Absence in human milk of bovine beta-lactoglobulin ingested by the mother. Unreliability of ELISA measurements.

Objectives: To analyze the presence of bovine beta-LG in breast milk.

Methods: Human milk samples from 14 healthy non-atopic women on diets with different cow's milk contents were examined. The total concentration of beta-LG immuno-like proteins (beta-LGIP) was determined by enzyme linked immunosorbent assay (ELISA). Identification of antigens was done by N-terminal sequencing.

Results: beta-LGIP reactivity of the milk from subjects on different diets was not significantly different. Human lactoferrin, beta-casein and alpha-lactalbumin, were identified as cross-reacting antigens.

Conclusions: False-positive results in ELISA determinations of bovine beta-LG in human milk might be due to cross-reactions between polyclonal antibodies and different protein antigens.