Phagocytosis is the uptake by cells of large particles into vacuoles. During this process, newly formed phagosomes fuse with endosomes and lysosomes. The Griffiths group has established the use of latex beads with macrophages as a model for studying phagocytosis, and set up an in vitro fusion assay between phagosomes and endocytic organelles. Several data suggest a role of actin in the phagosome-endosome fusion. I propose to characterize membrane and actin interactions, by identifying membrane proteins of the phagosome which directly or indirectly bind actin. The major proteins will be identified using high resolution 2D gel electrophoresis, and a collaboration could be set up with groups having expertise in molecular biology. This line of research will allow to more understand some steps in phagocytosis which plays a central role during host defense against infective agents.