The role of Probiotics in allergic diseases
Sonia Michail
Abstract
Allergic disorders are very common in the pediatric age group. While the exact etiology is unclear, evidence is mounting to incriminate environmental factors and an aberrant gut microbiota with a shift of the Th1/Th2 balance towards a Th2 response. Probiotics have been shown to modulate the immune system back to a Th1 response. Several in vitro studies suggest a role for probiotics in treating allergic disorders. Human trials demonstrate a limited benefit for the use of probiotics in atopic dermatitis in a preventive as well as a therapeutic capacity. Data supporting their use in allergic rhinitis are less robust. Currently, there is no role for probiotic therapy in the treatment of bronchial asthma. Future studies will be critical in determining the exact role of probiotics in allergic disorders.
Allergic disorders are very common in the pediatric age group. While the exact etiology is unclear, evidence is mounting to incriminate environmental factors and an aberrant gut microbiota with a shift of the Th1/Th2 balance towards a Th2 response. Probiotics have been shown to modulate the immune system back to a Th1 response. Several in vitro studies suggest a role for probiotics in treating allergic disorders. Human trials demonstrate a limited benefit for the use of probiotics in atopic dermatitis in a preventive as well as a therapeutic capacity. Data supporting their use in allergic rhinitis are less robust. Currently, there is no role for probiotic therapy in the treatment of bronchial asthma. Future studies will be critical in determining the exact role of probiotics in allergic disorders.
Introduction
Currently, an estimated 20% of the population worldwide is suffering from some form of allergic disorder with a prevalence that continues to rise. For example, the prevalence of childhood asthma in the USA increased by 50% from 1980 to 2000. Atopic diseases involve Th2 responses to allergens. These clinical disorders are characterized by immediate hypersensitivity. Although the exact etiology of allergic diseases remains ambiguous, many investigators have proposed that environmental exposures may be major trigger factors in the development of allergic diseases.
As the rise in prevalence of allergic diseases has been seen mostly in industrialized countries, this led investigators to formulate the hygiene hypothesis in an attempt to explain the basis of the disease. This hypothesis entails that reduced family size and childhood infections have lowered our exposure to microbes, which play a crucial role in the maturation of the host immune system during the first years of life. In addition to environmental factors, the intestinal flora may be a contributor to allergic disease due to its substantial effect on mucosal immunity. Allergic responses are thought to arise if there is absence of microbial exposure while the immune system is still developing. Exposure to microbial flora early in life allows for a change in the Th1/Th2 balance, favoring a Th1 cell response. Several reports suggest that the make-up of intestinal microflora can be different in individuals with allergic disorders and in those who reside in industrialized countries where the prevalence of allergy is higher. For example, children from an industrialized country like Sweden harbor less Lactobacilli and Bifidobacteria (and more Staphylococcus aureus and Clostridia) in their bowels in comparison to children who live in countries like Estonia where allergic disorders are not as common.
The concept that children with allergic disorder harbor a different profile of microflora has been supported by several other studie. Perhaps the most convincing of these is the KOALA study, which examined flora of 957 infants in the Netherlands. The study revealed that C. dificile colonization at one month of age was associated with an increased likelihood of eczema, recurrent wheezing, and atopic dermatitis. E. coli colonization was associated with eczema rather than recurrent wheezing or atopic dermatitis. No association with bifidobacteria colonization, B. fragilis or lactobacilli colonization was observed.
While this concept has been validated in several other studies, there are a few reports that do not show a significant difference in microflora composition. A recent study comparing microflora composition of 324 European infants showed no association between food sensitization or atopic dermatitis and the intestinal bacteria. In general, however, most studies suggest that an association exists.
Currently, an estimated 20% of the population worldwide is suffering from some form of allergic disorder with a prevalence that continues to rise. For example, the prevalence of childhood asthma in the USA increased by 50% from 1980 to 2000. Atopic diseases involve Th2 responses to allergens. These clinical disorders are characterized by immediate hypersensitivity. Although the exact etiology of allergic diseases remains ambiguous, many investigators have proposed that environmental exposures may be major trigger factors in the development of allergic diseases.
As the rise in prevalence of allergic diseases has been seen mostly in industrialized countries, this led investigators to formulate the hygiene hypothesis in an attempt to explain the basis of the disease. This hypothesis entails that reduced family size and childhood infections have lowered our exposure to microbes, which play a crucial role in the maturation of the host immune system during the first years of life. In addition to environmental factors, the intestinal flora may be a contributor to allergic disease due to its substantial effect on mucosal immunity. Allergic responses are thought to arise if there is absence of microbial exposure while the immune system is still developing. Exposure to microbial flora early in life allows for a change in the Th1/Th2 balance, favoring a Th1 cell response. Several reports suggest that the make-up of intestinal microflora can be different in individuals with allergic disorders and in those who reside in industrialized countries where the prevalence of allergy is higher. For example, children from an industrialized country like Sweden harbor less Lactobacilli and Bifidobacteria (and more Staphylococcus aureus and Clostridia) in their bowels in comparison to children who live in countries like Estonia where allergic disorders are not as common.
The concept that children with allergic disorder harbor a different profile of microflora has been supported by several other studie. Perhaps the most convincing of these is the KOALA study, which examined flora of 957 infants in the Netherlands. The study revealed that C. dificile colonization at one month of age was associated with an increased likelihood of eczema, recurrent wheezing, and atopic dermatitis. E. coli colonization was associated with eczema rather than recurrent wheezing or atopic dermatitis. No association with bifidobacteria colonization, B. fragilis or lactobacilli colonization was observed.
While this concept has been validated in several other studies, there are a few reports that do not show a significant difference in microflora composition. A recent study comparing microflora composition of 324 European infants showed no association between food sensitization or atopic dermatitis and the intestinal bacteria. In general, however, most studies suggest that an association exists.
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