Cell death in parasitic protozoa: regulated or incidental?

Regulated cell death is a key process in plant and animal development, but does it occur in parasitic protozoa? Jeremy Mottram and colleagues assess the evidence of regulated cell death in these organisms and propose that protozoan cell death should be classified as either necrotic or incidental. Apoptosis and other types of regulated cell death have been defined as fundamental processes in plant and animal development, but the occurrence of, and possible roles for, regulated cell death in parasitic protozoa remain controversial. A key problem has been the difficulty in reconciling the presence of apparent morphological markers of apoptosis and the notable absence of some of the key executioners functioning in higher eukaryotes. Here, we review the evidence for regulated cell death pathways in selected parasitic protozoa and propose that cell death in these organisms be classified into just two primary types: necrosis and incidental death. It is our opinion that dedicated molecular machinery required for the initiation and execution of regulated cell death has yet to be convincingly identified.