Membrane proteomics of phagosomes suggests a connection to autophagy.

Phagocytosis is the central process by which macrophage cells internalize and eliminate infectious microbes as well as apoptotic cells. During maturation, phagosomes containing engulfed particles fuse with various endosomal compartments through the action of regulatory molecules on the phagosomal membrane. In this study, we performed a proteomic analysis of the membrane fraction from latex bead-containing (LBC) phagosomes isolated from macrophages. The profile, which comprised 546 proteins, suggests diverse functions of the phagosome and potential connections to secretory processes, toll-like receptor signaling, and autophagy. Many identified proteins were not previously known to reside in the phagosome. We characterized several proteins in LBC phagosomes that change in abundance on induction of autophagy, a process that has been previously implicated in the host defense against microbial pathogens. These observations suggest crosstalk between autophagy and phagocytosis that may be relevant to the innate immune response of macrophages.