Electron microscopic evidence for phagocytic properties of human peripheral mononuclear cells cultured with PHA

The time course of the ultrastructural changes induced in human peripheral mononuclear cells, when cultured with PHA, has been studied. In addition to findings common to many mitotic cells, such as an increase in nuclear and nucleolar size, the presence of free polyribosomes, glycogen and lipid globules in the cytoplasma, and a high number of mitochondria, agglutinating properties due to PHA per se were observed in the first 12 hours. At 72 hours certain cells developed phagocytic-like properties, i.e. they were able to incorporate both material from the extracellular compartment and syngeneic cells. These results are discussed suggesting the possible presence of macrophages in culture or the ability of activated T cells to express it.