A.H. Guajardo J.R. Jameson S.C. Rothenberg M.E. Clinical and immunopathologic effects of swallowed fluticasone for eosinophilic esophagitis.Clin Gastroenterol Hepatol. 2004; 2: 568-575Abstract Full Text Full Text PDF PubMed Scopus (245) Google Scholar, 13Teitelbaum J. Fox V. Twarog F. Nurko S. Antonioli D. Gleich G. Badezagean K. Furuta G. Eosinophilic esophagitis in children: immunopathological analysis and response to fluticasone propionate.Gastroenterology. 2002; 122: 1216-1225Abstract Full Text Full Text PDF PubMed Scopus (409) Google Scholar This group conducted a carefully designed, double-blind, placebo-controlled trial of FP in well-defined patient populations from 2 geographically diverse centers. Investigators enrolled 36 patients who were treated with a standard dose of FP or placebo for 3 months. The primary endpoint was defined as the peak eosinophil count in the esophageal epithelium. To that end, they performed an exhaustive analysis of esophageal mucosal biopsies and determined that histologic remission was induce significantly more often in FP-treated patients than the placebo-treated group (50% vs 9%, respectively). Vomiting decreased significantly in FP-treated patients, whereas abdominal pain and dysphagia were unaffected. Secondary outcomes including endoscopically visible furrowing, epithelial hyperplasia, epithelial lymphocytosis, and mastocytosis were all significantly reduced by FP.This study raises several interesting questions about EE. First, why did certain subgroups of patients show different responsiveness to FP? For instance, FP’s eosinopenic impact appeared to be an all-or-none phenomenon; patients treated with FP had either complete resolution of epithelial eosinophilia or no change at all. This dramatic difference in response was observed especially when comparing nonallergic patients (normal skin prick tests to foods and aeroallergens) with allergic patients (positive skin prick tests). The majority of nonallergic patients responded to FP, whereas most allergic patients did not. These phenotypic differences suggest potential genotypic differences in EE patients. Second, why did almost 10% of the placebo-treated patients show a significant decline in epithelial eosinophilia over the 3 months? These placebo-treated patients with histologic improvement were “nonallergic,” suggesting that the effect was not due to changes in their environment or food. Time will tell whether indeed these patients “outgrew” EE or not. Finally, of the reported symptoms that included abdominal pain, dysphagia, and vomiting, why was only vomiting significantly impacted by FP? What happened to symptoms in FP- and placebo-treated patients with persistently abnormal biopsies? In this regard, we are still left with the persistent dilemma of what to designate as the end point of treatment in patients with EE.Taken together, these 2 studies pose important questions regarding intestinal eosinophilia. When is mucosal eosinophilia relevant? The dramatic phenotype observed by Cousins et al9Cousins L. Graham M. Tooze R. Carter C. Miller J.R. Powrie F.M. MacPherson G.G. Butcher G.W. Eosinophilic bowel disease controlled by the BB rat-derived lymphpeina/GIMP5 gene.Gastroenterology. 2006; 131: 1475-1485Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar was set on the background of limited histologic abnormalities. Intense eosinophilia was present in the lamina propria, but there was little in the way of villous architecture disruption, epithelial invasion, or goblet cell depletion, and classical features of mucosal inflammation. Unpublished clinical observations suggest that intestinal biopsies from patients with EGIDs may not contain easily recognized features of intestinal inflammation but rather, only a massive influx of eosinophils into the lamina propria. Deposition of eosinophil granules,14Parfitt J.R. Gregor J.C. Suskin N.G. Jawa H.A. Driman D.K. Eosinophilic esophagitis in adults: distinguishing features from gastroesophageal reflux disease: a study of 41 patients.Mod Pathol. 2006; 19: 90-96Crossref PubMed Scopus (197) Google Scholar eosinophil juxtaposition to resident mucosal cells such as mast cells, epithelium, neurons, and fibroblasts,15Durcan N. Costello R.W. McLean W.G. Blusztajn J. Madziar B. Fenech A.G. Hall I.P. Gleich G.J. McGarvey L. Walsh M.T. Eosinophil-mediated cholinergic nerve remodeling.Am J Respir Cell Mol Biol. 2006; 34: 775-786Crossref PubMed Scopus (44) Google Scholar, 16Furuta G.T. Nieuwenhuis E.E. Karhausen J. Gleich G. Blumberg R.S. Lee J.J. Ackerman S.J. Eosinophils alter colonic epithelial barrier function: role for major basic protein.Am J Physiol Gastrointest Liver Physiol. 2005; 289: G890-G897Crossref PubMed Scopus (119) Google Scholar, 17Gomes I. Mathur S.K. Espenshade B.M. Mori Y. Varga J. Ackerman S.J. Eosinophil-fibroblast interactions induce fibroblast IL-6 secretion and extracellular matrix gene expression: implications in fibrogenesis.J Allergy Clin Immunol. 2005; 116: 796-804Abstract Full Text Full Text PDF PubMed Scopus (97) Google Scholar and expression of new adhesion molecule patterns18Forbes E. Hulett M. Ahrens R. Wagner N. Smart V. Matthaei K.I. Brandt E.B. Dent L.A. Rothenberg M.E. Tang M. Foster P.S. Hogan S.P. ICAM-1-dependent pathways regulate colonic eosinophilic inflammation.J Leukoc Biol. 2006; 80: 330-341Crossref PubMed Scopus (50) Google Scholar may prove to be important features of EGIDs. This critical observation and increasing clinical experiences suggests a novel paradigm for EGIDs, indicating that significant clinical phenotypes can occur in the absence of traditional intestinal inflammatory hallmarks.In contrast to the dramatic, severe findings of the BB animal model, patients with asymptomatic eosinophilic esophageal inflammation are posing a new and vexing problem. It is not unusual for a posttreatment esophageal biopsy from a patient with EE to show the continued presence of large numbers of eosinophils as seen in the Konikoff study. To date, the significance of this finding is uncertain; does this represent a treatment failure because the epithelium is still abnormal, or a success if the patient is asymptomatic? The obvious question that arises is “why should a biopsy be performed in an asymptomatic patient?” Because the long-term outcome of EE is still uncertain, and potentially serious (esophageal stricture), resolution of mucosal eosinophilia has been the primary endpoint used by many just as in the Konikoff study. But some suggest that this approach is overly aggressive and unnecessary. As in other inflammatory diseases, such as inflammatory bowel disease and celiac disease, the argument could be made that clinical endpoints should focus on symptom resolution, not histologic normalcy. Until the incidence of complications associated with EE is established, it may be most prudent to use histologic normalization as one treatment endpoint in clinical studies and patient care.What stimulates the eosinophil’s invasion into the mucosa? Is it an epithelial or subepithelial antigen or luminal product? Eosinophilia observed in the lyp rat is restricted to the columnar-lined small intestine and colon. One could speculate that the epithelium possesses a unique antigen that drives eosinophils to the basolateral surface, but the data from the BB rat suggests that a novel autoantigen on fibroblast-like cells in the subepithelial layer. The identification of a unique intestinal antigen would be a landmark in understanding the pathogenesis of mucosal eosinophilia. If a similar antigen could be identified in patients with EGIDs, the potential arises for development of a noninvasive marker to assist in diagnosis and long-term follow-up, similar to serologic testing for celiac disease. Instead of columnar epithelium, patients with EE have eosinophilia that is limited to the squamous esophageal epithelium. These findings of Konikoff suggest that eosinophilia can be driven by exogenous molecules such as allergens (food or environmental). Until more is known about the potent immunologic milieu of affected EE patients, all patients should undergo allergy evaluations to identify potential target allergens.These 2 studies provide us with new insights into the potential role of eosinophils in gastrointestinal disease. Murine studies determined a role for eosinophils in airway mucus production, hyperreactivity, and tissue remodeling,19Humbles A.A. Lloyd C.M. McMillan S.J. Friend D.S. Xanthou G. McKenna E.E. Ghiran S. Gerard N.P. Yu C. Orkin S.H. Gerard C. A critical role for eosinophils in allergic airways remodeling.Science. 2004; 305: 1776-1779Crossref PubMed Scopus (739) Google Scholar, 20Lee J.J. Dimina D. Macias M.P. Ochkur S.I. McGarry M.P. O’Neill K.R. Protheroe C. Pero R. Nguyen T. Cormier S.A. Lenkiewicz E. Colbert D. Rinaldi L. Ackerman S.J. Irvin C.G. Lee N.A. Defining a link with asthma in mice congenitally deficient in eosinophils.Science. 2004; 305: 1773-1776Crossref PubMed Scopus (619) Google Scholar but within the gastrointestinal tract, speculation still abounds. Faced with the increasing clinical burden associated with mucosal eosinophilia, clinicians will benefit from these 2 recent studies in Gastroenterology that will certainly go on to spawn future investigations. See “A randomized double-blind placebo-controlled trial of fluticasone propionate for pediatric eosinophilic esophagitis” by Konikoff MR, Noel R, Blanchard C, Kirby C, Jameson SC, Buckmeier B, Akers R, Cohen MB, Collins MH, Assa’ad AH, Aceves SS, Putnam PE, and Rothenberg ME on page 1381 and “Eosinophilic bowel disease controlled by the BB rat-derived lymphopenia/Gimap5 gene” by Cousins L, Graham M, Tooze R, Carter C, Miller JR, Powrie FM, MacPherson GG, and Butcher GW on page 1475. See “A randomized double-blind placebo-controlled trial of fluticasone propionate for pediatric eosinophilic esophagitis” by Konikoff MR, Noel R, Blanchard C, Kirby C, Jameson SC, Buckmeier B, Akers R, Cohen MB, Collins MH, Assa’ad AH, Aceves SS, Putnam PE, and Rothenberg ME on page 1381 and “Eosinophilic bowel disease controlled by the BB rat-derived lymphopenia/Gimap5 gene” by Cousins L, Graham M, Tooze R, Carter C, Miller JR, Powrie FM, MacPherson GG, and Butcher GW on page 1475. See “A randomized double-blind placebo-controlled trial of fluticasone propionate for pediatric eosinophilic esophagitis” by Konikoff MR, Noel R, Blanchard C, Kirby C, Jameson SC, Buckmeier B, Akers R, Cohen MB, Collins MH, Assa’ad AH, Aceves SS, Putnam PE, and Rothenberg ME on page 1381 and “Eosinophilic bowel disease controlled by the BB rat-derived lymphopenia/Gimap5 gene” by Cousins L, Graham M, Tooze R, Carter C, Miller JR, Powrie FM, MacPherson GG, and Butcher GW on page 1475. The last decade brought changes in the eosinophil’s image as it transitioned from an overlooked, innocent bystander hidden within mucosal biopsies to an unmistakable, culpable marker of gastrointestinal diseases. In that light, a large body of literature associates mucosal eosinophilia with food allergies. In clinical practice, the mere presence of eosinophils in intestinal biopsies prompts an almost automatic diagnosis of food allergic enteropathy. Although this may be the case for many patients, the indiscriminant assignment of eosinophils to one disease is unfortunate; mucosal eosinophilia is associated with an increasingly broad differential diagnosis that includes infections, hypereosinophilic syndrome, inflammatory bowel disease, allergic enteropathy, collagen vascular disease, hypersensitivity reactions, peptic disease, and eosinophilic gastrointestinal diseases (EGIDs). EGIDs are a group of diseases (eosinophilic esophagitis, eosinophilic gastritis, eosinophilic gastroenteritis, eosinophilic colitis) characterized by gastrointestinal symptoms and mucosal eosinophilia.1Rothenberg M.E. Eosinophilic gastrointestinal disorders (EGID).J Allergy Clin Immunol. 2004; 113 (quiz 29): 11-28Abstract Full Text Full Text PDF PubMed Scopus (695) Google Scholar Although the etiology of these diseases is uncertain, many patients respond to nutritional management suggesting food as an inciting factor. Of these clinical subtypes, eosinophilic esophagitis (EE) is the best described; recent case reports and translational studies provide detailed analyses of this interesting group of patients characterized by chronic gastroesophageal reflux disease-like symptoms, which are unresponsive to acid blockade and esophageal biopsies that demonstrate intense epithelial eosinophilia.2Fox V.L. Nurko S. Furuta G.T. Eosinophilic esophagitis: it’s not just kid’s stuff.Gastrointest Endosc. 2002; 56: 260-270Abstract Full Text Full Text PDF PubMed Scopus (267) Google Scholar Patients with EE often are sensitive to food products and most respond to elimination or elemental diets. Those who are unresponsive or who are unable to comply with nutritional management typically improve with systemic or topical corticosteroids. Presently, the decision to treat patients with EE is often driven by the association of EE with esophageal strictures; this is guided by attempts to relieve symptoms and the incidence of long-term complications is still unknown. Limitations of our knowledge regarding eosinophil’s impact on the gut relates to the inadequate number of peripheral eosinophils for study, lack of commercially available reagents, limited animal models, and scarcity of affected human tissues. Few investigators have determined mechanisms of intestinal eosinophilia, but those who have are providing interesting results. Gut eosinophilia has been studied in animal models of infection, hapten-induced injury, allergen exposure, and genetic modeling. Allergen-induced models utilizing knock-out and transgenic mice demonstrated that interleukin (IL)-5 and eotaxin-3 play central roles in esophageal eosinophilia; eotaxin-1 is critical to eosinophilia of the stomach and small bowel.3Blanchard C. Wang N. Stringer K.F. Mishra A. Fulkerson P.C. Abonia J.P. Jameson S.C. Kirby C. Konikoff M.R. Collins M.H. Cohen M.B. Akers R. Hogan S.P. Assa’ad A.H. Putnam P.E. Aronow B.J. Rothenberg M.E. Eotaxin-3 and a uniquely conserved gene-expression profile in eosinophilic esophagitis.J Clin Invest. 2006; 116: 536-547Crossref PubMed Scopus (696) Google Scholar, 4Hogan S. Mishra A. Brandt E. Royalty M. Pope S. Zimmerman N. Foster P. Rothenberg M. A pathological function for eotaxin and eosinophils in eosinophilic gastrointestinal inflammation.Nat Immunol. 2001; 2: 353-360Crossref PubMed Scopus (275) Google Scholar, 5Mishra A. Hogan S.P. Brandt E.B. Rothenberg M.E. IL-5 promotes eosinophil trafficking to the esophagus.J Immunol. 2002; 168: 2464-2469PubMed Google Scholar The recent landmark translational study by Blanchard et al3Blanchard C. Wang N. Stringer K.F. Mishra A. Fulkerson P.C. Abonia J.P. Jameson S.C. Kirby C. Konikoff M.R. Collins M.H. Cohen M.B. Akers R. Hogan S.P. Assa’ad A.H. Putnam P.E. Aronow B.J. Rothenberg M.E. Eotaxin-3 and a uniquely conserved gene-expression profile in eosinophilic esophagitis.J Clin Invest. 2006; 116: 536-547Crossref PubMed Scopus (696) Google Scholar used a combination of microarray analysis of human esophageal tissues and murine systems to establish an EE signature panel of genes. Translational studies identified IL-5 and tumor necrosis factor-α in the affected epithelium of patients with EE.6Gupta S.K. Fitzgerald J.F. Kondratyuk T. HogenEsch H. Cytokine expression in normal and inflamed esophageal mucosa: a study into the pathogenesis of allergic eosinophilic esophagitis.J Pediatr Gastroenterol Nutr. 2006; 42: 22-26Crossref PubMed Scopus (151) Google Scholar, 7Straumann A. Kristl J. Conus S. Vassina E. Spichtin H.P. Beglinger C. Simon H.U. Cytokine expression in healthy and inflamed mucosa: probing the role of eosinophils in the digestive tract.Inflamm Bowel Dis. 2005; 11: 720-726Crossref PubMed Scopus (113) Google Scholar Although this emerging literature brings increased clinical awareness, no consensus diagnostic criteria for EE have yet been proposed. In fact, only recently have normal values for mucosal eosinophilia been published.8DeBrosse C.W. Case J.W. Putnam P.E. Collins M.H. Rothenberg M.E. Quantity and distribution of eosinophils in the gastrointestinal tract of children.Pediatr Dev Pathol. 2006; 9: 210-218Crossref PubMed Scopus (213) Google Scholar To address this problem, the North American Society of Pediatric Gastroenterology, Hepatology, and Nutrition organized The First International Gastrointestinal Eosinophil Research Symposium on October 17–18, 2006. Results of this symposium yielded practical clinical guidelines and a feasible research agenda in which we can begin to address important issues focusing on eosinophilia of the gut. In that light, this issue of Gastroenterology provides us with 2 exciting studies that emphasize the importance of chronic eosinophilic inflammation. In the first study, Cousins et al.9Cousins L. Graham M. Tooze R. Carter C. Miller J.R. Powrie F.M. MacPherson G.G. Butcher G.W. Eosinophilic bowel disease controlled by the BB rat-derived lymphpeina/GIMP5 gene.Gastroenterology. 2006; 131: 1475-1485Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar made the novel observation that the BioBreeding (BB) rat, characterized by lymphopenia secondary to GTPase of the immunity-associated protein family (GIMAP5) deficiency, developed progressive systemic and intestinal eosinophilia. Previously, this group and others utilized this model to investigate diabetes mellitus. In specific pathogen-free environments, animals developed significant body wasting by 20 weeks that progressed to include intestinal bloating and then death by 50 weeks. Necropsy revealed massively distended small and large bowels and histologic specimens identified intense eosinophilia of the lamina propria with preservation of villous structure. The esophagus and stomach were unaffected. Features identified here provide a novel model system to determine mechanisms of systemic and mucosal eosinophilia. Eosinophilia was dependent on the lyp gene that encodes for GIMAP5, a molecule thought to be responsible for, among other things, lymphocyte apoptosis and T-cell survival. To date, little is known about the impact of GIMAP5 on eosinophils. Other features of this model system included splenomegaly and enlargement of the mesenteric, but not peripheral, lymph nodes. A significant reduction in CD4+, CD8+, and natural killer T (NKT) cells compared with controls was observed. T- and B-cell functions were preserved and overall they carried a Th2 phenotype with significant increases in IL-4, -5, and -13 RNA levels and serum immunoglobulin (Ig) E. Finally, lyp animals in germ-free conditions were found to have an intestinal autoantibody; at 2–3 months of age, BB rat serum IgG bound to intestinal cells that resembled fibroblasts. IgG did not bind to other tissues including lung, spleen, and thymus, and this antibody appeared before histopathologic abnormalities were seen. This novel model system may help to determine mechanisms of systemic and mucosal gut eosinophilia. In the second article, Konikoff et al.10Konikoff M.R. Noel R.J. Blanchard C. Kirby C. Jameson S.C. Buckmeier B. Akers R. Cohen M.B. Collins M.H. Assa’ad A. Aceves S.S. Putnam P.E. Rothenberg M.E. A randomized, double-blind, placebo-controlled trial of fluticasone propionate for pediatric eosinophilic esophagitis.Gastroenterology. 2006; 131: 1381-1391Abstract Full Text Full Text PDF PubMed Scopus (513) Google Scholar determined the efficacy of gavaged fluticasone propionate (FP) for the treatment of EE.10Konikoff M.R. Noel R.J. Blanchard C. Kirby C. Jameson S.C. Buckmeier B. Akers R. Cohen M.B. Collins M.H. Assa’ad A. Aceves S.S. Putnam P.E. Rothenberg M.E. A randomized, double-blind, placebo-controlled trial of fluticasone propionate for pediatric eosinophilic esophagitis.Gastroenterology. 2006; 131: 1381-1391Abstract Full Text Full Text PDF PubMed Scopus (513) Google Scholar Previous investigators have shown the clinical impact of topical steroids in the treatment of EE, but none have performed a placebo-controlled trial.11Faubion Jr, W.A. Perrault J. Burgart L.J. Zein N.N. Clawson M. Freese D.K. Treatment of eosinophilic esophagitis with inhaled corticosteroids.J Pediatr Gastroenterol Nutr. 1998; 27: 90-93Crossref PubMed Scopus (288) Google Scholar, 12Noel R.J. Putnam P.E. Collins M.H. Assa’ad A.H. Guajardo J.R. Jameson S.C. Rothenberg M.E. Clinical and immunopathologic effects of swallowed fluticasone for eosinophilic esophagitis.Clin Gastroenterol Hepatol. 2004; 2: 568-575Abstract Full Text Full Text PDF PubMed Scopus (245) Google Scholar, 13Teitelbaum J. Fox V. Twarog F. Nurko S. Antonioli D. Gleich G. Badezagean K. Furuta G. Eosinophilic esophagitis in children: immunopathological analysis and response to fluticasone propionate.Gastroenterology. 2002; 122: 1216-1225Abstract Full Text Full Text PDF PubMed Scopus (409) Google Scholar This group conducted a carefully designed, double-blind, placebo-controlled trial of FP in well-defined patient populations from 2 geographically diverse centers. Investigators enrolled 36 patients who were treated with a standard dose of FP or placebo for 3 months. The primary endpoint was defined as the peak eosinophil count in the esophageal epithelium. To that end, they performed an exhaustive analysis of esophageal mucosal biopsies and determined that histologic remission was induce significantly more often in FP-treated patients than the placebo-treated group (50% vs 9%, respectively). Vomiting decreased significantly in FP-treated patients, whereas abdominal pain and dysphagia were unaffected. Secondary outcomes including endoscopically visible furrowing, epithelial hyperplasia, epithelial lymphocytosis, and mastocytosis were all significantly reduced by FP. This study raises several interesting questions about EE. First, why did certain subgroups of patients show different responsiveness to FP? For instance, FP’s eosinopenic impact appeared to be an all-or-none phenomenon; patients treated with FP had either complete resolution of epithelial eosinophilia or no change at all. This dramatic difference in response was observed especially when comparing nonallergic patients (normal skin prick tests to foods and aeroallergens) with allergic patients (positive skin prick tests). The majority of nonallergic patients responded to FP, whereas most allergic patients did not. These phenotypic differences suggest potential genotypic differences in EE patients. Second, why did almost 10% of the placebo-treated patients show a significant decline in epithelial eosinophilia over the 3 months? These placebo-treated patients with histologic improvement were “nonallergic,” suggesting that the effect was not due to changes in their environment or food. Time will tell whether indeed these patients “outgrew” EE or not. Finally, of the reported symptoms that included abdominal pain, dysphagia, and vomiting, why was only vomiting significantly impacted by FP? What happened to symptoms in FP- and placebo-treated patients with persistently abnormal biopsies? In this regard, we are still left with the persistent dilemma of what to designate as the end point of treatment in patients with EE. Taken together, these 2 studies pose important questions regarding intestinal eosinophilia. When is mucosal eosinophilia relevant? The dramatic phenotype observed by Cousins et al9Cousins L. Graham M. Tooze R. Carter C. Miller J.R. Powrie F.M. MacPherson G.G. Butcher G.W. Eosinophilic bowel disease controlled by the BB rat-derived lymphpeina/GIMP5 gene.Gastroenterology. 2006; 131: 1475-1485Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar was set on the background of limited histologic abnormalities. Intense eosinophilia was present in the lamina propria, but there was little in the way of villous architecture disruption, epithelial invasion, or goblet cell depletion, and classical features of mucosal inflammation. Unpublished clinical observations suggest that intestinal biopsies from patients with EGIDs may not contain easily recognized features of intestinal inflammation but rather, only a massive influx of eosinophils into the lamina propria. Deposition of eosinophil granules,14Parfitt J.R. Gregor J.C. Suskin N.G. Jawa H.A. Driman D.K. Eosinophilic esophagitis in adults: distinguishing features from gastroesophageal reflux disease: a study of 41 patients.Mod Pathol. 2006; 19: 90-96Crossref PubMed Scopus (197) Google Scholar eosinophil juxtaposition to resident mucosal cells such as mast cells, epithelium, neurons, and fibroblasts,15Durcan N. Costello R.W. McLean W.G. Blusztajn J. Madziar B. Fenech A.G. Hall I.P. Gleich G.J. McGarvey L. Walsh M.T. Eosinophil-mediated cholinergic nerve remodeling.Am J Respir Cell Mol Biol. 2006; 34: 775-786Crossref PubMed Scopus (44) Google Scholar, 16Furuta G.T. Nieuwenhuis E.E. Karhausen J. Gleich G. Blumberg R.S. Lee J.J. Ackerman S.J. Eosinophils alter colonic epithelial barrier function: role for major basic protein.Am J Physiol Gastrointest Liver Physiol. 2005; 289: G890-G897Crossref PubMed Scopus (119) Google Scholar, 17Gomes I. Mathur S.K. Espenshade B.M. Mori Y. Varga J. Ackerman S.J. Eosinophil-fibroblast interactions induce fibroblast IL-6 secretion and extracellular matrix gene expression: implications in fibrogenesis.J Allergy Clin Immunol. 2005; 116: 796-804Abstract Full Text Full Text PDF PubMed Scopus (97) Google Scholar and expression of new adhesion molecule patterns18Forbes E. Hulett M. Ahrens R. Wagner N. Smart V. Matthaei K.I. Brandt E.B. Dent L.A. Rothenberg M.E. Tang M. Foster P.S. Hogan S.P. ICAM-1-dependent pathways regulate colonic eosinophilic inflammation.J Leukoc Biol. 2006; 80: 330-341Crossref PubMed Scopus (50) Google Scholar may prove to be important features of EGIDs. This critical observation and increasing clinical experiences suggests a novel paradigm for EGIDs, indicating that significant clinical phenotypes can occur in the absence of traditional intestinal inflammatory hallmarks. In contrast to the dramatic, severe findings of the BB animal model, patients with asymptomatic eosinophilic esophageal inflammation are posing a new and vexing problem. It is not unusual for a posttreatment esophageal biopsy from a patient with EE to show the continued presence of large numbers of eosinophils as seen in the Konikoff study. To date, the significance of this finding is uncertain; does this represent a treatment failure because the epithelium is still abnormal, or a success if the patient is asymptomatic? The obvious question that arises is “why should a biopsy be performed in an asymptomatic patient?” Because the long-term outcome of EE is still uncertain, and potentially serious (esophageal stricture), resolution of mucosal eosinophilia has been the primary endpoint used by many just as in the Konikoff study. But some suggest that this approach is overly aggressive and unnecessary. As in other inflammatory diseases, such as inflammatory bowel disease and celiac disease, the argument could be made that clinical endpoints should focus on symptom resolution, not histologic normalcy. Until the incidence of complications associated with EE is established, it may be most prudent to use histologic normalization as one treatment endpoint in clinical studies and patient care. What stimulates the eosinophil’s invasion into the mucosa? Is it an epithelial or subepithelial antigen or luminal product? Eosinophilia observed in the lyp rat is restricted to the columnar-lined small intestine and colon. One could speculate that the epithelium possesses a unique antigen that drives eosinophils to the basolateral surface, but the data from the BB rat suggests that a novel autoantigen on fibroblast-like cells in the subepithelial layer. The identification of a unique intestinal antigen would be a landmark in understanding the pathogenesis of mucosal eosinophilia. If a similar antigen could be identified in patients with EGIDs, the potential arises for development of a noninvasive marker to assist in diagnosis and long-term follow-up, similar to serologic testing for celiac disease. Instead of columnar epithelium, patients with EE have eosinophilia that is limited to the squamous esophageal epithelium. These findings of Konikoff suggest that eosinophilia can be driven by exogenous molecules such as allergens (food or environmental). Until more is known about the potent immunologic milieu of affected EE patients, all patients should undergo allergy evaluations to identify potential target allergens. These 2 studies provide us with new insights into the potential role of eosinophils in gastrointestinal disease. Murine studies determined a role for eosinophils in airway mucus production, hyperreactivity, and tissue remodeling,19Humbles A.A. Lloyd C.M. McMillan S.J. Friend D.S. Xanthou G. McKenna E.E. Ghiran S. Gerard N.P. Yu C. Orkin S.H. Gerard C. A critical role for eosinophils in allergic airways remodeling.Science. 2004; 305: 1776-1779Crossref PubMed Scopus (739) Google Scholar, 20Lee J.J. Dimina D. Macias M.P. Ochkur S.I. McGarry M.P. O’Neill K.R. Protheroe C. Pero R. Nguyen T. Cormier S.A. Lenkiewicz E. Colbert D. Rinaldi L. Ackerman S.J. Irvin C.G. Lee N.A. Defining a link with asthma in mice congenitally deficient in eosinophils.Science. 2004; 305: 1773-1776Crossref PubMed Scopus (619) Google Scholar but within the gastrointestinal tract, speculation still abounds. Faced with the increasing clinical burden associated with mucosal eosinophilia, clinicians will benefit from these 2 recent studies in Gastroenterology that will certainly go on to spawn future investigations.