REVIEW URRENT C OPINION
Molecular pathogenesis of eosinophilic esophagitis Carine Blanchard
Purpose of review Eosinophilic esophagitis (EoE) is an esophageal disease characterized by an accumulation of eosinophils in the esophagus, which is normally devoid of eosinophils. The interest of the scientific community in EoE has grown considerably over the past two decades, and understanding of the molecular mechanisms involved in this disease has increased greatly in the last 2 years. Recent findings Important new insights into the pathogenesis of EoE recently have been achieved. Recent evaluations considering genetic and the environmental risk factors have led to the concept that some still-unknown environmental factors influence the risk of developing EoE more than the genetic predisposition. New molecules (in addition to interleukin-13, eotaxin-3, transforming growth factor-b1, thymic stromal lymphopoietin, filaggrin, or interleukin-5) also have been shown to be involved in the disease pathogenesis. Summary The present review describes recent advances in the understanding of the molecular mechanisms underlying EoE, and how these new findings have enhanced understanding of the pathogenesis of this new esophageal disorder. Keywords environmental exposure, eosinophilic esophagitis, genetics, interleukin-13, molecular, pathogenesis
INTRODUCTION Eosinophilic esophagitis (EoE) is a chronic inflammatory condition of the esophagus, characterized clinically by symptoms related to esophageal dysfunction and histologically by eosinophilic infiltration, with esophageal mucosal biopsy specimens showing 15 or more eosinophils per high power field (HPF) [1]. Along with eosinophils, numerous other cell types are found in increased numbers in the inflamed esophageal mucosa, including mast cells, invariant natural killer T (iNKT) cells, and lymphocytes. Other key histologic features of EoE are epithelial cell hyperplasia, and remodeling with fibrosis in the underlying lamina propria. A number of observations have highlighted the allergic, T-helper 2 (Th2)-type process that is associated with EoE: (1) The strong association with allergic disease identified in epidemiological studies. (2) The clinical observation that symptoms resolve when the causative foods are removed from the diet. (3) The preclinical studies showing that esophageal eosinophilic inflammation can be seen in animal models of allergic inflammation.
Most of our understanding of the molecular pathogenesis of EoE has emerged from studies on patients with EoE, using genome-wide screening technologies that have provided insights into the numerous molecular changes that occur in the disease. Conjointly, candidate gene studies also have enabled insights into the molecular pathogenesis, although a lot still needs to be unraveled to understand the molecular mechanisms that lead to the full disease phenotype.
EPIDEMIOLOGY: NOT ONLY A DISEASE OF WHITES Initial epidemiologic studies on EoE, which were performed largely in the United States and in Europe Nutrition and Health Research, Nestec Ltd, Nestle´ Research Center, Lausanne, canton of Vaud, Switzerland Correspondence to Carine Blanchard, Nutrition and Health Research, Nestec Ltd, Nestle´ Research Center, Route du Jorat 57, PO Box 44, CH-1000 Lausanne 26, Switzerland. Tel: +41 21 785 8510; e-mail: [email protected] Curr Opin Gastroenterol 2015, 31:321–327 DOI:10.1097/MOG.0000000000000186
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KEY POINTS A twin study emphasizes a larger role for environmental exposures than for genetics in EoE disease risk. Epidemiologic studies suggest that African Americans may be as likely as whites to develop EoE. The molecular pathogenesis of EoE involves the interaction between external environmental triggers and genetic traits in predisposed and exposed individuals. Esophageal epithelial cell genes dysregulation (TSLP, eotaxin-3), IL-13-induced inflammation, decreased esophageal epithelial barrier function, and increased esophageal immune cell infiltration (eosinophils, lymphocytes, mast cell, iNKT) are all hallmarks of the molecular pathogenesis of EoE.
[2–4], indicated that EoE was a disease that affected white males primarily. A recent report by Weiler et al. [5 ] suggests that these initial reports were misleading in regard to the ethnic distribution of EoE. In Weiler’s study of patients with EoE, whites comprised only 42% of the study population, whereas African Americans, Asians, and other ethnicities comprised 42%, 4%, and 12%, respectively. The investigators did note some differences between white and African American patients in the clinical presentation of EoE, however, with failure to thrive, vomiting, and a history of atopic dermatitis found more frequently in African Americans [5 ]. These data highlight the fact that EoE is not just a disease of whites, and it should be considered in the differential diagnosis for African Americans with esophageal dysfunction. This also suggests that there might not be large differences in the genetic predisposition to EoE between populations. Indeed, although the identification of familial cases of EoE led to the hypothesis that genetic predisposition was the major pathogenetic factor in EoE [6], recent data have challenged this concept to favor the environment as more important in the pathogenesis of EoE [7 ] (Fig. 1). &&
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GENETICS VERSUS ENVIRONMENT Genetic variants associated with the risk of developing EoE have been identified by case–control studies and genome-wide association studies (GWAS). GWAS initially identified risk variants in locus 5q22 of the thymic stromal lymphopoietin (TSLP) gene, and risk alleles such as rs3806932 also have been identified in the TSLP gene locus. Compared to healthy controls, esophageal expression of TSLP mRNA is increased in patients with active EoE, 322
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and TSLP is a credible candidate in EoE pathogenesis [8]. TSLP, which is expressed by epithelial cells, is a master regulator of allergic inflammation capable of activating diverse immune cells. These initial GWAS findings recently have been expanded to include new loci such as 2p23.1 spanning CAPN14, 8p23 in the intron XKR6, and 15q13 between LOC283710 and KLF13 [9]. Other new EoE loci also include 1p13 SLC25A24, 5q23 near SEMA6A, 10p12 in MIR467S, 11q13.5 of locus containing c11orf30, 11q14 in the intron of CCDC81, 12q13.3 spanning STAT6, 19q13.11 spanning ANKRD27, and 21q22 in HSF2BP gene (Table 1) [9,10]. The authors of these recent studies focused on CAPN14, an interleukin (IL)-13induced gene that encodes for calpain 14, which is a calcium-activated cysteine protease. CAPN14 mRNA expression is upregulated in esophageal biopsies of patients with active EoE. The substrate for CAPN14’s proteolytic activity includes inflammatory mediators relevant to allergic disease, but its role in EoE has not yet been defined. A recent study has tried to associate genetic variants with EoE symptoms or comorbidities rather than with the risk of developing EoE itself. The authors identified variants in the cluster of IL5–IL13 region that were associated principally with eosinophilia and, to some extent, with EoE disease [11]. These studies suggest a polygenic cause for EoE. Investigators have identified multiple genetic variants that are associated with EoE, but none that appear to be capable of causing the disease independently. These data also highlight the missing heritability of EoE, meaning the factors that are required to develop the disease but that remain unknown. There are multiple potential genetic and environmental factors underlying phenotypic variation in the EoE population. A recent twin study designed to elucidate the relative contributions of genetics and environment in the pathogenesis of EoE demonstrated that the genetic contribution has been greatly overestimated, whereas the role of environmental factors has been underestimated. This study evaluated patients with EoE and their first-degree relatives, focusing especially on the risk of developing EoE in monozygotic and dizygotic twins. For patients with EoE, the risk of EoE for other siblings was 2.4%, whereas the risk was 22% for dizygotic twins and 41% for monozygotic twins. This study suggests that genetics explains only 14% of the phenotypic variance in EoE whereas environment explains 81% [7 ]. A number of early life factors seem to influence EoE risk, such as the birth season, breastfeeding, and penicillin allergy [7 ]. Indeed, Jensen et al. [12] found that infants exposed to antibiotics in early infancy were six [1.7–20.8] times more likely to &&
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Molecular pathogenesis of eosinophilic esophagitis Blanchard
Table 1
Genetics
Early life exposure (Penicillin, birth season, breastfeeding…)
Environment
Eosinophilic esophagitis Milk sphingolipids Allergens, Other?
Desmoglein 1
Impaired barrier function
Filaggrin
↑
iNKT
↑ TSLP
↑ CAPN14
IL-13
Th2
↑IgG4
↑
NTRK1 Stimulated by NGF
↑ miR21
Epithelial cell hyperplasia
Eosinophilic recruitment
↑ BANCR
↑ Eotaxin-3
↑ RELMα Lamina propria fibrosis
↑ Periostin
↑ PDG2 Smad3
↑CPA3 Angiogenesis
Smooth muscle hyperplasia & contractibility
↑ PLN
↑ TRVP1
Nerve sensing
↑ VCAM-1
Basophils
DCs
Mast cells
Lymphocyte
Eosinophils
iNKT
TGF-β1
FIGURE 1. Molecular pathogenesis of eosinophilic esophagitis (EoE). A larger role for the environmental exposure than the genetics in EoE disease risk has recently been demonstrated. Molecular pathogenesis of EoE is at the interface between external triggers and genetic traits in individuals that are exposed and predisposed. The epithelial cell gene dysregulation (TSLP, eotaxin-3), the IL-13-induced inflammation, the decreased barrier function (filaggrin, desmoglein 1), and the increased immune cell infiltration [eosinophils, lymphocytes, mast cells, invariant natural killer T (iNKT)] are all hallmarks of the molecular pathogenesis. Figure was produced using Servier Medical Art, www.servier.com.
develop EoE than the normal population. Other groups also have focused on identifying differentiating environmental factors in EoE cohorts [13].
THE MOLECULAR PATHOGENESIS: THE QUEST FOR NONINVASIVE BIOMARKERS Several studies have identified alterations in microRNA expression in esophageal biopsies from patients with EoE. miR-21, which is involved in the downregulations of IL-12, has been found to be consistently dysregulated in active EoE, and
miR-21 appears to play a key role in the establishment of a full Th2 phenotype. Although esophageal microRNA dysregulation appears to be common in active EoE, more studies are needed to confirm these findings and to elucidate the importance of microRNA alterations in this disease. MicroRNAs tend to be extremely stable, and thus could be good blood biomarkers for EoE. However, only one study has found a difference between patients with EoE and normal patients in the expression of some miR (miR-146a, miR-146b, and miR-223) in the blood. These data are still
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Esophagus Table 1. Polymorphisms associated with EoE Gene symbol
Gene name
Gene function
Chromosome
FLG
Filaggrin
Barrier function
1q21.3
SLC25A24
Solute carrier family 25 (mitochondrial carrier; phosphate carrier), member 24
CAPN14
Calpain 14
Protease
2p23
TSLP
Thymic stromal lymphopoietin
Initiator of Th2 response, basophil response
5q22.1
WDR36
WD repeat domain 36
5q22.1
SEMA6A
Sema domain, transmembrane domain (TM), and cytoplasmic domain, (semaphorin) 6A
5q23
CCL26
Chemokine (C-C motif) ligand 26 (eotaxin-3)
XKR6
XK, Kell blood group complex subunit-related family, member 6
8p23
C11orf30
Chromosome 11 open reading frame 30 / EMSY
11q13.5
CCDC81
Coiled-coil domain containing 81
STAT6
Signal transducer and activator of transcription 6
Loc283710/KLF13
Loc283710/Kruppel-Like Factor 13
ANKRD27
Ankyrinrepeatdomain 27 (VPS9 domain)
TGFB1
Transforming growth factor, b1
Remodeling
19q13.1
CRLF2
Cytokine receptor-like factor 2
TSLP receptor
Xp22.33 Yp11.3
1p13
Chemoattraction of eosinophils
7q11.23
11q14 Th2 response
12q13.3 15q13 19q12.11
Derived in part from [8–10].
encouraging, however, because a trend was identified for miR-203 in another study [14–17]. Studies have shown that blood eosinophils from patients with EoE express differently surface markers than those from normal patients. A recent study by Lingblom et al. [18] showed that corticosteroids modify the expression of some eosinophil surface markers such as CD18, CD44, or CRTH2, and the ability of eosinophils to adhere to cellular matrix component. These effects may explain in part the ability of steroids to decrease esophageal eosinophilia in patients with EoE [18]. No single marker yet identified in the esophagus or in the blood can be used as a reliable diagnostic test for EoE. Therefore, researchers have focused on the development of panels of biomarkers that might differentiate EoE from non-EoE diseases or from inactive EoE. In a prospective study, panels of different blood cytokines were shown to be less sensitive than esophageal molecular markers [19]. Wen et al. [20] have recently developed a panel of markers in esophageal biopsies that can differentiate EoE from nonEoE patients. The panel is composed of 94 EoE transcript and two housekeeping genes derived from the EoE transcriptome. Scores were developed to separate EoE from normal patients (with a sensitivity of 92% and a specificity of 96%) and to separate glucocorticoid responders from normal patients and patients with active EoE. However, the EoE score was not optimal for differentiating patients who had an 324
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intermediate level of eosinophils (between 6 and 14 eosinophils per HPF) [20]. Other investigators used immunohistochemistry to identify epithelial cellderived gene expression patterns for differentiating EoE from patients with gastroesophageal reflux disease and normal controls [21]. The strength of this technique is that it could be performed retrospectively using paraffin-embedded tissues; the weakness is the fact that upper gastrointestinal endoscopy is still needed for the diagnosis. Although topical swallowed glucocorticoids are used widely to treat the esophageal inflammation of EoE, a considerable proportion of patients do not respond to steroids [22]. Wolf et al. [22] have found that a baseline low level of eotaxin-3 expression, a low number of mast cells, and esophageal dilatation at baseline are associated with a decreased rate of response to glucocorticoid therapy. In conclusion, the quest for noninvasive biomarkers for EoE continues, and attempts to identify a marker or a panel of markers that could be used as diagnostic tests or to predict the response to therapy, are still in their infancy.
INTERLEUKIN-13 AND EPITHELIAL CELLS ARE KEY PLAYERS IN EOSINOPHILIC ESOPHAGITIS PATHOGENESIS The Th2 IL-13 has been shown to be highly involved in the molecular pathogenesis of EoE. Indeed, IL-13 Volume 31 Number 4 July 2015
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has been shown to be involved in the upregulation of numerous genes in the esophagus of patients with EoE. One such gene is CCL26 (also called eotaxin-3), an eosinophil chemoattractant responsible for the accumulation of eosinophils in the esophagus of patients with EoE [23]. Recent data suggest that activated mast cells also may contribute to the chemoattraction of eosinophils in the esophagus through prostaglandin D2 [24]. A strong hyperplasia of esophageal epithelial cells is observed in biopsies from patients with EoE. This is associated with decreased expression of genes involved in the epidermal differentiation complex, which is regulated by IL-13 [25]. In an animal model, it was recently found that Resistinlike molecule alpha could induce thickening of the basal layer of the esophageal epithelium [26]. IL-13 is also responsible for the downregulation of desmoglein 1, which might contribute to decreased barrier function in the esophagus [27 ]. Microarray analyses have identified numerous genes that are dysregulated in the esophagus of patients with EoE. This ‘EoE transcriptome’ has recently been extended using RNA sequencing technology. Indeed, 66% of genes identified by RNA sequencing were not identified using microarray. RNA sequencing has identified some long noncoding RNAs (lncRNA) that are known to regulate gene expression. For example, the lncRNA BANCR, which is overexpressed in EoE, is induced by IL-13, and BANCR expression correlates with levels of eosinophils and with levels of some well-known transcripts (e.g., periostin) previously identified as involved in the molecular pathogenesis of EoE. Indeed, silencing experiments suggest that BANCR overexpression by esophageal epithelial cells may lead to dysregulation of other genes (such as CASP14) and may be indirectly involved in epithelial cell hyperplasia [28]. Recently, neurotropic tyrosine kinase receptor type 1 (NTRK1), an early transcriptional target of IL-13, was found to be upregulated in EoE esophageal tissues. With the upregulation of IL-13 in EoE, there is consequent upregulation of NTRK1, causing increased responsiveness of epithelial cells to NGF, the NTRK1 ligand. This results in synergistic dysregulation of downstream target gene expression such as eotaxin-3 and SerpinB4 by esophageal epithelial cells. Taken together, these data suggest that synergistic effects among multiple different factors are necessary to display the full EoE phenotype [29]. IL-13 upregulation appears to play a key role in EoE pathogenesis, and a recent study found that the administration of an intravenous antibody to IL-13 resulted in a 60% decrease in the eosinophil count in the esophagus of patients with EoE. &
However, based on a desired response of at least a 75% decrease in the peak eosinophil count, the difference between the antibody-treated group and the placebo group did not reach statistical significance (12.5% response in placebo vs. 40% in the antibody-treated group) [30].
FIBROSIS AND REMODELING Transforming growth factor–b1 (TGF-b1) is a key regulator of the remodeling that occurs in the esophageal lamina propria in EoE, and TGF-b1 contributes to the upregulation of genes involved in eosinophil accumulation and fibrosis. Recently, TGF-b1 was shown to increase matrix metalloproteinase 2 (MMP2), a remodeling associated molecule. Other MMPs also are upregulated in EoE esophageal biopsies. For example, MMP14 expression is increased in patients with EoE, and its level correlates with the severity of fibrosis [31]. TGF-b1 also can induce and phosphorylate phospholambda in esophageal smooth muscle cells. Phospholambda is upregulated in patients with EoE, and its inhibition in primary cells significantly decreases their contractibility [32]. Finally, Smad3 is an important molecule in the TGF-b signaling pathway and, using Smad3-knockout animals, some investigators have shown that Smad3 plays a role in esophageal eosinophilia [33]. Esophageal dysfunction, heartburn, and chest pain occur frequently in EoE. A recent study in guinea pigs with esophageal eosinophilic inflammation induced by ovalbumin found that the esophageal eosinophilia was associated with increased acid responsiveness of vagal afferent neurons through transient receptor potential vanilloid type 1. This mechanism could underlie the heartburn and chest pain that are common symptoms in patients with EoE [34].
NEW IMMUNE COMPONENTS INVOLVED IN EOSINOPHILIC ESOPHAGITIS PATHOGENESIS iNKT cells recently have been identified as contributors to EoE pathogenesis [35–38]. Esophageal biopsies from patients with EoE exhibit dysregulation of iNKT, their receptors, and associated chemokines. Activation of iNKT by intranasal instillation of PBS57 in an animal model is sufficient to induce esophageal eosinophilia and, in an allergen-induced EoE model, neutralization of iNKT cells protects against the development of the esophageal inflammation [38]. Milk sphingolipids may stimulate iNKT cells to produce Th2 cytokines and may thus contribute to the development of EoE [35]. These data
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suggest that iNKT cells might be a novel pharmaceutical target for EoE therapy. Several interesting recent studies have shown that oral immunotherapy (OIT) can occasionally (estimated frequency: 2.7% of patients) lead to the development of EoE [39 ]. The disease symptoms may remit when OIT is discontinued, and these findings might provide important clues to the pathogenesis of EoE. OIT is known to enable the production of immunoglobulin (Ig) IgG4. One recent study has found that total IgG4 is increased 20-fold in esophageal biopsies from adult patients with EoE, and that IgG4 reactive to food also is increased [40]. These data suggest that IgE may not be the key contributor to EoE symptoms, which would explain why omalizumab (an antibody against IgE) did not significantly reduce EoE symptoms in a randomized, placebo-controlled trial. The finding that IgG4 might play an important role in EoE pathogenesis also could explain why OIT, which can induce a transient rise in IgG4, can be complicated by the development of EoE. IgE-independent animal models of EoE also have highlighted the importance of TSLP-elicited basophil responses in the induction of EoE [41]. A potential new strategy for EoE treatment has emerged from recent studies showing that epicutaneous immunotherapy in mice leads to Treg-dependent, long-term protection from esophageal eosinophilia, and that this protection is not necessarily limited only to the antigen administered in the epicutaneous immunotherapy. Studies on the safety and efficacy of epicutaneous immunotherapy for EoE appear to be warranted. &&
CONCLUSION The studies discussed in this report all converge on two major goals: to find noninvasive biomarkers to diagnose EoE and to find new pharmacologic targets for therapy. Although we have achieved some major strides in these areas, some puzzling questions remain to be answered. The recent evidence that the environment plays a greater role in EoE pathogenesis than genetics adds a new level of complexity to our understanding of this fascinating new disease. Studies of large cohorts will be needed to identify the causative factors and epigenetic mechanisms which lead to EoE in predisposed and exposed individuals. Acknowledgements We thank Fiona Paratte for administrative assistance. Financial support and sponsorship This review was supported by the Nestle´ Research Center and Nestle´ Health Science. 326
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Conflicts of interest C.B. is employed by Nestec Ltd.
REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Liacouras CA, Furuta GT, Hirano I, et al. Eosinophilic esophagitis: updated consensus recommendations for children and adults. J Allergy Clin Immunol 2011; 128:3–20. 2. Liacouras CA, Spergel JM, Ruchelli E, et al. Eosinophilic esophagitis: a 10-year experience in 381 children. Clin Gastroenterol Hepatol 2005; 3:1198–1206. 3. Noel RJ, Putnam PE, Rothenberg ME. Eosinophilic esophagitis. N Engl J Med 2004; 351:940–941. 4. Straumann A, Spichtin HP, Grize L, et al. Natural history of primary eosinophilic esophagitis: a follow-up of 30 adult patients for up to 11.5 years. Gastroenterology 2003; 125:1660–1669. 5. Weiler T, Mikhail I, Singal A, Sharma H. Racial differences in the clinical && presentation of pediatric eosinophilic esophagitis. J Allergy Clin Immunol Pract 2014; 2:320–325. This study highlights for the first time a similar prevalence of EoE in African American and white populations. 6. Collins MH, Blanchard C, Abonia JP, et al. Clinical, pathologic, and molecular characterization of familial eosinophilic esophagitis compared with sporadic cases. Clin Gastroenterol Hepatol 2008; 6:621–629. 7. Alexander ES, Martin LJ, Collins MH, et al. Twin and family studies reveal && strong environmental and weaker genetic cues explaining heritability of eosinophilic esophagitis. J Allergy Clin Immunol 2014; 134:1084–1092. This is the first study deciphering the key role of the environment in EoE etiology and identifying that the environment might have more influence on the occurrence of EoE than genetics. 8. Rothenberg ME, Spergel JM, Sherrill JD, et al. Common variants at 5q22 associate with pediatric eosinophilic esophagitis. Nat Genet 2010; 42:289– 291. 9. Kottyan LC, Davis BP, Sherrill JD, et al. Genome-wide association analysis of eosinophilic esophagitis provides insight into the tissue specificity of this allergic disease. Nat Genet 2014; 46:895–900. 10. Sleiman PM, Wang ML, Cianferoni A, et al. GWAS identifies four novel eosinophilic esophagitis loci. Nat Commun 2014; 5:5593. 11. Namjou B, Marsolo K, Caroll RJ, et al. Phenome-wide association study (PheWAS) in EMR-linked pediatric cohorts, genetically links PLCL1 to speech language development and IL5-IL13 to eosinophilic esophagitis. Front Genet 2014; 5:401. 12. Jensen ET, Kappelman MD, Kim H, et al. Early life exposures as risk factors for pediatric eosinophilic esophagitis. J Pediatr Gastroenterol Nutr 2013; 57: 67–71. 13. Lee YJ, Redd M, Bayman L, et al. Comparison of clinical features in patients with eosinophilic esophagitis living in an urban and rural environment. Dis Esophagus 2015; 28:19–24. 14. Lu S, Mukkada VA, Mangray S, et al. MicroRNA profiling in mucosal biopsies of eosinophilic esophagitis patients pre and posttreatment with steroids and relationship with mRNA targets. PLoS One 2012; 7:e40676. 15. Lu TX, Lim EJ, Wen T, et al. MiR-375 is downregulated in epithelial cells after IL-13 stimulation and regulates an IL-13-induced epithelial transcriptome. Mucosal Immunol 2012; 5:388–396. 16. Lu TX, Sherrill JD, Wen T, et al. MicroRNA signature in patients with eosinophilic esophagitis, reversibility with glucocorticoids, and assessment as disease biomarkers. J Allergy Clin Immunol 2012; 129:1064–1075. 17. Zahm AM, Menard-Katcher C, Benitez AJ, et al. Pediatric eosinophilic esophagitis is associated with changes in esophageal microRNAs. Am J Physiol Gastrointest Liver Physiol 2014; 307:G803–G812. 18. Lingblom C, Bergquist H, Johnsson M, et al. Topical corticosteroids do not revert the activated phenotype of eosinophils in eosinophilic esophagitis but decrease surface levels of CD18 resulting in diminished adherence to ICAM-1, ICAM-2, and endothelial cells. Inflammation 2014; 37:1932– 1944. 19. Blanchard C, Stucke EM, Rodriguez-Jimenez B, et al. A striking local esophageal cytokine expression profile in eosinophilic esophagitis. J Allergy Clin Immunol 2011; 127:208–217; 217. 20. Wen T, Stucke EM, Grotjan TM, et al. Molecular diagnosis of eosinophilic esophagitis by gene expression profiling. Gastroenterology 2013; 145:1289–1299. 21. Matoso A, Mukkada VA, Lu S, et al. Expression microarray analysis identifies novel epithelial-derived protein markers in eosinophilic esophagitis. Mod Pathol 2013; 26:665–676.
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Molecular pathogenesis of eosinophilic esophagitis Blanchard 22. Wolf WA, Cotton CC, Green DJ, et al. Predictors of response to steroid therapy for eosinophilic esophagitis and treatment of steroid-refractory patients. Clin Gastroenterol Hepatol 2015; 13:452–458. 23. Blanchard C, Wang N, Stringer KF, et al. Eotaxin-3 and a uniquely conserved gene-expression profile in eosinophilic esophagitis. J Clin Invest 2006; 116:536–547. 24. Zhang S, Wu X, Yu S. Prostaglandin D2 receptor D-type prostanoid receptor 2 mediates eosinophil trafficking into the esophagus. Dis Esophagus 2014; 27:601–606. 25. Blanchard C, Stucke EM, Burwinkel K, et al. Coordinate interaction between IL-13 and epithelial differentiation cluster genes in eosinophilic esophagitis. J Immunol 2010; 184:4033–4041. 26. Mavi P, Niranjan R, Dutt P, et al. Allergen-induced resistin-like molecule-alpha promotes esophageal epithelial cell hyperplasia in eosinophilic esophagitis. Am J Physiol Gastrointest Liver Physiol 2014; 307:G499–G507. 27. Sherrill JD, Kc K, Wu D, et al. Desmoglein-1 regulates esophageal epithelial & barrier function and immune responses in eosinophilic esophagitis. Mucosal Immunol 2014; 7:718–729. This study shows a barrier defect in the esophagus of EoE patients, and emphasizes the key role of epithelial cells and IL-13 in disease pathogenesis. 28. Sherrill JD, Kiran KC, Blanchard C, et al. Analysis and expansion of the eosinophilic esophagitis transcriptome by RNA sequencing. Genes Immun 2014; 15:361–369. 29. Rochman M, Kartashov AV, Caldwell JM, et al. Neurotrophic tyrosine kinase receptor 1 is a direct transcriptional and epigenetic target of IL-13 involved in allergic inflammation. Mucosal Immunol 2014. [Epub ahead of print] 30. Rothenberg ME, Wen T, Greenberg A, et al. Intravenous anti-IL-13 mAb QAX576 for the treatment of eosinophilic esophagitis. J Allergy Clin Immunol 2015; 135:500–507. 31. Beppu L, Yang T, Luk M, et al. MMPs-2 and -14 are elevated in eosinophilic esophagitis and reduced following topical corticosteroid therapy. J Pediatr Gastroenterol Nutr 2014. [Epub ahead of print]
32. Beppu LY, Anilkumar AA, Newbury RO, et al. TGF-b1-induced phospholamban expression alters esophageal smooth muscle cell contraction in patients with eosinophilic esophagitis. J Allergy Clin Immunol 2014; 134:1100–1107. 33. Cho JY, Doshi A, Rosenthal P, et al. Smad3-deficient mice have reduced esophageal fibrosis and angiogenesis in a model of egg-induced eosinophilic esophagitis. J Pediatr Gastroenterol Nutr 2014; 59:10–16. 34. Hu Y, Liu Z, Yu X, et al. Increased acid responsiveness in vagal sensory neurons in a guinea pig model of eosinophilic esophagitis. Am J Physiol Gastrointest Liver Physiol 2014; 307:G149–G157. 35. Jyonouchi S, Smith CL, Saretta F, et al. Invariant natural killer T cells in children with eosinophilic esophagitis. Clin Exp Allergy 2014; 44:58–68. 36. Lexmond WS, Neves JF, Nurko S, et al. Involvement of the iNKT cell pathway is associated with early-onset eosinophilic esophagitis and response to allergen avoidance therapy. Am J Gastroenterol 2014; 109:646–657. 37. Rajavelu P, Rayapudi M, Moffitt M, et al. Significance of para-esophageal lymph nodes in food or aeroallergen-induced iNKT cell-mediated experimental eosinophilic esophagitis. Am J Physiol Gastrointest Liver Physiol 2012; 302:G645–G654. 38. Rayapudi M, Rajavelu P, Zhu X, et al. Invariant natural killer T-cell neutralization is a possible novel therapy for human eosinophilic esophagitis. Clin Transl Immunol 2014; 3:e9. 39. Lucendo AJ, Arias A, Tenias JM. Relation between eosinophilic esophagitis && and oral immunotherapy for food allergy: a systematic review with metaanalysis. Ann Allergy Asthma Immunol 2014; 113:624–629. This study is a review and meta-analysis of available data on the risk of developing EoE during oral immunotherapy. 40. Clayton F, Fang JC, Gleich GJ, et al. Eosinophilic esophagitis in adults is associated with IgG4 and not mediated by IgE. Gastroenterology 2014; 147:602–609. 41. Noti M, Wojno ED, Kim BS, et al. Thymic stromal lymphopoietin-elicited basophil responses promote eosinophilic esophagitis. Nat Med 2013; 19: 1005–1013.
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327
Molecular pathogenesis of eosinophilic esophagitis Carine Blanchard
Purpose of review Eosinophilic esophagitis (EoE) is an esophageal disease characterized by an accumulation of eosinophils in the esophagus, which is normally devoid of eosinophils. The interest of the scientific community in EoE has grown considerably over the past two decades, and understanding of the molecular mechanisms involved in this disease has increased greatly in the last 2 years. Recent findings Important new insights into the pathogenesis of EoE recently have been achieved. Recent evaluations considering genetic and the environmental risk factors have led to the concept that some still-unknown environmental factors influence the risk of developing EoE more than the genetic predisposition. New molecules (in addition to interleukin-13, eotaxin-3, transforming growth factor-b1, thymic stromal lymphopoietin, filaggrin, or interleukin-5) also have been shown to be involved in the disease pathogenesis. Summary The present review describes recent advances in the understanding of the molecular mechanisms underlying EoE, and how these new findings have enhanced understanding of the pathogenesis of this new esophageal disorder. Keywords environmental exposure, eosinophilic esophagitis, genetics, interleukin-13, molecular, pathogenesis
INTRODUCTION Eosinophilic esophagitis (EoE) is a chronic inflammatory condition of the esophagus, characterized clinically by symptoms related to esophageal dysfunction and histologically by eosinophilic infiltration, with esophageal mucosal biopsy specimens showing 15 or more eosinophils per high power field (HPF) [1]. Along with eosinophils, numerous other cell types are found in increased numbers in the inflamed esophageal mucosa, including mast cells, invariant natural killer T (iNKT) cells, and lymphocytes. Other key histologic features of EoE are epithelial cell hyperplasia, and remodeling with fibrosis in the underlying lamina propria. A number of observations have highlighted the allergic, T-helper 2 (Th2)-type process that is associated with EoE: (1) The strong association with allergic disease identified in epidemiological studies. (2) The clinical observation that symptoms resolve when the causative foods are removed from the diet. (3) The preclinical studies showing that esophageal eosinophilic inflammation can be seen in animal models of allergic inflammation.
Most of our understanding of the molecular pathogenesis of EoE has emerged from studies on patients with EoE, using genome-wide screening technologies that have provided insights into the numerous molecular changes that occur in the disease. Conjointly, candidate gene studies also have enabled insights into the molecular pathogenesis, although a lot still needs to be unraveled to understand the molecular mechanisms that lead to the full disease phenotype.
EPIDEMIOLOGY: NOT ONLY A DISEASE OF WHITES Initial epidemiologic studies on EoE, which were performed largely in the United States and in Europe Nutrition and Health Research, Nestec Ltd, Nestle´ Research Center, Lausanne, canton of Vaud, Switzerland Correspondence to Carine Blanchard, Nutrition and Health Research, Nestec Ltd, Nestle´ Research Center, Route du Jorat 57, PO Box 44, CH-1000 Lausanne 26, Switzerland. Tel: +41 21 785 8510; e-mail: [email protected] Curr Opin Gastroenterol 2015, 31:321–327 DOI:10.1097/MOG.0000000000000186
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KEY POINTS A twin study emphasizes a larger role for environmental exposures than for genetics in EoE disease risk. Epidemiologic studies suggest that African Americans may be as likely as whites to develop EoE. The molecular pathogenesis of EoE involves the interaction between external environmental triggers and genetic traits in predisposed and exposed individuals. Esophageal epithelial cell genes dysregulation (TSLP, eotaxin-3), IL-13-induced inflammation, decreased esophageal epithelial barrier function, and increased esophageal immune cell infiltration (eosinophils, lymphocytes, mast cell, iNKT) are all hallmarks of the molecular pathogenesis of EoE.
[2–4], indicated that EoE was a disease that affected white males primarily. A recent report by Weiler et al. [5 ] suggests that these initial reports were misleading in regard to the ethnic distribution of EoE. In Weiler’s study of patients with EoE, whites comprised only 42% of the study population, whereas African Americans, Asians, and other ethnicities comprised 42%, 4%, and 12%, respectively. The investigators did note some differences between white and African American patients in the clinical presentation of EoE, however, with failure to thrive, vomiting, and a history of atopic dermatitis found more frequently in African Americans [5 ]. These data highlight the fact that EoE is not just a disease of whites, and it should be considered in the differential diagnosis for African Americans with esophageal dysfunction. This also suggests that there might not be large differences in the genetic predisposition to EoE between populations. Indeed, although the identification of familial cases of EoE led to the hypothesis that genetic predisposition was the major pathogenetic factor in EoE [6], recent data have challenged this concept to favor the environment as more important in the pathogenesis of EoE [7 ] (Fig. 1). &&
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GENETICS VERSUS ENVIRONMENT Genetic variants associated with the risk of developing EoE have been identified by case–control studies and genome-wide association studies (GWAS). GWAS initially identified risk variants in locus 5q22 of the thymic stromal lymphopoietin (TSLP) gene, and risk alleles such as rs3806932 also have been identified in the TSLP gene locus. Compared to healthy controls, esophageal expression of TSLP mRNA is increased in patients with active EoE, 322
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and TSLP is a credible candidate in EoE pathogenesis [8]. TSLP, which is expressed by epithelial cells, is a master regulator of allergic inflammation capable of activating diverse immune cells. These initial GWAS findings recently have been expanded to include new loci such as 2p23.1 spanning CAPN14, 8p23 in the intron XKR6, and 15q13 between LOC283710 and KLF13 [9]. Other new EoE loci also include 1p13 SLC25A24, 5q23 near SEMA6A, 10p12 in MIR467S, 11q13.5 of locus containing c11orf30, 11q14 in the intron of CCDC81, 12q13.3 spanning STAT6, 19q13.11 spanning ANKRD27, and 21q22 in HSF2BP gene (Table 1) [9,10]. The authors of these recent studies focused on CAPN14, an interleukin (IL)-13induced gene that encodes for calpain 14, which is a calcium-activated cysteine protease. CAPN14 mRNA expression is upregulated in esophageal biopsies of patients with active EoE. The substrate for CAPN14’s proteolytic activity includes inflammatory mediators relevant to allergic disease, but its role in EoE has not yet been defined. A recent study has tried to associate genetic variants with EoE symptoms or comorbidities rather than with the risk of developing EoE itself. The authors identified variants in the cluster of IL5–IL13 region that were associated principally with eosinophilia and, to some extent, with EoE disease [11]. These studies suggest a polygenic cause for EoE. Investigators have identified multiple genetic variants that are associated with EoE, but none that appear to be capable of causing the disease independently. These data also highlight the missing heritability of EoE, meaning the factors that are required to develop the disease but that remain unknown. There are multiple potential genetic and environmental factors underlying phenotypic variation in the EoE population. A recent twin study designed to elucidate the relative contributions of genetics and environment in the pathogenesis of EoE demonstrated that the genetic contribution has been greatly overestimated, whereas the role of environmental factors has been underestimated. This study evaluated patients with EoE and their first-degree relatives, focusing especially on the risk of developing EoE in monozygotic and dizygotic twins. For patients with EoE, the risk of EoE for other siblings was 2.4%, whereas the risk was 22% for dizygotic twins and 41% for monozygotic twins. This study suggests that genetics explains only 14% of the phenotypic variance in EoE whereas environment explains 81% [7 ]. A number of early life factors seem to influence EoE risk, such as the birth season, breastfeeding, and penicillin allergy [7 ]. Indeed, Jensen et al. [12] found that infants exposed to antibiotics in early infancy were six [1.7–20.8] times more likely to &&
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Molecular pathogenesis of eosinophilic esophagitis Blanchard
Table 1
Genetics
Early life exposure (Penicillin, birth season, breastfeeding…)
Environment
Eosinophilic esophagitis Milk sphingolipids Allergens, Other?
Desmoglein 1
Impaired barrier function
Filaggrin
↑
iNKT
↑ TSLP
↑ CAPN14
IL-13
Th2
↑IgG4
↑
NTRK1 Stimulated by NGF
↑ miR21
Epithelial cell hyperplasia
Eosinophilic recruitment
↑ BANCR
↑ Eotaxin-3
↑ RELMα Lamina propria fibrosis
↑ Periostin
↑ PDG2 Smad3
↑CPA3 Angiogenesis
Smooth muscle hyperplasia & contractibility
↑ PLN
↑ TRVP1
Nerve sensing
↑ VCAM-1
Basophils
DCs
Mast cells
Lymphocyte
Eosinophils
iNKT
TGF-β1
FIGURE 1. Molecular pathogenesis of eosinophilic esophagitis (EoE). A larger role for the environmental exposure than the genetics in EoE disease risk has recently been demonstrated. Molecular pathogenesis of EoE is at the interface between external triggers and genetic traits in individuals that are exposed and predisposed. The epithelial cell gene dysregulation (TSLP, eotaxin-3), the IL-13-induced inflammation, the decreased barrier function (filaggrin, desmoglein 1), and the increased immune cell infiltration [eosinophils, lymphocytes, mast cells, invariant natural killer T (iNKT)] are all hallmarks of the molecular pathogenesis. Figure was produced using Servier Medical Art, www.servier.com.
develop EoE than the normal population. Other groups also have focused on identifying differentiating environmental factors in EoE cohorts [13].
THE MOLECULAR PATHOGENESIS: THE QUEST FOR NONINVASIVE BIOMARKERS Several studies have identified alterations in microRNA expression in esophageal biopsies from patients with EoE. miR-21, which is involved in the downregulations of IL-12, has been found to be consistently dysregulated in active EoE, and
miR-21 appears to play a key role in the establishment of a full Th2 phenotype. Although esophageal microRNA dysregulation appears to be common in active EoE, more studies are needed to confirm these findings and to elucidate the importance of microRNA alterations in this disease. MicroRNAs tend to be extremely stable, and thus could be good blood biomarkers for EoE. However, only one study has found a difference between patients with EoE and normal patients in the expression of some miR (miR-146a, miR-146b, and miR-223) in the blood. These data are still
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Esophagus Table 1. Polymorphisms associated with EoE Gene symbol
Gene name
Gene function
Chromosome
FLG
Filaggrin
Barrier function
1q21.3
SLC25A24
Solute carrier family 25 (mitochondrial carrier; phosphate carrier), member 24
CAPN14
Calpain 14
Protease
2p23
TSLP
Thymic stromal lymphopoietin
Initiator of Th2 response, basophil response
5q22.1
WDR36
WD repeat domain 36
5q22.1
SEMA6A
Sema domain, transmembrane domain (TM), and cytoplasmic domain, (semaphorin) 6A
5q23
CCL26
Chemokine (C-C motif) ligand 26 (eotaxin-3)
XKR6
XK, Kell blood group complex subunit-related family, member 6
8p23
C11orf30
Chromosome 11 open reading frame 30 / EMSY
11q13.5
CCDC81
Coiled-coil domain containing 81
STAT6
Signal transducer and activator of transcription 6
Loc283710/KLF13
Loc283710/Kruppel-Like Factor 13
ANKRD27
Ankyrinrepeatdomain 27 (VPS9 domain)
TGFB1
Transforming growth factor, b1
Remodeling
19q13.1
CRLF2
Cytokine receptor-like factor 2
TSLP receptor
Xp22.33 Yp11.3
1p13
Chemoattraction of eosinophils
7q11.23
11q14 Th2 response
12q13.3 15q13 19q12.11
Derived in part from [8–10].
encouraging, however, because a trend was identified for miR-203 in another study [14–17]. Studies have shown that blood eosinophils from patients with EoE express differently surface markers than those from normal patients. A recent study by Lingblom et al. [18] showed that corticosteroids modify the expression of some eosinophil surface markers such as CD18, CD44, or CRTH2, and the ability of eosinophils to adhere to cellular matrix component. These effects may explain in part the ability of steroids to decrease esophageal eosinophilia in patients with EoE [18]. No single marker yet identified in the esophagus or in the blood can be used as a reliable diagnostic test for EoE. Therefore, researchers have focused on the development of panels of biomarkers that might differentiate EoE from non-EoE diseases or from inactive EoE. In a prospective study, panels of different blood cytokines were shown to be less sensitive than esophageal molecular markers [19]. Wen et al. [20] have recently developed a panel of markers in esophageal biopsies that can differentiate EoE from nonEoE patients. The panel is composed of 94 EoE transcript and two housekeeping genes derived from the EoE transcriptome. Scores were developed to separate EoE from normal patients (with a sensitivity of 92% and a specificity of 96%) and to separate glucocorticoid responders from normal patients and patients with active EoE. However, the EoE score was not optimal for differentiating patients who had an 324
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intermediate level of eosinophils (between 6 and 14 eosinophils per HPF) [20]. Other investigators used immunohistochemistry to identify epithelial cellderived gene expression patterns for differentiating EoE from patients with gastroesophageal reflux disease and normal controls [21]. The strength of this technique is that it could be performed retrospectively using paraffin-embedded tissues; the weakness is the fact that upper gastrointestinal endoscopy is still needed for the diagnosis. Although topical swallowed glucocorticoids are used widely to treat the esophageal inflammation of EoE, a considerable proportion of patients do not respond to steroids [22]. Wolf et al. [22] have found that a baseline low level of eotaxin-3 expression, a low number of mast cells, and esophageal dilatation at baseline are associated with a decreased rate of response to glucocorticoid therapy. In conclusion, the quest for noninvasive biomarkers for EoE continues, and attempts to identify a marker or a panel of markers that could be used as diagnostic tests or to predict the response to therapy, are still in their infancy.
INTERLEUKIN-13 AND EPITHELIAL CELLS ARE KEY PLAYERS IN EOSINOPHILIC ESOPHAGITIS PATHOGENESIS The Th2 IL-13 has been shown to be highly involved in the molecular pathogenesis of EoE. Indeed, IL-13 Volume 31 Number 4 July 2015
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has been shown to be involved in the upregulation of numerous genes in the esophagus of patients with EoE. One such gene is CCL26 (also called eotaxin-3), an eosinophil chemoattractant responsible for the accumulation of eosinophils in the esophagus of patients with EoE [23]. Recent data suggest that activated mast cells also may contribute to the chemoattraction of eosinophils in the esophagus through prostaglandin D2 [24]. A strong hyperplasia of esophageal epithelial cells is observed in biopsies from patients with EoE. This is associated with decreased expression of genes involved in the epidermal differentiation complex, which is regulated by IL-13 [25]. In an animal model, it was recently found that Resistinlike molecule alpha could induce thickening of the basal layer of the esophageal epithelium [26]. IL-13 is also responsible for the downregulation of desmoglein 1, which might contribute to decreased barrier function in the esophagus [27 ]. Microarray analyses have identified numerous genes that are dysregulated in the esophagus of patients with EoE. This ‘EoE transcriptome’ has recently been extended using RNA sequencing technology. Indeed, 66% of genes identified by RNA sequencing were not identified using microarray. RNA sequencing has identified some long noncoding RNAs (lncRNA) that are known to regulate gene expression. For example, the lncRNA BANCR, which is overexpressed in EoE, is induced by IL-13, and BANCR expression correlates with levels of eosinophils and with levels of some well-known transcripts (e.g., periostin) previously identified as involved in the molecular pathogenesis of EoE. Indeed, silencing experiments suggest that BANCR overexpression by esophageal epithelial cells may lead to dysregulation of other genes (such as CASP14) and may be indirectly involved in epithelial cell hyperplasia [28]. Recently, neurotropic tyrosine kinase receptor type 1 (NTRK1), an early transcriptional target of IL-13, was found to be upregulated in EoE esophageal tissues. With the upregulation of IL-13 in EoE, there is consequent upregulation of NTRK1, causing increased responsiveness of epithelial cells to NGF, the NTRK1 ligand. This results in synergistic dysregulation of downstream target gene expression such as eotaxin-3 and SerpinB4 by esophageal epithelial cells. Taken together, these data suggest that synergistic effects among multiple different factors are necessary to display the full EoE phenotype [29]. IL-13 upregulation appears to play a key role in EoE pathogenesis, and a recent study found that the administration of an intravenous antibody to IL-13 resulted in a 60% decrease in the eosinophil count in the esophagus of patients with EoE. &
However, based on a desired response of at least a 75% decrease in the peak eosinophil count, the difference between the antibody-treated group and the placebo group did not reach statistical significance (12.5% response in placebo vs. 40% in the antibody-treated group) [30].
FIBROSIS AND REMODELING Transforming growth factor–b1 (TGF-b1) is a key regulator of the remodeling that occurs in the esophageal lamina propria in EoE, and TGF-b1 contributes to the upregulation of genes involved in eosinophil accumulation and fibrosis. Recently, TGF-b1 was shown to increase matrix metalloproteinase 2 (MMP2), a remodeling associated molecule. Other MMPs also are upregulated in EoE esophageal biopsies. For example, MMP14 expression is increased in patients with EoE, and its level correlates with the severity of fibrosis [31]. TGF-b1 also can induce and phosphorylate phospholambda in esophageal smooth muscle cells. Phospholambda is upregulated in patients with EoE, and its inhibition in primary cells significantly decreases their contractibility [32]. Finally, Smad3 is an important molecule in the TGF-b signaling pathway and, using Smad3-knockout animals, some investigators have shown that Smad3 plays a role in esophageal eosinophilia [33]. Esophageal dysfunction, heartburn, and chest pain occur frequently in EoE. A recent study in guinea pigs with esophageal eosinophilic inflammation induced by ovalbumin found that the esophageal eosinophilia was associated with increased acid responsiveness of vagal afferent neurons through transient receptor potential vanilloid type 1. This mechanism could underlie the heartburn and chest pain that are common symptoms in patients with EoE [34].
NEW IMMUNE COMPONENTS INVOLVED IN EOSINOPHILIC ESOPHAGITIS PATHOGENESIS iNKT cells recently have been identified as contributors to EoE pathogenesis [35–38]. Esophageal biopsies from patients with EoE exhibit dysregulation of iNKT, their receptors, and associated chemokines. Activation of iNKT by intranasal instillation of PBS57 in an animal model is sufficient to induce esophageal eosinophilia and, in an allergen-induced EoE model, neutralization of iNKT cells protects against the development of the esophageal inflammation [38]. Milk sphingolipids may stimulate iNKT cells to produce Th2 cytokines and may thus contribute to the development of EoE [35]. These data
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suggest that iNKT cells might be a novel pharmaceutical target for EoE therapy. Several interesting recent studies have shown that oral immunotherapy (OIT) can occasionally (estimated frequency: 2.7% of patients) lead to the development of EoE [39 ]. The disease symptoms may remit when OIT is discontinued, and these findings might provide important clues to the pathogenesis of EoE. OIT is known to enable the production of immunoglobulin (Ig) IgG4. One recent study has found that total IgG4 is increased 20-fold in esophageal biopsies from adult patients with EoE, and that IgG4 reactive to food also is increased [40]. These data suggest that IgE may not be the key contributor to EoE symptoms, which would explain why omalizumab (an antibody against IgE) did not significantly reduce EoE symptoms in a randomized, placebo-controlled trial. The finding that IgG4 might play an important role in EoE pathogenesis also could explain why OIT, which can induce a transient rise in IgG4, can be complicated by the development of EoE. IgE-independent animal models of EoE also have highlighted the importance of TSLP-elicited basophil responses in the induction of EoE [41]. A potential new strategy for EoE treatment has emerged from recent studies showing that epicutaneous immunotherapy in mice leads to Treg-dependent, long-term protection from esophageal eosinophilia, and that this protection is not necessarily limited only to the antigen administered in the epicutaneous immunotherapy. Studies on the safety and efficacy of epicutaneous immunotherapy for EoE appear to be warranted. &&
CONCLUSION The studies discussed in this report all converge on two major goals: to find noninvasive biomarkers to diagnose EoE and to find new pharmacologic targets for therapy. Although we have achieved some major strides in these areas, some puzzling questions remain to be answered. The recent evidence that the environment plays a greater role in EoE pathogenesis than genetics adds a new level of complexity to our understanding of this fascinating new disease. Studies of large cohorts will be needed to identify the causative factors and epigenetic mechanisms which lead to EoE in predisposed and exposed individuals. Acknowledgements We thank Fiona Paratte for administrative assistance. Financial support and sponsorship This review was supported by the Nestle´ Research Center and Nestle´ Health Science. 326
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Conflicts of interest C.B. is employed by Nestec Ltd.
REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest 1. Liacouras CA, Furuta GT, Hirano I, et al. Eosinophilic esophagitis: updated consensus recommendations for children and adults. J Allergy Clin Immunol 2011; 128:3–20. 2. Liacouras CA, Spergel JM, Ruchelli E, et al. Eosinophilic esophagitis: a 10-year experience in 381 children. Clin Gastroenterol Hepatol 2005; 3:1198–1206. 3. Noel RJ, Putnam PE, Rothenberg ME. Eosinophilic esophagitis. N Engl J Med 2004; 351:940–941. 4. Straumann A, Spichtin HP, Grize L, et al. Natural history of primary eosinophilic esophagitis: a follow-up of 30 adult patients for up to 11.5 years. Gastroenterology 2003; 125:1660–1669. 5. Weiler T, Mikhail I, Singal A, Sharma H. Racial differences in the clinical && presentation of pediatric eosinophilic esophagitis. J Allergy Clin Immunol Pract 2014; 2:320–325. This study highlights for the first time a similar prevalence of EoE in African American and white populations. 6. Collins MH, Blanchard C, Abonia JP, et al. Clinical, pathologic, and molecular characterization of familial eosinophilic esophagitis compared with sporadic cases. Clin Gastroenterol Hepatol 2008; 6:621–629. 7. Alexander ES, Martin LJ, Collins MH, et al. Twin and family studies reveal && strong environmental and weaker genetic cues explaining heritability of eosinophilic esophagitis. J Allergy Clin Immunol 2014; 134:1084–1092. This is the first study deciphering the key role of the environment in EoE etiology and identifying that the environment might have more influence on the occurrence of EoE than genetics. 8. Rothenberg ME, Spergel JM, Sherrill JD, et al. Common variants at 5q22 associate with pediatric eosinophilic esophagitis. Nat Genet 2010; 42:289– 291. 9. Kottyan LC, Davis BP, Sherrill JD, et al. Genome-wide association analysis of eosinophilic esophagitis provides insight into the tissue specificity of this allergic disease. Nat Genet 2014; 46:895–900. 10. Sleiman PM, Wang ML, Cianferoni A, et al. GWAS identifies four novel eosinophilic esophagitis loci. Nat Commun 2014; 5:5593. 11. Namjou B, Marsolo K, Caroll RJ, et al. Phenome-wide association study (PheWAS) in EMR-linked pediatric cohorts, genetically links PLCL1 to speech language development and IL5-IL13 to eosinophilic esophagitis. Front Genet 2014; 5:401. 12. Jensen ET, Kappelman MD, Kim H, et al. Early life exposures as risk factors for pediatric eosinophilic esophagitis. J Pediatr Gastroenterol Nutr 2013; 57: 67–71. 13. Lee YJ, Redd M, Bayman L, et al. Comparison of clinical features in patients with eosinophilic esophagitis living in an urban and rural environment. Dis Esophagus 2015; 28:19–24. 14. Lu S, Mukkada VA, Mangray S, et al. MicroRNA profiling in mucosal biopsies of eosinophilic esophagitis patients pre and posttreatment with steroids and relationship with mRNA targets. PLoS One 2012; 7:e40676. 15. Lu TX, Lim EJ, Wen T, et al. MiR-375 is downregulated in epithelial cells after IL-13 stimulation and regulates an IL-13-induced epithelial transcriptome. Mucosal Immunol 2012; 5:388–396. 16. Lu TX, Sherrill JD, Wen T, et al. MicroRNA signature in patients with eosinophilic esophagitis, reversibility with glucocorticoids, and assessment as disease biomarkers. J Allergy Clin Immunol 2012; 129:1064–1075. 17. Zahm AM, Menard-Katcher C, Benitez AJ, et al. Pediatric eosinophilic esophagitis is associated with changes in esophageal microRNAs. Am J Physiol Gastrointest Liver Physiol 2014; 307:G803–G812. 18. Lingblom C, Bergquist H, Johnsson M, et al. Topical corticosteroids do not revert the activated phenotype of eosinophils in eosinophilic esophagitis but decrease surface levels of CD18 resulting in diminished adherence to ICAM-1, ICAM-2, and endothelial cells. Inflammation 2014; 37:1932– 1944. 19. Blanchard C, Stucke EM, Rodriguez-Jimenez B, et al. A striking local esophageal cytokine expression profile in eosinophilic esophagitis. J Allergy Clin Immunol 2011; 127:208–217; 217. 20. Wen T, Stucke EM, Grotjan TM, et al. Molecular diagnosis of eosinophilic esophagitis by gene expression profiling. Gastroenterology 2013; 145:1289–1299. 21. Matoso A, Mukkada VA, Lu S, et al. Expression microarray analysis identifies novel epithelial-derived protein markers in eosinophilic esophagitis. Mod Pathol 2013; 26:665–676.
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Molecular pathogenesis of eosinophilic esophagitis Blanchard 22. Wolf WA, Cotton CC, Green DJ, et al. Predictors of response to steroid therapy for eosinophilic esophagitis and treatment of steroid-refractory patients. Clin Gastroenterol Hepatol 2015; 13:452–458. 23. Blanchard C, Wang N, Stringer KF, et al. Eotaxin-3 and a uniquely conserved gene-expression profile in eosinophilic esophagitis. J Clin Invest 2006; 116:536–547. 24. Zhang S, Wu X, Yu S. Prostaglandin D2 receptor D-type prostanoid receptor 2 mediates eosinophil trafficking into the esophagus. Dis Esophagus 2014; 27:601–606. 25. Blanchard C, Stucke EM, Burwinkel K, et al. Coordinate interaction between IL-13 and epithelial differentiation cluster genes in eosinophilic esophagitis. J Immunol 2010; 184:4033–4041. 26. Mavi P, Niranjan R, Dutt P, et al. Allergen-induced resistin-like molecule-alpha promotes esophageal epithelial cell hyperplasia in eosinophilic esophagitis. Am J Physiol Gastrointest Liver Physiol 2014; 307:G499–G507. 27. Sherrill JD, Kc K, Wu D, et al. Desmoglein-1 regulates esophageal epithelial & barrier function and immune responses in eosinophilic esophagitis. Mucosal Immunol 2014; 7:718–729. This study shows a barrier defect in the esophagus of EoE patients, and emphasizes the key role of epithelial cells and IL-13 in disease pathogenesis. 28. Sherrill JD, Kiran KC, Blanchard C, et al. Analysis and expansion of the eosinophilic esophagitis transcriptome by RNA sequencing. Genes Immun 2014; 15:361–369. 29. Rochman M, Kartashov AV, Caldwell JM, et al. Neurotrophic tyrosine kinase receptor 1 is a direct transcriptional and epigenetic target of IL-13 involved in allergic inflammation. Mucosal Immunol 2014. [Epub ahead of print] 30. Rothenberg ME, Wen T, Greenberg A, et al. Intravenous anti-IL-13 mAb QAX576 for the treatment of eosinophilic esophagitis. J Allergy Clin Immunol 2015; 135:500–507. 31. Beppu L, Yang T, Luk M, et al. MMPs-2 and -14 are elevated in eosinophilic esophagitis and reduced following topical corticosteroid therapy. J Pediatr Gastroenterol Nutr 2014. [Epub ahead of print]
32. Beppu LY, Anilkumar AA, Newbury RO, et al. TGF-b1-induced phospholamban expression alters esophageal smooth muscle cell contraction in patients with eosinophilic esophagitis. J Allergy Clin Immunol 2014; 134:1100–1107. 33. Cho JY, Doshi A, Rosenthal P, et al. Smad3-deficient mice have reduced esophageal fibrosis and angiogenesis in a model of egg-induced eosinophilic esophagitis. J Pediatr Gastroenterol Nutr 2014; 59:10–16. 34. Hu Y, Liu Z, Yu X, et al. Increased acid responsiveness in vagal sensory neurons in a guinea pig model of eosinophilic esophagitis. Am J Physiol Gastrointest Liver Physiol 2014; 307:G149–G157. 35. Jyonouchi S, Smith CL, Saretta F, et al. Invariant natural killer T cells in children with eosinophilic esophagitis. Clin Exp Allergy 2014; 44:58–68. 36. Lexmond WS, Neves JF, Nurko S, et al. Involvement of the iNKT cell pathway is associated with early-onset eosinophilic esophagitis and response to allergen avoidance therapy. Am J Gastroenterol 2014; 109:646–657. 37. Rajavelu P, Rayapudi M, Moffitt M, et al. Significance of para-esophageal lymph nodes in food or aeroallergen-induced iNKT cell-mediated experimental eosinophilic esophagitis. Am J Physiol Gastrointest Liver Physiol 2012; 302:G645–G654. 38. Rayapudi M, Rajavelu P, Zhu X, et al. Invariant natural killer T-cell neutralization is a possible novel therapy for human eosinophilic esophagitis. Clin Transl Immunol 2014; 3:e9. 39. Lucendo AJ, Arias A, Tenias JM. Relation between eosinophilic esophagitis && and oral immunotherapy for food allergy: a systematic review with metaanalysis. Ann Allergy Asthma Immunol 2014; 113:624–629. This study is a review and meta-analysis of available data on the risk of developing EoE during oral immunotherapy. 40. Clayton F, Fang JC, Gleich GJ, et al. Eosinophilic esophagitis in adults is associated with IgG4 and not mediated by IgE. Gastroenterology 2014; 147:602–609. 41. Noti M, Wojno ED, Kim BS, et al. Thymic stromal lymphopoietin-elicited basophil responses promote eosinophilic esophagitis. Nat Med 2013; 19: 1005–1013.
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