Project description:Background Human monocytotropic ehrlichiosis is an emerging life-threatening zoonosis caused by obligately intracellular bacterium, Ehrlichia chaffeensis. E. chaffeensis is transmitted by the lone star tick, Amblyomma americanum, and replicates in mononuclear phagocytes in mammalian hosts. Differences in the E. chaffeensis transcriptome in mammalian and arthropod hosts are unknown. Thus, we determined host-specific E. chaffeensis gene expression in human monocyte (THP-1) and in Amblyomma and Ixodes tick cell lines (AAE2 and ISE6) using a whole genome microarray. Methodology/Principal Findings The majority (~80%) of E. chaffeensis genes were expressed during infection in human and tick cells. There were few differences observed in E. chaffeensis gene expression between the vector Amblyomma and non-vector Ixodes tick cells, but extensive host-specific and differential gene expression profiles were detected between human and tick cells, including higher transcriptional activity in tick cells and identification of gene subsets that were differentially expressed in the two hosts. Differentially and host-specifically expressed ehrlichial genes encoded major immunoreactive tandem repeat proteins (TRP), the outer membrane protein (OMP-1) family, and hypothetical proteins that were 30–80 amino acids in length. Consistent with previous observations, high expression of p28 and OMP-1B genes was detected in human and tick cells, respectively. Notably, E. chaffeensis genes encoding TRP32 and TRP47 were highly upregulated in the human monocytes and expressed as proteins; however, although TRP transcripts were expressed in tick cells, the proteins were not detected in whole cell lysates demonstrating that TRP expression was post transcriptionally regulated. Conclusions/Significance Ehrlichia gene expression is highly active in tick cells, and differential gene expression among a wide variety of host-pathogen associated genes occurs. Furthermore, we demonstrate that genes associated with host-pathogen interactions are differentially expressed and regulated by post transcriptional mechanisms. A microarray (4-plex) study using E. chaffeensis cultivated in each cell line (THP-1, AAE2 and ISE6), three biological replicates/cell line. For each cell line, RNA was also extracted from uninfected cells (negative controls) and was processed similar to the infected cells; these samples were used for background subtraction during data analysis.

Project description:Background Human monocytotropic ehrlichiosis is an emerging life-threatening zoonosis caused by obligately intracellular bacterium, Ehrlichia chaffeensis. E. chaffeensis is transmitted by the lone star tick, Amblyomma americanum, and replicates in mononuclear phagocytes in mammalian hosts. Differences in the E. chaffeensis transcriptome in mammalian and arthropod hosts are unknown. Thus, we determined host-specific E. chaffeensis gene expression in human monocyte (THP-1) and in Amblyomma and Ixodes tick cell lines (AAE2 and ISE6) using a whole genome microarray. Methodology/Principal Findings The majority (~80%) of E. chaffeensis genes were expressed during infection in human and tick cells. There were few differences observed in E. chaffeensis gene expression between the vector Amblyomma and non-vector Ixodes tick cells, but extensive host-specific and differential gene expression profiles were detected between human and tick cells, including higher transcriptional activity in tick cells and identification of gene subsets that were differentially expressed in the two hosts. Differentially and host-specifically expressed ehrlichial genes encoded major immunoreactive tandem repeat proteins (TRP), the outer membrane protein (OMP-1) family, and hypothetical proteins that were 30–80 amino acids in length. Consistent with previous observations, high expression of p28 and OMP-1B genes was detected in human and tick cells, respectively. Notably, E. chaffeensis genes encoding TRP32 and TRP47 were highly upregulated in the human monocytes and expressed as proteins; however, although TRP transcripts were expressed in tick cells, the proteins were not detected in whole cell lysates demonstrating that TRP expression was post transcriptionally regulated. Conclusions/Significance Ehrlichia gene expression is highly active in tick cells, and differential gene expression among a wide variety of host-pathogen associated genes occurs. Furthermore, we demonstrate that genes associated with host-pathogen interactions are differentially expressed and regulated by post transcriptional mechanisms.

Project description:Infection of humans with Ehrlichia chaffeensis, the etiologic agent of human monocytic ehrlichiosis, can cause hepatitis of varying severity. When the three human isolates of E. chaffeensis, each belongs to different geno-groups, are inoculated into severe combined immunodeficiency mice, the severity of clinical signs and bacterial burden detected in the liver are strain Wakulla>Liberty>Arkansas. Disseminated and granulomatous inflammation is evident in the liver of mice infected with strains Wakulla and Arkansas, respectively, but not in mice infected with strain Liberty. In this paper, we used microarray analysis to define transcriptional profiles characteristic to the histopathological features in the mouse liver. Cytokine and chemokine profiles were strikingly different among three strains of E. chaffeensis: IFN-Î³, CCL5, CXCL1, CXCL2, CXCL7 and CXCL9 were highly up-regulated with strain Arkansas, TNF-Î±, CCL2, CCL3, CCL5, CCL6, CCL12, CCL20, CXCL2, CXCL7, CXCL9 and CXCL13 were highly up-regulated with strain Wakulla. With strain Liberty, only CXCL13 was highly up-regulated. In the livers infected with the Arkansas strain, monocytes/macrophages and NK cells were enriched in the granulomas and increase of NK cell-marker mRNAs was detected. Livers infected with the Wakulla strain displayed infiltration of significantly more neutrophils and increase of neutrophil-marker mRNAs. Genes up-regulated commonly in the liver infected with the three stains are other host innate immune and inflammatory response genes including several acute phase proteins. Genes down-regulated commonly are related to host physiologic functions. The results suggest that marked modulation of host cytokine and chemokine profiles by E. chaffeensis strains underlie the distinct host liver disease. Experiment Overall Design: E. chaffeensis strains Arkansas, Wakulla and Liberty were propagated in DH82 cells. Three to four week-old male ICR-scid mice were infected intraperitoneally with 10^6 E. chaffeensis-infected DH82 cells (typically >95% infected) containing approximately the same number of bacteria. At day 15 post infection (PI) mice were euthanized and livers were harvested. Experiment Overall Design: Total RNAs were extracted from E. chaffeensis-infected or mock-infected (uninfected) mouse liver. About 8 ug of each RNA sample was applied to double-strand cDNA preparation. The labeled cRNA was hybridized to GeneChip Mouse Genome 430 2.0 Array (Affymetrix). After washing and staining with streptoavidin phycoerythrin, the array was scanned. Experiment Overall Design: Three mice were examined for each of the 4 groups.

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