Programmed cell death in a human intestinal parasite, Blastocystis hominis

Although programmed cell death (PCD) has been associated with multicellular organisms, there have been more reports of its presence in some protozoans . Our study shows the existence of PCD in an intestinal protozoan, Blastocy stis hominis. Light and electron microscopy, biochemical and flow cytometry studies showed apoptosis-like death in B. hominis cells exposed to a cytot oxic monoclonal antibody (MAb 1D5). B. hominis cells displayed key morpholo gical and biochemical features of apoptosis, namely, nuclear condensation a nd in situ fragmentation, reduced cytoplasmic volume, some externalization of phosphatidylserine and maintenance of plasma membrane integrity. No olig onucleosomal DNA laddering was observed in gel electrophoresis. This study supports earlier observations that the cellular machinery that is required to carry out PCD may have existed before the advent of multicellularity. Ou r study also ascribes a novel function for the B. hominis central vacuole i n apoptosis; it acts as a repository where apoptotic bodies are stored befo re being released into the extracellular space.