Background: The rate of caesarean deliveries has increased 10-fold worldwide during the past decades. Objective: To evaluate differences in the establishment of gut microbiota in infants born by vaginal or caesarean delivery and its impact on mucosal immunity. Methods: Altogether, 165 consecutive children, prospectively followed from birth at our clinic in Turku, Finland, were gathered; 141 (85%) were born by vaginal delivery and 24 (15%) by caesarean section. Blood was drawn at physician visits for indirect evaluation of mucosal immunity by ELISPOT assay. Faecal samples were obtained for determination of the gut microbiota by fluorescence in situ hybridization of bacterial cells. Results: Infants delivered by caesarean section harboured fewer bifidobacteria at an early age and were shown to mount a stronger humoral immune response. At 1 month of age, the total gut bacterial cell counts per 1 g faeces were higher in vaginally delivered infants (9.9 × 109, 95% CI 7.9 × 109–1.2 × 1010) as compared to caesarean section delivered (3.1 × 109, 95% CI 1.1 × 109–8.6 × 109) (p = 0.001). This distinction was mainly due to the greater number of bifidobacteria in vaginally delivered infants (1.9 × 109, 95% CI 6.3 × 108–5.6 × 109 vs. 1.5 × 106, 95% CI 4.1 × 102–5.7 × 109, respectively) (p = 0.001). During the first year of life, the total number of IgA-, IgG- and IgM-secreting cells was lower (p = 0.03, p = 0.02, p = 0.11, respectively) in infants born by vaginal delivery than in those born by caesarean section, possibly reflecting excessive antigen exposure across the vulnerable gut barrier. Conclusions: Our findings demonstrate that the mode of delivery may have, possibly via gut microbiota development, significant effects on immunological functions in the infant (http://www.clinicaltrials.gov/ct/gui/show/NCT00167700).
Infants of atopic mothers, specifically when breastfed exclusively over 2.5 months or totally over 6 months, had a higher risk of sensitization at the age of 12 months. This risk could be reduced by the use of probiotics during pregnancy and lactation, partly by resulting in a beneficial composition of the breast milk.
Prevalence of sensitization to airborne allergens, unlike that to dietary allergens, has increased over a long period of time. Our results support the concept of the immune function being programmed by external factors early in life. They also call for caution when interpretations of the pace and possible causes of the allergy epidemic are made on the basis of short-term studies.
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