The Role of PPE25 in Mycobacterial Infections of Polymorphonuclear Neutrophils

Objective To determine the role of PPE25 in the infection of M. smegmatis (MS) in polymorphonuclear neutrophils (PMNs). Methods In MS-ppe25 group, PPE25 was expressed in non-pathogenic fast-growing M. tuberculosis (Mtb) that infected PMNs. The empty vector MS (MS-vec group) was served as control. Their colony formation was observed, including the size and growth curves of single colonies. The colony forming unit (CFU) indicated bacterial vitality. The percentage of lactate dehydrogenase (LDH) release measured PMN death. The role of PPE25 protein in MS infections was analyzed by reactive oxygen species (ROS) detected by flow cytometry, nitric oxide (NO) level detected by nitrate reductase, cytokine interleukin (IL) and tumor necrosis factor-α (TNF-α) detected by ELISA. Results PPE25 protein had no effect on MS growth, colony formation and the size of single colonies. MS-infected PMN had higher percentages of CFU and LDH release 2, 6, and 12 h after infections compared with the MS-vec group (P<0.05). MS-infected PMN also had lower levels of ROS and NO levels 2 h after infections (P<0.01), consistently higher levels of TNF-α (P<0.01), and higher levels of IL-1β infusion 6 h after MS infections (P<0.01). Conclusion PPE25 protein increases the survival of MS in PMN, induces cell necrosis, inhibits the expressions of ROS and NO, and changes the secretion of cytokines, which helps spread of the pathogen by evading host immunity.