IFNG and infection: Stimulation of macrophages with the pro-inflammatory cytokine interferon γ (IFN-γ) prior to infection by L. pneumophila/Timer for 24 h led to a fivefold increase in the number of intracellular nongrowers compared with infected naive macrophages, and reached ca. 50% of the total intracellular bacteria (Fig. 6a, b).