Lessons from Nod2 studies: towards a link between Crohn's 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-kappaB signaling pathways. Recent progress has enabled research to demonstrate genetically that NOD2 (CARD15) is involved in the predisposition to Crohn's 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 Crohn's disease and Blau syndrome, and bacterial sensing.