Milk was obtained from nonimmunized cows and cows immunized with a mixture of various human gut bacteria. Each milk was administered orally to 2-mo-old C57BL/6 mice at a dose of 150 g · kg-1 · d-1 for either 6 or 16 mo. The study group had fewer enteric bacteria and a lower concentration of the serum antibodies against enteric bacteria compared with the control group at 8 and 18 mo of age. Furthermore, the study group at 18 mo old had a higher redirected cytotoxicity of intestinal intraepithelial lymphocytes, a higher proliferative response of mesenteric lymph nodes cells against mitogenic or alloantigenic stimulation and a greater ability of the spleen cells to produce anti-sheep erythrocytes IgG antibody after systemic immunization with sheep erythrocytes. A lower level of autoantibodies was observed at 8 mo and 18 mo of age in the study group compared with the control group. These results suggest that the senescence of the murine immune system may be delayed by consumption of milk from immunized cows.
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