Role of PPE18 Protein in Intracellular Survival and Pathogenicity of Mycobacterium tuberculosis in Mice

Background: Ever since its discovery the mycobacterial proline-proline-glutamic acid (PPE) family of proteins has generated a huge amount of interest. Understanding the role of these proteins in the pathogenesis of Mycobacterium tuberculosis (Mtb) is important. We have demonstrated earlier that the PPE18 protein of Mtb induces IL-10 production in macrophages with subsequent downregulation of pro-inflammatory cytokines like IL-12 and TNF-alpha and favors a T-helper (Th) 2-type of immune response. Methodology/Principal Findings: Using a ppe18 genetic knock-out Mtb strain, we have now carried out infection studies in mice to understand the role of PPE18 in Mtb virulence. The studies reveal that lack of PPE18 leads to attenuation of Mtb in vivo. Mice infected with the ppe18 deleted strain have reduced infection burden in lung, liver and spleen and have better survival rates compared to mice infected with the wild-type Mtb strain. Conclusions/Significance: Taken together our data suggest that PPE18 could be a crucial virulence factor for intracellular survival of Mtb.