EEA1 is recruited to normal phagosomes (arrowheads), but is excluded by mycobacteria.
In a classic example of microbiological payback, mycobacteria have evolved the ability to parasitize macrophages, cells that ordinarily digest bacteria circulating in the blood. After a macrophage endocytoses a mycobacterium, the resulting phagosome deviates from the normal maturation process and becomes a safe haven for the pathogen rather than an acidic digestive compartment for the macrophage. Fratti et al. (page 631) used this system to dissect the molecular mechanism of phagosome biogenesis, providing important new insights into phagosomal maturation and mycobacterial pathogenesis.
Phagosomes containing latex beads recruit EEA1, a Rab5 effector and regulator of vesicular trafficking, but phagosomes containing mycobacteria exclude this protein. The authors attempted to make the latex-bead phagosomes behave like mycobacteria-containing phagosomes, and found that inhibitors of PI-3-kinase activity or microinjection of antibodies against EEA1 and the PI-3-kinase...
