NOD1NOD2

NOD1NOD2 refers to a pair of intracellular pattern recognition receptors belonging to the NOD-like receptor (NLR) family. These receptors are crucial components of the innate immune system, playing a vital role in detecting bacterial pathogens. NOD1, also known as CARD4, and NOD2, also known as CARD15, are primarily expressed in myeloid cells, epithelial cells, and other cell types throughout the body.

NOD1 recognizes a breakdown product of peptidoglycan, a major component of the cell wall of Gram-positive and Gram-negative bacteria, specifically meso-diaminopimelic acid (iE-DAP). NOD2 recognizes a different peptidoglycan component, muramyl dipeptide (MDP), found in a broader range of bacteria. Upon recognizing their respective ligands, NOD1 and NOD2 undergo conformational changes and recruit downstream signaling molecules.

This recruitment typically involves the CARD (caspase recruitment domain) containing adaptor protein RIPK2 (receptor-interacting protein kinase 2). Activation of the NOD1 and NOD2 signaling pathways leads to the activation of transcription factors, such as NF-κB and MAPKs. This ultimately results in the production of pro-inflammatory cytokines and chemokines, which orchestrate an immune response to clear the infection. Dysregulation of NOD1 and NOD2 signaling has been implicated in various inflammatory and autoimmune diseases, highlighting their importance in maintaining immune homeostasis. Genetic variations in the NOD2 gene, in particular, have been strongly associated with an increased risk of Crohn's disease.