Animal models of eosinophilic esophagitis, review and perspectives

Abstract

Eosinophilic oesophagitis (EoE) is an allergen/immune‐mediated chronic esophageal disease characterized by esophageal mucosal eosinophilic infiltration and esophageal dysfunction. Although the disease was originally attributed to a delayed allergic reaction to allergens and a Th2‐type immune response, the exact pathogenesis is complex, and the efficacy of existing treatments is unsatisfactory. Therefore, the study of the pathophysiological process of EOE has received increasing attention. Animal models have been used extensively to study the molecular mechanism of EOE pathogenesis and also provide a preclinical platform for human clinical intervention studies of novel therapeutic agents. To maximize the use of existing animal models of EOE, it is important to understand the advantages or limitations of each modeling approach. This paper systematically describes the selection of experimental animals, types of allergens, and methods of sensitization and excitation during the preparation of animal models of EoE. It also discusses the utility and shortcomings of each model with the aim of providing the latest perspectives on EoE models and leading to better choices of animal models.

Different modeling methods and primary pathological characteristics of eosinophilic oesophagitis (EoE) mouse models, which include models of EoE induced by antigens such as Aspergillus fumigatus, ovalbumin, peanuts, indoor insects/detergents, as well as models induced by IL‐10 and genetic engineering. All of these models can lead to esophageal eosinophilia and esophageal remodeling.

1. INTRODUCTION

Eosinophilic esophagitis (EOE) is an allergen/immune‐mediated chronic esophageal disease characterized by eosinophilic infiltration of the esophageal mucosa (≥15 eosinophils per high‐powered field) and esophageal dysfunction, with clinical symptoms of chest pain, heartburn, and epigastric pain, and difficulty in swallowing solid food as the most common clinical manifestations. ^{1 , 2} The pathogenesis of EoE is complex; it arises from a negative interaction between environmental factors and genetic background, causing an impaired esophageal epithelial barrier with subsequent abnormal allergen exposure activating T helper type 2 (Th2) inflammation. ³ Patients with EoE often suffer from other allergic diseases such as asthma, atopic dermatitis and eosinophilic gastroenteritis. The treatment for EoE consists of topical and systemic glucocorticoids, dietary elimination, elemental diets, and proton pump inhibitors. ^{4 , 5} Most recently, dupilumab, a monoclonal antibody targeting IL‐4, received approval for use in patients aged 12 years or older with EoE. ⁶ However, these treatments still have significant challenges regarding efficacy, safety, expense, and patient adherence. Meanwhile, the prevalence of EoE has increased significantly over the past 30 years, resulting in a considerable public health and economic burden. ⁷ Therefore, the pathophysiological process of EOE is receiving more and more attention from researchers, with the purpose of continuously refining its pathogenesis and treatment. Due to the limitations of human studies and ethical requirements, animal models of EoE are of great significance in exploring the etiology and pathogenesis of EoE, as well as in the development of new drugs. There are limited published studies on the selection of experimental animals and the establishment of models for studying EOE, and there is a lack of standardized criteria on the type and dose of allergens, as well as the pathway and time of sensitization. This paper reviews the selection of experimental animals, types of allergens, and methods of sensitization and stimulation in preparing EoE animal models.

2. SELECTION OF LABORATORY ANIMALS AND THEIR CHARACTERISTICS

The model animals currently used to study EoE are mice, guinea pigs, and pigs. ^{8 , 9 , 10} Guinea pigs are easily sensitized and react highly after exposure to allergens. However, the lack of guinea pig strains with well‐defined genotypes and relevant immunological and molecular biological reagents makes further in‐depth studies of immune and genetic mechanisms difficult. Pigs are larger mammals whose esophagus is highly similar to the human esophagus and can better mimic the pathophysiological features of human diseases. Cortes et al. showed that after intraperitoneal sensitization and oral challenge with a food allergen, swine develop esophageal eosinophilia, which closely mimics human EoE. ¹¹ This model not only induces the underlying immune markers but also the micro‐ and macro‐pathological hallmarks of human EoE. However, pigs are expensive, have a long breeding cycle, and are more complex to operate than rodents, which limits their large‐scale use in medical research. In numerous studies, mice are the most commonly used EoE model animals, with their small size, low maintenance costs, and short reproduction and generation times. Mice have a clearer immunogenetic background, are more homogeneous, and share 99% of the same genome as humans, making them the only mammal after humans whose genome has been sequenced. ¹² The most commonly used mouse strains are BALB/c mice and C57BL mice, and with the development of genetic engineering techniques, genetically engineered mice have become very common in experimental research. In this review, we summarize the characteristics of the EOE mouse model and the different modeling approaches (Figure 1). The experimental details, as well as the merits and limitations of each method, are categorized and summarized to help investigations of the pathogenesis and immunology of EoE (Table 1).

FIGURE. 1.

Different modeling methods and primary pathological characteristics of eosinophilic oesophagitis (EoE) mouse models, which include models of EoE induced by antigens such as A. fumigatus, ovalbumin, peanuts, indoor insects/detergents, as well as models induced by IL‐10 and genetic engineering. All of these models can lead to esophageal eosinophilia and esophageal remodeling.

TABLE 1.

Summary of representative preclinical mouse models of eosinophilic oesophagitis.

Category	Characteristic		Intervention		Reference
Induced models by allergen	Merits	Limitations	Sensitization phase	Challenge phase
Aspergillus fumigatus	Similar to the pathologic features of EoE in humans Mimics human exposure	Long‐term process of sensitization	Sterile gauze containing 100 μg of Aspergillus fumigatus solution was fixed at on the shaved backs of mice for 1 week, following a rest period of 2 weeks, this procedure was repeated 2 times	25 μg of Aspergillus fumigatus nasal drip for once	[21]
Ovalbumin (OVA)	Consistent with the natural pathogenesis of human EoE disease Inducing esophageal eosinophilia and esophageal remodeling Mimics human exposure	Not show the full pathologic features of EoE in humans Long‐term process	50 μg of OVA and 1 mg of Al(OH)3 adjuvant dissolved in PBS for intraperitoneal injection on day 0 and 14	150 μg of OVA was used with nasal drops starting from day 15, and 7 times in 10 days	[13]
			50 μg of OVA and 1 mg of Al(OH)3 adjuvant dissolved in PBS for intraperitoneal injection on day 0 and 14	10 mg of OVA was injected into the esophagus 3 times per week for 4 weeks	[23]
			2 nmol MC903 in 100% EtOH applied to the skin of ears in the presence of 100 μg OVA for 14 days	Oral gavage with 50 mg of OVA twice, and OVA (1.5 g/L) was added to daily drinking water in 4 days	[26]
			100 μg of OVA solution into the sensitized mice via subcutaneous injection 4 times in 12 days	Oral gavage with 50 mg of OVA twice, and OVA (1.5 g/L) was added to daily drinking water in 4 days	[27]
Peanut extract	Similar to the pathologic features of EoE in humans Cause higher levels of eosinophils in the esophagus, compared to aerial allergens Mimics human exposure	Fewer relevant studies and need to be further explored Long‐term process	200 μg of peanut extract and 1 mg of alum adjuvant by intraperitoneal injection on day 0 and 14	100 μg of peanut extract was used with nasal drops on days 21, 23, and 25	[29]
			100 μg of peanut extract and 1 mg of alum adjuvant by intraperitoneal injection on day 0 and 14	50 μg of peanut extract was used with nasal drops on days 21, 23, and 25, followed by oral gavage with 2 mg peanut extract on days 27 and 29	[30]
			200 μg of peanut extract and 1 mg of alum adjuvant by intraperitoneal injection on day 0, 7 and 14; secured 200 μg of sterile gauze containing peanut extract was fixed on the shaved backs of mice for 1 week at a time on day 1, 21 and 42	Oral gavage with 2 mg peanut extract on days 29, 31, 33, 35, 38, 41, 43, 45, 47, and 49	[32]
Indoor insect detergents	Eosinophil in esophageal tissue increased with increasing allergen dose and exposure time	Fewer relevant studies and need to be further explored Not replicate typical exposure as humans may experience	100 μg of dust mites extract was used with nasal drip for 4 weeks on day 3, 4 and 5 every week		[34]
			0.5% SDS was added in drinking water for 14 days		[37]
Induced models by recombinant interleukin	Histologically similar to EoE in humans Short‐term process	Inconsistent with the natural pathogenesis of EoE in humans	10 μg of recombinant IL‐13 by intratracheal administration for once		[39]
			10 μg of recombinant IL‐13 was used with nasal drip for once		[40]
Genetically engineered models	Pathologic features of EoE may occur spontaneously	Technically demanding, complex, costly, low success rate Cannot fully reflect the actual status of the disease	Treatment with AAVrh.10mAnti‐Eos		[32]
			Nik−/− mice		[41]
			CC10‐iIL‐13 transgenic mice		[42]
			L2‐IL5 transgenic mice		[43]

3. METHODS OF ESTABLISHING A MOUSE MODEL OF EOE

3.1. Allergen induced mouse model of EOE

3.1.1. The experimental model induced by Aspergillus fumigatus

A. fumigatus is a common airborne saprophytic fungus whose spores are tiny in diameter and can be passively inhaled into the human body. The first EoE model was established by Mishra et al. in 2001 using A. fumigatus extract introduced into mice. The model was prepared in a similar way to the animal model of asthma by dissolving 100 μg of A. fumigatus in 50 μL of saline and administering nasal drops to the mice, three times a week for three weeks. ¹³ The model showed features similar to human EoE, such as eosinophilia, eosinophil degranulation, eosinophilic microabscesses, and epithelial cell hyperplasia within the esophageal epithelium. This study also explored the induction effects of A. fumigatus when administered orally and by gavage and found that mice exposed to oral or gastric allergens did not develop esophageal eosinophilia. In contrast, mice exposed to intranasal allergens exhibited significant esophageal eosinophilic infiltration and substantial changes in eosinophil levels in the stomach or small intestine were not found. Several studies have used this approach to establish a mouse model of EoE. In addition, these studies have shown that this model not only exhibits esophageal eosinophilia, but also esophageal remodeling, such as thickening of the esophageal basal lamina, subepithelial collagen deposition, muscularis propria thickening, and an increase in the esophageal perimeter, which are very similar to the pathologic features of EoE in humans. ^{14 , 15} There is no standardized single dose of A. fumigatus nose drops; Blanchard et al. used a 50 μg dose, while Vicari et al. used a 15 μg dose, both of which were successful in the preparation of EoE models. ^{16 , 17} In addition to nose drops, there have also been studies using the endotracheal route of administration to induce EoE. Mishra et al., in their study published in 2006, compared the two ways of induction, intranasal and endotracheal, and eosinophilia was observed in mouse esophageal and bronchoalveolar lavage fluid at comparable levels in both models. ¹⁸ The above studies suggest an interaction between the lungs and esophagus and a correlation between the development of EoE disease and asthma. The establishment of animal models of EoE can also be carried out in two stages: sensitization and elicitation, and studies have shown that sensitization to allergens can occur at sites where the skin barrier is damaged. ^{19 , 20} In these studies, Akei et al. sensitized mice by fixing sterile gauze containing 100 μg of A. fumigatus solution to a site on the back of the mice from which hair had been removed. They then used 25 μg of A. fumigatus in a nasal drip challenge, and found that the mice that were exposed to A. fumigatus only in the sensitization phase showed atopic dermatitis‐like manifestations. In contrast, mice that received A. fumigatus in both the sensitization and challenge phases showed esophageal eosinophilic infiltration, eosinophil degranulation, and epithelial cell hyperplasia. ²¹ A similar sensitization and challenge method was used by Holvoet et al., but the duration of sensitization was longer, and the dose of A. fumigatus used in the challenge phase was higher. ²² A. fumigatus produces endotoxins during growth; Mishra et al. induced mice with endotoxin‐free A. fumigatus extracts and found no significant difference in eosinophil levels in the esophagus of the mice as compared to the original A. fumigatus extract‐induced model, which suggests that the induction of esophageal eosinophilia by A. fumigatus is independent of endotoxin and that it triggers immune, rather than toxic, responses in the mouse, and esophageal eosinophil infiltration plays a significant role in the process. ¹⁸ While the mouse model induced by A. fumigatus is very similar to human EoE in terms of esophageal histology, it is important to note that the induction method lacks a standardized approach, and further studies are needed to fully understand the role of Aspergillus as a potential airborne sensitizer of EoE.

3.1.2. The experimental model induced by ovalbumin (OVA)

Egg is a common food allergen in patients with EoE, and dietary elimination and elemental diets can largely improve the clinical symptoms and histologic features of patients with EoE. OVA, an egg‐derived protein, induces a mouse model more consistent with the natural pathogenesis of human EoE disease. OVA is a heterotrimeric protein with strong antigenicity and immunogenicity and is often used with adjuvants such as Al(OH)₃. The experimental model of OVA‐induced EoE generally consists of two phases: sensitization and challenge; however, the manipulation of sensitization and challenge varies from researcher to researcher. The sensitization phase includes intraperitoneal sensitization, subcutaneous sensitization, and sensitization of damaged skin by OVA. The challenge phase includes esophageal injection, nasal drip, and oral administration with OVA. EoE was induced by Rubinstein et al. using intraperitoneal injection of OVA (50 μg of OVA and 1 mg of aluminum hydroxide adjuvant dissolved in PBS) for sensitization, and injection of 100 μL of OVA solution (100 mg/mL) into the esophagus of mice during the challenge stage. ²³ In this model, mice showed esophageal eosinophilic infiltration, an increased number of small blood vessels in the lamina propria, fibronectin deposition, and TGF‐β1‐positive cell infiltration. However, they did not show significant thickening of the basal region of esophageal tissue or esophageal fibrosis. Since then, several studies have applied this method to prepare EoE mouse models, which have successfully demonstrated esophageal eosinophilia and esophageal remodeling, but no study has yet reported the changes in the histological characteristics of the stomach and intestines of mice in this model. ^{24 , 25} Similar to the asthma model, Mishra et al. used intraperitoneal injection for sensitization and nasal drops for the challenge; 50 μg of OVA and 1 mg of aluminum hydroxide adjuvant were dissolved in sterile saline and injected intraperitoneally on days 0 and 14, and 50 μL of OVA solution (3 mg/mL) was used for the challenge with nasal drops, starting from day 15. The nasal drip was applied seven times in 10 days, and this study reported that this model did not induce significant esophageal eosinophilic infiltration. ¹³ Azouz et al. successfully established an EoE mouse model using intraperitoneal injection sensitization and nasal drip challenge, but the dose and timing of the sensitizing agent differed from the study by Mishra et al. They injected 100 μg of OVA in the sensitization period, and used 50 μL of OVA solution (2 mg/mL) for the nasal drip challenge, starting from the 26th day, with drops applied once every other day, four times in total, and the model showed significant esophageal eosinophilic infiltration. ²⁵ In addition to sensitization by intraperitoneal injection of OVA, a mouse model of EoE can also be induced by the action of OVA on the skin. Noti et al. developed a model of EoE associated with thymic stromal lymphopoietin (TSLP) overexpression, in which the vitamin D analog MC903 and OVA were applied to the skin of mice to increase the expression of TSLP in the skin. The mice were then stimulated by gavage with 50 mg of OVA, and OVA was added to their daily drinking water (1.5 g/L). ²⁶ Analysis of the digestive tract tissues of the mice in this model revealed significant eosinophilic infiltration, eosinophil degranulation, and epithelial cell hyperplasia in the esophageal tissues, and some of the mice developed food embeddedness, which was similar to human EoE patients. This model may be useful for simulating some patients with EoE with gastrointestinal allergic disorders. Sokulsky et al. used 100 μg of OVA solution to sensitized mice via subcutaneous injection, after which they were given two gavages with 50 mg of OVA during the challenge phase, with the addition of OVA (1.5 g/L) to their daily drinking water. The mice developed esophageal eosinophilia, esophageal fibrosis, and an increase in esophageal circumference. ²⁷ Venturelli et al. sensitized mice by fixing sterile gauze containing 100 μg of OVA solution on their backs at a site from which the hair had been removed. They used 30 mg of OVA in nasal drops during the challenge phase. ²⁸ The model exhibited significant esophageal eosinophilic infiltration, and the eosinophilia was confined to the esophagus, with no significant changes in eosinophil levels in the stomach and intestine. In addition, the method induced allergic reactions by disrupting the skin barrier without adjuvants, which is similar to the development of EoE disease in humans. However, these models do not yet show the full pathologic features of human EoE disease.

3.1.3. The experimental model induced by peanut extract

Peanut is a common food allergen. Induction of an animal model of EoE with peanut extract also involves two phases of sensitization and challenge. Rajavelu et al. sensitized mice with 200 μg of peanut extract and 1 mg of alum adjuvant by intraperitoneal injection and subsequently compared the effects of three different challenge modalities on mice: nasal drip, oral administration, and gavage. ²⁹ The study found that mice receiving peanut extract orally failed to develop esophageal eosinophilia during the challenge phase; mice gavaged with peanut extract showed not only esophageal eosinophilic infiltration but also eosinophilia in the small intestine; and mice treated with nasal drops showed more pronounced esophageal eosinophilic aggregation and eosinophilic degranulation and did not show eosinophilia in the lower digestive tract. These findings showed that the use of peanut extract nasal drip challenge is more advantageous than oral administration and gavage in simulating the histological characteristics in the esophagus of EoE. Most studies have used an intraperitoneal injection for sensitization and a nasal drip challenge to induce the EoE animal model. However, a uniform standard for the dosage and scheduling of the peanut challenge has not yet been established. Vanoni et al. sensitized mice with 100 μg of peanut extract and 1 mg of alum adjuvant by intraperitoneal injection, followed by three nasal drops of 50 μg of peanut extract and two oral doses of peanut powder at a later stage; the model showed marked esophageal eosinophilia and basal cell hyperplasia. ³⁰ Camilleri et al. sensitized mice with two intraperitoneal injections in the first week, with a one‐week break, followed by five consecutive weeks of nasal drip excitation, followed by another one‐week nasal drip after a three‐week break, for a total of 11 weeks of modeling. ³¹ The study found that mice developed esophageal eosinophilia and food impaction at weeks 4 and 11. Experimental models have also been induced by attacking the damaged skin barrier of mice with an allergen in conjunction with sensitization and provocation operations. Lianto et al. administered three intraperitoneal injections of 200 μg of peanut extract and 2 mg of alum adjuvant, followed by ten gavages of 2 mg of peanut extract, and secured 200 μg of sterile gauze containing peanut extract to the shaved backs of mice for one week at a time, two weeks apart, for a total of three times. In this model, eosinophilia was observed in the esophagus, but was not limited to the esophagus, and eosinophil aggregation was also observed in the small intestine. ³² Peanuts are very common in our daily life and are one of the major food allergens of EoE. Most patients with EoE can improve clinically and histologically by eliminating peanuts and related substances from their diets. Reintroducing this food will lead to the reappearance of the manifestations of EoE. ³³ The above‐mentioned study demonstrated that the experimental model of peanut extract‐induced EoE has many similar features to human EoE and that eosinophil levels in the esophagus of mice exposed to peanut allergens were higher than those previously reported for aerial allergens. ¹³ Still, there are fewer relevant studies in this area, which needs to be further explored in the future.

3.1.4. The experimental model induced by indoor insects and detergents

Indoor insects, especially dust mites and cockroaches, have been recognized as major inhalant allergens in adults and children, and many EoE patients are allergic to dust mites and cockroaches. ³⁴ The etiologic role of aeroallergens in the pathogenesis of EOE has been demonstrated. ¹³ Rayapudi et al. treated mice 12 times with nasal drops using 100 μg of cat, dog, dust mite, and cockroach extracts, and analyzed and compared the effects of different allergens on the mice. ³⁴ It was found that mice treated with cat or dog extracts did not have significantly elevated levels of esophageal eosinophils compared to saline‐treated controls, whereas mice treated with dust mite and cockroach extracts both showed significant esophageal eosinophil infiltration, with levels of esophageal eosinophils elevated by approximately 8‐ to 10‐fold compared to the control group, and that the two allergens had a superimposed effect in inducing esophageal eosinophilia. The study also found that eosinophil levels in mouse esophageal tissue increased with increasing allergen dose and exposure time. This model showed similar features to human EoE, such as the presence of intraepithelial eosinophils, eosinophil degranulation, and epithelial cell hyperplasia in the esophagus, and the absence of eosinophilia in the gastric tissues. However, the level of elevated esophageal eosinophils in the mouse model was lower than that of the experimental model of A. fumigatus induction previously reported. Dust mites and cockroaches are common allergens in indoor environments; they are more frequently used in the installation of asthma animal models, and are seldom used in the study of EoE animal models. Their application in EoE animal models needs to be further explored and improved.

In addition, detergents, like sodium dodecyl sulfate (SDS), are common ingredients in household products like dish soap and toothpaste. Studies suggest SDS can disrupt airway and skin epithelial barriers and promote Th2 inflammation. ^{35 , 36} EOE also is a delayed allergic reaction to allergens and a Th2‐type immune response. Doyle et al. constructed a mouse model of EOE by adding 0.5% SDS in drinking water for 14 days. ³⁷ This model showed increased IL‐33 protein expression, basal zone hyperplasia, CD4+ T cell infiltration, and esophageal eosinophilia. However, this model may not replicate typical exposure as humans may experience chronic, intermittent exposure to numerous household detergents, including during early development, along with other potential environmental factors. Importantly, previous studies suggest SDS may act as an adjuvant to promote the development of immune responses to exogenous antigens. ³⁸ Based on this model, detergent alone can mediate pathology with similarities to EoE. However, it is still unknown whether oral detergents promote an allergic sensitization to food or environmental allergens alone or in combination with other environmental factors.

3.2. Recombinant interleukin (IL)‐induced mouse model of EOE

EoE is an immunoreactive disease in which Th2 cells and their secretion of various cytokines (e.g., IL‐4, IL‐5, IL‐9, IL‐10, and IL‐13) are involved in the process of its immune response, and patients with EoE tend to have elevated levels of a variety of Th2 cytokines. Mishra et al. administered three different doses (0.5, 1.0, and 10 μg) of recombinant IL‐13 by intratracheal administration in mice and found that the higher the concentration of IL‐13, the higher level of eosinophils in the esophageal tissues of the mice. The study further compared and analyzed the effects of IL‐4, IL‐9, IL‐10, and IL‐13 on mice and found that only IL‐13 could successfully induce EoE. However, in the experiments comparing the various interleukins, the researchers only used a dose of 1.0 μg. More comparisons at different amounts are needed to further clarify their induction effects in mice. Histological analysis of the recombinant IL‐13‐induced experimental model showed significant eosinophilic infiltration and epithelial cell hyperplasia in esophageal tissues of mice, while eosinophil levels in gastrointestinal tissues were not significantly altered. ³⁹ In addition to its action in the trachea, recombinant IL‐13 has also been used to induce EoE through nasal drops. Niranjan et al. treated mice with 10 μg of recombinant IL‐13 in nasal drops and found that its effect on the esophagus of mice was similar to that using the previous treatment regime. ⁴⁰ IL‐13 promotes local infiltration of eosinophils in the esophageal mucosa by stimulating the production of eosinophil‐activated chemokine 3, which plays a vital role in the disease progression of EoE. Although the recombinant IL‐13‐induced mouse model is histologically similar to human EoE, studies have shown that food and aeroallergens are the primary triggers of EoE, and the use of recombinant IL‐13 to induce an experimental model of EoE is not quite in line with the natural pathogenesis of the human disease.

3.3. Application of genetic engineering technology in EoE disease research

Currently, most animal models of EoE require allergen induction, and the development of genetic engineering technology has led to more in‐depth research on spontaneous EoE animal models. Eden et al. found that Nik^−/− mice (lacking NF‐κB‐inducible kinase) could be used as a spontaneous animal model of EoE. The inflammatory manifestations of the gastrointestinal tract in this mouse model are essentially confined to the esophagus, and significant esophageal eosinophilic infiltration, eosinophilic degranulation, intraepithelial eosinophilic microabscesses, mucosal thickening, and basal cell hyperplasia may occur spontaneously. ⁴¹ In addition, other transgenic mice can exhibit experimental EoE. CC10‐iIL‐13 transgenic mice were able to express IL‐13 specifically in the lungs after being fed doxycycline, and histological analysis of their digestive tracts revealed that eosinophil levels in the esophagus of the mice were significantly elevated to approximately 47‐fold over the control group, while eosinophil levels in the gastrointestinal tissues were not significantly altered. The study also found that the esophagus underwent significant tissue remodeling, such as proliferation of esophageal epithelial cells, deposition of extracellular collagen, increase in the number of blood vessels, and increase in esophageal circumference. ⁴² Unlike CC10‐iIL‐13 mice that produce gene overexpression in ectopic locations, L2‐IL5 transgenic mice could specifically express IL‐5 in the esophagus. Masterson et al. sensitized L2‐IL5 transgenic mice by applying oxazolone (OXA) to their skin, and then locally stimulated their esophagus with OXA, and found that the model showed characteristic pathological changes of EoE such as eosinophil degranulation and microabscess formation, and basal cell hyperplasia. ⁴³ Genetic engineering techniques play an essential role in the study of the pathogenesis of EoE by utilizing transgenic mice or genetically defective mice based on a specific gene to study the effect of this gene product on the process of disease development. It has been found that IL‐5‐positive transgenic mice induced by sensitizers produce more significant pathological changes in EoE under the same circumstances, whereas IL‐5‐deficient mice are unable to induce EoE successfully. It has also been shown that signal transducer and activator of transcription 6 (STAT6)‐ and eotaxin‐1‐deficient mice fail to develop esophageal eosinophilic infiltration in response to sensitizers; these findings suggest that IL‐5, eotaxin‐1, and STAT6 are key effector molecules in the disease development of EoE. ¹⁵ EoE is a chronic disease that cannot be cured, and the primary treatment is dietary control and glucocorticosteroids, but once treatment is stopped, most patients will soon relapse. EoE can be reversed by genetic engineering, and relevant animal studies have been published. Camilleri et al. applied genetic engineering to synthesize the AAVrh.10mAnti‐Eos (a viral vector encoding an anti‐Siglec‐F monoclonal antibody) and introduced it into mice. A single treatment with AAVrh.10mAnti‐Eos produced sustained, high levels of Siglec‐F antibody expression, and the study found a single treatment with AAVrh.10mAnti‐Eos resulted in long‐term inhibition of esophageal eosinophil accumulation and improved esophageal remodeling. ³² Research using genetic engineering technology is receiving more and more attention from scholars, but there are still some shortcomings in its application to the study of EoE, which is technically demanding, complex, costly, has a low success rate, and may not always be able to fully correspond to the actual state of the disease because very few diseases are caused by the abnormal expression of single genes only, but rather by multifactorial interactions.

4. EVALUATION INDEXES OF ANIMAL MODELS OF EOSINOPHILIC ESOPHAGITIS

To date, there is no agreed standard successful EoE animal model. Ideal EoE animal models should mimic the pathogenesis of human EoE and have the pathophysiological characteristics of human EoE. Usually, mouse models with pathological changes characteristic of EoE, such as esophageal eosinophil aggregation and esophageal remodeling, can be considered successful. Esophageal eosinophilia is the most important pathological feature of EoE. The number of esophageal eosinophils in animal models is mainly detected by immunohistochemistry in esophageal tissue sections. The number of esophageal eosinophils in EoE mice is higher than that in normal mice, and the difference between the two is statistically significant. In addition, many mouse models show eosinophil degranulation and eosinophilic microabscesses within the esophageal epithelium. Another important feature of EoE is esophageal remodeling, manifested by major pathological changes such as esophageal epithelial cell hyperplasia, thickening of the basal region, angiogenesis, extracellular matrix protein deposition, and increase in esophageal circumference. After esophageal remodeling occurs, EoE mice tend to develop esophageal dysfunction, such as food impaction.

5. SUMMARY

The pathogenesis of EoE is complex, research on its etiology and pathophysiology is still in the exploratory stage, and there is a lack of effective therapy. Animal models used to study EoE can provide important information on the pathogenesis of EoE and enable us to explore the therapeutic options for EoE. Establishing a suitable animal model of EoE is therefore crucial. Ideal animal models should have the pathogenic features and characteristics of human EoE. Despite the wide variety of EoE animal models currently available, the models have many limitations. First, there are differences between animal models and human EoE; the structure of the esophagus in animals is different from that in humans, and it is not possible to completely simulate the histopathological changes in the human esophagus. Second, most of the causative factors of current animal models are single, while human EoE has multifactorial causes. Moreover, EoE is a chronic disease, and present technology does not allow long‐term observation and multiple sampling of the same animal model. There is still a need to develop animal models of EoE that are closer to human disease to promote further in‐depth EoE research and provide more effective therapeutic options for patients.

AUTHOR CONTRIBUTIONS

Manuscript preparation: Dong Li; Manuscript editing: Yujia Wei; Literature search: Jing Wang; Concept, manuscript review: Bo Wang. All the authors read and approved the final manuscript.

FUNDING INFORMATION

This work was supported by Natural Science Foundation of Hubei Province (2021CFB401).

CONFLICT OF INTEREST STATEMENT

The authors declare that they have no competing interests.

ETHICS STATEMENT

None.

Li D, Wei Y, Wang J, Wang B. Animal models of eosinophilic esophagitis, review and perspectives. Anim Models Exp Med. 2024;7:127‐135. doi: 10.1002/ame2.12391