Lessons from Nod2 studies: towards a link between Crohnʹs disease and bacterial sensing

Nod2 (Card15) belongs to the family of the recently described Nod molecules, which also includes the closely related protein Nod1 (Card4). Nod proteins have been initially described as intracellular activators of the caspase and NF-κB signaling pathways. Recent progress has enabled research to demonstrate genetically that NOD2 (CARD15) is involved in the predisposition to Crohnʹs disease and Blau syndrome. In addition, biochemical evidence has unraveled the role of Nod1 (Card4) and Nod2 (Card15) as intracellular sensors of bacterial peptidoglycan. Together, studies on Nod2 (Card15) provide a conceptual link between inflammatory disorders, such as Crohnʹs disease and Blau syndrome, and bacterial sensing.