The concentration of bovine IgG in human breast milk measured using different methods

The bovine IgG concentration in human breast milk was measured using three different methods: competition radioimmunoassay (RIA), competition enzyme-linked immunosorbent assay (ELISA) and sandwich ELISA. In 36 samples of human breast milk taken from mothers on diets including cow's milk, the concentration of bovine IgG was significantly higher when measured by either competition RIA or ELISA (mean 324.9 +/- 97.4 ng/ml and 396.7 +/- 58.7 ng/ml, respectively) than by sandwich ELISA (3.44 +/- 0.48 ng/ml). In 7 samples of human breast milk taken from mothers on cow's-milk-free diets of more than one month, the concentration of bovine IgG was still within a detectable range (112.3 +/- 41.4 ng/ml) using competition ELISA, whereas it was not detected when using sandwich ELISA, suggesting that competition ELISA might measure some unknown substances in addition to bovine IgG. Gel filtration of pooled human breast milk revealed three large fractions. The concentration of bovine IgG in every fraction was significantly higher using competition compared with sandwich ELISA, suggesting that the difference between these assays does not result from measuring different quantities of bovine IgG, or of fragments of this protein. The time course of the bovine IgG level was different between each human breast milk sample after taking cow's milk. We showed that human breast milk contains bovine IgG at a concentration of approximately 3 ng/ml when analysed using sandwich ELISA. This level is comparable to the quantity of either casein or of beta-lactoglobulin in human breast milk. Bovine IgG might be an important allergen in cow's milk allergy due to the quantity in human breast milk.