Porphyromonas gingivalis (P. gingivalis) is one of the three well-documented major periodontal pathogens that play a key role in the pathogenesis of periodontitis by disrupting host immune homeostasis (132) and in this model, exosomes were extracted from periodontal ligament stem cells (PDLSCs) in the chronic inflammatory milieu and compared with normal PDLSC exosomes, and again found that microRNA-155-5p in inflammatory PDLSCs-EV increased SIRT1 expression in CD4+ T cells, thereby attenuating inflammatory response in chronic periodontitis (73). This evidence concerns the gene CD4 and periodontitis.