🦠Gut microbiota & Food allergy
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Probiotics are defined by the World Health Organization as ‘live micro-organisms that when administered in adequate amount, confer a health benefit to the host’. The use of probiotics(beneficial microbiota) in atopic conditions stems from the possibility that by protecting against colonization with pathogenic bacteria, probiotic may protect intestinal barrier and decrease susceptibility allergens.
Substantial evidence exists that a ‘healthy’ intestinal microbiota (Beneficial microbiota) facilitates the development of immune tolerance . Earlier studies showed that gut associated lymphoid tissues (GALT) including Peyer’s patches are poorly developed or absent in germ-free mice. It has been shown that introduction of Bacteroides fragilis (a probiotic) into the lower gut in the neonatal period of germ-free mice can lead to a re-development of GALT and induction of tolerances. Inability to establish and maintain immune tolerance early in life increases the host’s risk of developing allergic and inflammatory diseases.
A recent study by Azad et al. found that, in 166 infants participating in the population-based Canadian Healthy Infant Longitudinal Development (CHILD) study, 12 (7.2%) became sensitized to 1 or more common food allergens at 1year of age. Food sensitization was defined as a food-specific wheal size of 2mm or greater compared to the one elicited by the negative control.
The authors found that gut microbiota richness (not diversity) at 3 months of age was lower in food-sensitized patients compared with control infants, though this difference did not persist at 1 year of age. Enterobacteriaceae were higher and Bacteroidaceae (Beneficial bacteria) were lower in the fecal samples at 3 and 12 months in sensitized patients. Each quartile increase in richness of Bacteroidaceae (Beneficial bacteria) at 3 months was associated with a 55%reduction in risk of sensitization to food at 1 year, while each quartile increase in Enterobacteriaceae/Bacteroidaceae ratio was associated with a two-fold increased risk of sensitization.
Several factors impact the developing gut microbiome in early life, including diet, mode of delivery, antibiotic treatment, and pet and environmental exposures.
The commensal gut microbiota induce IL-22 that promotes mucosal integrity, preventing seepage of protease-resistant allergens through the intestinal mucosal barrier.
Another mechanism by which the commensal flora promote tolerance is through the production of short chain fatty acids (SCFAs), generated by bacterial fermentation of dietary fibers. SCFA act on T cells via a G-protein-coupled receptor (GPR43) and protect mice from intestinal inflammation.
Food allergy is associated with alterations in the gut microbiota or dysbiosis early in life that may be predictive of disease persistence versus tolerance acquisition. Evidence for the benefits of adjunct therapy with probiotics for the prevention of food allergies and for potentiating oral immunotherapy remains circumstantial, with further studies needed to validate its use. Studies in murine models of food allergy suggest that microbial therapy with few bacterial species holds promise in future applications for prevention or therapy of food allergy.
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