Objective: The purpose of this study was to determine the impact of chronic zinc deficiency (ChrZD) on T and B cell lymphopoiesis, myelopoiesis and erythropoiesis in mice.
Methods: Young adult mice were fed a zinc adequate (ZA) or ChrZD synthetic diet for 34, 45, and 50 days. The cellular composition of the thymus and marrow were determined to assess the impact of ChrZD on lymphopoietic and hematopoietic processes using flow cytometry. Body weights, serum zinc and corticosterone (Cs) were monitored.
Results: For ChrZD mice growth was reduced 10% and serum zinc declined 15% by d 34 compared to ZA mice. By d 50 a 25% decrease in growth and 70% depression in serum zinc was noted though there was never any significant reduction in diet intake. Corticosterone rose 2.5 fold by d 34 and remained elevated in ChrZD mice indicating induction of the stress axis. At d 34 the thymus of ChrZD mice was normal but by d 50 there was a 50% cell loss and a 10% reduction in the proportion of Pre-T cells. Most importantly there was a 60% increase in Pre-T cells undergoing apoptosis in ChrZD mice. Pro-T, T helper, and T cytolytic populations were more resistant to ChrZD. Bone marrow cellularity and granulocyte, monocyte, and lymphocyte compartments remained unchanged in ChrZD mice. However, the erythroid compartment was reduced by 35% at d 50.
Conclusions: The thymus was the most sensitive primary tissue to ChrZD. By d 50 it had atrophied by 36% with significant loss of Pre-T cells via apoptosis such that T-cell lymphopoiesis was disrupted. Significant reductions were also noted in the erythropoietic population by d 50. Conversely the marrow maintained myelopoiesis and B cell lymphopoiesis for the 50 d period indicating greater ability to survive a chronic zinc deficiency and exposure to Cs. The anemia and T cell lymphopenia associated with ChrZD in both rodents and humans may result from a greater sensitivity of their precursor cells to zinc deficiency and elevated Cs.