Secretion of Peanut Protein With IgE Crosslinking Capacity in Human Milk

Human milk provides an infant one of the first routes of exposure to dietary antigens. A better understanding of the levels and functional capacity of maternal dietary proteins in human milk (HM) and their impact on infant food allergy (FA) is needed.

To measure the quantity and biologic activity of maternal dietary proteins in HM and determine factors associated with their presence.

HM samples from mothers of infants with or without FA were collected before and serially after consumption of a meal with prespecified amounts of peanut, egg, and cow's milk protein. Ara h 2 from peanut, egg ovalbumin, and bovine β-lactoglobulin in HM was detected using ELISA. IgE-crosslinking capacity of Ara h 2 was assessed by the basophil activation test (BAT). Maternal intestinal permeability was measured with the lactulose/mannitol test.

Thirty-nine mothers were included and 69% had measurable Ara h 2 in HM. Secretion of food allergens was variable between different mothers and across allergens, but did not correlate with intestinal permeability. Atopic mothers' milk had a higher peak Ara h 2 concentration (median 246 pg/mL, range 2.0-1634) than nonatopic mothers (median 0 pg/mL, range 0-135, p = 0.017). In samples with the most BAT reactivity, there was a significant correlation between BAT reactivity and Ara h 2 level (R = 0.72, p = 2 × 10^-8). Multiple monoclonal antibodies directed at different epitopes detected Ara h 2 at similar levels.

Ara h 2 is secreted in HM as intact protein or significant parts of it that are capable of IgE-crosslinking, found in higher levels in atopic mothers. HM levels of peanut lack correlation with other dietary proteins, which suggests antigen specificity of the secretion of dietary protein into HM.