Fig 1 is the summary of interactions between pathogen and PRR, NOD1 detection. NOD1 detects a dipeptide, meso-diaminopimelic acid (iE-DAP), found in gram-negative bacterial peptidoglycans (PG). iE-DAP enters cells after degradation of a bacterial pathogen, endocytosis of bacterial PG, transport of PG into cells by bacterial secretion systems, or in tandem with TLR pathogen recognition. NOD1 initiates intracellular host cell immune responses independently of TLR activation, emphasizing the importance of this receptor's pattern recognition ability. The activation of NOD1 triggers an immune response by activating transcription factor, NF-๐ B, through CARD-CARD interactions and mitogen-activated protein kinases (MAPK). These host effector molecules stimulate the expression of immune particles, like cytokines, and immune signal transduction pathways.