Phagocytosis is a pivotal process by which macrophages eliminate microorganisms after recognition by pathogen sensors. Here we unexpectedly found that the self ligand and cell surface receptor SLAM functioned not only as a costimulatory molecule but also as a microbial sensor that controlled the killing of Gram-negative bacteria by macrophages. SLAM regulated activity of the NADPH oxidase NOX2 complex and phagolysosomal maturation after entering the phagosome, following interaction with the bacterial outer membrane proteins OmpC and OmpF. SLAM recruited a complex containing the intracellular class III phosphatidylinositol kinase Vps34, its regulatory protein kinase Vps15 and the autophagy-associated molecule beclin-1 to the phagosome, which was responsible for inducing the accumulation of phosphatidylinositol-3-phosphate, a regulator of both NOX2 function and phagosomal or endosomal fusion. Thus, SLAM connects the Gram-negative bacterial phagosome to ubiquitous cellular machinery responsible for the control of bacterial killing.

nowledge of EV biogenesis pathways and biological activities has grown rapidly in the past decade 1 (Fig. 1a,b). EVs are membrane-enclosed structures that are released into the extracellular milieu by all organisms and cell types studied so far. EVs are a diverse family in which subtypes have been defined based on subcellular origin, size, and composition: endosome-derived vesicles (including multivesicular endosome-derived exosomes with a diameter of 50-150 nm and secretory autophagosome-derived EVs); ectosomes and other microvesicles that bud from the plasma membrane (PM) as small as exosomes or up to several µm in size; midbody remnants released by dividing cells (Box 1); migrasomes trailing behind migrating cells 2,3 ; apoptotic bodies dislodged from

Endocytosis of surface receptors and their polarized recycling back to the plasma membrane are central to many cellular processes, such as cell migration, cytokinesis, basolateral polarity of epithelial cells and T cell activation. Little is known about the mechanisms that control the organization of recycling endosomes and how they connect to receptor endocytosis. Here, we follow the endocytic journey of the T cell receptor (TCR), from internalization at the plasma membrane to recycling back to the immunological synapse. We show that TCR triggering leads to its rapid uptake through a clathrin-independent pathway. Immediately after internalization, TCR is incorporated into a mobile and long-lived endocytic network demarked by the membrane-organizing proteins flotillins. Although flotillins are not required for TCR internalization, they are necessary for its recycling to the immunological synapse. We further show that flotillins are essential for T cell activation, supporting TCR nanoscale organization and signaling.