Apoptosis of endothelial cell line ECV304 persistently infected with Orientia tsutsugamushi

Endothelial cells are major targets of Orientia tsutsugamushi, To examine t he consequences of the infection of endothelial cells with O, tsutsugamushi , we used human endothelial cell line ECV304, Persistent infection was esta blished and infected cultures could be maintained for over seven months wit hout the addition of normal cells. The heavily infected cells became round and floated in the culture medium, harboring large numbers of organisms ins ide them. Some of the infected ECV304 cells showed features of apoptotic ce lls, as determined by the terminal deoxytransferase-mediated dUTP nick end- labeling reaction and DNA fragmentation. We also found that O, tsutsugamush i increased transcription of the mRNAs of proinflammatory cytokines such as IL-6 and IL-8, These results show the first evidence of in vitro-persisten t infection by O, tsutsugamushi, which may be related to in vivo persistenc e reported previously.