Analysis of target organs for the latency of murine cytomegalovirus DNA using specific pathogen free and germfree mice

nanoString evaluation of murine Cytomegalovirus transcription in vivo and in vitro

BACKGROUND

Next Generation Sequencing allows for deep analysis of transcriptional activity in cells and tissues, however it is still a cost intensive method that demands well versed data handling. Reverse transcription quantitative PCR (RT-qPCR) is the most commonly used method to measure gene expression levels, however the information gathered is quite small in comparison to NGS. A newer method called nanoString allows for highly multiplexed gene expression analysis by detecting mRNAs without the use of enzymes for reverse transcription or amplification even for single cells or low input material. The method can be done in 1.5 days and data are quickly analyzed by the accompanied user friendly software. Our aim was to investigate this new method and compare it to the existing alternatives, while investigating murine Cytomegalovirus (mCMV) infection and latency.

METHODS

mCMV infected murine embryonic fibroblasts (MEF), lung and salivary glands from BALB/c mice were evaluated at different stages of infection. A set of 30 custom designed nanoString probes were tested, 20 probes specific for mCMV genes, 6 probes for host genes known to be influenced by viral infection and 4 reference gene specific probes. nanoString counts were compared to published RNA-Seq RPKM.

RESULTS

We found that nanoString can be used for analysis of cytomegalovirus gene expression during acute infection in vitro and in vivo, both for virus specific and host genes. Although some transcripts show different expression rates in comparison to NGS data, the most abundant transcripts are comparable. When tissues are infected, there are significantly fewer transcripts than in MEFs, and consistent with previous work there are significant differences in relevant abundance between MEF and tissues. We were unable to detect our viral transcripts of interest in latently infected tissue.

CONCLUSIONS

For viruses with annotated transcriptomes, nanoString allows simultaneous quantitation of multiple virus and host genes. One huge advantage of the platform is rapid turnaround and simplicity of analysis. It should prove to be very useful to explore host virus interactions during acute infection, but it is unclear if it has adequate sensitivity for analysis during latency in immunocompetent mice.

Platelet-endothelial associations may promote cytomegalovirus replication in the salivary gland in mice

Platelet decline is a feature of many acute viral infections, including cytomegalovirus (CMV) infection in humans and mice. Platelet sequestration in association with other cells, including endothelium and circulating leukocytes, can contribute to this decline and influence the immune response to and pathogenesis of viral infection. We sought to determine if platelet-endothelial associations (PEAs) contribute to platelet decline during acute murine CMV (mCMV) infection, and if these associations affect viral load and production. Male BALB/c mice were infected with mCMV (Smith strain), euthanized at timepoints throughout acute infection and compared to uninfected controls. An increase in PEA formation was confirmed in the salivary gland at all post-inoculation timepoints using immunohistochemistry for CD41+ platelets co-localizing with CD34+ vessels. Platelet depletion did not change amount of viral DNA or timecourse of infection, as measured by qPCR. However, platelet depletion reduced viral titer of mCMV in the salivary glands while undepleted controls demonstrated robust replication in the tissue by plaque assay. Thus, platelet associations with endothelium may enhance the ability of mCMV to replicate within the salivary gland. Further work is needed to determine the mechanisms behind this effect and if pharmacologic inhibition of PEAs may reduce CMV production in acutely infected patients.

Determination of suitable reference genes for RT-qPCR analysis of murine Cytomegalovirus in vivo and in vitro

Reverse transcription quantitative PCR (RT-qPCR) is the most commonly used method to evaluate gene expression. Reliable qPCR results are highly dependent on accurate normalization using suitable reference genes. We investigated expression of commonly used reference genes during murine Cytomegalovirus (mCMV) infection and latency to determine those genes least perturbed by infection. Following mCMV infection in BALB/c mice, lung, salivary gland, liver, spleen and kidney were evaluated. Liver sinusoidal endothelial cells and NIH-3T3 cells were also evaluated. RT-qPCR was performed during acute and latent mCMV infection for 11 commonly used reference genes with comparisons made to uninfected samples. Normfinder, BestKeeper, GeNorm and the comparative delta CT method produced comparable analyses that were combined in RefFinder to generate an overall ranking. Ppia, B2m and Gapdh are the most stable reference genes for in vitro infection studies. For in vivo studies the most suitable reference genes were highly tissue and cell type dependent. Comparing infected and uninfected groups revealed viral influence on transcription of some genes. We provide reference gene guidelines for investigations of gene expression for mCMV Smith strain infection of Balb/cJ mice or NIH-3T3 cells. These results also suggest careful consideration of reference genes for different host tissues evaluated.

Murine natural killer cell licensing and regulation by T regulatory cells in viral responses

Natural killer (NK) cells show differential functionality based on their capability of binding to self-MHC consistent with licensing. Here we show in vivo confirmation of the physiologic effects of licensing with differential effects of NK subsets on anti-murine cytomegalovirus (anti-MCMV) responses after syngeneic hematopoietic stem cell transplantation (HSCT) or regulatory T-cell (Treg) depletion. After HSCT, depletion of licensed NK cells led to far greater viral loads in target organs early after infection compared with nondepleted and unlicensed depleted mice. There was a preferential expansion of licensed, C-type lectin-like activating receptor Ly49H+ NK cells with increased IFNγ production after infection in nondepleted mice post-HSCT and after Treg depletion. Adoptive transfer of licensed NK subsets into immunodeficient hosts provided significantly greater MCMV resistance compared with transfer of total NK populations or unlicensed subsets. In non-HSCT mice, only concurrent depletion of Tregs or TGF-β neutralization resulted in detection of NK licensing effects. This suggests that licensed NK cells are the initial and rapidly responding population of NK cells to MCMV infection, but are highly regulated by Tregs and TGF-β.

Mouse cytomegalovirus antigenic immune stimulation is sufficient to aggravate atherosclerosis in hypercholesterolemic mice

We have previously demonstrated that mouse cytomegalovirus (MCMV) infection aggravates atherosclerosis by stimulating the ongoing inflammatory process in the vascular wall. Here we investigated whether MCMV antigenic immune stimulation by UV-MCMV injection is sufficient to aggravate atherosclerosis. In addition we analyzed whether low viral doses are sufficient to stimulate atherosclerosis. Therefore, apoE(-/-) mice received a low dose injection with infectious virus (MCMV) or replication-deficient virus (UV-inactivated MCMV, UV-MCMV). Atherosclerosis progression, influx of inflammatory cells in atherosclerotic lesions and internal organs and the number of MCMV DNA copies in various organs were determined at 2 weeks after injection. After injection with infectious virus, MCMV DNA was present in internal organs, while no MCMV DNA could be detected after UV-MCMV injection. Interestingly, both MCMV and UV-MCMV significantly increased mean atherosclerotic lesion area and T cell number in the atherosclerotic lesions, while only MCMV infection increased T cell numbers in the internal organs. These data indicate that in apoE(-/-) mice both low dose infectious MCMV as well as MCMV antigenic injections are sufficient for atherosclerosis aggravation.

Improved detection and quantification of mouse cytomegalovirus by real-time PCR

During latent cytomegalovirus (CMV) infection, viral presence cannot be detected by plaque assay. Therefore, we assessed the applicability of real-time PCR for temporal determination of virus dissemination in two different mouse strains. Eight-week-old BALB/c and C57BL/6J mice were infected with mouse CMV (MCMV) and sacrificed at 1, 2, 4, 6, 14 and 28 days post infection. Real-time PCR was used to determine MCMV copy number in the heart, bone marrow cells, aorta and blood. In lung, liver, salivary gland and spleen the presence of MCMV was determined both by plaque assay and real-time PCR. In analogy with the plaque assay, the real-time PCR technique revealed higher numbers of MCMV genomic copies in all organs obtained from BALB/c mice when compared with C57BL/6J mice, demonstrating the applicability of the technique. A significant correlation was observed between both assays when a positive test result was seen with both assays. Nonetheless, lower viral infectivity titers were found compared to real-time PCR data. Thus, the real-time PCR technique is more sensitive in detecting the presence of MCMV and is therefore well suited for (dose-response) intervention studies aimed at studying virus eradication.

Restraint stress elevates the plasma interleukin-6 levels in germ-free mice

Several recent reports demonstrated that restraint stress elevates plasma IL-6 levels; however, the precise mechanism whereby stress stimuli trigger the production of IL-6 remains to be clarified. In this study, in order to elucidate whether or not the intestinal microflora contribute to the stress-induced IL-6 elevation, the plasma IL-6 response of germ-free (GF) mice, which are indeed devoid of indigenous microflora, was compared to that of specific pathogen-free (SPF) mice. The plasma IL-6 level increased after 1 h of restraint stress and thereafter gradually decreased in GF mice as well as in SPF mice. In addition, such a stress-induced IL-6 elevation was also found in the mice reconstituted with SPF feces. The expression levels of IL-6 mRNA in the liver increased after 1 h of stress in both GF and SPF mice based on the findings of a semiquantitative RT-PCR method, although no such increase was observed in the spleen and kidney of both groups of mice. These results thus indicate that restraint stress is capable of elevating the plasma IL-6 levels independently of the intestinal microflora and the liver is one of the main sources responsible for the increased plasma IL-6 during stress.

Dietary nucleic acids promote a shift in Th1/Th2 balance toward Th1-dominant immunity

BACKGROUND

Dietary sources of nucleic acids and their relative components are known to affect host immune function; however, it has not yet been clarified whether such dietary nucleic acids influence the pathogenesis of allergic reaction.

OBJECTIVE

The purpose of this study is to elucidate the effect of dietary nucleic acids on Th1/Th2 balance.

METHODS

Both human flora-associated and specific pathogen-free BALB/c mice were maintained on either nucleic acid-free, or -supplemented diets. The effects of nucleic acids on both in vivo antibody levels and in vitro splenocyte cytokine production were compared using these mice.

RESULTS

Supplementation of nucleic acids caused a reduction in the serum antibody levels of total IgM, IgG, IgG1, and IgE in the human flora-associated mice without affecting the composition of intestinal flora. In contrast, there was no significant difference of the serum IgG2a levels between nucleic acid-free and -supplemented mice. Such a phenomenon as that, the supplementation of dietary nucleic acids reduces the serum IgE or IgG1 levels, but not the IgG2a level, was also seen in the specific pathogen free mice. Moreover, when the mice were systematically challenged with ovalbumin, the supplementation of nucleic acids also suppressed the serum ovalbumin-specific IgE and IgG1 antibody levels as well as in vitro IL-4 and IL-10 secretion, while enhancing both the serum ovalbumin-specific IgG2a antibody levels and in vitro IFN gamma secretion.

CONCLUSION

These results suggested that dietary nucleic acids may play an important role in promoting a shift in Th1/Th2 balance toward Th1-dominant immunity.

The role of intestinal bacterial flora in the tuning of the T cell repertoire

The role of the intestinal bacterial flora on the Vbeta repertoire was examined using the gnotobiotic murine model. The ratio of Vbeta6-positive T cells in the periphery of DBA/2 mice under SPF conditions was only 2.2% (mean, n = 4), since the cells were eliminated by the endogenous superantigen Mls(a). However, the ratio in germ-free (GF) mice was 31.7%. Similarly, the contamination of the GF Mice with the intestinal flora from SPF mice reduced the ratio of Vbeta6 in GF mice from 22.9% to 13.7%. In contrast, in BALB/c mice (Mls(b)) in which Vbeta6 cells do not react with this endogenous superantigen, the ratio of Vbeta6 cells do not react with this endogenous superantigen, the ratio of Vbeta6 of SPF mice (15.4%, mean, n = 3) was found to be comparable to that of GF mice (15.6%, n = 3). These data suggested that the absence of intestinal flora deteriorated a part of the Mls(a) determinant, which reacted with the Vbeta6 T cells and thereby eliminated them, thus resulting in an increase of these cells in GF mice. Moreover, the alloantigenicity of minor histocompatible alloantigen(s) (mHAg) in SPF mice, which was detected in H-2 identical MLR experiments and a murine graft-versus-host (GVH) model, was reduced in GF and decontaminated SPF mice, thus indicating that the intestinal flora upregulated the mHAg including a part of Mls determinant. These results therefore suggest that the intestinal flora plays a role in the upregulation of mHAg including a part of endogenous superantigen and the consequent tuning of the Vbeta repertoire.

Fas-Mediated Apoptosis of the Hematopoietic Progenitor Cells in Mice Infected With Murine Cytomegalovirus

The effects of cytomegalovirus (CMV) infection on hematopoietic progenitor cells in vivo were investigated to elucidate the pathogenesis of CMV-induced myelosuppression. BALB/c mice were inoculated with 0.2LD50 of murine CMV (MCMV). Lineage marker negative, c-kit positive (Lin−c-kit+) and Lin−CD34+ cells, which are both phenotypically defined as hematopoietic progenitor cells, showed a significant reduction in number on day 3 postinfection (pi). Moreover, the reduction in the number of day-14 colony-forming units-spleen (CFU-S), another indicator to identify hematopoietic progenitor cells, was noted on day 3 pi. To clarify the mechanism of such depletion, we examined the cells undergoing apoptosis in the Lin− populations and found a 15-fold increase in the apoptosis-induction of these cells. Furthermore, an increase in the expression level of Fas, which mediates apoptosis, was observed in such Lin−c-kit+ and Lin−Sca-1+ cells on day 3 pi. In vitro treatment with the anti-Fas antibody accelerated the apoptosis in Lin− cells, but not in the uninfected control cells, thus indicating that the upregulated Fas on Lin− cells is directly related to the acceleration of apoptosis found in these cells in vivo. These results suggest that MCMV infection reduces the number of hematopoietic progenitor cells in bone marrow at least in part due to Fas-mediated apoptosis, and this phenomenon is thus considered to contribute to CMV-induced myelosuppression.

Fas-Mediated Apoptosis of the Hematopoietic Progenitor Cells in Mice Infected With Murine Cytomegalovirus

The effects of cytomegalovirus (CMV) infection on hematopoietic progenitor cells in vivo were investigated to elucidate the pathogenesis of CMV-induced myelosuppression. BALB/c mice were inoculated with 0.2LD50 of murine CMV (MCMV). Lineage marker negative, c-kit positive (Lin−c-kit+) and Lin−CD34+ cells, which are both phenotypically defined as hematopoietic progenitor cells, showed a significant reduction in number on day 3 postinfection (pi). Moreover, the reduction in the number of day-14 colony-forming units-spleen (CFU-S), another indicator to identify hematopoietic progenitor cells, was noted on day 3 pi. To clarify the mechanism of such depletion, we examined the cells undergoing apoptosis in the Lin− populations and found a 15-fold increase in the apoptosis-induction of these cells. Furthermore, an increase in the expression level of Fas, which mediates apoptosis, was observed in such Lin−c-kit+ and Lin−Sca-1+ cells on day 3 pi. In vitro treatment with the anti-Fas antibody accelerated the apoptosis in Lin− cells, but not in the uninfected control cells, thus indicating that the upregulated Fas on Lin− cells is directly related to the acceleration of apoptosis found in these cells in vivo. These results suggest that MCMV infection reduces the number of hematopoietic progenitor cells in bone marrow at least in part due to Fas-mediated apoptosis, and this phenomenon is thus considered to contribute to CMV-induced myelosuppression.