Clinical efficacy and mechanism of probiotics in allergic diseases

Abstract

A complex interplay between genetic and environmental factors partially contributes to the development of allergic diseases by affecting development during prenatal and early life. To explain the dramatic increase in the prevalence of allergic diseases, the hygiene hypothesis proposed that early exposure to infection prevented allergic diseases. The hygiene hypothesis has changed to the microbial hypothesis, in which exposure to microbes is closely linked to the development of the early immune system and allergic diseases. The intestinal flora may contribute to allergic disease through its substantial effect on mucosal immunity. Based on findings that exposure to microbial flora early in life can change the Th1/Th2 balance, thus favoring a Th1 cell response, probiotics may be beneficial in preventing allergic diseases. However, evidence from clinical and basic research to prove the efficacy of probiotics in preventing allergy is lacking. To date, studies have yielded inconsistent findings on the usefulness of probiotics in allergic diseases. It is difficult to demonstrate an exact effect of probiotics on asthma, allergic rhinitis, and food allergy because of study limitations, such as different first supplementation period, duration, different strains, short follow-up period, and host factors. However, many studies have demonstrated a significant clinical improvement in atopic dermatitis with the use of probiotics. An accurate understanding of the development of human immunity, intestinal barrier function, intestinal microbiota, and systemic immunity is required to comprehend the effects of probiotics on allergic diseases.

Regulation of TWIK-related potassium channel-1 (Trek1) restitutes intestinal epithelial barrier function

“…This treatment restored the epithelial barrier function and facilitated the therapeutic effect of SIT on allergic responses in the intestine. The beneficial effect of probiotics has been recognized for use as a therapeutic supplement in a number of diseases; 25,26 the present data are in agreement with those from previous reports. It is noteworthy that using probiotics alone induced significant improvement in the barrier function and attenuated the allergic responses.…”

Three Novel Candidate Probiotic Strains with Prophylactic Properties in a Murine Model of Cow's Milk Allergy

“…Numerous preclinical and clinical trials have evaluated their effectiveness in the prevention or treatment of allergic diseases, but results are conflicting. Indeed, some studies showed beneficial effects in the prevention of FA (8), atopic dermatitis (9), and respiratory allergies (10), while others did not (11,12). Thereby, currently available evidence failed to indicate that probiotic supplementation reduces the risk of developing allergy in children, and the European Food Safety Authority did not deliver favorable opinions following some requests.…”

Understanding probiotics’ role in allergic children

“…In fact, in a mouse asthma model, it has been reported that Th17 induces allergic inflammation but probiotics suppress it through repression of interferon-g (Th1-related cytokines), IL-4 (Th2-related cytokines), and Th17 cells in splenic CD4 T cells, involving the expression of IL-10 and TGFb in mesenteric lymph nodes [28]. The suppression of Th17 response by probiotics administration was also demonstrated in mouse affected by atopic dermatitis [20]. These outcomes may be restricted to some bacterial species, such as Lactobacillus reuteri and Lactobacillus casei, but not Lactobacillus plantarum, which triggers monocyte-derived dendritic cells to conduct the regulatory T-cell development [22].…”

“…Optimal probiotics should exert several functions or meet the following requisites: high cells adhesion; reduction or exclusion of pathogenic adherence; persistence of multiplication and production of acids, H 2 O 2 , and bacteriocin antagonistic to pathogens; production of short chain fatty acids (SCFA) in order to improve epithelial barrier and potentiate anti-inflammatory action; biosynthesis of Vitamin K; fermentation of indigestible dietary fiber; positive influence on peristalsis; safety, noninvasiveness, noncarcinogenicity, and nonpathogenicity; co-aggregation mechanisms to form a normal balanced gut microbiota [18][19][20] (Fig. 2).…”