Anti-Bacterial Effect of CpG-DNA Involves Enhancement of the Complement Systems.

CpG-DNA activates the host immune system to resist bacterial infections. In this study, we examined the protective effect of CpG-DNA in mice against () K1 infection. Administration of CpG-DNA increased the survival of mice after K1 infection, which reduces the numbers of bacteria in the organs. Pre-injection of mice with CpG-DNA before K1 infection increased the levels of the complement C3 but not C3a and C3b. The survival of the mice after K1 infection was significantly decreased when the mice were pre-injected with the cobra venom factor (CVF) removing the complement compared to the non-CVF-treated mice group. It suggests that the complement has protective roles against K1 infection. In addition, the survival of complement-depleted mice was increased by CpG-DNA pre-administration before K1 infection. Therefore, we suggest that CpG-DNA enhances the anti-bacterial activity of the immune system by augmenting the levels of complement systems after K1 infection and triggering other factors as well. Further studies are required to investigate the functional roles of the CpG-DNA-induced complement regulation and other factors against urgent bacterial infection.