Reduced thymocyte proliferation but not increased apoptosis as a possible cause of thymus atrophy in iron-deficient mice

Abstract

Iron deficiency induces thymus atrophy in laboratory animals and very likely in humans by unknown mechanisms. The atrophy is associated with impaired cell-mediated immunity. In this study, we tested the hypothesis that thymus atrophy is a result of increased apoptosis and reduced thymocyte proliferation. Thymocytes were obtained from twenty-seven control, twenty-seven pairfed, twenty-seven iron-deficient (ID) mice; twelve and fourteen ID mice that received the control diet (0·9 mmol/kg versus 0·09 mmol/kg for the ID diet) for 1 d (repletion, R 1 ) and 3 d (R 3 ), respectively. Cell cycle analysis and apoptosis were studied by flow cytometry using propidium iodide staining and terminal deoxyuridine nick end labeling of DNA breaks assay respectively. When mice were killed, haemoglobin, haematocrit, and liver iron stores of ID, R 1 , and R 3 mice were 25–40 % of those of control and pairfed mice (P<0·01). Absolute and relative thymus weights and thymocyte numbers were 19 to 68 % lower in ID, R 1 , and R 3 than in control and pairfed groups (P<0·05). We found no significant difference among groups in the percentage of cells undergoing apoptosis. A higher percentage of thymocytes from ID and R 1 mice than those of control, pairfed, and R 3 mice were in the resting phase of the normal cell cycle (P<0·05). Conversely, a lower percentage of thymocytes from ID and R 1 mice than those from control, pairfed, and R 3 mice were in the DNA synthesis phase and late phase of DNA synthesis and onset of mitosis (G 2 -M) (P<0·05). Indicators of iron status positively correlated ( r 0·3 to 0·56) with the percentage of thymocytes in the G 2 -M phase (P<0·05). Results suggest that reduced cell proliferation but not increased apoptosis is the cause of thymus atrophy associated with iron deficiency.