Figure 8.

Schematic representation of the proposed role of LAMPs in maturation. Following sealing, the phagosome (left vertical path) is propelled into the cell where a series of successive fusion events with endocytic vesicles (right vertical sequence) occurs. Phagosome maturation begins with fusion to early endosomes (1) that coincides with acquisition of PI(3)P and Rab5. These are needed for subsequent interactions with late endosomes. We propose that LAMP-1 and LAMP-2 can be acquired independently and before Rab7 (2). LAMP isoforms promote docking of phagosomes onto microtubules and centripetal movement (downward) by association with dynein/dynactin directly or via an unknown adaptor. LAMPs then mediate fusion with traditional late endosomes carrying Rab7 (3). Maturation culminates with phagosome-lysosome fusion (4), forming a microbicidal organelle.