7.3.2 IMMUNOMODULATORY PEPTIDES FROM MINOR PROTEINS IN MILK
Not only casein-derived peptides exert immunomodulating activities. Many studies have shown that peptides derived from whey or lactoferrin also exhibit important physiological activities. A pepsin-generated hydrolysate of lactoferrin has been shown to contain immunostimulating peptides, which can enhance the proliferation of spleen cells65 and stimulate the phagocytic activity of human neutrophils.66 Peptides obtained by tryptic hydrolysis of bovine o-lactoglobulin have been shown to induce oral tolerance in mice.67 Hydrolyzed o-lactalbumin enhances murine humoral responses to sheep and human red blood cells caused by the modulation of both B lymphocyte and T helper cell activities.68 Commercial hydrolyzed o-lactalbumin stimulates B lymphocytes in the absence of T cell cooperation due to an enhanced
immune response to the T-cell-independent antigen TNP-Ficoll.69 Bovine lactoferricin B, a peptide released from the hydrolysis of lactoferrin, has been found to suppress IL-6 production by human monocytic cells in response to LPS stimulation.70 Lactoferricin has also been shown to be able to stimulate the release of neutrophctivating chemokine IL-8 from human polymorphonuclear, leucocytes.71
Bioactive peptides might exert an indirect effect on the immune system. Opioidpeptides, such as B-endorphins, enhance lymphocyte proliferation, NK activity and neutrophil locomotion. 72.73 These effects could be explained by the presence of opioid it receptors on T lymphocytes and human phogocytic leucocytes. B-casokinin inhibits ACE enzymes, causing a decrease of blood pressure and aldosterone and acts on bradykinin, a hormone with immune enhancing effects. Bradykinin is able to stimulate macrophages, enhance lymphocyte migration, and increase secretion of lynhokines.74,75 Thus, this chain of events indirectly produces an overall immunostinulating response.