FIG. 1.

M. tuberculosis. M. tuberculosis cells replicate in a phagosome where the normal maturation process has been blocked at an early stage. The phagosome retains Rab5, Rab14, and Rab22 but does not acquire Rab7 and does not fuse with lysosomes. The phagosome receives iron by continued fusion with early/recycling endosomes and also receives cargo from the trans-Golgi network (such as immature cathepsins). Despite the presence of Rab5 on M. tuberculosis phagosomes, its downstream effector EEA1 was not recruited. Bacterial products target the formation/retention of PI3P on M. tuberculosis phagosomes to block phagosome maturation. EE, early endosome; RE, recycling endosome; LE, late endosome; Lys, lysosome.