Keigairengyoto, a traditional Japanese medicine, promotes bacterial clearance by activating innate immune cells in mouse cutaneous infection models

Abstract

Prompt elimination of pathogens including bacteria and dead cells prevents the expansion of secondary and prolonged inflammations and tissue damage. Keigairengyoto (KRT) is a traditional Japanese medicine prescribed for dermatoses such as purulent inflammations. Our aim is to clarify the actions of KRT in bacterial clearance and to examine the cell-kinetic profiles of phagocytes. In a mouse cutaneous infection model using living Staphylococcus aureus, KRT drastically reduced the number of bacteria in the infection sites. To evaluate the bacterial clearance, pseudo-infection was induced in mouse ears by intradermal injection of FITC-conjugated dead S. aureus. Biochemical and histological examinations revealed that KRT promoted bacterial clearance at 6 and 24 h post-injection. The numbers and phagocytic activities of neutrophils and macrophages in the ears were evaluated histologically using anti-Ly6G and F4/80 antibodies. KRT reduced bacterial deposition and increased the accumulation of F4/80+ resident macrophages around the lesion site. FACS analysis was performed on single cell suspensions dispersed enzymatically from skin lesions, followed by an investigation of CD11b+Ly6G+ (neutrophils) and CD11b+Ly6G– (monocytes/macrophages) cells. KRT increased the mean fluorescent intensity of FITC in CD11b+Ly6G–cells and the number of FITC-positive CD11b+Ly6G+ cells, while KRT did not change the numbers of these cells. To investigate the active constituents of KRT, phagocytosis assay using macrophages was performed, resulting in that some flavonoid glucuronides of KRT derivatives augmented phagocytosis. Collectively, KRT promoted bacterial clearance by enhancing the phagocytic capability of neutrophils and macrophages. KRT may exert unique properties in preventive and therapeutic strategies for skin infectious inflammation.