Immunomodulatory effects of breast milk on food allergy

Abstract

Objective: To summarize the literature on immunomodulatory effects of breast milk on sensitization and possible mechanisms of action.

Data sources: Animal and human studies in PubMed that assessed breastfeeding or breast milk composition in food allergy.

Study selections: All recent studies and some older key publications focusing on this topic.

Results: Human milk composition is highly variable among mothers, which can affect the developing infant immune system. Human milk also affects the infant gut microbiome, which is associated with food allergy. High levels of human milk immune factors (IgA, cytokines, oligosaccharides) are associated with reduced risk of food allergy in the infant; it remains uncertain whether these are directly protective or biomarkers of transferred protection. Animal studies highlight potential mechanisms of protection provided by antigens, transforming growth factor β, and immunocomplexes, yet their relevance is poorly understood in humans. The role of food antigens in human milk in initial sensitization or tolerance induction is unclear.

Conclusion: The protection against allergy development provided by human milk may be attributable to the effect on the infant gut microbiome or direct effects on immune system. Studies evaluating the effect of breastfeeding and human milk composition on food allergy are needed.

Figure 1.

Maternal and breast milk factors that influence the development of the neonatal immune system.

Figure 2.

In order to estimate the effect of maternal diet during lactation on FA outcomes in the offspring (bold arrow), it is necessary to control for the effect of maternal diet during pregnancy. Without statistically controlling for this variable given its association to both the outcome (child FA) and the exposure (maternal diet during lactation), the resulting effect estimate would not reflect the true association of interest.