Illustration of a proposed role for FcRn in phagocytosis. IgG-opsonized bacteria engage leukocyte FcγR (1), which initiates the phagocytic process involving FcR-ITAM signaling motifs and downstream effectors (2). Activation leads to fusion of granules containing proton-pump components and FcRn with nascent phagosomes, which lowers the pH and promotes FcRn recognition of IgG (3). This process subsequently facilitates internalization of IgG-coated targets (4). In the absence of FcRn, efficient phagocytosis does not take place (see main text).