NOD2 and viral infectious disease: Upon entry of the virus by endocytosis in airway epithelial cells, viral infection can be detected through many innate sensors such as Toll-like receptors (TLR) [61,62], retinoic acid-induced like receptor (RIG-I), melanoma-differentiation gene 5 (MDA5) and Nod-like receptor 2 (NOD2).