The reduced proportion of New splenic T-cells in the zinc-deficient growing rat is not due to increased susceptibility to apoptosis

Abstract

Dietary zinc deficiency has been associated with an increased risk of infection. It has been reported that zinc-deficient rats have fewer New T-cells (TCRαβ+CD90+) compared to diet-restricted and control rats, which over time could adversely affect the ability of the organism to fight off infections. We hypothesized that the lower proportion of New T-cells in zinc deficiency is due to an increased susceptibility to apoptosis. Weanling, Sprague Dawley rats were assigned to one of four dietary treatment groups for 3 weeks: zinc-deficient (ZD, <1mg zinc/kg, ad libitum), diet-restricted (DR, 30mg zinc/kg, limited to the amount of feed as consumed by ZD), marginally zinc-deficient (MZD, 10mg zinc/kg, ad libitum) or control (CTL, 30mg zinc/kg, ad libitum). Thymocytes and splenocytes were labeled for flow cytometric determination of cell surface markers and DNA staining (for simultaneous determination of the phenotype of apoptotic cells) and assessed by Western blotting for apoptotic markers. Cells were analyzed immediately, or after incubation for 7h with or without dexamethasone. There was no difference in the proportion of CD90+ thymocytes; however ZD rats had a higher proportion of Cytotoxic (CD90+4−8+) thymocytes compared to MZD and CTL. ZD had a lower proportion of splenic New T-cells compared to DR, MZD and CTL. There was no effect of diet on the proportion of apoptotic thymocytes or splenocytes, except ZD splenoctyes had a lower Bax/Bcl-xl ratio compared to DR and CTL. We characterized the splenic New T-cells into Helper and Cytotoxic subsets and found that ZD had a higher ratio of Helper to Cytotoxic New T-cells compared to MZD and CTL. These results do not support the hypothesis of increased apoptotic removal of New T-cells in ZD in growing rats. The regulation of CD90 expression should be explored in future studies.