Maternal immune markers in serum during gestation and in breast milk and the risk of asthma-like symptoms at ages 6 and 12 months: a longitudinal study

BACKGROUND: The role of breast milk on the risk of childhood asthma is in dispute. The aim of this prospective study is to determine the relationship of immune markers in maternal serum during gestation and breast milk to asthma-like symptoms (AS) in infancy. METHODS: Pregnant women were recruited in Columbia and Charleston, South Carolina. Blood (median: three weeks before delivery) and breast milk (three weeks after delivery) samples were collected. Concentrations of interferon (IFN)-γ, IFN gamma-induced protein 10 (IP-10 or CXCL10), CCL11, interleukin (IL) 1β, IL-4, IL-5, IL-6, CXCL8, IL-10, IL-12(p70), IL-13, transforming growth factor (TGF)-β1, and immunoglobulin (Ig) A in both maternal serum and milk whey were determined via immunoassays. Asthma-like symptoms (AS) of the infant were ascertained at 6 and 12 months, respectively. Generalized estimating equations assessed relative risks (RRs) of immune markers for repeated measurements of AS, considering intra-individual correlations and adjusting for confounders. To provide comparable risk estimates, quartiles of the immune markers were used, except for IL-5 in whey and IgA in serum, which were dichotomized. RESULTS: Of 178 women, 161 provided blood and 115 breast milk samples. IL-12(p70), IL-4, IL-10, IL-1β, and CCL11 in serum and in whey were not further considered for the statistical analyses since the proportion of non-detectable values was high. Most immune markers in serum and milk whey were moderately or highly correlated; however, IgA was negatively correlated. Infants in the highest quartile of IL-13 in both serum and whey were at a higher risk of AS (RR = 3.02 and 4.18; respectively) compared to infants in the first quartile. High levels of IL-5 in serum and whey was also identified as a risk. In addition, increased secretory IgA and TGF-β1 in breast milk reduced the risks of AS. CONCLUSIONS: Maternal serum and whey levels of IL-5 and IL-13 are risk markers for AS; whey IgA and TGF-β1 seem to be protective. Only focusing on breast milk portend that milk cytokines IL-5 and IL-13 have adverse effects. However, similar immune exposures during late gestation and via milk suggest that both may enhance AS among infants.