CD4 and periodontitis: The infiltration of CD4+ T cells has been reputed to participate in the aggravation of periodontitis and colitis.53,54 Tregs and Th17 cells are subpopulations of CD4+ T cells.55 Disturbance of the balance between Th17 cells and Tregs has been found to aggravate periodontitis and colitis.56,57 Thus, we investigated the ability of the 3D-exos to reduce the Th17 population and increase the Treg population in the inflamed periodontium (Fig. 4a).