Effects of bovine beta-casein (1-28) and its chemically synthesized partial fragments on proliferative responses and immunoglobulin production in mouse spleen cell cultures.

Effects of bovine beta-casein (1-28) having a phosphoserine-rich region (Glu14-SerP-Leu-SerP-SerP-SerP-Glu-Glu21) and its chemically synthesized partial fragments on proliferation of lymphocytes and immunoglobulin production were investigated in mouse spleen cell cultures. The parent fragment 1-28 and all fragments containing SerP-Leu-SerP and/or SerP-SerP-SerP had a significant mitogenic effect, stimulated proliferation of lymphocytes induced by lipopolysaccharide, phytohemagglutinin, or concanavalin A, and increased immunoglobulin (IgG + IgM + IgA) or IgA levels in the cell cultures. In contrast, dephosphorylated beta-casein (14-21) and SerP-SerP amide had hardly any immunoregulatory activity. On the other hand, SerP-Leu-SerP amide reacted little with antibodies specific to bovine beta-casein (1-28), but beta-casein (14-21), and SerP-SerP-SerP amide obviously reacted with the antibody. These results confirm that the immunoregulatory activity of casein phosphopeptides is attributable to SerP-X-SerP, which may well be available as a non-allergic food ingredient having an adjuvant activity for mucosal IgA responses.