ABSTRACT
Objective To determine the effect of apoptosis in different host cells induced by L. in- terrogans and the associated intracellular signaling pathway. Methods L. interrogans serogroup Icterohaem- orrhagiae serovar icterohaemorrhagiae strain Lai infected cell models in mouse mono-macrophage like cell J774A. 1, human EVC304 cells and A549 cells were established, respectively. Flow cytometry with fluores- cein labeling of FITC-Annexin V/PI was performed to examine the apoptosis or necrosis of the infected cells. Fluorometry as well as Western blot assay was applied to measure the activity of caspase-3, -8, -9 and the expression levels of apoptotic associated protein FADD in the infected cells , respectively . Results 36.70%-63.70% of the L. interrogans strain Lai infected J774A. 1 cells displayed obvious early apoptosis during the infection for 1-6 h, and then altered to later apoptosis / necrosis (53.68%) as the major injury pattern when infected for 12 h. 78.52% of the L. interrogans strain Lai infected A549 cells only showed later apoptosis / necrosis. However, no obvious apoptosis and / or necrosis could be found in the L. interrogans strain Lai infected EVC304 cells. The maximal activities of caspase-3 and -8 in the infected J774A. 1 cells were (1453.41±36.07) and (1402.15± 59.09) FU, respectively, which were the 16.38-fold and 29.99- fold of those the non-infected cells. The caspase-9 activity of the infected J774A. 1 cells slightly increased [(89.42±5.08) FU ], which significantly lower than those of caspase-3 and -8 (P <0.001). The FADD expression level of the infected J774A. 1 cells was gradually increased in an infection time-dependent man- ner. Conclusion There is a distinct diversity of apoptosis in different cells induced by L. interrogans, and FADD→caspase-8→caspase-3 is the major signaling pathway to mediate L. interrogans infection associated cell apoptosis.