Respiratory viral infections in children with asthma: do they matter and can we prevent them?

Ahanchian, Hamid; Jones, Carmen M; Chen, Yueh-sheng; Sly, Peter D

Reduced bacterial diversity in the infant's gastrointestinal tract has been associated with an increased risk of allergic sensitization and allergic rhinitis but not asthma or atopic dermatitis [102] . In the first year of life, especially the first few weeks, the microbiota of the newborn is highly variable during this critical time of post-natal maturation of the immune system. Microbiota is shaped by genetic and environmental factors including: mode of delivery, neonates born by means of vaginal delivery are exposed to mothers gut, skin, and vaginal flora [104] ; breast feeding and diet [105] ; farm or urban living [106] ; vitamin D status [107] ; and antibiotic consumption [98, 108] . This knowledge stimulated interest in the use of probiotics and prebiotics as the intentional introduction or encouragement of specific microbes to shape immune system development. Specifically, the microbiota can activate distinct tolerogenic dendritic cells in the gut and through this interaction can drive regulatory T-cell differentiation that modulates both Th1 and Th2 responses inside and outside the gut [109] [110] [111] . Probiotics have been successfully used for the treatment of several gastrointestinal disorders (viral and antibiotic-associated diarrhea, inflammatory bowel disease) [112, 113] . However, attempts to prevent or treat allergic disorders such as eczema, asthma and allergic rhinitis have had inconsistent results [99, 109, [114] [115] [116] .