TNFSF11 and periodontitis: Also, GCs downregulate osteoprotegerin (OPG), an activator of the receptor activator of the nuclear factor kappa-Β ligand (RANKL) that potentially increases the activity of osteoclasts.6 Bostanci et al31 reported that RANKL and OPG were oppositely regulated in gingival crevicular fluid in periodontitis patients.