ADGRE5 and immune system disorder: CD97, an adhesion G protein-coupled receptor (aGPCR), was first identified in haematopoietic cells.22 This molecule has well-documented effects on immune system diseases and epithelial cell-derived malignancies, but recently, the mechanosensory function of CD97 has attracted increased attention.23 Nevertheless, the expression of CD97 in periodontal tissue has not been reported.