NCR1 and infection: To detect and visualize NK cells, we used mice in which one copy of the Ncr1 gene had been replaced with a green fluorescence protein (GFP) reporter.26 These mice were infected via the physiologically relevant oral route with tissue cysts of the type II Prugniaud strain engineered to express tdTomato, allowing us to monitor the infection levels in NK cells by flow cytometry.6 Five days after oral infection, 0.72±0.14% of NK cells in the draining mesenteric lymph nodes contained parasites (Figures 1a and b).