The relative paucity of IgE in human milk

The levels of IgE were determined in paired samples of serum and milk when whey obtained 3 to 8 days of postpartum, from 16 human lactating mothers who had reported a history of allergy to a variety of common allergens. Two assay procedures were employed to measure total IgE, a double-antibody assay and a commercially available solid phase assay (RIST). In addition, each sample of serum and whey was tested for specific IgE antibodies to a variety of allergens by the RAST test. The levels of total serum IgE were between 30 and 2300 I.U./ml and relatively good agreement was observed for both the double-antibody and RIST methods. In contrast, total IgE levels in milk whey were either undetectable (less than 3.0 I.U./ml in 14 of 16 subjects) or very low when analyzed by the double-antibody method, but were very high (400 to 1650 I.U./ml when analyzed by the RIST method. However, IgE added to milk whey could be measured by the double-antibody procedure indicating that the low levels detected in milk were not a fault of the double-antibody assay. It was assumed that the RIST test was subject to nonspecific interference by factors in milk whey which caused the determination of high, but incorrect, levels of IgE. Specific IgE antibodies were detected in the serum of 10 of 16 subjects but were not present in milk whey. A comparison of the whey/serum ratios of albumin, IgA, and IgE suggested that little, if any, IgE is selectively synthesized or secreted in the mammary gland.