CD4 and periodontitis: Activated CD4 + T cells, regulatory T cells, immature B cells, activated B cells, and myeloid-derived suppressor cells were dominant in periodontitis tissues, whereas central memory CD8 + T cells, effector memory CD8 + T cells, follicular helper T cells, eosinophils, mast cells, monocytes, and neutrophils were mainly expressed in normal gingival tissues.