Mycobacterium tuberculosis PPE7 Enhances Intracellular Survival of Mycobacterium smegmatis and Manipulates Host Cell Cytokine Secretion Through Nuclear Factor Kappa B and Mitogen-Activated Protein Kinase Signaling.

The PE/PPE family proteins of Mycobacterium tuberculosis have been associated with its virulence and interaction with the host immune system. The highly virulent modern lineage of M. tuberculosis possesses a lineage-specific PPE gene (PPE7), which arises from an ancestral mutation and is rarely studied. Here we examined the role of PPE7 in mycobacterial pathogenicity and survival by expressing M. tuberculosis PPE7 in Mycobacterium smegmatis. We show that, PPE7 activates host inflammation by increasing expression of pro-inflammatory cytokines including tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1ß, and IL-6, while suppressing the expression of anti-inflammatory cytokines such as IL-10, possibly through the nuclear factor kappa B, ERK1/2, and p38 mitogen-activated protein kinase pathways. Overexpressing PPE7 in M. smegmatis could enhance bacterial intracellular survival of infected macrophages. Furthermore, higher level of bacterial persistence, higher levels of TNF-α, IL-1ß, and IL-6 cytokines, and more injury in the lung, liver, and spleen tissues of infected mice has been discovered. In conclusion, PPE7 could manipulate host immune response and increase bacterial persistence.