Indeed, NOD1 and NOD2 play a critical role in protection against the intracellular Legionella pneumophila-induced pneumonia by promoting PMN recruitment into the lung (29), whereas deficiency in either NOD1 or NOD2 led to an impaired bacterial clearance of Chlamydophila pneumophia, a gram-negative intracellular pathogen (30). Here, NOD1 is linked to susceptibility to pneumonia measurement.