Modulation of immune system development and function in broilers by dietary vitamin E

The effect of dietary vitamin E (VE) supplementation on aspects of immune system development and functions in broilers was evaluated. In each of our studies, VE was supplemented in broiler diets in a form of α-tocopherol acetate at levels 10× and 20× higher than recommended by the NRC. At 3, 5 and 7 weeks of age abdominal exudate (AE) macrophages were elicited into the abdominal cavity by the injection of Sephadex for in vitro functional analysis. At 3 weeks of age, an increased phagocytic ability of AE macrophages was observed. This was manifested with increased proportions of phagocytically active macrophages and increased numbers of antibody-opsonized SRBC phagocytosed by each individual macrophage. Based on previous observations that broilers maintained on high VE diets throughout the entire 7 week growing period had increased proportions of CD4+ T helper lymphocytes in the spleen and thymus (Erf et al., 1998), a study was conducted to examine the effect of VE on lymphocyte profiles in blood, spleen, and thymus in broilers provided with high VE diets for the first 3 weeks versus the entire growing period. Using this approach enhanced proportions of CD4+ lymphocytes were only observed when high VE was provided in the diet for the entire growing period. As VE appeared to specifically affect T helper cells, a follow-up study was conducted to examine differential effects of VE on type 1 (Th1) or type 2 (Th2) T helper cells. At 4 weeks of age, broilers were challenged with either live (induces a strong Th1-mediated cell mediated response in mice) or killed S. typhimurium antigen (induces a strong Th2-mediated humoral response in mice). Due to environmental exposure of broilers to Salmonella during the study, the results of this experiment were inconclusive. These studies provide important insight into the effects of dietary VE supplementation on the immune system. Considering the importance of macrophages and T helper cells in the regulation of immune function, the beneficial effects of VE on these cell populations may have far-reaching effects on poultry health.