Effect of dietary high doses of vitamin E on the cell size of T and B lymphocyte subsets in young and old CBA mice

Abstract

Using anti-CD5 and anti-SIgM fluorescent monoclonal antibodies, four subsets of lymphocytes can be distinguished in CBA mice, SIgM + (T2) and SIgM − (T1) T lymphocytes and, CD5 + (B1) and CD5 − (B2) B lymphocytes. L3T4 anti-CD4 and Lyt2 anti-CD8 positivities delineate two major T lymphocyte subsets. The cell size of these subsets has been evaluated by their forward light scatter in flow cytometry after cell fixation. The mean cell size of the different subsets differs, according to subset, age and vitamin E treatment. Globally, there is an age-related increase in size for all subsets. In vitamin-E treated young animals, all subsets are smaller, and the percentages of the biggest B1 and B2 cells decrease. In old mice, the vitamin-E effect is far more variable. B2 cells tend to increase in size but the percentage of the biggest cells diminishes. On the contrary, there is a marked expansion of the large B1 cells. No effect is discernible on CD5 + T lymphocytes, but L3T4 and Lyt2 subpopulations increase in size. This study is a retrospective one and the mechanisms affecting cell size are speculative. Since the lymphocyte cell size was measured after fixation in an hypertonic medium devised for human blood processing, we cannot differentiate a real size modification from a differential volume resistance to experimental conditions. Whatever the case, the changes in cell volume argue for age-related changes in cell membrane permeability and volume homeostasis. For some subsets, cell activation and consequent size increase must also be considered. As far as vitamin E has marked anti-oxidant properties, its effect on cell size provides indirect evidence for a role of free radicals in the observed changes and gives support to the oxidant stress theory of ageing in immune senescence.