Cell membrane labeling of Eimeria tenella sporozoites with the fluorescent dye PKH-67 GL for tracking parasite-host interactions.

The fluorescent cell linker dye PKH-67 GL was used as a vital stain for sporozoites of Eimeria tenella for tests on viability, invasion of cultured primary chick kidney cells, flow cytometric analysis and fluorescence microscopy. The effect of PKH-67 GL on sporozoites was tested at a range of concentrations of dye and sporozoites. In flow cytometric analysis, 0.5-40x10(-6) M of PKH-67 GL labeled sporozoites to some degree, with the percentage of labeled sporozoites increasing with higher dye concentrations. The optimum concentration was 2x10(-6) M, allowing easy observation by fluorescence microscopy. Morphological changes in the sporozoite at concentrations greater than 5x10(-6) M were accompanied by loss of viability according to a propidium iodide inclusion assay. Sporozoite penetration of primary chick kidney cells was unaffected by the optimal level of 2x10(-6) M, allowing observation of intracellular activities. Overall, the cell linker dye greatly facilitated observation of E. tenella in vitro and in flow cytometric analysis.