MMP8 and periodontitis: Melatonin is a hormone mainly secreted by the pineal gland, which can passively diffuse into saliva through the blood stream.14 It has been shown to be an important enhancer of the immune system by activating monocytes and neutrophils.19 In diseased periodontal tissues, especially periodontitis, the melatonin level in GCF drops significantly.1 MMP-8 is one of the major proteolytic enzymes released by neutrophils during the inflammatory process.