Tregs are highly enriched in the bone-destructive form of periodontal disease -periodontitis- but not in the inflammatory but not destructive form -gingivitis- as demonstrated by the identification of CD4+CD25+CTLA-4+ cells and the increased expression of CTLA-4, GITR, CD103, CD45RO, and Foxp3 in gingival biopsies23. Here, TNFRSF18 is linked to periodontitis.