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Iron and Transferrin Uptake by Phytohemagglutinin‐Stimulated Human Peripheral Blood Lymphocytes

Iron (Fe) and transferrin (TF) uptake by human peripheral blood lymphocytes stimulated in vitro with phytohemagglutinin was measured. Pulses of 59FeTF or 125I‐TF were added to the cultures either at time 0 or 8 hr before the end of a 72‐hr incubation. In time‐course experiments, peak iron and transferrin uptake coincided with the peak of tritiated thymidine uptake taken as a measure of cellular activation. Iron, but not transferrin, was accumulated by the cells. Non‐linear relationships existed between both iron and transferrin uptake and the degree of activation. Both rose markedly above basal levels only at a level of activation at least 50% of the maximum observed. The results suggest that although iron utilization is related to cellular activity, the uptake mechanism is only activated when an increased iron metabolism has exhausted internal stores.