Lytic granules, secretory lysosomes and disease.

Lytic granules harbour many of the dangerous apoptosis-inducing molecules of the immune system, including perforin, granzymes and Fas ligand. Safe transport, storage and release of these lytic components is vital. As a secretory lysosome, the lytic granule is able to accomplish these roles, as well as conferring the lysosomal functions of cytotoxic T lymphocytes and natural killer cells. Secretory lysosomes are common to many other haemopoietic cells and also melanocytes. Many of the proteins used in lysosomal secretion are found in both melanocytes and hemopoietic cells, and are dysfunctional in genetic diseases with defects in these proteins. The genetically heterogeneous Hermansky-Pudlak syndrome represents an excellent model for revealing proteins involved in secretory lysosome functioning. However, studies of this disease reveal differences between the various different types of secretory lysosomes, including lytic granules.