Infection of Porphyromonas gingivalis in Alzheimer’s Disease and the Suppression of Immunity

Alzheimer disease is one of the most frequent neurodegenerative diseases. Porphyromonas gingivalis is the key pathogen of chronic periodontitis, and it has a virulence factor known as gingipain. Gingipain is a proteolytic enzyme capable of penetrating the blood–brain barrier to reach the brain’s center of cognition. Gingipain that reaches the brain is suspected of having a relationship with an amyloid-beta plaque and neurofibrillary tangle, which play a critical role in the formation of Alzheimer disease. These bacteria may also suppress the immune system by reducing cytokine tumor growth factor (TGF-beta) and Interferon (IFN-gamma) and imbalance of Th17/Treg (Regulatory T cells). Besides that, the involvement of P. gingivalis in the brain may trigger neuroinflammation and lead to neuron defect and worsen Alzheimer disease. This review aims to discuss the correlation between P. gingivalis and the development of Alzheimer disease.