Phagocytes engulf microbes by enveloping them in a patch of membrane that invaginates to form a phagosome; this then fuses with a lysosome, which contributes the enzymes that destroy the internalized pathogen. Trivedi et al. exposed mouse macrophages to latex beads to investigate how immunoglobulin G (IgG)-class antibodies, which stimulate phagocytosis, might promote the latter stages of this process. When macrophages incubated with beads coated with either bovine serum albumin or IgG at 15°C (allowing bead engulfment but not fusion) were warmed to 37°C, the association of IgG-coated beads with phagolysosomes was faster than that of the albumin-coated beads. Cytosol from cells transfected with human Fcγ receptor (making them phagocytic) and incubated with IgG beads promoted phagosomelysosome interactions more effectively than that from unexposed cells, an effect enhanced by transfection of the cells with protein kinase C (PKC). Inhibition of PKC abolished the stimulatory effect of IgG, and further pharmacological analysis indicated that IgG stimulated the actindependent tethering or docking (or both) of phagosomes and lysosomes. Thus, facilitation of phagosome-lysosome attachment by way of PKC appears to be one mechanism whereby IgG signaling stimulates phagocytosis. -- EMA
Proc. Natl. Acad. Sci. U.S.A. 103, 18226 (2006).
