Figure 3.

Periodontitis caused by defective killing of bacteria. Knockout of pattern recognition receptors such as Toll-like receptors, knockout of lysosomal membrane protein LAMP-2, antimicrobial protein lactoferrin, or plasminogen causes defective clearance of bacteria, leading to activation of the Th1 signaling pathway, and initiating chronic inflammation Alternatively, knockout of genes important for the induction of the Th2 reaction and influx of T regulatory cells such as IL-4, CCL2, and CCR4 that modulate the infection, also lead to enhanced inflammation and an endured Th1 presence, such as shown by Araujo-Pires et al. (8). It can be envisaged that bacterial products accumulate due to ineffective clearance.