IFNG and pneumonia: Group 1 ILCs, including NK cells, are a rapid source of interferon-γ (IFN-γ), and mice deficient in IFN-γ develop more severe K. pneumoniae or L. pneumophila-induced pneumonia upon intratracheal inoculation of the pathogen due to impaired IL-1 and IL-6 production, and the defective clearance of the bacteria (115, 116).