Colonization by P. gingivalis impairs innate immunity by subverting complement-TLR crosstalk, leading to increased numbers of periodontal bacteria and therefore enhanced inflammation through the activation of synergistic complement and TLR pathways. The inflammatory environment is favorable to further bacterial growth, since the gingival inflammatory exudate is a rich source of nutrients (e.g., degraded host proteins and hemin, a source of essential iron). These environmental changes, moreover, can alter the composition of the oral microbiota, favoring those bacteria (e.g., proteolytic and asaccharolytic organisms) that can better exploit these environmental changes. These changes result in even higher inflammation and bone resorption, leading to increased niche space (deeper periodontal pockets) for the bacteria, thereby perpetuating a vicious cycle of periodontal tissue destruction. Adapted from Hajishengallis et al (ref. ).