CTL secretory lysosomes: biogenesis and secretion of a harmful organelle.

Cytotoxic T cells (CTL) clear virally infected cells and tumorigenic cells. CTL kill their targets by releasing very potent cytotoxic proteins stored in preformed secretory organelles termed secretory lysosomes. The accurate killing is assured by a vectorial movement of secretory lysosomes along microtubules and focused secretion within the immunological synapse. Some of the proteins controlling these secretion steps have been identified studying CTL from patients affected by severe immunodeficiency. Here we present an over view of how these key regulators such as AP-3 adaptor protein, RabGGTase enzyme, Rab27a small GTP binding protein, Lyst and Munc13-4 act in a very orchestrated way to deliver the "kiss of the death".