C5AR1 and Alzheimer disease: In the oral microbiota, P. gingivalis which has been repeatedly linked to AD [54–56], is able to evade human and mouse neutrophils and macrophages by initiating crosstalk between C5aR1 and TLR2 by bypassing host protective MyD88 signaling pathways and instead inducing a pro-inflammatory TLR2–TIRAP–PI3K pathway, in which phagocytosis is inhibited [57–59].