IFNG and bacterial infectious disease: However, IFN-γ was shown to be expressed in the alveolar cell line A549 after bacterial infections: IFN-γ mRNA expression was detected in cells infected with Mycoplasma pneumoniae and Chlamydia pneumoniae [21,22] and release of high concentrations of IFN-γ was shown in A549 cells infected with Mycobacterium tuberculosis [20].