1. Measurements of T-lymphocyte surface ferritin using flow cytometry show that phytohaemagglutinin (PHA) stimulation causes a marked increase in the number of cells bearing spleen-type (S) and heart-type (H) ferritin on their membrane, whereas no such change occurs in non-stimulated cells. This coincides with increases in interleukin-2 receptors, transferrin receptors and HLA-DR antigen. 2. There is an increase in the intracellular concentration of both S- and H-ferritin in lymphocytes after PHA stimulation: H-ferritin increases five- to seven-fold, but S-ferritin only two- to three-fold. The maximum H/S ratio is about 15/1. However, these increases also occur in cells cultured in the absence of PHA. 3. Small amounts of both S- and H-ferritin are released into the medium, especially from stimulated cells, but the H/S ratios are lower than intracellular ratios. 4. The present findings suggest that lymphocyte stimulation followed by ferritin synthesis is accompanied by an increase in the amount of intracellular and cell surface ferritin and, possibly, the amount released from the cells.
1. The erythroblasts from four normal bone marrows were enriched by using an anti-myeloid monoclonal antibody (TG-1), and a polyclonal antibody against mononuclear cells to effect complement mediated lysis of unwanted cells. 2. The erythroblasts were cultured for 2h in medium containing [ 59 Fe]transferrin and [ 3 H]-leucine, then fractionated on Percoll gradients according to their density. 3. Whole cell iron uptake by early erythroblasts was greater than in the dense late erythroblasts. In all marrows, iron uptake into ferritin was highest in fractions containing the earliest erythroblasts and decreased with increasing erythroblast maturity. In three of the four marrows this paralleled the pattern of ferritin synthesis. 4. It seems likely that apoferritin is synthesized in response to the amount of iron taken into the cell and this iron is incorporated within the protein shell to form ferritin.
1. Erythroblasts were enriched from human bone marrow samples and fractionated on Percoll gradients according to maturity. 2. Heart-type and spleen-type ferritin was measured in each fraction by an immunoradiometric assay. 3. In normal marrow, heart-type ferritin content was higher in the early erythroblast fractions and fell with maturation. Spleen-type ferritin content showed no such consistent change. 4. Megaloblastic erythroblasts had a significantly higher ferritin content.