Inhibition effect of blunting Notch signaling on food allergy through improving T_H1/T_H2 balance in mice

Abstract

Background

Notch signaling regulates proliferation, differentiation, and function of dendritic cells, T cells, and mast cells, as well as many other immune cells, which act as important parts in food allergy, Notch signaling may play an important role in food allergy.

Objective

To investigate the role of Notch signaling in IgE-mediated food allergy.

Methods

An ovalbumin-induced food allergy mouse model was built (cholera toxin as adjuvant) and Notch signaling was blunted by FLI-06 and MW167, which inhibited Notch receptor–expressing phase and the γ-secretase–affecting phase, respectively. Then food allergy indicators, including levels of serum antibodies, cytokines, and degranulation, were examined. Meanwhile, clinical features, such as vascular permeability changes, intestinal permeability changes, body temperature changes, and symptoms, were also observed.

Results

After blunting Notch signaling, the levels of serum ovalbumin specific IgE and IgG₁ were decreased significantly, suggesting that blunting Notch signaling inhibited antibody responses. The levels of T_H1 cytokines (interferon-γ) were increased significantly, whereas the levels of T_H2 cytokines (interleukin-4, -5, and -13) were decreased significantly, suggesting T_H2 polarization was suppressed after blunting Notch signaling. The expression of T-bet was significantly increased, whereas the expression of Gata-3 was significantly reduced in both messenger RNA and protein levels, indicating T_H2 polarization was inhibited and T_H1 polarization was enhanced after blunting Notch signaling. Moreover, allergic clinical features of mice were alleviated after blunting Notch signaling.

Conclusion

Food allergy was inhibited by blunting Notch signaling through suppressing T_H2 polarization, enhancing T_H1 cell differentiation and promoting T_H1/T_H2 balance in mice. Notch signaling plays a key role in IgE-mediated food allergy.

Introduction

Food allergy often induces severe allergic diseases complications and seriously affects quality of life. A total of 3% to 4% of adults and 5% of infants have food allergies every year in developed countries.¹ The underlying mechanism of this immune disorder currently remains a mystery. Most food allergies are IgE-mediated type 1 immediate hypersensitivity. CD4⁺ T cells activation and differentiation are key steps in IgE-mediated food allergy.² The naive CD4⁺ T cells selectively differentiate into different subtypes, including interferon-γ (IFN-γ)–producing T_H1; interleukin (IL)-4, IL-5, IL-13 secreting T_H2, IL-17A producing T_H17; and inducible regulatory T cell lineages. T_H2 polarization and T_H2-dominant immune response are major contributors to food allergy.[3], [4] Unfortunately, the mechanism of T_H2 polarization induction is still unclear. The differentiation of naive T cells depends on various factors; the recognition of allergen presented to CD4⁺ T cells by antigen-presenting cells (APCs) is a major effector axis. Many molecules expressed on the surface of T cells and APCs have capacities to drive T_H1 or T_H2 polarization, such as Toll-like receptors on dendritic cells inducing T_H1 polarization⁵ and the costimulatory molecules OX40 on T cells and OX40L on APCs driving T_H2 polarization.⁶

Recently, the expression of Notch ligands on APCs in concert with Notch receptors on T cells has been found to play a key role in T_H1- or T_H2-promoting stimuli.[7], [8], [9], [10] Four Notch receptors (Notch1, 2, 3, and 4) and 5 known ligands (Jagged 1 and 2 and Delta-like 1, 3, and 4) have been found in mammals.¹¹ As a highly conserved signaling pathway, Notch signaling is induced when the Notch receptor encounters the ligand. This interaction finally initiates the release of Notch intracellular domain (NICD), which is affected by γ-secretase. Then the NICD translocates to the nucleus to induce the transcription of genes.¹² Data from several laboratories revealed that Notch signaling is required in T_H2-cell differentiation.[13], [14], [15] However, the role of Notch signaling in T_H1 differentiation is still controversial. Many studies have found that Delta-like proteins indeed promoted the differentiation of naive CD4⁺ T cells into the T_H1-cell lineage,[16], [17], [18] but some researchers found that it was not essential to T_H1 cell differentiation by using Notch knockout mice.[13], [19] A number of studies have found that Notch signaling plays an important role in a variety of diseases, such as cancer,²⁰ diabetes,²¹ and asthma,²² but its role in food allergy was not explored.

In this study, the role of Notch signaling in IgE-mediated food allergy was explored. We speculated that Notch signaling was necessary in IgE-mediated food allergy. An ovalbumin-induced IgE-mediated food allergy mouse model was built, and Notch signaling was blunted by FLI-06 and MW167, which inhibited Notch receptor–expressing phase and the γ-secretase–affecting phase, respectively. Then, related indicators of food allergy were examined. The study will define the role of Notch signaling in IgE-mediated food allergy and provide evidence of potential therapy of food allergy.