Abstract
Infants who are breastfed are at an immunological advantage when compared with formula fed infants, evidenced by decreased incidence of infections and diminished propensity for long term conditions, including chronic wheeze and/or asthma. Exclusive breastfeeding reduces the duration of hospital admission, risk of respiratory failure and requirement for supplemental oxygen in infants hospitalised with bronchiolitis suggesting a potentially protective mechanism. This review examines the evidence and potential pathways for protection by immunomodulatory factors in human milk against the most common viral cause of bronchiolitis, respiratory syncytial virus (RSV), and subsequent recurrent wheeze in infants. Further investigations into the interplay between respiratory virus infections such as RSV and how they affect, and are affected by, human milk immunomodulators is necessary if we are to gain a true understanding of how breastfeeding protects many infants but not all against infections, and how this relates to long-term protection against conditions such as chronic wheezing illness or asthma.
Highlights
The development of the infant immune system is influenced by primary exposure to antigens that will promote either antibody dominant humoral immune responses (T helper lymphocyte (Th)2 mediated) or cytokine-cell mediated responses (Th1 mediated) [1,2,3,4]
Many significant antigens encountered in early infancy are allergens, such as house dust mite and animal dander, and viruses such as respiratory syncytial virus (RSV), all of which have the potential to promote a Th2 polarised response
Lymphocytes and by week 11, there are B lymphocytes present in foetal tissues that are capable of producing IgE [13,14,15]. This indicates a substantial maturation of the infant immune system during exposure to this highly Th2 predominant environment that may be further skewed by genetic or epigenetic factors predisposing to atopy. The effects of this may be demonstrated in part by the inhibition of IFN-γ production by cord and peripheral blood mononuclear cells (PBMC) and the expression of IL-13 (Th2 cytokine) mRNA by ovalbumin stimulated PBMCs of infants at birth, who later present with food-associated atopic eczema [16,17]
Summary
The development of the infant immune system is influenced by primary exposure to antigens that will promote either antibody dominant humoral immune responses (T helper lymphocyte (Th) mediated) or cytokine-cell mediated responses (Th1 mediated) [1,2,3,4]. Infants who are breastfed are at an immunological advantage when compared with formula fed infants, as evidenced by both decreased incidence of infections during infancy and diminished propensity for a number of long term conditions, including chronic wheeze and/or asthma [7,8,9,10] These advantages indicate a biological link between a mother and her infant via the factors supplied in the milk. Potential immunomodulators which continue to be identified in human milk include most established mediators, such as cytokines and maternally derived leukocytes, but may include epigenetic factors These immunomodulators may affect development through both direct and indirect influences on the naive cells of the immature infant immune system during the early, formative stages of immune development (Table 1). Secondary mediator release, phagocytosis and viral clearance, promotion of inflammatory cascade or tissue repair
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