Tracing iron and transferrin in the macrophage by visual means.

The purpose of the study was to investigate the movement of iron and transferrin in the macrophage using light and electron microscopy. First, depicted here are the phagocytosis of antibody sensitized murine red cells by the murine bone marrow derived macrophage and the formation of red cell phagosomes. Second, we show the fusion of the lysosomes with the red cell phagosome to form a lysophagosome and the lysis of the red cell using acid phosphatase as a lysosome marker. Third by autoradiography, the presence of 55Fe silver grains in the phagocytosed red cells and its delivery to the organelles of the macrophage are demonstrated. Fourth a transferrin species is shown in red cells of all ages, in the phagocytosed as well as the non-phagocytosed, and in the phagocytosed as well as the non-phagocytosed, and in the macrophage itself. Transferrin was detected using immunogold and fluorescence labelling. These studies suggest that iron, using vesicles as means of transport, moves from the effete red cells inside the macrophage to the outside possibly bound to transferrin.