Transferrin uptake by rabbit alveolar macrophages in vitro.
Rabbit alveolar macrophages were shown to bind 125I-human transferrin in vitro. The binding reaction was characterized by three stages: (1) adsorption of transferrin to the cells, followed by (2) rapid uptake of the protein to reach (3) a constant level of cell-bound transferrin. The latter two stages were dependent upon temperature and metabolic energy. Macrophages released 125I-transferrin rapidly when incubated with unlabelled transferrin. Small quantities of 125I-rabbit and 125I-bovine serum albumin, by comparison, were bound to and released by the cells; the attachment of these proteins may be solely the result of adsorption. Transferrin, 80% saturated with iron, was bound to a greater extent than 10 or 50% saturated transferrin; 10% saturated transferrin was bound more readily than the 50% saturated preparation. The findings are consistent with the presence of a transferrin receptor on the cell membrane of the alveolar macrophage and imply that transferrin may interact directly with this cell type in order to remove or donate iron.
D000327:Adsorption; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007501:Iron; D008264:Macrophages / Q000378:metabolism*; D011485:Protein Binding; D011650:Pulmonary Alveoli / Q000166:cytology; D011817:Rabbits; D013696:Temperature; D014168:Transferrin / Q000378:metabolism*
D014168:Transferrin; D007501:Iron