Effect of milk proteins and their hydrolysates on in vitro immune responses

The aim of this study was to perform a screening of various milk protein samples of both cow and goat origin to study their in vitro immunomodulating properties on human peripheral blood mononuclear cells (PBMC). The protein content in the milk of the two different species varies most notably in the amount of αs1-casein. A high degree of genetic polymorphism is related to the goat αs1-casein genes resulting in a variable amount of total protein in the goat milk. The milk proteins were hydrolysed using human gastric and duodenal juice or commercial pig derived enzymes to simulate in vivo digestion. Although different immunomodulating effects caused by various milk protein components have been observed, the mechanisms underlying these effects are not always known. In addition, most studies on the immunomodulating properties of milk protein digests have used a wide variety of commercial enzymes to simulate in vivo digestion. Exploring the difference in immunomodulating properties of milk protein-derived peptides produced by the aid of enzymes from human gastric secretions, compared to those produced by commercial enzymes, is a novel approach that may be of great importance. It could help to explore which peptides are actually produced during in vivo early digestion of milk and how they influence the immune system. Especially the whey protein concentrates from goat and cow showed a dose-dependent inhibition of human PBMC proliferation in vitro. This effect could neither be explained by a toxic effect on the PBMCs as shown by a standard viability test, nor by induction of apoptosis caused by the same milk protein samples. We suggest that intact or hydrolysed components in the milk protein samples affect the production of activation signals thereby inhibiting lymphocyte proliferation.