Transfer of food allergen to breast milk and its physiological significance

为了阐明母乳过敏的机制，对母乳中的食物过敏原进行了分析。在人乳的凝胶过滤实验中，主要食物过敏原--鸡蛋中的类卵粘蛋白(28 KDa)在相对分子质量约为450 kDa的部分被洗脱，这与类卵粘蛋白和SIgA免疫复合物的相对分子质量相当。类似的结果表明，食物过敏原作为一种免疫复合体出现在母乳中，其特定的SIgA也在其他食物中观察到，如牛奶、小麦、荞麦和花生。这种现象本身并不是婴儿过敏的直接原因，因为母乳中免疫复合体的种类和水平与喝了它的婴儿的过敏之间没有合理的关系。然而，在非常罕见的情况下，在母乳中发现了游离食物蛋白质，这可能是过敏原。母乳与过量的β-乳球蛋白孵育后，其与SIgA的免疫复合体增加，游离SIgA减少，但不影响SIgA抗卵粘液的模式。饲喂荞麦可诱导母乳中荞麦蛋白特异的SIgA水平。这些发现可能的生理学意义与婴儿肠道免疫的发展有关。

To clarify the mechanism of allergy sensitization via breast milk, food allergens in human breast milk were analyzed. On gel-filtration experiments of human breast milk, the major food allergen, ovomucoid (28 kDa) of hen's egg, was eluted at the fractions with a molecular weight of about 450 kDa, which corresponded to that for the immune complex of ovomucoid and sIgA. Similar results, showing the occurrence of a food allergen as an immune complex with its specific sIgA in breast milk, have also been observed for other foods such as cow's milk, wheat, buckwheat, and peanut. This phenomenon itself would not be a direct cause of baby's allergy because there was no reasonable relationship between the kind and level of the immune complex in mother's milk and the allergy of the baby who drank it. In the very rare case, however, free food proteins were found in breast milk, which might act as allergens. Incubation of breast milk with excess amount of β-lactoglobulin resulted in the increase of its immune complex with sIgA and decrease of its free sIgA without affecting the pattern of the sIgA against ovomucoid. Maternal feeding of buckwheat induced the level of the sIgA specific to buckwheat proteins in breast milk. Possible physiological importance of these findings is discussed in connection with development of intestinal immunity of infants.