ACP5 and periodontitis: Besides a qPCR-measurement of their induction during the experimental periodontitis, we assessed the osteoclast-activity based on the induction of the tartrate-resistant acid-phosphatase (TRAP), an enzyme responsible for bone resorption by osteoclasts [61] and growth-arrest-specific-6 (GAS6), that has been reported to be a key factor for establishment of oral homeostasis [62] and that activates osteoclasts via the Tyrosine-protein-kinase-receptor Tyro-3 [63].