Mixed infection of human U-937 cells by two different species of Leishmania.

Mixed infections by different Leishmania species could explain differences in the clinical course of these infections. Moreover, mixed infections of the same macrophage could be the basis for parasite recombination. We stained three strains of Leishmania (L. mexicana amazonensis, L. donovani DD8, and L. infantum D2, respectively) with different fluorescent dyes and analyzed them using a fluorescence-activated cell scanner. The simultaneous infection of one cell by Leishmania belonging to two different species was demonstrated. In additional experiments, cells with mixed infections were separated by a fluorescence-activated cell sorter and monitored for 24 hr. Preinfecting human monocytic U-937 cells with one Leishmania species did not exclude a second species added after 3 hr.