Comparison of different staining procedures for the flow cytometric analysis of U-937 cells infected with different Leishmania-species.

The human macrophage cell line U-937 infected with different Leishmania species, Leishmania mexicana amazonensis (Lma), Leishmania donovani (Ld) and Leishmania infantum (Li), was analyzed by flow cytometry (FCM). Leishmania spp. were labeled with different stains prior to the infection of the U-937 cells (BCECF-Am, PKH2-GL and SYTO 17) or after the infection (AO, FITC-conjugated monoclonal antibodies, PI). Infected cells were analyzed by flow cytometry, fluorescence microscopy and in parallel microscopically after Giemsa staining. The data obtained by these two methods were compared to decide which method is mostly appropriate for detection and estimation of the infection rate. Three fluorescent stains were suitable: BCECF-Am, SYTO 17 and FITC-conjugated MoAb with 0.02% digitonin. None of the vital stains gave evaluable results after 3 days of incubation.