IFNG and legionellosis: By contrast, protection was critically dependent on MAIT cell-derived IFN-γ: when donor MAIT cells were deficient in IFN-γ, survival was decreased (P < 0.0001) and there was a 2.8 log-fold increase in bacterial burden (t-test P < 0.001) amongst the small proportion (3/21) of animals which survived till 23 DPI.In separate similar experiments, all mice transferred with IFN-γ deficient MAIT cells, succumbed within 35 days post Legionella infection.