a risk factor for Crohn's disease development as well as ATG16L2. ATG16L1 appears to be an essential protein for the function of intestinal stem cells, morphological structure of intestinal cells and granule exocytosis pathway of the Paneth cells in animal models. Bacteria invasion leads to ATG16L1 recruiting by NOD1 and NOD2. This results in autophagy in RIP2/NF-κB independent manner. It is also known that NOD2 interacts with ATG16L, ATG5 and ATG7 and provides antibacterial immune response through autophagy induction and MHC class II antigen-specific CD4+ T cell responses. It has also been shown that low levels of ATG16L1 result in lower ATG16L1-NOD2 complex formation, which is crucial for bacterial autophagy in the bacterial entry site. Inhibition of autophagy leads to a NOD2 signaling through RIP2 kinase and induction of cytokine responses. This promotes an increase in mRNA expression of highly potent pro-inflammatory cytokines as interkleukin-1 (IL-1β). ATG16L1 also plays a role in viral infections. Through autophagy viral particles are delivered into the lysosome degradation pathway and interrogate with a specific type of pattern recognition receptor to initiate type I interferon (IFN-I) expression and viral clearance. Interestingly, ATG5-ATG12/ATG16L1 complex negatively regulates RIG-I-like receptor pathway and IFN-I expression. A mouse with a deletion in one of these genes appears to be resistant to virus replication. It is most likely due to an unregulated overexpression of IFN-I, which interferes with the virus life cycle. ATG16L2 is a related protein, which is also highly conserved (both ATG16L1 and 2 share 94 and 83% sequence identity). It has been shown that changes in ATG16L2 expression are correlated with Multiple Sclerosis (MS) and can be used as a serum biomarker of the disease and specifically for the prediction of relapse rates. Interestingly ATG16L2 mRNA expression was significantly reduced (~4-fold lower) in T cells isolated from the peripheral blood of MS patients in comparison to healthy age-matched controls, which may reflect their abnormal activation. References External links Further reading