Ixodes ovatus Ehrlichia Exhibits UniqueUltrastructural Characteristics inMammalian Endothelialand Tick-derived Cells

摘要

Tick-borne pathogens in the genus Ehrlichia cause emerging zoonoses. Although labo-ratory mice are susceptible to Ehrlichia infections, many isolates do not cause clinicalillness. In contrast, the Ixodes ovatus Ehrlichia-like agent (IOE) causes disease and im-mune responses in mice comparable to the human illness caused by Ehrlichia chaffeen-sis. No culture system had been developed for IOE, however, which limited studies ofthis pathogen. We reasoned that endothelial and tick cell lines could potentially serve ashost cells, since the IOE is found in ticks and in endothelial cells in mice. Infected spleencells from RAG-deficient mice were overlaid onto ISE6 and RF/6A cultures, and coloniestypical of Ehrlichia were noted in RF/6A cells within 2 weeks. Infection of ISE6 cells wasestablished after transfer of IOE from RF/6A cells. Electron microscopy revealed denselypacked inclusions in infected RF/6A and ISE6 cells; these inclusions contained copiousamounts of filamentous structures, apparently originating from Ehrlichial cells. In par-ticular, within RF/6A cells the structures assumed an ordered morphology of finelycombed hair. IOE from RF/6A cells, when inoculated into C57BL/6 and RAG-deficientmice, induced fatal disease. These data reveal unique structural features of IOE thatmay contribute to the pathogen's high virulence.