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.