Macrophage Surveillance and Immunity: Eating, Drinking, and Digesting

Professional phagocytes actively patrol the tissues to remove debris, pathogens, and apoptotic bodies. This daunting task requires clearance of hundreds of billions of apoptotic cells produced each day and the never-ending assault by external pathogens. In the phagocyte toolbox are macropinocytosis to sample large volumes of extracellular fluid, and phagocytosis to internalize objects >0.5 μm in diameter. These processes form the core of phagocyte activity and require 1) efficient formation of the macropinosome/phagosome, 2) maturation of the resultant compartment, and finally 3) fusion with acidic lysosomes. In this dissertation, I explore each of these three topics presented as self-contained chapters. I characterize the organization of integrins and F-actin within the forming phagocytic cup to form podosome-like structures under the coordination of phosphoinositide signaling. The function of these structures is demonstrated to be the formation of a progressively expanding sealing zone with the phagocytic prey. I also explore the fate of luminal calcium in the maturing macropinosome and its transport into the phagocyte cytosol. In the final study I characterize a novel sensor for the labeling and study of acidic compartments, including phagolysosomes. Crucially, this probe, cresyl violet, is demonstrated to be both more stable and affordable than current alternatives.Ph.D