Review: Lymphocytes, cytokines, chemokines and the T-helper 1–T-helper 2 balance in canine atopic dermatitis

BACKGROUND: The development of atopic dermatitis (AD) and other cutaneous hypersensitivities involves the activation and differentiation of allergen-specific lymphocytes. Although hypersensitivity is often considered to be a \u27T-helper 2-polarized\u27 lymphocyte response, recent evidence suggests that clinical disease is associated with the development of multiple lymphocyte phenotypes. OBJECTIVES: The purpose of this paper is to review recent advances in the understanding of the roles of lymphocytes, cytokines and noncytokine factors in the pathogenesis of canine AD. METHODS: Citation databases, abstracts and proceedings from international meetings published between 2001 and 2013 were reviewed in this update. Where necessary, older articles were included for background information. RESULTS: The development of canine AD is associated with changes in both cutaneous and circulating lymphocyte populations. These lymphocyte responses are characterized by the production of a complex variety of cytokines, including not only T-helper 2 but also T-helper 1, T-helper 17 and regulatory T-cell responses. In addition, microarray gene expression analysis has enabled the identification of a number of noncytokine factors that appear to be associated with atopic inflammation. These include the calcium-binding protein S100A8, serum amyloid A and a number of protease inhibitors, as well as genes involved in epidermal barrier formation, innate immunity receptors, cell cycle proteins and apoptosis. CONCLUSIONS: The development of AD in dogs is characterized by the development of a delicate balance between a variety of T-cell phenotypes and inflammatory mediators, including cytokines, chemokines and noncytokine factors

Atopic dermatitis in the domestic dog

Dogs may develop a syndrome of spontaneous, inflammatory, pruritic dermatitis that shares many features with human atopic dermatitis, including a young age of onset, characteristic lesion distribution, immunoglobulin E sensitization to common environmental allergen sources, and evidence of epidermal barrier dysfunction. There are also several important differences between canine and human atopic dermatitis. Although dogs may suffer from multiple-organ hypersensitivity syndromes, there is no evidence that this species experiences the progressive evolution from cutaneous to respiratory allergy characteristic of the human atopic march. Despite the presence of epidermal barrier derangement, there is no significant association between canine atopic dermatitis and mutations in filaggrin. Finally, treatment of canine disease relies much less heavily on topical therapy than does its human counterpart, while allergy testing and allergen-specific immunotherapy provide an often essential component of effective clinical management of affected dogs