Cultivation of the causative agent of human neoehrlichiosis from clinical isolates identifies vascular endothelium as a target of infection.

Candidatus (Ca.) Neoehrlichia mikurensis is the cause of neoehrlichiosis, an emerging tick-borne infectious disease characterized by fever and vascular events. The bacterium belongs to the Anaplasmataceae, a family of obligate intracellular pathogens, but has not previously been cultivated, and it is uncertain which cell types it infects. The goals of this study were to cultivate Ca. N. mikurensis in cell lines and to identify possible target cells for human infection. Blood components derived from infected patients were inoculated into cell lines of both tick and human origin. Bacterial growth in the cell cultures was monitored by real-time PCR and imaging flow cytometry. Ca. N. mikurensis was successfully propagated from the blood of immunocompromised neoehrlichiosis patients in two Ixodes spp. tick cell lines following incubation periods of 7-20 weeks. Human primary endothelial cells derived from skin microvasculature as well as pulmonary artery were also susceptible to infection with tick cell-derived bacteria. Finally, Ca. N. mikurensis was visualized within circulating endothelial cells of two neoehrlichiosis patients. To conclude, we report the first successful isolation and propagation of Ca. N. mikurensis from clinical isolates and identify human vascular endothelial cells as a target of infection.

Mechanisms to create a safe haven by members of the family Anaplasmataceae.

Members of the family Anaplasmataceae are obligatory intracellular bacteria with unique host cell specificities. Depending on each bacterial species, granulocytes, platelets, endothelial cells, monocytes, macrophages, red blood cells, and cells of invertebrates are specifically infected. This unique host cell specificity has been the major hurdle to overcome in order to cultivate this group of bacteria. Because these bacteria cannot survive outside host cells, once released from a host cell, they need to rapidly induce signals for their own internalization into another host cell unique to each species. How these bacteria enter and continue to survive and replicate within the host milieu, then exit the host cell is largely unknown. Recently, however, unique strategies employed by some of these bacteria for successful parasitism of mammalian leukocytes have begun to be uncovered. When these bacteria interact with host cells, signals are transduced both inside the host cells and inside the bacteria. These signals disable the alarm system, as well as microbicidal mechanisms, of the leukocytes and condition the host cells to accept these intruders to share space and nutrient resources. Signals transduced inside the bacteria allow them to finely tune their metabolism and physiology in the new host cell environment and to disguise themselves as "insiders" so that their sojourn does not upset the host cell physiology until they have sufficiently multiplied. This paper discusses our recent findings on these topics.

Susceptibility of the female reproductive tract of mice to Tyzzer's organism.

Susceptibility of the reproductive tract of ICR adult female mice to Tyzzer's organisms was examined by intravenous and intravaginal inoculation at various stage of pregnancy. After intravenous inoculation, the uterus was most severely affected when inoculation was made at the midpregnancy. Severe involvement of the uterus was also seen after intravaginal inoculation made either at late-pregnancy or shortly before and after parturition. While non-pregnant female mice were less susceptible to intravenous or intravaginal inoculation, the growth of organisms in the uterine epithelium was recognized after intrauterine inoculation. In 4CS adult female mice showing a constant 4-day-estrous cycle the endometrium was found to be the most susceptible at the estrus phase. Such difference in susceptibility of the female reproductive tract depending upon stage of pregnancy and estrous cycle might be related to metabolic changes of the endometrium controlled by sex hormones, whereas increased blood circulation and modified immune response during pregnancy and estrous cycle might be also involved.