The NOD2 gene is strongly associated with susceptibility to Crohn’s disease (CD) of the terminal ileum. It interacts with bacterial lipopolysaccharide (LPS) and induces cellular activation.
The mechanisms by which NOD2 mutations cause terminal ileitis are unknown.
NOD2 is expressed most highly by peripheral blood monocytes, which are distributed ubiquitously and readily respond to LPS via cell-surface receptors.
Paneth cells are numerous in the terminal ileum. They are important in enteric antibacterial defense, and respond to LPS through undefined pathways.
|NOD2 was detected readily in monocytes.|
In this study, researchers from England and the United States determined whether these specialized intestinal epithelial cells also expressed the NOD2 gene.
The team used in situ hybridization, immunohistochemistry, and laser-capture microdissection to determine RNA and protein expression in tissue sections.
They used real-time reverse-transcription PCR to quantitate gene expression in intestinal epithelial cells and peripheral blood mononuclear cells.
The researchers found that NOD2 was detected readily in monocytes. However, it was not detected in mature macrophages in the lamina propria or within granulomas.
The team found that levels declined as monocytes differentiated into macrophages in vitro, so that Caco-2 cells expressed more NOD2 mRNA than macrophages.
They determined that NOD2 mRNA was enriched in crypts compared with villi.
In situ, Paneth cells were the most prominent cells expressing NOD2 in normal and CD-affected intestinal tissue, where they also strongly expressed tumor necrosis factor alpha RNA.
Dr Sanjay Lala's team concluded, "The NOD2 gene product is most abundant in Paneth cells in the terminal ileum, which could therefore play a critical and hitherto unrecognized role in the pathogenesis of NOD2-associated CD".