Phagocytosis is essential for the clearance of microbial pathogens by immune cells and involves the activity of the NADPH oxidase 2 (NOX2) complex, which produces reactive oxygen species (ROS) that not only help to kill the pathogen but also contribute to an altered antigen presentation to T cells. NOX2 consists of cytosolic subunits and membrane-integral cytochrome b558, which is recruited to phagosomes from vesicles that originate from both recycling endosomes and lysosomes. However, how these vesicles are delivered to their destination is it is not well understood, although soluble NSF attachment protein receptors (SNAREs) are likely to be involved. In their work on page 1285, Geert van den Bogaart and co-workers elucidate the recruitment of cytochrome b558 to phagosomes – that contain zymosan in order to mimic microbial infection – within dendritic cells derived from human blood-isolated monocytes. They show that cytochrome b558 is already recruited to the phagosome from the plasma membrane during initial formation of phagosomes, with its subsequent replenishment from late endosomes/lysosomes. The authors demonstrate that SNAP23, the Q-SNAREs syntaxin-7 and the R-SNARE VAMP8, which – as shown here for the first time – form a complex, mediate the recruitment of these vesicles to the phagosome. On the basis of their findings, the authors propose that this means of NOX2 trafficking allows dendritic cells to sustain ROS production after antigen uptake in order to initiate appropriate T cell responses.
