A transdifferentiated human macrophage-like cell line to elucidate the cell-to-cell spread of Leishmania major (Exit WS)

Abstract text

Leishmania is the causative agent of the tropical neglected disease leishmaniasis and it infects macrophages as its definitive host cell. While the routes of initial infection are well understood, the mechanism of parasite spread to other cells remains vague, partially due to lack of genome editing methods in human macrophages. Hence, we set up an infection model in BLaER1 cells, which can be edited on a genomic level and transdifferentiated into a macrophage-like phenotype. To proof their suitability as infection model, we first examined the immunophenotype of BLaER1 cells and found it to be comparable with macrophages. We also confirmed their susceptibility for the infection with Leishmania promastigotes using confocal microscopy. The infection rate and cytokine responses were very similar when comparing infected BLaER1 and macrophages. Focusing on host cell death as a possible mechanism of the cell-to-cell spread of Leishmania, we induced pyroptosis in BLaER1 and used BLaER1 GSDMD knockout cells as a control. As expected, we found BLaER1 GSDMD knockout cells to be more resistant to pyroptosis induction than BLaER1 wild type cells based on the duration until IL-1ß release and cell death. Live cell imaging revealed that induction of pyroptosis results in release of parasites from host cells and it is clearly delayed in the BLaER1 GSDMD knockout cells. Finally, we quantified the rate of parasite transfer to new host cells in a co-incubation assay. Here, the transfer rate was significantly increased in a pyroptosis dependent manner. Taken together, these findings demonstrate the suitability of BLaER1 cells as a Leishmania infection model to study cell to cell spread on a cell biological level and suggests pyroptosis as a cell death mechanism that can contribute to the spread of the parasites to new host cells.