IgG₄ in eosinophilic esophagitis: perpetrator, accomplice or bystander?

Eosinophilic esophagitis (EoE) is a T-helper type 2 (Th2) mediated disease characterized by an eosinophilic dominant esophageal inflammatory response that is thought to promote esophageal remodeling and reduced esophageal caliber leading to vomiting, dysphagia, chest pain, food impaction and decreased health-related quality of life (1). The cellular and molecular processes that underlie the pathophysiology of EoE are not yet fully understood, however a combination of environmental and genetic factors interwoven with host immunity is thought to drive the clinical manifestations of disease (2-5).

The demonstration of histologic and clinical improvement following elemental and elimination diets has led to the concept that food allergens and IgE are important contributors to the pathogenesis of EoE (6-10). This is further supported by the demonstration that EoE individuals have increased incidence of IgE-mediated food sensitization and levels of food specific IgE (11-13). However, elimination of foods based upon skin prick testing (SPT) or elevated serum IgE levels and anti-IgE therapy (omalizumab) have had limited success (14-17).

Recent clinical datasets have revealed a link between IgG₄ and pediatric and adult EoE (17-19). Notably, investigators have demonstrated increased levels of serum IgG₄ and esophageal IgG₄⁺ plasma cells (PCs) in EoE patients compared to control individuals. Assessment of cow’s milk protein specific IgG₄ antibodies in a pediatric EoE cohort has revealed serum IgG₄/IgE ratios to be >10,000 in EoE patients and, following adjustment for age and milk consumption, high titers of IgG₄ to CM protein strongly correlated with EoE with an odds ratio of >20 (19). IgG₄ is considered to be an anti-inflammatory antibody as it possesses a short hinge and low Fab arm flexibility, can undergo a process termed “Fab arm exchange” which precludes cross-linking of identical antigens, and has a low affinity for the Fc gamma activating receptors (20,21). So the link between elevated levels of IgG₄ and EoE was somewhat surprising and led to the speculation that EoE may be an IgG₄-associated disease. However, how IgG₄ contributes to EoE pathogenesis remains unclear.

A recent case-control study by Rosenberg et al., published in the journal Allergy, examined the role of IgG₄ in pediatric patients with EoE (22). The authors revealed a relationship between immunoglobulin levels, in particularly IgG₄, and histologic and transcriptomic profiles of esophageal biopsy samples from EoE (n=17) and control (n=19) pediatric patients. Moreover, the authors observed increased levels of IgM, IgA, IgG₁, IgG₂, IgG₃ and IgG₄ in esophageal tissue of patients with EoE compared to controls. Most striking, the esophageal IgG₄ levels in EoE patients were 22-fold higher than that observed in control individuals. No significant differences in esophageal IgE levels were observed in patients with EoE compared to control individuals.

To analyze of the relationship between IgG₄ levels and EoE severity the authors employed the validated EoE histology scoring system (EoEHSS) (23). Rosenberg and colleagues revealed that levels of IgG₄ in esophageal tissue correlated with mean histologic grade and stage in pediatric EoE. Notably, the strongest correlation was with basal zone hyperplasia (BZH) and esophageal eosinophilia. Transcriptional analyses of cytokine levels revealed a correlation between esophageal interleukin (IL)-4, IL-10 and IL-13 mRNA levels and IgG₄, but there was no association with transforming growth factor beta (TGF-β). IL-4 and IL-13 are known Th2 cytokines that induce B-cell class switching promoting production of IgE and IgG₄ (24,25). On the other hand, IL-10 which is produced at high levels by regulatory T cells (Treg) as well as eosinophils and enhances production of IgG₄ as opposed to IgE (26-28). Comparison of esophageal IgG₄ levels with gene expression in EoE using the EoE Diagnostic panel, a panel of 96 EoE genes (29), revealed a significant correlation with 62 genes that are involved in the biological processes including epithelial barrier, cell adhesion, inflammation, ion channels, chemokines/cytokines as well as proliferation. It would be interesting to know whether the observed increased levels of other immunoglobulins were associated with EoE severity and transcriptome profile to determine whether this was specifically related to IgG₄ or a general phenomenon related to increased inflammatory disease. Despite this, the positive correlation with the inflammatory pathways and observed histologic link suggests that IgG₄ may play a pro-inflammatory role contributing to the ongoing inflammation and esophageal epithelial remodeling in EoE.

Recently there has been a number of studies evaluating esophageal immunoglobulin levels in EoE patients (17-19). In an adult EoE cohort, investigators reported increased IgG₄ levels in esophageal tissue samples from patients with EoE compared to controls, however, levels of IgM, IgA, IgG₁, IgG₂, IgG₃ were not different between groups. Mohammad and colleagues reported increased IgG₄⁺-plasma cells (PC) in a pediatric EoE cohort compared with age- and sex-matched controls (18). Notably, IgG₄⁺-PC levels did not correlate with esophageal eosinophilia or therapeutic outcomes. Similarly, Schuler et al. (19) reported high sera CM-specific IgG₄ in a pediatric EoE cohort compared to controls. However, they did not observe any relationship between CM-specific IgG₄ levels and disease remission following CM elimination diet (19). Rosenberg and colleagues did not observe significant differences in esophageal IgE levels in EoE compared with controls. This would be in contrast to previous reports demonstrating heightened levels of IgE and IgE-PCs in esophageal biopsy samples in EoE compared with controls (12,13,19,30). In a randomized, double-blind, placebo-controlled trial of adults with EoE given an antibody against IgE (omalizumab) investigators reported that treatment with anti-IgE (omalizumab) did not alter symptoms or esophageal eos/HPF compared with placebo treatment (17) suggesting that EoE may not be an IgE-mediated disease process. It is important to note that Rosenberg et al. report that the ratio of IgG₄ to IgE was 10:1 in control subjects and was 224:1 in patients with EoE. Consistent with this, Schuyler et al., observed a similar increase in the CM-specific sIgG₄/sIgE ratio in pediatric patients with EoE (19). The discrepancies between these studies related to IgG₄ and IgE association with disease severity and therapeutic outcomes maybe reflective of differential roles for IgG₄ between pediatric and adult EoE or a differential contribution during the natural history of disease where IgE-mediated processes are involved in the initial disease course and then transition to primarily IgG₄-associated disease.

There were some limitations with this study. Firstly, the authors only analyzed n=17 non-EoE controls and n=19 EoE individuals and the small sample size is underpowered to evaluate the relationship between different treatment modalities impacts on IgG₄ levels. Furthermore, EoE individuals were selected without regard to atopic status, treatment status and it was not specified whether patients underwent or undergoing PPI trial which could impact the immunological and histologic outcome measurements. Furthermore, there was no exploration of the food sensitization status of those individuals in the control group. A future case-control study evaluating the levels of esophageal immunoglobulins in the setting of food sensitization could be of value. Furthermore, all the patients were of Caucasian descent which may influence the generalizability of these findings to broader populations.

Despite these limitations, the study by Rosenberg and colleagues adds further weight to the emerging concept of a role for IgG₄ in EoE. However, there are many unanswered questions including (I) whether heightened IgG₄ levels is just an epiphenomenon in EoE patients related to the elevated CD4⁺ Th2 and eosinophilic response or whether IgG₄ directly contributes to disease pathogenesis or (II) what is the predictive value of IgG₄/IgE ratio to EoE disease state and responsiveness to treatment modalities? Questions that will only be fully answered by additional clinical studies in both pediatric and adult EoE cohorts.

Acknowledgments

Funding: This work was supported by NIH R01 AI073553, R01 DK090119, Department of Defense W81XWH-15-1-0517 and Food Allergy Research Education (FARE).

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Annals of Esophagus. The article did not undergo external peer review.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/aoe.2018.09.03). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

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.e6; quiz 1-2.
2. Furuta GT, Katzka DA. Eosinophilic Esophagitis. N Engl J Med 2015;373:1640-8. [Crossref] [PubMed]
3. Clayton F, Peterson K. Eosinophilic Esophagitis: Pathophysiology and Definition. Gastrointest Endosc Clin N Am 2018;28:1-14. [Crossref] [PubMed]
4. Dowling PJ, Neuhaus H, Polk BI. The Role of the Environment in Eosinophilic Esophagitis. Clin Rev Allergy Immunol 2018; [Epub ahead of print]. [Crossref] [PubMed]
5. Spergel J, Aceves SS. Allergic components of eosinophilic esophagitis. J Allergy Clin Immunol 2018;142:1-8. [Crossref] [PubMed]
6. Markowitz JE, Spergel JM, Ruchelli E, et al. Elemental diet is an effective treatment for eosinophilic esophagitis in children and adolescents. Am J Gastroenterol 2003;98:777-82. [Crossref] [PubMed]
7. Gonsalves N, Yang GY, Doerfler B, et al. Elimination diet effectively treats eosinophilic esophagitis in adults; food reintroduction identifies causative factors. Gastroenterology 2012;142:1451-9.e1; quiz e14-5.
8. Gonzalez-Cervera J, Angueira T, Rodriguez-Dominguez B, et al. Successful food elimination therapy in adult eosinophilic esophagitis: not all patients are the same. J Clin Gastroenterol 2012;46:855-8. [Crossref] [PubMed]
9. Lucendo AJ, Arias A, Gonzalez-Cervera J, et al. Empiric 6-food elimination diet induced and maintained prolonged remission in patients with adult eosinophilic esophagitis: a prospective study on the food cause of the disease. J Allergy Clin Immunol 2013;131:797-804. [Crossref] [PubMed]
10. Spergel JM, Brown-Whitehorn TF, Cianferoni A, et al. Identification of causative foods in children with eosinophilic esophagitis treated with an elimination diet. J Allergy Clin Immunol 2012;130:461-7.e5. [Crossref] [PubMed]
11. Vicario M, Blanchard C, Stringer KF, et al. Local B cells and IgE production in the oesophageal mucosa in eosinophilic oesophagitis. Gut 2010;59:12-20. [Crossref] [PubMed]
12. Erwin EA, Tripathi A, Ogbogu PU, et al. IgE Antibody Detection and Component Analysis in Patients with Eosinophilic Esophagitis. J Allergy Clin Immunol Pract 2015;3:896-904.e3. [Crossref] [PubMed]
13. Erwin EA, James HR, Gutekunst HM, et al. Serum IgE measurement and detection of food allergy in pediatric patients with eosinophilic esophagitis. Ann Allergy Asthma Immunol 2010;104:496-502. [Crossref] [PubMed]
14. Lucendo AJ, Molina-Infante J, Arias A, et al. Guidelines on eosinophilic esophagitis: evidence-based statements and recommendations for diagnosis and management in children and adults. United European Gastroenterol J 2017;5:335-58. [Crossref] [PubMed]
15. Aceves SS. Food allergy testing in eosinophilic esophagitis: what the gastroenterologist needs to know. Clin Gastroenterol Hepatol 2014;12:1216-23. [Crossref] [PubMed]
16. Rocha R, Vitor AB, Trindade E, et al. Omalizumab in the treatment of eosinophilic esophagitis and food allergy. Eur J Pediatr 2011;170:1471-4. [Crossref] [PubMed]
17. Clayton F, Fang JC, Gleich GJ, et al. Eosinophilic esophagitis in adults is associated with IgG4 and not mediated by IgE. Gastroenterology 2014;147:602-9. [Crossref] [PubMed]
18. Mohammad N, Avinashi V, Chan E, et al. Pediatric Eosinophilic Esophagitis Is Associated With Increased Lamina Propria Immunoglobulin G4-Positive Plasma Cells. J Pediatr Gastroenterol Nutr 2018;67:204-9. [Crossref] [PubMed]
19. Schuyler AJ, Wilson JM, Tripathi A, et al. Specific IgG4 antibodies to cow's milk proteins in pediatric patients with eosinophilic esophagitis. J Allergy Clin Immunol 2018;142:139-48.e12. [Crossref] [PubMed]
20. Crescioli S, Correa I, Karagiannis P, et al. IgG4 Characteristics and Functions in Cancer Immunity. Curr Allergy Asthma Rep 2016;16:7. [Crossref] [PubMed]
21. Aalberse RC, Stapel SO, Schuurman J, et al. Immunoglobulin G4: an odd antibody. Clin Exp Allergy 2009;39:469-77. [Crossref] [PubMed]
22. Rosenberg CE, Mingler MK, Caldwell JM, et al. Esophageal IgG4 levels correlate with histopathologic and transcriptomic features in eosinophilic esophagitis. Allergy 2018;73:1892-901. [Crossref] [PubMed]
23. Collins MH, Martin LJ, Alexander ES, et al. Newly developed and validated eosinophilic esophagitis histology scoring system and evidence that it outperforms peak eosinophil count for disease diagnosis and monitoring. Dis Esophagus 2017;30:1-8. [PubMed]
24. Lundgren M, Persson U, Larsson P, et al. Interleukin 4 induces synthesis of IgE and IgG4 in human B cells. Eur J Immunol 1989;19:1311-5. [Crossref] [PubMed]
25. Punnonen J, Aversa G, de Vries JE. Human pre-B cells differentiate into Ig-secreting plasma cells in the presence of interleukin-4 and activated CD4+ T cells or their membranes. Blood 1993;82:2781-9. [PubMed]
26. Chaudhry A, Samstein RM, Treuting P, et al. Interleukin-10 signaling in regulatory T cells is required for suppression of Th17 cell-mediated inflammation. Immunity 2011;34:566-78. [Crossref] [PubMed]
27. Jeannin P, Lecoanet S, Delneste Y, et al. IgE versus IgG4 production can be differentially regulated by IL-10. 1998;160:3555-61.
28. Spencer LA, Szela CT, Perez SA, et al. Human eosinophils constitutively express multiple Th1, Th2, and immunoregulatory cytokines that are secreted rapidly and differentially. J Leukoc Biol 2009;85:117-23. [Crossref] [PubMed]
29. Wen T, Stucke EM, Grotjan TM, et al. Molecular diagnosis of eosinophilic esophagitis by gene expression profiling. Gastroenterology 2013;145:1289-99. [Crossref] [PubMed]
30. Erwin EA, Kruszewski PG, Russo JM, et al. IgE antibodies and response to cow's milk elimination diet in pediatric eosinophilic esophagitis. J Allergy Clin Immunol 2016;138:625-8.e2. [Crossref] [PubMed]