Establishment of a rat cell line inducible for the expression of human cytomegalovirus immediate-early gene products by protein synthesis inhibition

Identification of a cis-acting element required for dendritic targeting of activity-regulated cytoskeleton-associated protein mRNA

The mRNA encoding activity-regulated cytoskeleton-associated protein (Arc) is known to be targeted to dendritic regions that have received strong synaptic inputs. However, the cis-acting elements in Arc mRNA that mediate dendritic targeting have not been identified. To identify the dendritic targeting element (DTE) in rat Arc mRNA, we expressed reporter mRNAs containing various regions of Arc in primary hippocampal neurones and analysed their subcellular distribution by in situ hybridization. Here, we report that the 3'-untranslated region of rat Arc mRNA contains a 350-nucleotide DTE with strong dendritic targeting activity and another 370-nucleotide sequence with weaker dendritic targeting activity. The 350-nucleotide DTE does not share any obvious sequence similarity with other known DTEs previously reported.

Enhancement of cytomegalovirus detection in mink lung cells using CMV Turbo

BACKGROUND

Detection of HCMV from clinical specimens was a slow process until the development of shell vial method with staining for immediate early antigen (IEA). Culture though still considered insensitive is widely used for other than blood samples. A method to improve culture sensitivity is desirable.

OBJECTIVES

TurboTreat, a CMV pretreatment medium from Diagnostic Hybrids Inc., was evaluated on Mv1Lu, R-Mix and MRC-5 cells for improved sensitivity for HCMV detection.

STUDY DESIGN

Monolayers of Mv1Lu, R-Mix and MRC-5 cells in 48-well plates were treated with TurboTreat for overnight (o/n), 4 h or left untreated and then inoculated with previously positive HCMV specimens. After o/n incubation, cells were fixed, stained and positive cells counted.

RESULTS

CMV TurboTreat enhanced detection 2-3-fold after 4 h treatment and 4-6-fold after o/n treatment in Mv1Lu and R-Mix cells and to a lesser extend in MRC-5 cells with clinical isolates of HCMV. With frozen clinical specimens, Mv1Lu cells treated o/n, 4 h or untreated detected 23, 21 and 15 positive specimens, respectively. R-Mix cells detected 19, 18, and 14 positives, respectively and MRC-5 cells detected 16, 15 and 15 positives, respectively. In no case was a positive detected in another cell line regardless of treatment that was not detected in Mv1Lu treated o/n.

CONCLUSION

The o/n pretreatment with CMV TurboTreat on Mv1Lu cells is the optimum condition of treatment and significantly enhanced the detection of HCMV. Even 4 h pretreatment of Mv1Lu cells showed significant enhancement over untreated Mv1Lu, R-Mix and MRC-5 cells. Pretreatment of Mv1Lu cells with CMV TurboTreat for 4 h or longer increased the sensitivity of rapid HCMV detection.

Human cytomegalovirus DNA in plasma and serum specimens of renal transplant recipients is highly fragmented

Quantitation of cytomegalovirus (CMV) DNA in plasma and serum by PCR is increasingly used to identify patients at risk for developing CMV disease and to monitor the efficacy of antiviral therapy. Although CMV DNA levels are generally interpreted as viral loads, the exact nature of the viral DNA in these specimens is unknown. We studied the state of CMV DNA in plasma and serum specimens obtained from three renal transplant recipients at peak viral DNA levels during primary CMV infection. For this purpose, DNA isolated from these specimens was fractionated by size, and CMV DNA levels in the resulting DNA fractions were measured by quantitative PCR targeted at large (578-bp) and small (134-bp) amplicons. These experiments showed that the molecular sizes of DNA fragments from which CMV DNA is amplified were small (<2,000 bp), indicating that CMV DNA in plasma and serum is highly fragmented. Furthermore, CMV DNA levels were consistently higher when targeted at the smaller amplicon, providing additional evidence for the fragmentation of viral DNA. In conclusion, the first results with three patients have shown that CMV DNA in plasma and serum is highly fragmented and does not necessarily reflect the amount of infectious virus. These observations have potential consequences for understanding CMV pathogenesis and interpreting CMV DNA levels in individual patient management.

Kinetics of HCMV immediate early mRNA expression in stably transfected fibroblasts

Compelling evidence supports an intimate link in time and space between eukaryotic pre-mRNA synthesis and processing and nucleocytoplasmic transport of mature mRNA. In this study, we analyzed the kinetic behavior of these processes in a quantitative manner. We used FISH and confocal scanning laser microscopy to detect transcripts produced by an inducible human cytomegalovirus immediate early (HCMV-IE) expression system. Upon induction, a large amount of pre-mRNA accumulated in nuclear foci at or near their transcription sites and, at later time, throughout the nucleoplasm. Inhibition of RNA polymerase II activity resulted in a rapid decrease in the number of transcripts in the nuclear RNA foci (half time ∼two minutes), indicating that accumulated transcripts were rapidly spliced and then released. The dispersed nucleoplasmic transcripts exited the nucleus with a half time of ∼10 minutes. Both processes were temperature dependent, suggesting that mRNA export is an active process. RNA polymerase II activation revealed that production of mature HCMV IE mRNAs required less than five minutes. Transcripts radiated from the gene at an average speed of ∼0.13 μm2/sec from this time on. Thus, it appears that these processes are tightly linked in time and space, with the splicing reaction as a rate-limiting factor.

Linear 2' O-Methyl RNA probes for the visualization of RNA in living cells

U1snRNA, U3snRNA, 28 S ribosomal RNA, poly(A) RNA and a specific messenger RNA were visualized in living cells with microinjected fluorochrome-labeled 2' O-Methyl oligoribonucleotides (2' OMe RNA). Antisense 2' OMe RNA probes showed fast hybridization kinetics, whereas conventional oligodeoxyribonucleotide (DNA) probes did not. The nuclear distributions of the signals in living cells were similar to those found in fixed cells, indicating specific hybridization. Cytoplasmic ribosomal RNA, poly(A) RNA and mRNA could hardly be visualized, mainly due to a rapid entrapment of the injected probes in the nucleus. The performance of linear probes was compared with that of molecular beacons, which due to their structure should theoretically fluoresce only upon hybridization. No improvements were achieved however with the molecular beacons used in this study, suggesting opening of the beacons by mechanisms other than hybridization. The results show that linear 2' OMe RNA probes are well suited for RNA detection in living cells, and that these probes can be applied for dynamic studies of highly abundant nuclear RNA. Furthermore, it proved feasible to combine RNA detection with that of green fluorescent protein-labeled proteins in living cells. This was applied to show co-localization of RNA with proteins and should enable RNA-protein interaction studies.

In fibroblasts Vegf-D expression is induced by cell-cell contact mediated by cadherin-11

Vascular endothelial growth factors (VEGFs) are a highly conserved family of growth factors all angiogenic in vivo with mitogenic and chemotactic activity on endothelial cells. VEGFs are expressed in fibroblasts either in hypoxia or in response to growth factors. Here we report that, differently from the other members of the family, Vegf-D is induced by cell-cell contact. By in situ hybridization we demonstrated that noninteracting fibroblasts express low levels of Vegf-D mRNA, whereas contacting cells express high levels of Vegf-D transcripts. By immunostaining we observed that the surface protein cadherin-11 is localized at the opposite sites of interacting cell surfaces. Ca(2+) deprivation from the culture medium determined the loss of cadherin-11 from the cell surfaces and down-regulation of Vegf-D mRNA. Moreover, a cadherin-11 antisense RNA construct inhibited Vegf-D expression in confluent BALB/c fibroblasts, whereas in NIH 3T3 cells, which express low levels of cadherin-11, Vegf-D induction could be obtained by overexpression of cadherin-11. This suggests that cell interaction mediated by cadherin-11 induces the expression of the angiogenic factor Vegf-D in fibroblasts.

Detection and quantitation of human cytomegalovirus DNA in faeces

The development and performance of a robust and sensitive PCR assay are described for the detection and quantitation of human cytomegalovirus DNA in human faecal specimens. In this assay, CMV DNA was purified by an optimised DNA extraction protocol together with internal control DNA that monitored both DNA extraction efficiency and PCR efficiency. The lower detection limit of the assay was reached at about 100 CMV particles per ml of (25-50%) faecal suspension. CMV DNA could be quantitated in the range of about 300-100000 molecules per ml of faecal suspension. CMV DNA loads obtained in clinical faeces specimens suggest that the assay can be used to monitor the efficacy of antiviral treatment. Reconstruction experiments that monitored the efficiency of DNA extraction of a preliminary DNA extraction protocol, showed low DNA yields for 9% of the specimens (n = 78). In all cases, low DNA extraction efficiency seemed to be due to a component present in faeces that prevented DNA binding to silica particles, presumably by competitive binding. Choosing the right ratio of silica particles to faeces specimen solved this problem. Similarly, reconstruction experiments showed that the strong PCR inhibition that was observed in 8% of the specimens could effectively be relieved by the inclusion of alpha-casein in the PCR mixtures.

A highly sensitive assay for detection and quantitation of human cytomegalovirus DNA in serum and plasma by PCR and electrochemiluminescence

We describe a diagnostic PCR assay (D-PCR) and a quantitative PCR assay (Q-PCR) for the detection of human cytomegalovirus (CMV) in plasma and serum. In the D-PCR, DNA was purified from plasma or serum together with internal control (IC) DNA, which monitored both DNA extraction efficiency and PCR efficiency. DNA was subjected to PCR with a single primer pair, and the amount of PCR products was determined by electrochemiluminescence (ECL) in the QPCR System 5000 (Perkin-Elmer) after hybridization with Tris (2,2'-bipyridine) ruthenium (II) chelate-labeled probes. The lower limit of sensitivity of the D-PCR was reached at about 25 CMV particles/ml. Even with extremely low DNA inputs (four molecules of IC DNA/200 microl of plasma), very high yields (near 100%) were reached. DNA extracted from specimens that were CMV positive by the D-PCR was subsequently used in the Q-PCR, which was similar to the D-PCR. The viral load was calculated directly from the ratio of CMV and IC signals obtained by ECL. The Q-PCR assay is quantitative in the range of 100 to 150,000 copies of CMV/ml, independent of the anticoagulant. Interassay variation, intra-assay variation, and interspecimen variation were about 25%, suggesting that the Q-PCR will reliably detect fourfold differences in viral load. Comparison of paired serum and plasma specimens from CMV-infected individuals showed that serum CMV loads were frequently more than 10-fold lower than plasma CMV loads.

RNA polymerase II localizes at sites of human cytomegalovirus immediate-early RNA synthesis and processing

Pre-mRNA synthesis in eukaryotic cells is preceded by the formation of a transcription initiation complex and binding of unphosphorylated RNA polymerase II (Pol II) at the promoter region of a gene. Transcription initiation and elongation are accompanied by the hyperphosphorylation of the carboxy-terminal domain (CTD) of Pol II large subunit. Recent biochemical studies provided evidence that RNA processing factors, including those required for splicing, associate with hyperphosphorylated CTDs forming "transcription factories." To directly visualize the existence of such factories, we simultaneously detected human cytomegalovirus immediate-early (IE) DNA and RNA with splicing factors and Pol II in rat 9G cells inducible for IE gene expression. Combined in situ hybridization and immunocytochemistry revealed that, after induction, both splicing factors and Pol II are present at the sites of IE mRNA synthesis and of IE mRNA processing that extend from the transcribing gene. Noninduced cells revealed no such associations. When IE mRNA-synthesizing cells were treated with a transcription inhibitor, these associations disappeared within 30 min. Our results show that the association of Pol II and splicing factors with IE DNA is dependent on its transcriptional activity and furthermore suggest that splicing factors are still associated with Pol II during active splicing.

Repression of gene expression upon infection of cells with herpes simplex virus type 1 mutants impaired for immediate-early protein synthesis

Herpes simplex virus type 1 (HSV-1) mutants defective in immediate-early (IE) gene expression do not readily enter productive replication after infection of tissue culture cells. Instead, their genomes are retained in a quiescent, nonreplicating state in which the production of viral gene products cannot be detected. To investigate the block to virus replication, we used the HSV-1 triple mutant in1820K, which, under appropriate conditions, is effectively devoid of the transactivators VP16 (a virion protein), ICP0, and ICP4 (both IE proteins). Promoters for the HSV-1 IE ICP0 gene or the human cytomegalovirus (HCMV) major IE gene, cloned upstream of the Escherichia coli lacZ coding sequences, were introduced into the in1820K genome. The regulation of these promoters and of the endogenous HSV-1 IE promoters was investigated upon conversion of the virus to a quiescent state. Within 24 h of infection, the ICP0 promoter became much less sensitive to transactivation by VP16 whereas the same element, when used to transform Vero cells, retained its responsiveness. The HCMV IE promoter, which is not activated by VP16, also became less sensitive to the HCMV functional homolog of VP16. Both elements remained available for transactivation by HSV-1 IE proteins at 24 h postinfection, showing that the in1820K genome was not irreversibly inactivated. The promoters controlling the HSV-1 ICP4, ICP22, and ICP27 genes also became essentially unresponsive to transactivation by VP16. The ICP0 promoter was induced when hexamethylene bisacetamide was added to cultures at the time of infection, but the response to this agent was also lost by 24 h after infection. Therefore, promoter elements within the HSV-1 genome are actively repressed in the absence of IE gene expression, and repression is not restricted specifically to HSV-1 IE promoters.

Monocytes harboring cytomegalovirus: interactions with endothelial cells, smooth muscle cells, and oxidized low-density lipoprotein. Possible mechanisms for activating virus delivered by monocytes to sites of vascular injury

Cytomegalovirus (CMV) infection and its periodic reactivation from latency may contribute to atherogenesis and restenosis. It is unknown how CMV is delivered to the vessel wall and is reactivated. We examined the following hypothesis: CMV, present in monocytes recruited to sites of vascular injury, is activated by endothelial cell (EC) or smooth muscle cell (SMC) contact and by oxidized low-density lipoproteins (oxLDLs). The CMV major immediate-early promoter (MIEP) controls immediate-early (IE) gene expression, and thereby viral replication. To determine whether elements of the vessel wall can activate CMV present in monocytes, we transiently transfected the promonocytic cell line HL-60 with a chloramphenicol acetyltransferase reporter gene construct driven by MIEP. MIEP activity increased 1.7 +/- 0.5-fold (P = .02) when the transfected HL-60 cells were cocultured with ECs, 4.5 +/- 1.5-fold when cocultured with SMCs (P = .03), and 2.0 +/- 0.5-fold (P = .01) when exposed to oxLDL. The combination of oxLDL and EC coculture increased MIEP activity over 7-fold. We also found that freshly isolated human monocytes, infected with endothelium-passaged CMV, were capable of transmitting infectious virus to cocultured ECs or SMCs. CMV-related progression of atherosclerosis or restenosis may, at least in part, involve monocyte delivery of the virus to the site of vascular injury, where the vascular milieu, ie, contact with ECs, SMCs, and oxLDL, can contribute to viral reactivation and/or replication by enhancing CMV IE gene expression. The virus may then infect neighboring ECs or SMCs, initiating a cascade of events predisposing to the development of atherogenesis-related processes.

The dynamics of a pre-mRNA splicing factor in living cells

Pre-mRNA splicing is a predominantly co-transcriptional event which involves a large number of essential splicing factors. Within the mammalian cell nucleus, most splicing factors are concentrated in 20-40 distinct domains called speckles. The function of speckles and the organization of cellular transcription and pre-mRNA splicing in vivo are not well understood. We have investigated the dynamic properties of splicing factors in nuclei of living cells. Here we show that speckles are highly dynamic structures that respond specifically to activation of nearby genes. These dynamic events are dependent on RNA polymerase II transcription, and are sensitive to inhibitors of protein kinases and Ser/Thr phosphatases. When single genes are transcriptionally activated in living cells, splicing factors leave speckles in peripheral extensions and accumulate at the new sites of transcription. We conclude that one function of speckles is to supply splicing factors to active genes. Our observations demonstrate that the interphase nucleus is far more dynamic in nature than previously assumed.

Splicing factors associate with nuclear HCMV-IE transcripts after transcriptional activation of the gene, but dissociate upon transcription inhibition: evidence for a dynamic organization of splicing factors

Before being transported to the cytoplasm, intron-containing pre-mRNAs have to be spliced somewhere in the cell nucleus. Efficient splicing requires an ordered assembly of splicing factors onto the pre-mRNAs. To accomplish this, intron containing genes may be preferentially localized at nuclear sites enriched for splicing factors or alternatively, splicing factors may circulate throughout the nucleus and have the ability to associate with randomly positioned nascent transcripts. Combined detection of HCMV-IE mRNA/DNA and splicing factors in rat 9G cells that can be induced for IE gene expression shows that IE genes are not associated with speckled regions enriched for splicing factors when transcriptionally inactive, but ‘attract’ splicing factors when transcriptionally activated. This process proved reversible after transcription inhibition. IE transcripts appeared to be retained near the transcription site in track-like domains by splicing factors associated with them until splicing has been completed. Double-hybridization experiments revealed that a substantial part of the accumulated transcripts contain a poly(A) tail suggesting that most, if not all, IE transcripts are polyadenylated at the site of transcription. These results indicate that RNA processing may occur independent of the position of the gene in the cell nucleus relative to speckle domains.

Evaluation of pepsin treatment for electron microscopic RNA in situ hybridization on ultra-thin cryosections of cultured cells

The in situ hybridization (ISH) technique, as applied to electron microscopic detection of RNAs, was evaluated for ultra-thin cryosections of cultured rat fibroblasts (rat 9G). Experimental variables to balance penetration of detection reagents and preservation of ultrastructural morphology included various strengths of aldehyde fixation and pepsin treatment. We performed ISH for 28S ribosomal RNA (rRNA) followed by ultra-small colloidal gold immunocytochemistry and silver enhancement. An acceptable balance for 28S rRNA ISH detection was obtained using mild cross-linking fixation followed by treatment with a relative high concentration of pepsin for a short time. The ISH method presented in this study was compatible with immunocytochemical detection of protein as demonstrated by double-labeling experiments.

Cell-cycle-dependent gene expression studied by two-colour fluorescent detection of a mRNA and histone mRNA

We investigated whether a probe specific for histone H3 mRNA could be used as a marker to study cell-cycle dependency of gene expression by double-fluorescent RNA in situ hybridization (FISH). First, we showed that all S-phase cells in cell cultures having incorporated BrdU revealed histone H3 mRNA expression by RNA FISH, indicating that histone H3 expression is a reliable marker for S-phase cells. Second, we analysed whether the expression of human cytomegalovirus immediate early genes in rat 9G cells, which are known to be induced in an S-phase dependent way by cycloheximide, correlated with the expression of histone H3 mRNA. Double-hybridization experiments with a digoxigenin-labelled probe for IE mRNA and a fluoresceinated probe for histone H3 mRNA revealed that cells expressing IE mRNA also expressed histone H3 mRNA. Third, we examined the cell-cycle dependency of luciferase gene expression in X1 cells. Luciferase mRNA is heterogeneously expressed in X1 cell cultures, but cells expressing luciferase did not necessarily express histone H3 mRNA. This indicates that luciferase gene expression in X1 cells is not induced during S-phase. The results of our study show that histone H3 mRNA expression can be successfully used as a marker to establish cell-cycle dependency of gene expression by double-RNA FISH.

RNAs radiate from gene to cytoplasm as revealed by fluorescence in situ hybridization

Genes for Epstein-Barr virus, human cytomegalovirus immediate early antigen and luciferase are abundantly transcribed in Namalwa, rat 9G and X1 cells, respectively. The EBV transcripts and HCMV-IE transcripts are extensively spliced, while in the luciferase transcript only a small intron sequence has to be spliced out. EBV transcripts are hardly localized in the cytoplasm while the luciferase and HCMV-IE transcripts are present in the cytoplasm and translated into proteins. We have correlated these characteristics with nuclear RNA distribution patterns as seen by fluorescence in situ hybridization. Transcripts of the HCMV-IE transcription unit were shown to be present in a main nuclear signal in the form of a track or elongated dot and as small nuclear RNA signals that radiate from this site towards the cytoplasm. A similar distribution pattern of small RNA signals was observed for transcripts of the luciferase gene, whereas the main nuclear signal was always observed as a dot and never as a track or elongated dot. In Namalwa cells, EBV transcripts were only present as track-like signals. The results suggest that when the extent for splicing is high, unspliced or partially spliced mRNAs begin to occupy elongated dot or track-like domains in the vicinity of the gene. When the extent of splicing is low, splicing is completed co-transcriptionally, leading to a bright dot-like signal. The presence of small nuclear spots in addition to the main signal correlates with cytoplasmic mRNA expression. The small spots most likely represent, therefore, mRNAs in transport to the cytoplasm.

Methodologies for specific intron and exon RNA localization in cultured cells by haptenized and fluorochromized probes

We have determined optimal conditions for the detection of mRNA sequences in cultured cells by nonradioactive in situ hybridization. For this purpose a number of different cell lines have been used: rat 9G cells for the detection of human cytomegalovirus immediate early mRNA, and HeLa as well as 5637 carcinoma cells for the detection of housekeeping gene mRNAs. Extensive optimization of fixation and pretreatment conditions revealed that most intense hybridization signals are obtained when cells are grown on glass microscope slides, fixed with a mixture of formaldehyde and acetic acid, pretreated with pepsin and denatured prior to hybridization. In addition, we also studied the potential of fluorochromized probes for the direct detection of multiple RNA sequences. The optimized in situ hybridization procedure revealed that immediate early mRNA transcripts are, in addition to a cytoplasmic localization, localized within nuclei of rat 9G cells. Double hybridization experiments showed that intron and exon sequences colocalize within the main nuclear signal. In addition, the presence of small, intron-specific, fluorescent spots scattered around the main nuclear signals indicates that intron sequences which are spliced out can be visualized. Additional information about the functioning of cells could be obtained by the detection of mRNA simultaneously with bromodeoxyuridine, incorporated during S-phase, or its cognate protein. The sensitivity of these methods is such that mRNAs of abundantly expressed housekeeping genes can be detected in a variety of cell lines with high signal to noise ratios.

Detection of human cytomegalovirus in clinical specimens by centrifugation culture with a nonhuman cell line

The sensitivities of MRC-5 and mink lung (ML) cells in centrifugation culture were compared simultaneously for the detection of cytomegalovirus (CMV) IE antigen (immediate-early antigen) from clinical specimens. Of 413 samples assayed, 51 (12%) were positive for CMV by both centrifugation and standard cell culture. At 20 h postinoculation (p.i.), 46 of 51 (90.2%) CMV-positive specimens were detected in ML cells. At 40 h p.i., 50 of 51 (98.0%) CMV-positive specimens were detected in ML cells, compared with 48 of 51 (94.0%) in MRC-5 cells. There was no significant difference in the detection of CMV in either cell line by centrifugation culture. However, in 19 of 23 positive samples that had countable foci at 20 h p.i., there was a 25% increase in the number of positive foci observed for ML cells compared with MRC-5 cells. Less toxicity was also noted for ML cells than for MRC cells, particularly in viral blood specimens. These data suggest that ML cells are comparable to MRC-5 cells for the rapid detection of CMV by centrifugation culture.

Bicolor fluorescence in situ hybridization to intron and exon mRNA sequences

The technique of nonradioactive in situ hybridization has been used to visualize the DNA and mRNA expression of human cytomegalovirus (HCMV) immediate early antigen (IEA) in a transfected rat fibroblast cell line. Expression of the transfected HCMV immediate early DNA can be induced by a cycloheximide treatment and is S-phase-dependent. In addition to cytoplasmic mRNA localization, a nuclear RNA hybridization signal was found. In a substantial part of the cells the nuclear signal was in the form of a "track," possibly showing transport of IEA mRNA from the site of transcription to the cytoplasm. The use of PCR-generated intron- and exon-specific probes in a double hybridization revealed that intron and exon mRNA sequences coexist in the nuclear RNA signal. This shows the applicability of multiple-color fluorescence hybridization to obtain information about the site of pre-mRNA splicing in the nucleus. In addition, by combining the technique of in situ hybridization with an immunocytochemical procedure we illustrate the possibility of visualizing transcribed mRNAs simultaneously with their translation products.

Fine specificity of cellular immune responses in humans to human cytomegalovirus immediate-early 1 protein

Cell-mediated immunity is important in maintaining the virus-host equilibrium in persistent human cytomegalovirus (HCMV) infection. The HCMV 72-kDa major immediate early 1 protein (IE1) is a target for CD8+ cytotoxic T cells in humans, as is the equivalent 89-kDa protein in mouse. Less is known about responses against this protein by CD4+ T cells, which may be important as direct effector cells or helper cells for antibody and CD8+ responses. Proliferative-T-cell responses to HCMV IE1 were studied in normal seropositive subjects. Peripheral blood mononuclear cells from 85% of seropositive subjects proliferated in response to HCMV from infected fibroblasts, and of these, 73% responded to recombinant baculovirus IE1. Responding cells were predominantly CD3+ CD4+. IE1 antigen preparations, including baculovirus recombinant protein, transfected rat cell nuclei, and synthetic peptides, induced IE1-specific T-cell lines which cross-reacted between the preparations. The fine specificity of these IE1-specific T-cell lines was studied by using overlapping synthetic peptides encompassing the entire sequence of the IE1 protein. The regions of the IE1 molecule recognized were identified and these varied between individuals, possibly reflecting differences in major histocompatibility complex (MHC) class II haplotype. In one subject, the peptide specificities of proliferative and MHC class I-restricted cytotoxic determinants on IE1 were spatially distinct. Thus, no single immunodominant T-cell determinant within HCMV IE1 was identified, suggesting that multiple peptides or a region of the 72-kDa IE1 protein would be required to induce specific T-cell responses in humans.

Gene expression from heterologous promoters in a replication-defective avian retrovirus vector in quail cells

Avian retrovirus vectors, with potential for use in avian transformation, were constructed to evaluate the relative efficiency of promoters placed internal to the viral long terminal repeats (LTR). The vectors are replication-defective reticuloendotheliosis plasmids that contain the neomycin phosphotransferase gene under control of the 5' LTR and an internal promoter that directs expression of the chloramphenicol acetyltransferase gene. The internal promoters were the SV40 early, the mouse metallothionein I, and the human cytomegalovirus immediate early (HCMV-IE) promoters. Under transient conditions in QT6 cells, the HCMV-IE promoter construct was by far the strongest. However, expression dropped greatly from the HCMV-IE promoter after integration into the quail cell genome. Evidence suggests that the HCMV-IE promoter is selectively suppressed by methylation after stable transfection but not after infection.

Epstein-Barr virus in a CD8-positive T-cell lymphoma

In contrast to its role in B-lymphomagenesis, Epstein-Barr Virus (EBV) only incidentally has been associated with T-cell lymphomas. In the present report we describe a fourth patient with EBV-related T-cell lymphoma. The patient presented with an angio-immunoblastic lymphadenopathy (AILD)-like T-cell lymphoma. Serology was compatible with chronic Epstein-Barr (EBV) infection. After a 1-year period of waxing and waning lymphadenopathy, this lymphoma evolved to an aggressive CD8+ Immunoblastic T-cell lymphoma. A relationship with the chronic EBV infection was indicated by the finding of EBV genome in the tumor tissue by Southern blot analysis. Moreover, EBV nuclear antigen (EBNA) was detected in situ within individually defined CD8+ tumor cells by two-color immunofluorescence. Two alternative possibilities, namely that EBV primarily played a role in lymphomagenesis of the AILD-like T-cell lymphoma or that the virus was an additional oncogenic event in the final process of tumor progression to the immunoblastic lymphoma, are discussed.

Increased sensitivity for rapid detection of cytomegalovirus by shell vial centrifugation assay using mink lung cell cultures

A comparative study was made of various human and non-human cell cultures to determine their sensitivity for cytomegalovirus (CMV) as detected by the production of CMV early antigen using the shell vial centrifugation assay. Mink lung cell cultures, frequently used for detection of herpes simplex virus in clinical specimens, were found to be significantly more sensitive to infection by CMV than other cell cultures tested. Using the shell vial centrifugation assay, the mink lung cell cultures were more sensitive than human diploid fibroblasts for the detection of the Davis strain of human CMV and CMV from clinical specimens.

Expression of the acidic nuclear immediate-early protein (IE1) of human cytomegalovirus in stable cell lines and its preferential association with metaphase chromosomes

Stable DNA-transfected Vero cell lines that express the major immediate-early nuclear antigen (IE68) of HCMV-(Towne) have been established. Immunofluorescence staining with monoclonal antibodies revealed that the protein was distributed either in a uniform diffuse nuclear pattern or as punctate nuclear granules in up to 80% of the cells in these cultures. In addition, 1 to 2% of the positive nuclei gave a distinctive staining pattern suggesting an association with the chromosomes of mitotic cells. Colcemid-blocking studies confirmed that most of the IE antigen was localized in the vicinity of condensed chromosomes in all metaphase cells after methanol fixation. In contrast, the SV40 large T-antigen protein was found to be preferentially excluded from metaphase chromosomes in a similar colcemid-treated human cell line. In transient expression assays, 1 to 2% of IE antigen-positive Vero, 293, or Balb/c3T3 cells also displayed a metaphase chromosome association pattern. Mapping studies using deletion and truncation mutants revealed that the monoclonal antibodies recognized epitopes encoded within the small NH2-terminal exons that are common to both the IE1 and IE2 gene products. However, an intact exon-4 (IE1) region, but not the exon-5 (IE2) region of the HCMV IE gene complex, was required for conferring both the normal diffuse nuclear localization pattern and the chromosome-association properties. Furthermore, removal of the glutamic acid-rich COOH-terminal coding portions of exon-4 resulted in aberrant staining patterns with production of large, phase-dense nuclear globules in all positive cells. An association between the IE68 IE1 protein and metaphase chromosomes was also detected after HCMV-(Towne) infection in a small proportion of both nonpermissive Balb/c3T3 cells and permissive HF cells. We conclude that the IE1 acidic nuclear phosphoprotein displays some properties similar to those of the EBNA-1 protein of Epstein-Barr virus and suggest that it may potentially play a role in maintenance of the latent state of HCMV DNA.

Human cytomegalovirus-specific cytotoxic T cells. Relative frequency of stage-specific CTL recognizing the 72-kD immediate early protein and glycoprotein B expressed by recombinant vaccinia viruses

CTL are held to be an important host defense mechanism in persistent herpes-virus infections. We have therefore studied the nature and specificity of human cytomegalovirus (HCMV)-specific CTL in normal persistently infected individuals. This was achieved by using vaccinia recombinants encoding viral genes expressed at different stages of the virus replicative cycle, a structural glycoprotein gB (vac.gB) and the major 72-kD immediate early nonstructural protein (vac.IE) of HCMV, combined with limiting dilution analysis of the CTL response. In two subjects, 43 and 58% of HCMV CTL precursors (CTLp) lysed vac.IE-infected cells, in contrast to less than 6% lysing gB-infected cells. HCMV-specific CTL could also be generated by secondary in vitro stimulation with vac.gB- but not vac.IE-infected autologous fibroblasts. The high frequency of 72-kD IE protein-specific CTL suggests that this is at least a major recognition element for the HCMV-specific CTL response in asymptomatic persistently infected individuals, and CTL with this specificity may be important in maintaining the normal virus/host equilibrium.

Sensitivity of in situ detection with biotinylated probes of human papilloma virus type 16 DNA in frozen tissue sections of squamous cell carcinomas of the cervix

The sensitivity of human papilloma virus type 16 (HPV-16) DNA detection by DNA in situ hybridization using biotinylated probes (bio-DISH) was estimated by performing this technique on snap-frozen tissue sections of 10 cervical squamous cell carcinomas containing increasing amounts of HPV-16 as determined by Southern blot hybridization. A protocol using serial sections for bio-DISH and DNA extraction was used. The number of positively stained cells and the detection limit were strongly dependent on the treatment of the sections with proteinase K prior to hybridization. At low proteinase K concentration (0.1 micrograms/ml), the detection limit appeared to be 30-40 HPV-16 DNA copies per carcinoma cell, whereas morphology was preserved. A high proteinase K concentration (1-5 micrograms/ml) often resulted in an increase in the number of positively stained cells but also in a poor morphology. The detection limit was improved to at least 20 HPV-16 DNA copies per carcinoma cell.

Cell lines containing varicella-zoster virus open reading frame 62 and expressing the "IE" 175 protein complement ICP4 mutants of herpes simplex virus type 1

Vero cells were cotransfected with pSV2neo and a recombinant plasmid containing the varicella-zoster virus (VZV) open reading frame 62 (ORF62). Three neomycin-resistant cell lines were isolated and shown to complement two different ICP4 mutants (tsB21 and d120) of herpes simplex virus (HSV) type 1 (HSV-1). VZV-specific RNA could not be detected in these cell lines, but following infection with tsB21, a 4.3-kilobase VZV transcript was detected. This RNA increased in quantity when cells were infected in the presence of cycloheximide. A VZV-specific protein of 175 kilodaltons was detected in extracts of all three cell lines following infection with wild-type HSV-1 but not in uninfected cells. That VZV RNA and protein were detected only in HSV-1 infected cells suggests that a component of the HSV virion activates the expression of VZV ORF62. The increase in RNA expression seen in the presence of cycloheximide indicates that the protein encoded by VZV ORF62, "IE"175, may be autoregulatory. These data provide further evidence that VZV "IE"175 is the functional analog of the HSV ICP4.

Novel induction by herpes simplex virus of hybrid interferon gene transcripts driven by the strong cytomegalovirus IE94 promoter

We have constructed stable DNA-transfected LTK+ cell lines containing two different coselected hybrid interferon (IFN) genes driven by the usually strong and constitutive promoter from the immediate-early 94K protein (IE94) gene of simian cytomegalovirus. Surprisingly, and unlike hybrid IE94-chloramphenicol acetyltransferase gene constructs, both of the IE94-IFN genes (one with and one without the complex spliced intron region) produced relatively low basal titers of biologically active human IFN in the mouse cell lines. However, IFN expression could be stimulated up to 120-fold by superinfection with herpes simplex virus (HSV), although not with cytomegalovirus. To examine the mechanism of this unexpected HSV induction process, we measured the levels of both IE94-IFN mRNA and IFN protein produced under various infection protocols. Compared with similar previously characterized cell lines containing hybrid IFN genes under the control of HSV IE or delayed-early (DE) promoters, activation of IFN expression first occurred at an intermediate time. Both IE94-IFN cell lines also produced an unusual pattern of response to infection with the HSV IE regulation-deficient mutants tsK and tsB7: stimulation of IFN synthesis occurred in the absence of a functional HSV IE175 (or ICP4) gene product, but did not occur in the absence of uncoating of virus capsids. Cycloheximide treatment (without virus infection) also gave a rapid 30-fold increase in steady-state levels of correctly initiated mRNA from both types of IE94-IFN hybrid genes, but had no effect on cells containing the IE175-IFN construct. Therefore, we conclude that the use of the IE94-IFN constructs identifies a novel HSV regulatory response that requires a previously unrecognized function of HSV and does not involve either IE175 or the pre-IE "virion factor" trans-activators that are known to stimulate transcription of HSV IE and DE genes, respectively.

Immunofluorescence for detection of antibodies against human cytomegalovirus-induced membrane antigens

This paper describes an improved method for the in vitro detection of antibodies specifically directed against human cytomegalovirus (CMV)-induced membrane antigens present on the surface of CMV-infected fibroblasts (CMV-MA). Viable cells were found to be essential for specific visualization of CMV-MA staining. The addition of divalent cations (2.6 mM Ca2+ and 2.2 mM Mg2+) and glucose (180 mM) to the incubation and washing buffers improved the viability and morphology of the cells and increased the cell yield at the end of the assay. Clustering of antigen-antibody complexes on the surface of viable CMV-infected cells was prevented by low-temperature incubation (0 to 4 degrees C) rather than by the addition of agents which act on the metabolism of the cell. No interaction with the CMV-induced Fc receptor was observed at 0 degrees C with either human sera or murine monoclonal antibodies. The specificity of the CMV-MA reaction was confirmed by using monoclonal antibodies to CMV nuclear, cytoplasmic, and membrane-associated antigens. Furthermore, a microplate modification of the membrane fluorescence test is described which is suitable for multisample screening purposes. This method can be applied to the determination of anti-CMV-MA antibody titers in human sera and to the screening of hybridoma supernatants for the presence of antibodies with specificity for CMV-MA.