| Leptospires are thin, helical bacteria classified into two major groups, Leptospira. interrogans (L. interrogans) which contain at least 12 pathogenic species and L. biflexa which contain 4 saprophytic species. L. interrogans are the aetiological agents of leptospirosis, a zoonosis widespread throughout the world, and china is also one of the major epidemic areas. Humans most commonly become infected through occupational, or domestic contact with the urine of carrier animals, either directly or via contaminated water or soil. Therefore, leptospires enter the body through small cuts or abrasions, via mucous membranes and circulate in the blood stream, and then disseminate to the lung, liver and kidney. Human leptospirosis varies from mild to severe Weil's syndrome characterized by jaundice, hemorrhage and severe renal failure depending on the serovar of Leptospira involved and how virulent it is. Animals recovering from leptospirosis may become asymptomatic carriers harboring leptospires in the renal tubules for extended periods and shedding infectious leptospires into the environment. The renal carrier state is thus a key component which is central to the persistence and epidemiology of leptospirosis. In order to further understand the invasive character and the survival of the leptospires within the kidney, three representative cell lines such as HEK293, J774A.1, and COS-7 were infected by the virulent Leptospira strain Lai and analyzed through a series of observation of transmission electron microscopy (TEM), immunofluorescence microscopy, confocal laser microscopy and analysis of western blot. Our results showed that the virulent Leptospira strain Lai could penetrate HEK293 cells without affecting the cell tight junctions (Zonula occludens-1, ZO-1) while saprophytic Leptospira were engulfed by HEK293 cell and formed the phagosomes within the cytosol, being accompanied with the decreased expression and density of ZO-1 protein. We also found that virulent strain of Leptospira can attach to J774A.1 cells with one end or both, and of which about 80% leptospires could be phagocytosed and result in the formation of phagosomes, which could further colocalized with late endosome/lysosome.TEM results showed that the maturation of leptospires-containing phagosomes fit the "kiss-and-run" theory that was raised by Desjardins. For COS-7 cells, there is only about 40% of the attached virulent leptospires can be phagocytosed, and later the leptospires that restrained within the phagosome could escape from the phagosomes and release into the cytoplasm. Although a complete picture of Leptospira pathogenic factors still needs to be drawn, our results verified the invasive capacity of Leptospira in its pathogenesis, revealed the outcome of leptospires within macrophages, and explored the survival of leptospires within kidney cells. Our study provide at least to some extent a theoretical reference for further study on how to prevent leptospirosis, and how to cut off the source of infection in order to control the spread of the disease. |
