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Epithelial Barrier: Protector and Trigger of Allergic Disorders

Izquierdo E1, Rodriguez-Coira J1, Delgado-Dolset MI1, Gomez-Casado C1,2, Barber D1, Escribese MM1

1IMMA, Departamento de Ciencias Médicas Básicas, Facultad de Medicina, Universidad San Pablo CEU, Madrid, Spain.
2Department of Dermatology, University Hospital Düsseldorf, Düsseldorf, Germany.

J Investig Allergol Clin Immunol 2023; Vol. 32(2)
doi: 10.18176/jiaci.0779

The epithelial barrier has been classically considered as only the first line of defense against irritants, pathogens, and allergens, but it is now known that it also plays an essential role in the immunological response against exogenous agents. In fact, recent reports postulate the epithelial barrier hypothesis as a possible explanation for the increasing incidence and severity of allergic diseases.
The epithelial barrier preserves the isolation of the inner tissues from potential external threats. Moreover, a coordinated interaction between epithelial and immune cells ensures the unique immune response taking place in mucosal tissues and that is has been reported to be dysregulated in allergic diseases.
Herein, we and others have demonstrated that in severe allergic phenotypes, the epithelial barrier experiments several histological modifications and increased in immune cells infiltration, leading to its dysfunction. This is common in atopic dermatitis, asthma, and/or food allergy. However, the precise role of the epithelial barrier in the mucosal biology during allergic diseases progression is not well understood yet.
In this review, we aim to compile recent knowledge regarding the histological structure and immunological function of the epithelial barrier and to shed light on the role of this compartment in the onset, and progression of allergic diseases.

Key words: Epithelium, Mucosal immunity, Allergy, Antigen, Immunoglobulin (Ig) switch, Inflammation