Effects of dietary vitamin E on the immune system in broilers: Altered proportions of CD4 T cells in the thymus and spleen

To gain insight into the immunomodulatory effects of vitamin E (VE), immune cell population analyses were conducted using thymus and spleen from male broilers fed diets with various levels of VE supplementation (0, 17, 46, and 87 mg dl-alpha-tocopherol acetate/kg of feed). At 2 and 7 wk of age, the percentages of B cells, macrophages, and T cell subsets, delineated by the expression of CD4, CD8, and T cell receptor (TCR) isotype, in thymus and spleen were determined by flow cytometry. The percentages of thymic and splenic B cells and macrophages from 2- and 7-wk-old chickens, as well as the percentage of thymic T cells in 2-wk-old chickens, were unaffected by VE treatment. However, 7-wk-old broilers maintained on 87 mg VE/kg feed had a higher percentage of CD4(+)CD8(-) thymocytes, a higher CD4(+)CD8(-) to CD4(-)CD8(+) thymocyte ratio, and a lower percentage of CD4(+)CD8(+) thymocytes than chickens receiving no dietary VE supplementation. The VE-induced increase in the percentage of CD4(+)CD8(-) thymocytes was due to an increase in the TCR2(+)CD4(+)CD8(-) thymocyte subset, whereas the decrease in the percentage of CD4(+)CD8(+) thymocytes involved all TCR defined T cell subsets. In the spleen, the percentage of CD4(+)CD8(-) T cells was lower in 2-wk-old chickens and higher in 7-wk-old chickens maintained on 87 mg/kg feed than in chickens receiving no dietary VE supplementation. The decrease in CD4(+)CD8(-) splenocytes at 2 wk of age was due to a decline in the percentage of TCR2(+)CD4(+)CD8(-) splenocytes, whereas the increase in CD4(+)CD8(-) splenocytes in 7-wk-old chicks was due to an increase in the percentages of all TCR defined CD4+CD8- T cell subsets. These data support an immunomodulatory effect of VE on CD4(+)CD8(-) T cells.