Effect of Intestinal Microbiota on the Immune System Clinical Trials

There is increasing evidence that the interaction between the intestinal microbiota and the intestinal epithelial and immune cells plays a key role in the postnatal development of the immune system. First studies with probiotics (74) and synbio-tics (40) demonstrate effects during infancy, and studies regarding the vaccination response in the elderly (75) indicate that the prebiotics might also influence the immune system. In particular, the animal experiments with prebiotics described above allow the hypothesis that prebiotics that are able to influence the composition of the entire intestinal microbiota toward microbiota found in breastfed infants might support the development of the immune system during infancy.

Clinical studies designed to prove this hypothesis should be focused on clinical outcome (incidence of infectious and allergic symptoms) and biomarkers representing the status of the immune system.

Based on the data derived from preclinical experiments with the mixture of GOS/lcFOS, a preventive study in term infants at risk for atopy was performed (51).

The study was designed to investigate the possible influence of this prebiotic mixture on the cumulative incidence of atopic dermatitis during the first 6 months of life in formula-fed infants at risk to develop allergy (paternal history of allergy). The study was performed as a prospective, double-blind, randomized, placebo (GOS/lcFOS was replaced by maltodextrin in the placebo formula) controlled study. Two hundred fifty nine infants with a family history of atopy were enrolled in the study. Fifty three infants left the trial before completing the study. The main reason for dropping out was the continuation or reestablishment of breastfeeding. One hundred two infants in the prebiotic group and 104 infants in the placebo group completed the study.

If the mother decided to start bottlefeeding, the infant was randomly assigned to one of two hydrolyzed protein formula groups (plus 0.8 g/100 ml pre-biotics or maltodextrine as placebo).

The infants were seen on a monthly basis. The interview of the parents was based on a diary kept by the parents. The primary outcome of the study was the cumulative incidence of atopic dermatitis during the first 6 months of life. The skin was investigated for atopic dermatitis according to the diagnostic criteria described by Harrigan and Rabinowitz (76) and Muraro et al. (69). The severity of the skin alterations was scored by the SCORAD index based on extension, intensity of the skin symptoms, as well as on the subjective symptoms pruritus and sleep loss as recommended by the European Task Force on atopic dermatitis (77,78).

In a subgroup of 98 infants, the parents allowed the collection of stool for microbiological analysis. In a subgroup of 86 infants, the parents allowed blood samples to be drawn for analysis of antibodies.

Intestinal microbiota was measured using plating techniques. In the plasma samples, subsequently total immune globulins, cow's milk protein (CMP), and DTP-specific immune globulins were measured.

Feeding the prebiotic mixture resulted in a significant stimulation of fecal bifidobacteria compared to the placebo group. Ten infants (9.8%; 95 CI: 5.417.1%) in the GOS/lcFOS group and 24 infants (23.1%; 95 CI: 16.0-32.1%) in the placebo group developed atopic dermatitis. The severity of the dermatitis was not influenced by diet. Supplementation of GOS/lcFOS resulted in a significant reduction of the plasma level of total IgE, IgG1, IgG2, and IgG3-Igs, whereas no effect on IgG4 was observed. CMP-specific IgG1 was significantly decreased. Other CMP-specific immune globulins and DTP-specific immune globulins were not affected at all by GOS/lcFOS supplementation indicating that the prebiotics induced an antiallergic immune globulins profile in this cohort of infants at risk (79).

More recently, the authors of this study reported results from a 2 years follow-up, which confirmed the findings at 6 months (80).

The effect of a prebiotic diet on the incidence of infectious symptoms was studied in a healthy infant population fed either a standard formula (n=162) or a formula supplemented with the prebiotic mixture of GOS/lcFOS (n=164). After 9 months, the prebiotic diet resulted in a reduction of the cumulative incidence of recurrent respiratory tract infections (<3 episodes) and of diarrhea (67).

These observations are in line with the findings that breastfeeding results in reduced incidence of atopic and allergic diseases (4-6) and reduced incidence of infections (7-9). Although the different effects of breastfeeding are of multifac-torial origin, the prebiotic oligosaccharides of breast milk might play a key role.

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