· High concentration of milk allergen-specific IgA in breast milk reduced transcytosis of milk allergen through gut lumen. · sIgA concentration in colostrum was higher in allergic mothers than those in nonallergic mothers. · Fecal sIgA concentration in breastfed infants was significantly higher in those in formula-fed infants regardless of maternal allergy status. This evidence concerns the gene CD79A and allergic disease.