Rat cytomegalovirus efficiently replicates in dendritic cells and induces changes in their transcriptional profile.

Dendritic cells (DC) play a crucial role in generating and maintaining antiviral immunity. While DC are implicated in the antiviral defense by inducing T cell responses, they can also become infected by Cytomegalovirus (CMV). CMV is not only highly species-specific but also specialized in evading immune protection, and this specialization is in part due to characteristic genes encoded by a given virus. Here, we investigated whether rat CMV can infect XCR1+ DC and if infection of DC alters expression of cell surface markers and migration behavior. We demonstrate that wild-type RCMV and a mutant virus lacking the γ-chemokine ligand xcl1 (Δvxcl1 RCMV) infect splenic rat DC ex vivo and identify viral assembly compartments. Replication-competent RCMV reduced XCR1 and MHCII surface expression. Further, gene expression of infected DC was analyzed by bulk RNA-sequencing (RNA-Seq). RCMV infection reverted a state of DC activation that was induced by DC cultivation. On the functional level, we observed impaired chemotactic activity of infected XCR1+ DC compared to mock-treated cells. We therefore speculate that as a result of RCMV infection, DC exhibit diminished XCR1 expression and are thereby blocked from the lymphocyte crosstalk.

Primary glia cells from bank vole propagate multiple rodent-adapted scrapie prions.

Since the beginning prion research has been largely dependent on animal models for deciphering the disease, drug development or prion detection and quantification. Thereby, ethical as well as cost and labour-saving aspects call for alternatives in vitro. Cell models can replace or at least complement animal studies, but their number is still limited and the application usually restricted to certain strains and host species due to often strong transmission barriers. Bank voles promise to be an exception as they or materials prepared from them are uniquely susceptible to prions from various species in vivo, in vitro and in cell-free applications. Here we present a mainly astrocyte-based primary glia cell assay from bank vole, which is infectible with scrapie strains from bank vole, mouse and hamster. Stable propagation of bank vole-adapted RML, murine 22L and RML, and hamster 263K scrapie is detectable from 20 or 30 days post exposure onwards. Thereby, the infected bank vole glia cells show similar or even faster prion propagation than likewise infected glia cells of the corresponding murine or hamster hosts. We propose that our bank vole glia cell assay could be a versatile tool for studying and comparing multiple prion strains with different species backgrounds combined in one cell assay.

Rat cytomegalovirus-encoded γ-chemokine vXCL1 is a highly adapted, species-specific agonist for rat XCR1-positive dendritic cells.

Dendritic cells (DCs) expressing the chemokine receptor XCR1 are specialized in antigen cross-presentation to control infections with intracellular pathogens. XCR1-positive (XCR1+) DCs are attracted by XCL1, a γ-chemokine secreted by activated CD8+ T cells and natural killer cells. Rat cytomegalovirus (RCMV) is the only virus known to encode a viral XCL1 analog (vXCL1) that competes for XCR1 binding with the endogenous chemokine. Here we show that vXCL1 from two different RCMV strains, as well as endogenous rat XCL1 (rXCL1) bind to and induce chemotaxis exclusively in rat XCR1+ DCs. Whereas rXCL1 activates the XCR1 Gi signaling pathway in rats and humans, both of the vXCL1s function as species-specific agonists for rat XCR1. In addition, we demonstrate constitutive internalization of XCR1 in XCR1-transfected HEK293A cells and in splenic XCR1+ DCs. This internalization was independent of ß-arrestin 1 and 2 and was enhanced after binding of vXCL1 and rXCL1; however, vXCL1 appeared to be a stronger agonist. These findings suggest a decreased surface expression of XCR1 during DC cultivation at 37°C, and subsequent impairment of chemotactic activity and XCR1+ DC function.

Cellular distribution of CD200 receptor in rats and its interaction with cytomegalovirus e127 protein.

CD200 is a membrane protein that interacts with CD200R on the surface of immune cells and delivers an inhibitory signal. In this study, we characterized the distribution of inhibitory CD200R in rats. In addition, we investigated if e127, a homologue of rat CD200 expressed by rat cytomegalovirus (RCMV), can suppress immune functions in vitro. RT-PCR analysis was carried out to test the expression of CD200R in different rat tissues and flow cytometry was performed to characterize CD200R at the cellular level. To test the inhibitory functions of e127, a co-culture system was utilized in which immune cells were incubated with e127-expressing cells. The strongest CD200R expression was detected in lymphoid organs such as bone marrow and spleen. Flow cytometry analyses showed that CD200R+ cells were mainly CD4- dendritic cells (DC) and CD4+ T cells in the spleen. In blood, nearly all monocytes and granulocytes expressed CD200R and in bone marrow the NKRP1low subset of natural killer cells highly expressed CD200R. In addition, both peritoneal macrophages and the NR8383 macrophage cell line carried CD200R. At the functional level, viral e127 conferred an inhibitory signal on TNFα and IL6 cytokine release from IFNγ-stimulated macrophages. However, e127 did not affect the cytotoxic activity of DC. CD200R in the rat is mainly expressed on myeloid cells but also on non-myeloid cell subsets, and RCMV e127 can deliver inhibitory signals to immune cells by engaging CD200R. The RCMV model provides a useful tool to study potential immune evasion mechanisms of the herpesviridae and opens new avenues for understanding and controlling herpesvirus infections.