Probiotics against airway allergy: host factors to consider

Abstract

The worldwide prevalence of allergic diseases has drastically increased in the past decades. Recent studies underline the importance of microbial exposure for the development of a balanced immune system. Consequently, probiotic bacteria are emerging as a safe and natural strategy for allergy prevention and treatment. However, clinical probiotic intervention studies have so far yielded conflicting results. There is increasing awareness about the importance of host-associated factors that determine whether an individual will respond to a specific probiotic treatment, and it is therefore crucial to promote a knowledge-based instead of an empirical selection of promising probiotic strains and their administration regimen.In this Review, we summarize the insights from animal model studies of allergic disease, which reveal how host-related factors – such as genetic makeup, sex, age and microbiological status – can impact the outcomes of preventive or curative probiotic treatment. We explore why and how these factors can influence the results of probiotic studies and negatively impact the reproducibility in animal experiments. These same factors might profoundly influence the outcomes of human clinical trials, and can potentially explain the conflicting results from probiotic intervention studies. Therefore, we also link these host-related factors to human probiotic study outcomes in the context of airway allergies.

Probiotics as a Possible Strategy for the Prevention and Treatment of Allergies. A Narrative Review

“…These allergies are caused by the response of an inappropriate immune response of Th2 lymphocytes to different antigens, including environmental or food antigens. The activation of this response leads to the secretion of interleukins (IL)-4, IL-5, and IL-13 and an allergen-specific IgE production, which drives allergic inflammation [ 1 , 10 ]. Interferon (INF)-γ inhibits Th1 activity by inducing these cytokine responses, thus maintaining an allergic phenotype [ 23 ].…”

“…Allergens act on innate immune cells. Repeated contact with an allergen triggers the activation of mast cells and basophils and the release of allergic mediators, resulting in symptoms ranging from sneezing and itchy rashes to severe shortness of breath and anaphylaxis [ 1 , 2 , 3 ]. Currently, the list of allergic diseases published by the WHO includes asthma, rhinitis, conjunctivitis, rhinosinusitis, anaphylaxis, atopic eczema, hives, and angioedema, as well as secondary reactions caused by drugs, foods, or insects [ 4 ].…”

“…Today, approximately 1 billion people worldwide suffer from allergies, and these numbers are estimated to increase to 4 billion in the next 30–40 years [ 1 ]. In recent years, the prevalence of allergic diseases has increased greatly, to the point that 30–40% of the world’s population now suffers from one or more allergic diseases.…”

Wheat allergy

“…Non-IgE mediated reactions are induced via a Th2 lymphocytic response independent from IgE-specific antibodies to wheat and are characterized by an eosinophilic infiltration inducing tissue inflammation, which is exacerbated by type 2 innate lymphoid cells (ILC2) action. 21 Thymic stromal lymphopoietin produced by the dysfunctional esophageal epithelium in genetically predisposed individuals could be one of the major initial drivers of the Th2 inflammation in eosinophilic esophagitis (EoE). 22 Clinical Picture of Wheat Allergy WA prevails chiefly in children with a family history of atopy.…”

“…The higher the wheat IgE levels, the older a child was when they developed tolerance to wheat. 36 24 ).…”