TLR9 and periodontitis: To investigate the type of periodontitis-derived cfDNA responsible for activating the TLR9, we used cfDNA isolated from periodontitis saliva and serum, genomic DNA (gDNA) and mitochondrial DNA (mtDNA) as part of DAMPs, and CpG DNA as part of MAMPs to stimulate the HEK-TLR9 receptor cells.