TLR9 and colitis: Thus, it is possible that the extracellular DNA associated with the purified curli preparations may also be stimulating the immune system via the cytosolic DNA sensors leading to immune homeostasis in the gut.68 TLR9 recognises bacterial double-stranded DNA.51 Polymorphisms in TLR2, NOD2, NLRP3 and TLR9 have all been identified as risk factors for developing inflammatory bowel disease.69–71 Thus, the success of curli treatment in colitis may be owing to the activation of multiple receptors with this bacterial component including TLR2 and NLRP3 and possibly TLR9.