Vitamin E supplementation induces an early recovery of cellular immunity decreased following X-ray irradiation

Antioxidants, radiation and mutation as revealed by sperm abnormality in barn swallows from Chernobyl

Reduced levels of antioxidants such as carotenoids and vitamins A and E can increase DNA damage caused by free radicals. Exposure to radiation has been proposed to reduce levels of antioxidants that are used for DNA repair and this reduction may be responsible for increased levels of mutation in radioactively contaminated areas. We test this hypothesis using field measures of antioxidants in blood, liver and eggs of the barn swallow Hirundo rustica while relating these to levels of mutation as reflected by the frequency of abnormal sperm. Antioxidant levels in blood, liver and eggs were reduced in Chernobyl, Ukraine, compared with an uncontaminated control area, and levels of antioxidants correlated negatively with levels of background radiation. The frequency of abnormal sperm was almost an order of magnitude higher in Chernobyl than in the control area and was negatively related to antioxidant levels in blood and liver. This is consistent with the hypothesis of a direct link between radiation and individual levels of antioxidants, suggesting that levels of mutation differ among individuals owing to individual differences in the abundance of antioxidants.

Vitamin E and immunity

Vitamin E is a potent antioxidant and has an ability to modulate host immune functions. This chapter consists of five parts: (1) vitamin E deficiency and immunity, (2) vitamin E supplementation and immunity, (3) vitamin E and the decreased cellular immunity with aging, (4) vitamin E and T-cell differentiation in the thymus, and (5) vitamin E and acquired immune deficiency syndrome (AIDS). In vitamin E deficiency most of the immune parameters show a downward trend, which is associated with increased infectious diseases and the incidence of tumors. In contrast, vitamin E supplementation has various beneficial effects on the host immune system. The decreased cellular immunity with aging or during the development of AIDS is markedly improved by the intake of a high vitamin E diet. In addition, vitamin E plays an important role in the differentiation of immature T cells in thymus. Vitamin E deficiency induces the decreased differentiation of immature T cells, which results in the early decrease of cellular immunity with aging in spontaneously hypertensive rats. Conversely, vitamin E supplementation induces a higher differentiation of immature T cells via increased positive selection by thymic epithelial cells, which results in the improvement of decreased cellular immunity in the aged. Furthermore, vitamin E supplementation induces the early recovery of thymic atrophy following X-ray irradiation. Taken together, these results suggest that vitamin E is an important nutrient for maintaining the immune system, especially in the aged.

The role of vitamin E in T-cell differentiation and the decrease of cellular immunity with aging

The purpose of this study is to investigate the effects of vitamin E on both the decrease of cellular immunity with aging (Section 2) and the differentiation of T-cells in thymus (Section 3). In Section 2, spontaneously hypertensive rats (SHR) as a model for aging were used in this experiment and fed regular (50 IU/kg diet) or a high vitamin E (500 IU/kg diet) diet for 6 weeks. At 12 weeks old, they were killed and assayed. Although proliferation of thymic lymphocytes was significantly decreased in SHR fed the regular diet compared to that of Wistar Kyoto rats (WKY) fed the same diet, the high vitamin E diet induced higher proliferation of thymic lymphocytes in SHR, which was almost the same as that of WKY fed the regular diet. In addition, the expressions of both CD4 and CD8 antigens on CD4+ CD8+ T-cells were also decreased in SHR, which was significantly improved by a high vitamin E diet. These results suggest that a high vitamin E diet enhances thymic lymphocyte proliferation through increased T-cell differentiation in the thymus. Then, the effect of vitamin E on T-cell differentiation in the thymus was investigated by using male Fisher rats. Rats were divided into three groups; vitamin E-free, regular and high vitamin E groups and fed a diet containing various levels of vitamin E (0, 50 and 500 IU/kg diet) for 7 weeks. Although the proportions of CD4+ CD8- and CD4- CD8+ T-cells in thymocytes were significantly greater in the high vitamin E group, the proportion of CD4+ CD8- T-cells inversely decreased in the vitamin E-free group compared to that of the regular group. We have tried to investigate the mechanism on the increased T-cell differentiation in the thymus of rats fed the high vitamin E diet through cytokine production, thymic epithelial cell (TEC) and macrophage functions. As their results, we have found that vitamin E enhances T-cell differentiation through the increase of not macrophage but TEC function in the thymus, which is associated with the increased binding capacity of TEC to immature T-cells via increased expression of the adhesion molecule, ICAM-1. These results suggest that vitamin E is a potent nutrient for promoting health in the aged via the improvement of cellular immunity decreased with aging.