Cytokine Gene Expression by Peripheral Blood Leukocytes in Dogs Experimentally Infected with a New Virulent Strain of Ehrlichia canis

Erythrocyte sedimentation rate, C-reactive protein, and interleukin-6 as inflammatory biomarkers in dogs naturally infected with Ehrlichia canis

Background and Aim

Canine monocytotropic ehrlichiosis (CME), a tick-borne disease, leads to a systemic inflammatory response syndrome; it is thus important to assess the intensity of inflammation in order to treat it appropriately. The current study was designed to evaluate hematological, biochemical, and inflammatory parameters in dogs naturally infected with Ehrlichia canis compared with those in healthy dogs. We also assessed the relationship among several inflammation-related parameters and considered these parameters for use as inflammatory biomarkers of CME.

Materials and Methods

Twenty-eight dogs were divided into two groups based on the results of nested polymerase chain reaction for detecting E. canis, comprising a healthy group (n=11) and an infected group (n=17). A blood sample was collected from each dog to evaluate hematological, biochemical, and inflammatory parameters, with the obtained results being statistically compared between the groups. Moreover, the correlations of erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and interleukin-6 (IL-6) were investigated in the 28 dogs.

Results

In the infected group, the mean levels of red blood cells, hemoglobin, and hematocrit were significantly lower than in the healthy group, while the mean lymphocyte and monocyte counts were higher. The mean levels of ESR and CRP were significantly higher (p<0.05) in the infected group, whereas no significant differences were found in IL-6 levels between the two groups. In the correlation analysis, ESR and CRP levels were highly correlated (p<0.01, r=0.531).

Conclusion

Elevated ESR and CRP levels were found in dogs naturally infected with E. canis, which also presented mild to moderate inflammation in this study. Moreover, CRP was significantly correlated with ESR, so ESR and CRP may serve as inflammatory biomarkers for monitoring CME.

Canine Monocytic Ehrlichiosis: An Update on Diagnosis and Treatment

Canine monocytic ehrlichiosis (CME) is a tick-borne disease of worldwide distribution. The major causative agent is Ehrlichia canis, a gram-negative, obligate intracellular, pleomorphic bacterium of the genus Ehrlichia, which infects monocytes, macrophages and lymphocytes, forming intracytoplasmic, membrane-bound bacterial aggregates, called morulae. After an incubation period of 8-20 days, the course of E. canis infection, can be sequentially divided into acute, subclinical and chronic phases, although these phases can hardly be distinguished in the clinical setting. Clinical recovery is the typical outcome of acutely infected dogs, entering the subclinical phase, during which they show no or minimal clinical signs and/or mild hematological abnormalities. Immunocompetent dogs may eliminate the infection during the acute or subclinical phases, but an unpredictable proportion of dogs will eventually develop the chronic phase, characterized by aplastic pancytopenia and high mortality, due to septicemia and/or severe bleeding. This article outlines briefly the pathogenesis of CME due to E. canis, and more thoroughly reviews the recent scientific literature pertaining to the diagnosis and treatment of this devastating disease.

Ehrlichioses: An Important One Health Opportunity

Ehrlichioses are caused by obligately intracellular bacteria that are maintained subclinically in a persistently infected vertebrate host and a tick vector. The most severe life-threatening illnesses, such as human monocytotropic ehrlichiosis and heartwater, occur in incidental hosts. Ehrlichia have a developmental cycle involving an infectious, nonreplicating, dense core cell and a noninfectious, replicating reticulate cell. Ehrlichiae secrete proteins that bind to host cytoplasmic proteins and nuclear chromatin, manipulating the host cell environment to their advantage. Severe disease in immunocompetent hosts is mediated in large part by immunologic and inflammatory mechanisms, including overproduction of tumor necrosis factor α (TNF-α), which is produced by CD8 T lymphocytes, and interleukin-10 (IL-10). Immune components that contribute to control of ehrlichial infection include CD4 and CD8 T cells, natural killer (NK) cells, interferon-γ (IFN-γ), IL-12, and antibodies. Some immune components, such as TNF-α, perforin, and CD8 T cells, play both pathogenic and protective roles. In contrast with the immunocompetent host, which may die with few detectable organisms owing to the overly strong immune response, immunodeficient hosts die with overwhelming infection and large quantities of organisms in the tissues. Vaccine development is challenging because of antigenic diversity of E. ruminantium, the necessity of avoiding an immunopathologic response, and incomplete knowledge of the protective antigens.

Therapeutic management of canine ehrlichiosis with aid of blood transfusion: a case report

An adult female Labrador Retriever dog was presented at referral veterinary polyclinic, IVRI in lateral recumbency with history of anorexia, high fever, severe panting, heavy tick infestation, and not responding to cephalosporins and fluoroquinolones since last 1 week. Clinical examination showed pale conjunctiva, enlarged popliteal lymph node however, electrocardiogram (ECG) report found to be normal. Haematological finding showed marked anaemia and thrombocytopenia. Parasitological examination found it to be positive for Ehrlichia canis and confirmed ticks to be Rhipicephalus sanguineus. Dog was treated with doxycycline @ 10 mg/kg for 28 days in divided dose with supportive therapy. Blood transfusion was done on second day to avoid complication. Dog showed marked recovery after 15 days and re-examination of blood revealed no parasitemia.

Molecular Pathogenesis of Ehrlichia chaffeensis Infection

Ehrlichia chaffeensis is an obligatory intracellular and cholesterol-dependent bacterium that has evolved special proteins and functions to proliferate inside leukocytes and cause disease. E. chaffeensis has a multigene family of major outer membrane proteins with porin activity and induces infectious entry using its entry-triggering protein to bind the human cell surface protein DNase X. During intracellular replication, three functional pairs of two-component systems are sequentially expressed to regulate metabolism, aggregation, and the development of stress-resistance traits for transmission. A type IV secretion effector of E. chaffeensis blocks mitochondrion-mediated host cell apoptosis. Several type I secretion proteins are secreted at the Ehrlichia-host interface. E. chaffeensis strains induce strikingly variable inflammation in mice. The central role of MyD88, but not Toll-like receptors, suggests that Ehrlichia species have unique inflammatory molecules. A recent report about transient targeted mutagenesis and random transposon mutagenesis suggests that stable targeted knockouts may become feasible in Ehrlichia.

Iron metabolism and oxidative profile of dogs naturally infected by Ehrlichia canis: Acute and subclinical disease

The aim of this study was to evaluate the oxidant profile and iron metabolism in serum of dogs infected by Ehrlichia canis. Banked sera samples of dogs were divided into two groups: negative control (n = 17) and infected by E. canis on acute (n = 24), and subclinical (n = 18) phases of the disease. The eritrogram, leucogram, and platelet counts were evaluate as well as iron, ferritin, and transferrin levels, latent iron binding capacity (LIBC), and transferrin saturation index (TSI) concentration. In addition, the advanced oxidation protein products (AOPP) and ferric reducing ability of plasma (FRAP) in sera were also analyzed. Blood samples were examined for the presence of E. canis by PCR techniques. History and clinical signals were recorded for each dog. During the acute phase of the disease, infected animals showed thrombocytopenia and anemia when compared to healthy animals (P < 0.05) as a consequence of lower iron levels. Ferritin and transferrin levels were higher in both phases (acute and subclinical) of the disease. The AOPP and FRAP levels increased in infected animals on the acute phase; however, the opposite occurred in the subclinical phase. We concluded that dogs naturally infected by E. canis showed changes in the iron metabolism and developed an oxidant status in consequence of disease pathophysiology.

Serum DHEA-S increases in dogs naturally infected with Ehrlichia canis

Adrenocortical disturbances are expected in canine ehrlichiosis due to the immunological challenges caused by infection and consequent inflammation. Thus, this study aimed to evaluate the occurrence of adrenocortical hormonal alterations in dogs naturally infected with Ehrlichia canis (n = 21) as positively confirmed by the presence of anti-E. canis antibodies (Dot-ELISA) and nested PCR (nPCR). Serum dehydroepiandrosterone sulfate (DHEA-S) concentrations were assessed via ELISA before and one hour after ACTH stimulation. Another 10 healthy dogs were subjected to the same stimulation protocol and used as controls. The results revealed that baseline and post-ACTH DHEA-S concentrations were significantly greater in sick dogs, regardless of gender, and this finding illustrates the stress induced by naturally acquired ehrlichiosis in dogs.

Inhibitory effect of interferon gamma on frequency of Ehrlichia canis-infected cells in vitro

Ehrlichia canis is an obligate intracellular bacterium that infects the macrophage-monocyte cells of dogs, causing canine monocytic ehrlichiosis. Interferon-γ (IFN-γ), along with other cytokines, mediates the immune response to such intracellular bacterial invasions. To determine the role of IFN-γ in the immunity of dogs to E. canis infection, peripheral blood mononuclear cells (PBMC) and white blood cells (WBC) were collected from E. canis-infected dogs and added to a culture of E. canis in DH82 cells. The number of E. canis inclusion-positive cells was significantly reduced in cultures containing PBMC and WBC from E. canis-infected dogs compared to uninfected dogs. However, this resistance was inhibited by the addition of an anti-dog IFN-γ antibody. Resistance was also observed when PBMC were added to the Cell Culture Inserts, which prohibited contact of PBMC to DH82 cells, while allowed the diffusion of soluble cell products. The results of this study indicate that resistance was not dependent on cell to cell contact, but was associated with soluble cell products, such as IFN-γ. The addition of recombinant canine IFN-γ to the E. canis culture also reduced the number of infected cells. A commercial recombinant canine IFN-γ, which is sold in Japan, was also effective at reducing E. canis-infected cell number. These results indicate that IFN-γ has an inhibitory effect on the frequency of E. canis-infected cells in vitro and that contact between effector and target cells is not necessary for the resistance.

Extracellular adenosine 5'-triphosphate and lipopolysaccharide induce interleukin-1β release in canine blood

Binding of extracellular adenosine 5'-triphosphate (ATP) or lipopolysaccharide (LPS) to the damage-associated molecular pattern receptor P2X7 or the pathogen-associated molecular pattern receptor Toll-like receptor (TLR)4, respectively, can induce the release of the pleiotropic cytokine interleukin (IL)-1β in humans and mice. However, the release of IL-1β in dogs remains poorly defined. Using a canine IL-1β enzyme-linked immunosorbent assay, this study investigated whether ATP or LPS could induce IL-1β release in a canine blood-based assay. Short-term incubations (30 min) with ATP induced IL-1β release in LPS-primed canine blood, and this process could be near-completely impaired by the P2X7 antagonist, A438079. In contrast, ATP failed to induce IL-1β release from blood not primed with LPS. ATP-induced IL-1β release was observed with LPS-primed blood from eight different pedigrees or cross breeds. Long-term incubations (24h) with LPS induced IL-1β release in canine blood in a concentration-dependent manner. This process was not altered by co-incubation with A438079. LPS-induced IL-1β release was observed with blood from 10 different pedigrees or cross breeds. These results demonstrate that both extracellular ATP and LPS can induce IL-1β release in dogs, and that ATP- but not LPS-induced IL-1β release in blood is dependent on P2X7 activation. These findings support the role of both P2X7 and TLR4 in IL-1β release in dogs.

Sequence and phylogenetic analysis of the gp200 protein of Ehrlichia canis from dogs in Taiwan

Ehrlichia (E.) canis is a Gram-negative obligate intracellular bacterium responsible for canine monocytic ehrlichiosis. Currently, the genetic diversity of E. canis strains worldwide is poorly defined. In the present study, sequence analysis of the nearly full-length 16S rDNA (1,620 bp) and the complete coding region (4,269 bp) of the gp200 gene, which encodes the largest major immunoreactive protein in E. canis, from 17 Taiwanese samples was conducted. The resultant 16S rDNA sequences were found to be identical to each other and have very high homology (99.4~100%) with previously reported E. canis sequences. Additionally, phylogenetic analysis of gp200 demonstrated that the E. canis Taiwanese genotype was genetically distinct from other reported isolates obtained from the United States, Brazil, and Israel, and that it formed a separate clade. Remarkable variations unique to the Taiwanese genotype were found throughout the deduced amino acid sequence of gp200, including 15 substitutions occurring in two of five known species-specific epitopes. The gp200 amino acid sequences of the Taiwanese genotype bore 94.4~94.6 identities with those of the isolates from the United States and Brazil, and 93.7% homology with that of the Israeli isolate. Taken together, these results suggest that the Taiwanese genotype represents a novel strain of E. canis that has not yet been characterized.

Ehrlichia canis (Jaboticabal strain) induces the expression of TNF-α in leukocytes and splenocytes of experimentally infected dogs

Canine ehrlichiosis is caused by the bacterium Ehrlichia canis and is characterized by a systemic febrile disease of unknown pathogenesis. This study evaluated the expression of cytokines TNF-α, IL-10, IFN-γ, in splenic cells and blood leukocytes during the acute phase of ehrlichiosis and after treatment with doxycycline hyclate in dogs experimentally infected with the E. canis Jaboticabal strain. The study results showed a significant expression of TNF-α 18 days post-inoculation, reducing by approximately 70% after treatment. There was a unique peak of expression of IL-10 and IFN-γ 18 and 30 days post-inoculation, respectively. This study suggests that TNF-α plays a role in the pathogenesis of the acute phase of canine ehrlichiosis and that treatment with doxycycline hyclate reduces the systemic effects of this cytokine, possibly by reducing or eliminating parasitemia.

Detection and characterization of four novel genotypes of Ehrlichia canis from dogs

The genetic diversity of Ehrlichia canis strains worldwide is currently poorly defined. The present study aimed to characterize E. canis strains in naturally infected dogs in Taiwan, using a combination of PCR and sequence analysis of the 16S rDNA and two antigen-encoding genes, gp19 and gp36. Genomic DNA was extracted from 34 parasitemic dogs and the genes of the pathogen were separately amplified, sequenced, and aligned with corresponding sequences available in GenBank. All 16S rDNA sequences (1623 bp) amplified from the Taiwanese isolates were identical and had very high similarity (99.4-100%) with previously reported E. canis sequences. Nevertheless, most of the gp19 gene sequences (414 bp) from the Taiwanese isolates had three specific nucleotide substitutions at positions 9, 323 and 371 that resulted in three amino acid changes. The gp36 gene of the Taiwanese isolates consists of three regions: a 5' end pre-repeat region (426 bp), a tandem repeat region with variable numbers of the 27-bp repeat unit depending on the isolate, and a 3' end region (87 bp). The nucleotide sequences of the 5' end region of gp36 from Taiwanese isolates were identical to each other, but unexpectedly, quite distinct from the sequences of eleven other E. canis strains previously published, with 86.7-87.2% identities only. A phylogenetic tree of E. canis strains based on the gp36 amino acid sequences showed that the Taiwanese isolates fell into a separate clade, indicating the presence of a novel strain that had not yet been characterized.

Proteomic analysis of and immune responses to Ehrlichia chaffeensis lipoproteins

Ehrlichia chaffeensis is an obligately intracellular gram-negative bacterium and is the etiologic agent of human monocytic ehrlichiosis (HME). Although E. chaffeensis induces the generation of several cytokines and chemokines by leukocytes, E. chaffeensis lacks lipopolysaccharide and peptidoglycan. Bioinfomatic analysis of the E. chaffeensis genome, however, predicted genes encoding 15 lipoproteins and 3 posttranslational lipoprotein-processing enzymes. The present study showed that by use of multidimensional liquid chromatography followed by tandem mass spectrometry, all predicted lipoproteins as well as lipoprotein-processing enzymes were expressed by E. chaffeensis cultured in the human promyelocytic leukemia cell line HL-60. Consistent with this observation, a signal peptidase II inhibitor, globomycin, was found to inhibit E. chaffeensis infection and lipoprotein processing in HL-60 cell culture. To study in vivo E. chaffeensis lipoprotein expression and host immune responses to E. chaffeensis lipoproteins, 13 E. chaffeensis lipoprotein genes were cloned into a mammalian expression vector. When the DNA constructs were inoculated into naïve dogs, or when dogs were infected with E. chaffeensis, the animals developed delayed-type hypersensitivity reactions at cutaneous sites of the DNA construct deposition and serum antibodies to these lipoproteins. This is the first demonstration of lipoprotein expression and elicitation of immune responses by a member of the order Rickettsiales. Multiple lipoproteins expressed by E. chaffeensis in vitro and in vivo may play key roles in pathogenesis and immune responses in HME.

Cytokine Responses in Dogs Infected with Ehrlichia canis Oklahoma Strain

Ehrlichia canis causes persistent infection of monocytes/macrophages and causes canine monocytic ehrlichiosis. Other than antibody development, very little is known how the dog immune system responds to this pathogen. In the present study, we examined the temporal expression of cytokine mRNA in peripheral blood mononuclear cells (PBMCs) from dogs inoculated with E. canis Oklahoma strain. We also examined production of interferon-gamma (IFN-gamma) by canine PBMCs infected with E. canis in vitro.