Differentiation of tissue cysts after in vitro culture. Parasites were induced to differentiate by high-pH culture for 7 days (“Induced”), and cyst development was detected by staining with fluoresceinated lectin DBL (green), followed by MAb to the parasite surface protein SAG1 conjugated to Alexa 594 (red). GT1 readily formed cysts under these conditions, whereas RH-ERP2009 did not. Neither strain converted to tissue cysts under normal growth conditions used for the plaque assay (“Normal”). All pictures shown were recorded under similar optical conditions, imaged with the same exposure time, and processed identically. Scale bars: 15 μm in the top panel and 40 μm in the remaining panels.