MMP9 and Alzheimer disease: Studies found that salivary IL-1, IL-6, interleukin-1 receptor antagonist (IL-1RN), and TNF-α decreased to a greater extent in the AD group than in the control group, while complement C4 (CC4), COX-2, caspase-8, IL-1β, and MMP-9 showed opposite results [21,44,45,69].