NOD2 and respiratory tract infectious disorder: The microbiota can protect against respiratory infection via granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling., These include Staphylococcus epidermidis in the upper airway and Lactobacillus reuteri, E. faecalis, and Lactobacillus crispatus in the gut [61], Through Nod2-mediated recognition of microbial peptidoglycan, the microbiota primes a shared innate defense against Gram-negative and Gram-positive respiratory pathogens by promoting IL-17 A-dependent GM-CSF production.