Use of a Probiotic Supplement to Prevent Asthma in Infants

BACKGROUND: During infancy, environmental factors may affect immune system development and lead to the development of asthma. The hygiene hypothesis suggests that the absence of endotoxin exposure leads to an unfavorable Th1/Th2 balance. Thus, a controlled antigen exposure during infancy may establish a Th1/Th2 balance that blocks the onset of asthma or slows the progression of the disease. Lactobacillus is a bacterium commonly found in many foods (e.g., yogurt) in the typical childhood diet. It is also used as a probiotic supplement to prevent the development of diarrhea. Due to its safety and availability, Lactobacillus is an ideal bacterium to use as an antigen exposure to test the hygiene hypothesis. Consistent with the hygiene hypothesis, observational studies suggest that early Lactobacillus exposure leads to decreased risk of developing atopic dermatitis, which has been associated with asthma in later years. The investigators are aware of no study that has examined the effect of Lactobacillus on the development of early markers of asthma in children at risk for developing the disease. They hypothesize that Lactobacillus can be used as an antigen exposure to establish a Th1/Th2 balance that blocks the development of early markers of asthma. DESIGN NARRATIVE: The hygiene hypothesis suggests that the absence of endotoxin exposure leads to an unfavorable Th1/Th2 balance. A controlled antigen exposure during infancy may help establish a Th1/ Th2 balance that blocks the onset or progression of asthma. Lactobacillus is a bacterium found in many foods in the typical pediatric diet, and is used as a supplement to prevent diarrhea. Due to the safety, feasibility, and early promising results in preventing atopic dermatitis, Lactobacillus is an ideal bacterium to use as an exposure to test the hygiene hypothesis. The investigators hypothesize that such an exposure may block or delay development of early markers of asthma. The study will use a randomized placebo-controlled trial design to measure the effect of a 6-month daily exposure of Lactobacillus, as an infant supplement, on immune system and asthma development during the first 3 years of life. The study will measure the effect of the antigen exposure on the presence and time to presentation of: (1) early clinical markers for asthma development (frequent wheezing, wheezing without colds, rhinitis, and atopic dermatitis); (2) early immunologic markers for asthma development (eosinophilia, immunoglobulin E); and (3) development of a T-helper phenotype (Th-1 vs Th-2). Investigators will characterize the Th phenotype by measuring the whole blood lymphocyte response to stimulants, focusing on Th1 (IFN-gamma, interleukin (IL)-12) and Th2 cytokines (IL-10, IL-4, IL-13), as well as real-time reverse transcriptase polymerase chain reaction (RT-PCR) with PCR amplification (TaqMan) to quantify RNA transcripts. Clinical and immunologic markers will be measured up to 3 years of age. Adherence will be assessed using diaries, pill count, and Lactobacillus stool cultures. The study will use intention-to-treat analysis and will control for the impact of family, environmental, diet, and demographic factors on outcomes using multivariate regression and survival analysis techniques. Investigators expect that when compared to controls, subjects receiving Lactobacillus will have decreased and delayed development of markers for asthma, and a greater likelihood of developing a Th1 phenotype.