Cold atmospheric plasma enhances immune clearance of Porphyromonas gingivalis via LC3-associated phagocytosis in mice with experimental periodontitis.

Periodontitis is a microbe-driven infectious disease, in which Porphyromonas gingivalis (Pg) plays a keystone role. As the front line to eliminate dysbiotic microbiota, macrophages are critical for recognition, phagocytosis and digestion of bacteria. However, deficiencies in the antimicrobial function of periodontal macrophages lead to diminished Pg clearance and destructive periodontal inflammation. Cold atmospheric plasma (CAP) enables non-invasive treatment by producing reactive species including reactive oxygen species (ROS), reactive nitrogen species (RNS) and electro-magnetic field, and is of great interest for infectious diseases. These radicals have a significant influence on cellular biochemistry and are crucial components of the immune system. The CAP jet using helium gas was developed and driven by the bipolar pulse high voltage. The negative voltage was 5 kV and the positive voltage was 10 kV. The irradiation time was set to 120 s for in vivo experiments and 80 s for in vitro experiments. In vivo experiments demonstrated that CAP significantly alleviated periodontitis. In addition to the directly antimicrobial effects, in vitro experiments demonstrated that CAP enhanced intracellular killing of Pg by bone marrow-derived macrophages (BMMs) and murine macrophage cell line RAW 264.7 in a ROS-dependent manner. BMMs were collected from the tibias and femurs of healthy C57BL/6 mice aged 6-8 weeks old. Mechanistically, it is found that CAP promotes microtubule-associated protein 1A/1B-light chain 3 (MAP1LC3, LC3)-associated phagocytosis (LAP) in macrophages to defend against Pg. Therefore, CAP is proposed a potential therapy for effectively alleviating periodontitis through regulating the bactericidal activity of macrophages.