Control of granule exocytosis in neutrophils

Neutrophils are granulocytes derived from bone marrow that circulate through the blood and become recruited to tissues during infection or inflammation. They are the most abundant white blood cell and comprise the first line of defence in the innate immune system. However, they are also capable of causing tissue damage in a wide range of diseases. Release of chemotactic signals from inflamed or infected tissues trigger neutrophil migration from the bloodstream to inflammatory foci, where they contribute to inflammation by undergoing receptor-mediated respiratory burst and degranulation. Degranulation from neutrophils has been implicated as a major causative factor in numerous inflammatory diseases. However, the mechanisms that control neutrophil degranulation are not well understood. Recent observations indicate that receptor-mediated granule release from neutrophils depends on activation of distal signaling pathways that include the src family of tyrosine kinases, beta-arrestins, the tyrosine phosphatase MEG2, the kinase MARCK, Rabs and SNAREs, and the Rho GTPase, Rac2. Some of these pathways are specifically required for membrane fusion between the granule and plasma membrane, leading to exocytosis. This review focuses on the understanding of distal molecular mechanisms controlling exocytosis from neutrophils.