Ehrlichial Infection Research Articles

Inhibition of infection of macrophages with Ehrlichia risticii by cytochalasins, monodansylcadaverine, and taxol.

The requirement of functions of clathrin, microfilaments, and microtubules in binding, internalization, proliferation, and spreading of Ehrlichia risticii in macrophages was studied. Monodansylcadaverine (MDC), which inhibits clustering and internalization of the ligand-receptor complexes into clathrin-coated vesicles; cytochalasin B or D, which depolymerizes microfilaments; and taxol, which binds and stabilizes polymerized microtubules, were found to prevent ehrlichial infection in murine peritoneal macrophages when they were present throughout the infection period. [35S]methionine-labeled ehrlichial binding to the macrophage was reduced by 0 to 22%; therefore, the binding was not the major point of inhibition. However, MDC, cytochalasin D, and taxol inhibited ehrlichial internalization into macrophages by 80, 58, and 32%, respectively. When MDC, cytochalasin B or D, or taxol was added immediately after internalization of E. risticii (3 h postinfection), ehrlichial replication in P388D1 cells was almost completely prevented. Also, all of these agents almost completely prevented ehrlichial spreading from P388D1 cells to THP-1 human monocytes. These agents were not found to be ehrlichiacidal when approximately 40%-infected P388D1 cells were treated for 2 days, although further intracellular proliferation was prevented. Furthermore, none of these compounds directly inhibited the metabolic activity of E. risticii, since 14CO2 production from L-[14C]glutamine by Percoll density gradient-purified host-cell-free E. risticii was not shown to be impaired. The action of taxol was probably due to impairment of the microtubule function since a microtubule-depolymerizing agent, colchicine, also inhibited intracellular proliferation of E. risticii. Neither reactive oxygen intermediates, nitric oxide, nor tumor necrosis factor alpha appeared to be involved in taxol-induced inhibition of E. risticii in macrophages. Thus, our findings indicate that ehrlichial internalization appears to take place by a mechanism that is more dependent on the functions of clathrin and less dependent on the functions of microfilaments or microtubules. Replication within macrophages and intercellular spreading appear to require clathrin, microfilaments, and microtubules. Consequently, alteration of these structures with inhibitors can result in complete prevention of infection.

Fatal Seronegative Ehrlichiosis in a Patient with HIV Infection

Human infection with Ehrlichia chaffeensis, a recently identified bacterium included in the family Rickettsiaceae,1,2 results in an acute, generally self-limited, febrile illness associated with cytopenia and hepatic-enzyme abnormalities. Several hundred cases of E. chaffeensis infection have been recognized since 1986, although ehrlichiosis has not been described in patients infected with the human immunodeficiency virus (HIV). We report the course of a fatal seronegative ehrlichial infection in a woman with advanced HIV infection. The infection was diagnosed by light and electron microscopy, immunohistochemical techniques, and the polymerase chain reaction. The potential for successful antimicrobial treatment, combined with the possible absence . . .

Development of neutralizing antibody in horses infected with Ehrlichia risticii

The role of the humoral immune response in ehrlichial infection is unknown. Development of neutralizing antibodies during a course of Ehrlichia risticii infection in a pony was examined in vitro by determining the inhibition of E. risticii infection of P388D 1 cells in the presence of the sera. The pony experimentally infected with E. risticii developed significant neutralizing activity in the sera by 15 days postinfection when parasitemia started to decline. Neutralizing activity continued to rise after recovery from the disease up to 34 days postinfection at which time the experiment was terminated. In vitro neutralizing activities in the sera from 3 additional ponies infected with E. risticii were lower at 2 weeks than at 4 weeks postinfection. The sera from vaccinated/challenged ponies had comparable neutralizing activity to those of the recovered ponies at approximately 3 to 4 weeks postchallenge. Equine sera from infected or vaccinated/challenged ponies were also effective in protecting mice from E. risticii infection. These studies demonstrated the significant development of neutralizing activity in the sera of recovered or vaccinated/challenged ponies.

L-arginine-dependent killing of intracellular Ehrlichia risticii by macrophages treated with gamma interferon.

Thioglycolate-induced murine peritoneal macrophages infected with Ehrlichia risticii and treated in vitro with gamma interferon (IFN-gamma) developed antiehrlichial activity that eliminated the intracellular bacteria. This antiehrlichial activity was suppressed by NG-monomethyl-L-arginine, a competitive inhibitor of nitric oxide synthesis from L-arginine, but not by L-tryptophan. Increased levels of nitrite, an oxidative product of nitric oxide, were measured in cultures of infected macrophages treated with IFN-gamma. Sodium nitroprusside, which spontaneously releases nitric oxide, also showed the antiehrlichial activity. The antiehrlichial activity by reactive nitrogen intermediates was not mediated by elevation of the cellular concentration of cyclic GMP since the addition of 8-bromo-cyclic GMP itself had no influence on ehrlichial infection of macrophages. Addition of the intracellular iron chelator deferoxamine also inhibited E. risticii infection in vitro. These results suggest that intracellular E. risticii survival is iron dependent and that production of reactive nitrogen intermediates triggers iron loss from critical target enzymes of E. risticii, leading to lethal metabolic inhibition. However, addition of excess FeSO4, ferric citrate, or iron-saturated transferrin did not counteract the antiehrlichial effect induced by IFN-gamma.

Platelet aggregation studies in dogs with acute Ehrlichia platys infection

SUMMARY Ten adult dogs (5 Beagles and 5 mixed-breed dogs) were inoculated IV with canine platelets containing Ehrlichia platys. Inclusions and morulae of E platys developed in platelets of infected dogs at 10 to 14 days after inoculation, followed by marked thrombocytopenia at 14 to 21 days. Parasitemia and marked thrombocytopenia recurred at 24 to 28 days after inoculation. Increased numbers of megakaryocytes were observed in marrow aspirate smears from infected dogs, indicative of regenerative thrombocytopenia. Prior to infection, platelet-rich plasma from these dogs was determined to have similar aggregatory response to arachidonate. After infection with E platys, the aggregatory response of platelet-rich plasma to collagen or 3 dilutions of adenosine diphosphate was evaluated. A statistically significant (P < 0.05) inhibition of platelet aggregatory response to the lowest dilution of adenosine diphosphate was detected for mixed-breed dogs, whereas aggregation responses were unchanged in Beagles. Results indicate that platelet activation may occur in dogs with acute ehrlichial infection.