Effect of Diet on the Development of the Immune System in the BB Rat.

Abstract

The incidence of autoimmune diabetes in the BB diabetic-prone (BBdp) rat can be substantially delayed or prevented by replacing cereal-based mixed ingredient (chow) rodent diets with semi-purified (SP) diets differing in protein sources. Replacing a chow diet with a casein-based SP diet early in life reduces the incidence of BB rat diabetes. Feeding soy-based SP diets results in lower diabetes rates than chow but higher than casein. The following study was conducted to determine the effect of early feeding of chow to casein and soy-based SP diets on the development of the immune system in the BB rat. BBdp and non-diabetes prone (BBn) rats were fed a defined chow (NIH) or one of a casein or soy SP diet, to the dams at least one week prior to birth and to the pups of 21-30 days of age. Pups were killed at 15 and 30 days of age and effects of early diet on several immune parameters were determined. At 30 days of age, all chow fed rats were heavier (p<0.05) than the rats of both SP diets. Although the BBdp rats in the chow and soy diet groups were significantly heavier (p<0.05) than BBn rats of the same diet groups, the body weights of casein-fed BBdp and BBn rats were similar. The BBdp animals had a lower (p<0.05) proportion of T cells than BBn rats at 30 days of age. However, the proportion of CD4 and CD8 cells did not differ significantly from BBn for the casein-fed rats. The BBdp animals had poor proliferative responses and their production of IL-2 was unchanged by diet, but the natural killer (NK) activity of the casein-fed rats was reduced (p<0.05) to a level not different from the BBn rats. Diet also altered the immune response of the BBn rats. Feeding a soy-based as compared to a casein-based diet reduced (p<0.05) T cell responses (proliferation and IL-2 production) but increased (p<0.05) parameters of the innate immune system (nitric oxide production and NK cell activity). The findings of this study have important implications in identifying an immune mechanism for dietary effects on the incidence of diabetes in the BB rat and are of potential interest in defining the role of dietary protein source on the development of the immune system.