In vitro proliferation of a canine granulocytic Ehrlichia

Anaplasma phagocytophilum infection in a dog: identifying the causative agent using PCR

A diagnosis of Anaplasma phagocytophilum infection was confirmed in a two-year-old male golden retriever displaying few clinical and haematological abnormalities. This was achieved by demonstrating ehrlichial organisms in circulating neutrophils, by indirect immunofluorescence assay using A phagocytophilum as an antigen, and by detecting DNA specific for the 16S rRNA gene of granulocytic Anaplasma by PCR. After treatment with doxycycline for 10 days the dog showed improvement and the laboratory values returned to normal.

Intracellular infection by the human granulocytic ehrlichiosis agent inhibits human neutrophil apoptosis

In patients with human granulocytic ehrlichiosis (HGE), the HGE agent has been seen only in the peripheral blood granulocytes, which have a life span too short for ehrlichial proliferation. To determine if the HGE agent delays the apoptosis of human peripheral blood neutrophils for its advantage, peripheral blood granulocytes consisting mostly of neutrophils were incubated with freshly freed host cell-free HGE agent in vitro. The HGE agent induced a significant delay in morphological apoptosis and the cytoplasmic appearance of histone-associated DNA fragments in the granulocytes. This antiapoptotic effect was dose dependent. Although much weaker than the HGE agent freshly freed from the host cells, noninfectious purified HGE agent stored frozen and thawed also had antiapoptotic effect, which was lost with proteinase K treatment but not with periodate treatment. Treatment of neutrophils with a transglutaminase inhibitor, monodansylcadaverine, blocked the antiapoptotic effect of the HGE agent. Addition of oxytetracycline, however, did not prevent or reverse the antiapoptotic effect of the HGE agent. These results suggest that binding of a protein component(s) of the HGE agent to neutrophils and subsequent cross-linking and/or internalization of the receptor and ehrlichiae are required for antiapoptotic signaling, but ehrlichial protein synthesis and/or proliferation is not required. MG-132, a proteasome inhibitor, and cycloheximide accelerated the apoptosis of neutrophils and overrode the antiapoptotic effect of the HGE agent. Studies with specific inhibitors suggest that protein kinase A, NF-kappaB, and interleukin 1beta are not involved in the antiapoptotic mechanism of the HGE agent.

Isolation of the equine granulocytic ehrlichiosis agent, Ehrlichia equi, in tick cell culture

The equine granulocytic ehrlichiosis agent, Ehrlichia equi, is closely related or identical to the human granulocytic ehrlichiosis (HGE) agent. Both are suspected of being transmitted by ticks. We have successfully isolated E. equi in a cell line, IDE8, derived from a putative vector, the tick Ixodes scapularis. Peripheral blood leukocytes from an experimentally infected horse were inoculated onto IDE8 monolayers. Cultures were incubated in a candle jar at 34 degrees C in tick cell culture medium with NaHCO3 and an organic buffer [3-(N-morpholino)-propanesulfonic acid] (MOPS). Within 2 weeks, infected cells were detected in Giemsa-stained culture samples, and the organisms subsequently spread to uninfected cells in the cultures. E. equi was passaged serially by transferring a portion of an infected culture to new cell layers every 2 to 3 weeks. The identity of the organisms was confirmed by PCR using oligonucleotide primers specific for E. equi and the HGE agent and by immunocytology. Homologous equine antibodies and human anti-HGE convalescent serum recognized E. equi grown in tick cell culture. Electron microscopy revealed electron-lucent and -dense ehrlichia-like forms developing within host cell endosomes. E. equi passaged twice in tick cell culture retained infectivity and pathogenicity for the equine host, as demonstrated by intravenous inoculation of a suspension of infected tick cells and subsequent reisolation from peripheral blood, in fulfillment of Koch's postulates. The horse developed severe clinical signs, i.e., fever, inappetence, thrombocytopenia, icterus, and limb edema, typical of granulocytic equine ehrlichiosis, within 1 week.