Secretory function of autophagy in innate immune cells

Eukaryotic cells utilize two main secretory pathways to transport proteins to the extracellular space. Proteins with a leader signal sequence often undergo co-translational transport into the endoplasmic reticulum (ER), and then to the Golgi apparatus before they reach their destination. This pathway is called the conventional secretory pathway. Proteins without signal peptides can bypass this ER-Golgi system and are secreted by a variety of mechanisms collectively called the unconventional secretory pathway. The molecular mechanisms of unconventional secretion are emerging. Autophagy is a conserved bulk degradation mechanism that regulates many intracellular functions. Recent evidence implicates autophagy in the secretory pathway. This review focuses on potential secretory roles of autophagy and how they could modulate the functions of innate immune cells that secrete a wide range of mediators in response to environmental and biological stimuli. We provide a brief overview of the secretory pathways, enumerate the potential mechanistic themes by which autophagy interacts with these pathways and describe their relevance in the context of innate immune cell function.