ABSTRACT
Objective To determine the modality of Leptospira interrogans invading human and murine mononuclear-macrophages and diversity of leptospiral phagocytotic vesicle formation. Methods Transmission electron microscopy was applied to observe the invasion of L. interrogans serogroup Icterohaemorrhagiae serovar Lai strain Lai into murine mononuclear-macrophage-like cell line J774A. 1 and PMA-activated human monocyte line THP-1 and the formation of leptospiral phagocytotic vesicles. By using immunofluorescence plus either laser confocal microscopy or fluorescence spectrophotometry, the changes of intracellular leptospiral numbers in J774A. 1 and PMA-activated THP-1 cells before and after block with endocytosis inhibitors monodansylcadaverin (MDC), phenylarsine oxide (PAO) and clathrin antibody were investigated. Results The leptospires in J774A. 1 cells were located in phagocytotic vesicles while the leptospires in THP-1 cells had no package with phagocytotic vesicle membrane. Both MDC and PAO presented the effect inhibiting endocytosis of L. interrogans into J774A. 1 and THP-1 cells in dose-dependent manner. The numbers of leptospires in J774A. 1 and THP-1 cells that pre-blocked with 10 μmol/L or above MDC and 1 μmol/L or above PAO were significantly less than that in the two cells untreated with MDC and PAO (P＜0.05＝. After J774A. 1 and THP-1 cells were blocked with clathrin antibody, the numbers of intracellular leptospires were also remarkbly decreased ( P<0.05 ).Conclusion Leptospira interrogans can invade into both human and murine mononuclear-macrophages through the way of clathrin-dependent endocytosis. There is an opposite diversity of leptospiral phagocytotic vesicle formations in human and murine mononuclear-macrophages, which may result in the difference of pathogenesis in human and mice after infected with L. interrogans.