Mechanisms of Lysosomal Exocytosis by Immune Cells

Abstract

Lysosomal exocytosis is an essential process to regulate various immune responses. Many cells of immune systems have cell-specific secretory lysosomes, which are secreted in response to external stimuli, including neutrophil azurophil granules, platelet dense granules, eosinophil granules, basophil and mast cell histamine granules, and cytotoxic T lymphocyte (CTL) lytic granules. On the other hand, phagocytes such as macrophages, neutrophils, and dendritic cells contain many conventional lysosomes, which fuse with phagosomes to degrade the engulfed particles, and then the waste materials are expelled by lysosomal exocytosis. A failure of this process can lead to accumulation of waste materials, which in turn may aberrantly activate the phagocytes. Recent studies have identified various proteins that regulate the lysosomal exocytosis, and their dysfunctions were shown to cause several genetic immune disorders. This chapter highlights the current understandings of the molecular mechanisms of lysosomal exocytosis by immune cells and their relevance to the development of chronic inflammation.