In vitro and In vivo Susceptibility of Baboons (Papio sp.) to Infection with and Apparent Antibody Reactivity to Simian Betaretrovirus (SRV)

Despite the lack of confirmed reports of an exogenous Simian betaretrovirus (SRV) isolated from baboons (Papio sp.), reports of simian endogenous gammaretrovirus (SERV) in baboons with complete genomes suggest that such viruses may be potentially infectious. In addition, serologic tests have repeatedly demonstrated antibody reactivity to SRV in baboons from multiple colonies. These findings complicate the management and use of such animals for research. To provide further insight into this situation, we performed in vitro and in vivo studies to determine if baboons are or can be infected with SRV. In our initial experiment, we were not able to isolate SRV from 6 seropositive or sero-indeterminate baboons by coculturing their peripheral blood mononuclear cells (PBMC) with macaque PBMC or permissive cell lines. In a subsequent experiment, we found that baboon PBMC infected in vitro with high dose SRV were permissive to virus replication. To test in vivo infectibil- ity, groups of naive baboons were infused intravenously with either (i) the same SRV tissue culture virus stocks used for the in vitro studies, (ii) SRV antibody positive and PCR positive macaque blood, (iii) SRV antibody positive or indeterminate, but PCR negative baboon blood, or (iv) SRV antibody and PCR negative baboon blood. Sustained SRV infection, as defined by reproducible PCR detection and/or antibody seroconversion, was confirmed in 2 of 3 baboons receiving tissue culture virus but not in any recipients of transfused blood from seropositive macaques or baboons. In conclusion, the data indicate that even though baboon cells can be infected experimentally with high doses of tissue culture grown SRV, baboons that are repeatedly SRV antibody positive and PCR negative are unlikely to be infected with exogenous SRV and thus are unlikely to transmit a virus that would threaten the SPF status of captive baboon colonies.

Is PBC a viral infectious disease?

The human betaretrovirus and the closely related mouse mammary tumor virus have been linked with the development of cholangitis and mitochondrial antibody production in patients with primary biliary cholangitis (PBC) and mouse models of autoimmune biliary disease, respectively. In vitro, betaretroviruses have been found to stimulate the expression of mitochondrial autoantigens on the cell surface of biliary epithelial cells. In vivo, both mitochondrial autoantigens and viral proteins have been shown to be co-expressed in biliary epithelium and lymphoid tissue. Notably, both mice and humans make poor antibody responses to betaretrovirus infection, whereas proinflammatory responses to viral proteins have been observed in T lymphocyte studies. Furthermore, proviral integration studies have confirmed the presence of human betaretrovirus in biliary epithelium of patients with PBC. Preliminary proof of principal studies using combination antiretroviral therapy have shown that suppression of viral expression is associated with sustained biochemical response. As the previous regimen used was poorly tolerated, further randomized controlled trials are planned to determine whether betaretrovirus infection plays an important role in the development of PBC.

Combination antiretroviral studies for patients with primary biliary cirrhosis

Following the characterization of a human betaretrovirus in patients with primary biliary cirrhosis (PBC), pilot studies using antiretroviral therapy have been conducted as proof of principal to establish a link of virus with disease and with the eventual aim to find better adjunct therapies for patients unresponsive to ursodeoxycholic acid. In the first open label pilot study, the reverse transcriptase inhibitor lamivudine had little demonstrable biochemical or histological effect after 1 year. Whereas, lamivudine in combination with zidovudine was associated with a significant reduction in alkaline phosphatase as well as improvement in necroinflammatory score, cholangitis and ductopenia over a 12 mo period. A double blind, multi-center randomized controlled trial using lamivudine with zidovudine for 6 mo confirmed a significant reduction in alkaline phosphatase, ALT and AST in patients on antiviral therapy. However, none of the patients achieved the stringent endpoint criteria for normalization of alkaline phosphatase. Furthermore, some patients developed biochemical rebound consistent with drug resistance. A major fault of these studies has been the inability to measure the viral load in peripheral blood and therefore, provide a direct correlation between improvement of hepatic biochemistry and reduction in viral load. Nevertheless, viral mutants to lamivudine with zidovudine were later characterized in the NOD.c3c4 mouse model of PBC that has been used to test other antiretroviral regimens to betaretrovirus. The combination of tenofovir and emtricitabine reverse transcriptase inhibitors and the HIV protease inhibitor, lopinavir were found to abrogate cholangitis in the NOD.c3c4 mouse model and the same regimen normalized the liver tests in a PBC patient with HIV and human betaretrovirus infection. This combination antiretroviral therapy has now been used in a double blind randomized controlled crossover study for patients with PBC followed by an open label extension study. Only a third of the PBC patients were able to tolerate the lopinavir but those maintained on tenofovir, emtricitabine and lopinavir experienced sustained and clinically meaningful reduction in hepatic biochemistry. While we await the histological and virological evaluation, it is clear that better tolerated regimens of antiretroviral treatment will be required in future clinical trials.

Characterization of a full-length endogenous beta-retrovirus, EqERV-beta1, in the genome of the horse (Equus caballus)

Information on endogenous retroviruses fixed in the horse (Equus caballus) genome is scarce. The recent availability of a draft sequence of the horse genome enables the detection of such integrated viruses by similarity search. Using translated nucleotide fragments from gamma-, beta-, and delta-retroviral genera for initial searches, a full-length beta-retrovirus genome was retrieved from a horse chromosome 5 contig. The provirus, tentatively named EqERV-beta1 (for the first equine endogenous beta-retrovirus), was 10434 nucleotide (nt) in length with the usual retroviral genome structure of 5'LTR-gag-pro-pol-env-3'LTR. The LTRs were 1361 nt long, and differed approximately 1% from each other, suggestive of a relatively recent integration. Coding sequences for gag, pro and pol were present in three different reading-frames, as common for beta-retroviruses, and the reading frames were completely open, except that the env gene was interrupted by a single stopcodon. No reading frame was apparent downstream of the env gene, suggesting that EqERV-beta1 does not encode a superantigen like mouse mammary tumor virus (MMTV). A second proviral genome of EqERV-beta1, with no stopcodon in env, is additionally integrated on chromosome 5 downstream of the first virus. Single EqERV-beta1 LTRs were abundantly present on all chromosomes except chromosome 24. Phylogenetically, EqERV-beta1 most closely resembles an unclassified retroviral sequence from cattle (Bos taurus), and the murine beta-retrovirus MMTV.

Simian betaretrovirus infection in a colony of cynomolgus monkeys (Macaca fascicularis)

Of the 419 laboratory-bred cynomolgus macaques (Macaca fascicularis) in a breeding colony at our institution, 397 (95%) exhibited antibodies or viral RNA (or both) specific for simian betaretrovirus (SRV) in plasma. Pregnant monkeys (n= 95) and their offspring were tested to evaluate maternal-infant infection with SRV. At parturition, the first group of pregnant monkeys (n = 76) was antibody-positive but RNA-negative, the second group (n = 14 monkeys) was positive for both antibody and RNA, and the last group (n = 5) was antibody-negative but RNA-positive. None of the offspring delivered from the 76 antibody-positive/RNA-negative mothers exhibited viremia at birth. Eight of the offspring (including two newborns delivered by caesarian section) from the 14 dually positive mothers exhibited SRV viremia, whereas the remaining 6 newborns from this group were not viremic. All of the offspring (including 2 newborns delivered by caesarian section) of the 5 antibody-negative/RNA-positive mothers exhibited viremia at birth. One neonatal monkey delivered by CS and two naturally delivered monkeys that were viremic at birth remained viremic at 1 to 6 mo of age and lacked SRV antibodies at weaning. Family analysis of 2 viremic mothers revealed that all 7 of their offspring exhibited SRV viremia, 6 of which were also antibody-negative. The present study demonstrates the occurrence of transplacental infection of SRV in viremic dams and infection of SRV in utero to induce immune tolerance in infant monkeys.

Reverse transcriptase activity in patients with primary biliary cirrhosis and other autoimmune liver disorders

BACKGROUND

Patients with biliary disease make retroviral antibodies and the Human Betaretrovirus has been characterized in patients with primary biliary cirrhosis.

AIM

To screen patients with autoimmune liver disease for evidence of retroviral infection.

METHODS

Real-time reverse transcriptase polymerase chain reaction was used to detect Human Betaretrovirus, and a reverse transcriptase assay to measure reverse transcriptase activity in plasma.

RESULTS

Using reverse transcriptase polymerase chain reaction, 24% of primary biliary cirrhosis samples were positive for Human Betaretrovirus when compared to 13% with autoimmune hepatitis, 5% of other liver diseases and 3% of the non-liver disease control subjects. Reverse transcriptase activity was found in 73% of patients with autoimmune hepatitis, 42% with primary biliary cirrhosis, 22% of liver patients without viral or autoimmune disease and 7% of subjects without liver disease. In patients with autoimmune liver disease, detection of reverse transcriptase activity was related to higher ALT levels, whereas others stabilized on immunosuppressive therapy either preliver or postliver transplantation were less likely to be reverse transcriptase-positive.

CONCLUSIONS

Most patients with autoimmune hepatitis have detectable reverse transcriptase activity. Investigations will be required to assess whether this represents the expression of endogenous retroviruses and retrotransposable elements in inflamed tissue, or signifies the presence of exogenous retroviral infection.

Search for DNA of exogenous mouse mammary tumor virus-related virus in human breast cancer samples

Earlier reports of a human exogenous retrovirus (HMTV) related closely to mouse mammary tumor virus (MMTV) led us to search for these viral sequences in breast cancer tissues and normal tissues. A real-time PCR was developed based on MMTV and published HMTV envelope sequences. The real-time PCR method can detect one to ten copies of MMTV target DNA. Tissue samples were collected prospectively from 18 breast cancer patients and 11 non-malignant control cases, as well as peripheral blood leukocytes from the same women. Despite the high sensitivity of the real-time PCR method used, none of the samples were positive for HMTV DNA or RNA. The absence of HMTV DNA in both breast cancer samples and controls indicates either that the concentration of putative HMTV DNA in the breast cancers was too low for detection or that it did not exist there.

Isolation and characterization of a new simian retrovirus type D subtype from monkeys at the Tsukuba Primate Center, Japan

Exogenous type D simian retroviruses (SRV/D) are prevalent in captive and feral populations of various macaque monkeys. Thus far, five subtypes of SRV/Ds have been reported, three of which (SRV-1, -2 and -3) have been molecularly characterized. Two SRV/D strains (N27 and T150) were isolated from seropositive cynomolgus macaques at the Tsukuba Primate Center (TPC) in Japan, showing clinical signs of SRV/D infection, including anemia and persistent unresponsive diarrhea. Electron microscopy demonstrated that both SRV/D isolates have a virion morphology typical of type D retrovirus. The SRV/D N27 and T150 isolates were essentially the same based on sequence analysis. From homology analysis of the entire gag sequence, the N27 isolate is closely related to the other known SRV/Ds but is distinct from the three molecularly characterized SRV/Ds. Thus, we have tentatively designated the N27 and T150 viruses isolated from TPC cynomolgus macaques as SRV/D-Tsukuba (SRV/D-T).

Does a betaretrovirus infection trigger primary biliary cirrhosis?

Patients with primary biliary cirrhosis develop progressive ductopenia associated with the production of antimitochondrial antibodies that react with a protein aberrantly expressed on biliary epithelial cells and peri-hepatic lymph nodes. Although no specific microbe has been identified, it is thought that an infectious agent triggers this autoimmune liver disease in genetically predisposed individuals. Previous serologic studies have provided evidence to suggest a viral association with primary biliary cirrhosis. Here we describe the identification of viral particles in biliary epithelium by electron microscopy and the cloning of exogenous retroviral nucleotide sequences from patients with primary biliary cirrhosis. The putative agent is referred to as the human betaretrovirus because it shares close homology with the murine mammary tumor virus and a human retrovirus cloned from breast cancer tissue. In vivo, we have found that the majority of patients with primary biliary cirrhosis have both RT-PCR and immunohistochemistry evidence of human betaretrovirus infection in lymph nodes. Moreover, the viral proteins colocalize to cells demonstrating aberrant autoantigen expression. In vitro, we have found that lymph node homogenates from patients with primary biliary cirrhosis can induce autoantigen expression in normal biliary epithelial cells in coculture. Normal biliary epithelial cells also develop the phenotypic manifestation of primary biliary cirrhosis when cocultivated in serial passage with supernatants containing the human betaretrovirus or the murine mammary tumor virus, providing a model to test Koch's postulates in vitro.

Prevalence of antibodies to selected viruses in a long-term closed breeding colony of rhesus macaques (Macaca mulatta) in Brazil

The rhesus macaque breeding colony of the Oswaldo Cruz Foundation (FIOCRUZ) was established in 1932 from a founding stock of 100 animals. This population has remained closed to new animal introductions for almost 70 years. A serologic survey was performed to determine the prevalence of antibodies to selected viruses as a first approach to identifying viral pathogens endemic in this population. Banked serum samples were tested for antibodies to simian immunodeficiency virus (SIV), simian T-lymphotropic virus (STLV), simian type D retrovirus (SRV), cercopithecine herpesvirus type-1 (B virus), rhesus cytomegalovirus (RhCMV), measles virus (MV), and hepatitis A virus (HAV). All samples were negative for antibodies against the simian retroviruses. The overall prevalence of antibodies was 95% for RhCMV, 45% for B virus, 35% for HAV, and 1% for MV. Prevalence was found to vary by age group.

Expression of endogenous betaretroviruses in the ovine uterus: effects of neonatal age, estrous cycle, pregnancy, and progesterone

The ovine genome contains 15 to 20 copies of endogenous retroviruses (enJSRVs) highly related to the oncogenic jaagsiekte sheep retrovirus (JSRV) and enzootic nasal tumor virus. enJSRVs are highly expressed in the endometrial lumenal epithelia (LE) and glandular epithelia (GE) of the ovine uterus. The effects of neonatal age, estrous cycle, pregnancy, and progesterone on expression of enJSRVs in the ovine uterus were determined. Expression of enJSRV RNAs was absent from the uterus of ewes at birth, but enJSRV RNAs were expressed specifically in the LE and developing GE from postnatal day (PND) 7 to PND 56. In adult ewes, enJSRV RNAs were detected only in the epithelia of the uterine endometrium, as well as epithelia of the oviduct, cervix, and vagina. In cyclic ewes, endometrial enJSRV RNA abundance was lowest on day 1, increased 12-fold between days 1 and 13, and then decreased to day 15. In pregnant ewes, levels of endometrial enJSRV RNAs were high on day 11, increased to day 13, and then decreased to day 19. In day 17 and 19 conceptuses, enJSRV RNAs were also detected in binucleate cells of the trophectoderm. Immunoreactive JSRV capsid and envelope proteins were detected in the endometrial LE and GE, as well as in the binucleate cells of the conceptus. In transfection assays utilizing ovine endometrial LE cells, progesterone increased transcriptional activity of several enJSRV long terminal repeats. Collectively, these results indicate that transcription of enJSRVs in the endometrial epithelia of the ovine uterus is increased by progesterone and might support a role for enJSRVs in conceptus-endometrium interactions during the peri-implantation period and early placental morphogenesis.

A PCR primer system for detecting oncoretroviruses based on conserved DNA sequence motifs of animal retroviruses and its application to human leukaemias and lymphomas

Many C- and D-type retroviruses are known to cause a broad spectrum of malignant diseases in animals. Certain genome regions of these animal retroviruses are highly conserved between different animal species. It should be possible to detect new members of the retrovirus family with consensus PCR primers derived from these conserved sequence motifs. The consensus PCR primers developed in this study are generic enough to detect nearly all known oncogenic mammalian and avian exogenous C- and D-type retroviruses but do not amplify human endogenous retroviral sequences. In contrast to previous investigations, the present study involved highly stringent PCR conditions and truly generic PCR primers. Forty-four samples from patients with various immunophenotyped malignant diseases (acute and chronic T-/B-cell lymphocytic leukaemias, acute myeloid leukaemias, T-/B-cell lymphomas, chronic myeloproliferative disorders) and three cell lines (Hodgkin's lymphoma, Burkitt's lymphoma) have thus far been investigated using these PCR primers. The fact that no retroviruses have been found argues against an involvement of known animal oncoretroviruses or related hitherto undetected human retroviruses in the aetiopathogenesis of these diseases. The retrovirus detection system developed here may be used to confirm suspected retroviral involvement in other (malignant or nonmalignant) human diseases as well as to identify new animal retroviruses.

Endogenous type D retrovirus in a marsupial, the common brushtail possum (Trichosurus vulpecula)

We have sequenced and characterized an endogenous type D retrovirus, which we have named TvERV(D), from the genome of an Australian marsupial, the common brushtail possum (Trichosurus vulpecula). Intact TvERV(D) gag, pro, pol, and env open reading frames were detected in the possum genome. TvERV(D) was classified as a type D retrovirus, most closely related to those of Old World monkeys, New World monkeys, and mice, based on phylogenetic analyses and genetic organization. Approximately 30 TvERV(D) proviruses are present in the genomes of possums, as detected by Southern hybridization. However, variability in fragment patterns between possums was observed and suggests recent (or ongoing) retrotranspositional activity.

An accessory open reading frame (orf-x) of jaagsiekte sheep retrovirus is conserved between different virus isolates

Jaagsiekte sheep retrovirus (JSRV) is the etiological agent of a contagious lung tumour of sheep known as sheep pulmonary adenomatosis (syn: ovine pulmonary carcinoma, jaagsiekte). JSRV exhibits a simple genetic organization, characteristic of the type D and type B retroviruses, with the canonical retroviral sequences gag, pro, pol and env encoding the structural proteins of the virion. An additional open reading frame (orf-x), of approximately 500 bp overlapping pol, is present in the only two complete sequences of JSRV published to date. Since very little information is available on the biology of JSRV it is important to establish if orf-x is conserved between different virus isolates. In this study we analysed the orf-x region of JSRV isolates collected from the United Kingdom, Italy, Spain and South Africa. In addition we also analysed the presence of orf-x in JSRV-related endogenous sequences (enJSRVs) present in the sheep genome. Orf-x was highly conserved in all the exogenous isolates (n=10) and in most of the endogenous sequences (n=8). Thus orf-x may be an accessory gene of JSRV and haves a biological function which might be advantageous to JSRV. Phenetic analysis conducted on the complete orf-x nucleotide sequences seems to highlight the presence of three distinct groups statistically well supported by bootstrapping: i) exogenous JSRV sequence from the UK; ii) exogenous JSRV sequences from Southern Europe and iii) the exogenous South African strain plus all the endogenous sequences analyzed and collected from Australia, Italy, UK and South Africa.

Sheep pulmonary adenomatosis: characterization of two pathological forms associated with jaagsiekte retrovirus

Pathological and immunohistochemical studies were performed on the lungs of 10 sheep with lesions of "classical" sheep pulmonary adenomatosis (SPA) and six sheep with "atypical" lung tumours. Lung tumour samples and other tissues from the same 16 animals were tested for the presence of jaagsiekte retrovirus (JSRV) by a polymerase chain reaction (PCR) that amplified a portion of the U3 long terminal repeat. The differences in the gross appearance of the classical and atypical forms paralleled the histopathological differences. The latter mainly concerned the stroma of the tumours which in the atypical cases was more heavily infiltrated by inflammatory cells and connective tissue fibres. JSRV major capsid protein was detected immunohistochemically in the epithelial transformed cells of both classical and atypical tumours, but the immune reactivity was slightly milder in atypical SPA. Proviral U3 sequences of JSRV were detected by specific PCR in all the tumour samples. Furthermore, the sequences of amplimers obtained from the two different pathological forms of the tumour were very similar. However, the dissemination of JSRV to other organs was greater in sheep with classical SPA than in those with atypical SPA. The pathological and virological features of these two forms of tumour are compared in an attempt to clarify whether classical and atypical SPA are two separate diseases or different expressions of a single disease spectrum.

Porcine endogenous retroviral mRNAs in pancreas and a panel of tissues from specific pathogen-free pigs

Pigs are potential providers of donor tissues for xenotransplantation (e.g. of pancreatic islets) in Type 1 diabetes. In this context, our group has studied the use of islets from specific pathogen-free (SPF) pigs as a means of reducing the risks of "conventional zoonosis". Although this approach does not prevent the transmission of pig endogenous retrovirus (PERV) to humans, we attempted to determine the presence of C-type PERV mRNAs for gag, pol, and env subtypes as a first descriptive step in the retroviral characterisation of SPF pig tissues (especially pancreas). Using semiquantitative reverse-transcriptase polymer chain reaction with 18S rRNA and beta-actin as internal controls, PERV mRNA levels were compared in a large panel of tissues from SPF and conventional pigs. PERV mRNAs for gag, pol, env-A and env-B were present in all tissues studied from the nine SPF pigs tested. Signals for env-C mRNAs were of much lower intensity than those for env-A and B, and most often undetectable in pancreas. The mRNA levels for gag, pol, env-A, env-B and env-C mRNAs were lower in pancreas (p < 0.01) than in all other tissues. Among other porcine tissues likely to be grafted in man, the highest retroviral mRNA levels were detected in kidney (p < 0.01), followed by liver, lung and heart. Amplified PERV mRNA signals were about 17 times less frequent in pig pancreas than in the retroviral-producing porcine cell line G2, while kidney contained about 6 times more PERV mRNAs than pancreas. The levels of gag, pol, env-A, env-B, and env-C mRNAs also varied between tissues of conventional pigs: PERV mRNA levels were lowest in pancreas, and env-C mRNAs were most often undetectable. For all SPF tissues tested, pol, gag, env-A, env-B, and env-C mRNA levels were in the same range or slightly higher than in corresponding tissues of conventional pigs. In summary, this study of C-type PERV mRNAs in a large panel of tissues from SPF pigs, in the context of our strategy of quality assurance and sanitary control, indicated that PERV mRNA levels were in the same range in SPF and corresponding conventional pig tissues, confirming that the use of SPF pigs would not prevent the risk of PERV transmission to human recipients of xenografts. PERV-A and PERV-B may be mainly represented, and PERV-C much less, in these pig tissues (particularly pancreas). The fact that pancreas expressed the lowest PERV mRNA levels and kidney the highest, among porcine tissues likely to be grafted, could be of interest from a clinical point of view. Pig tissues may differ in their loads of PERV sequences, which could be a factor in the risk of PERV transmission during xenotransplantation.

Jaagsiekte sheep retrovirus is necessary and sufficient to induce a contagious lung cancer in sheep

Sheep pulmonary adenomatosis (SPA) is a contagious and experimentally transmissible lung cancer of sheep resembling human bronchiolo-alveolar carcinoma. A type D retrovirus, known as jaagsiekte sheep retrovirus (JSRV), has been associated with the etiology of SPA, but its exact role in the induction of the tumor has not been clear due to the lack of (i) a tissue culture system for the propagation of JSRV and (ii) an infectious JSRV molecular clone. To investigate the role of JSRV in the etiology of SPA, we isolated a full-length JSRV proviral clone, pJSRV21, from a tumor genomic DNA library derived from a natural case of SPA. pJSRV21 was completely sequenced and showed open reading frames in agreement with those deduced for the original South African strain of JSRV. In vivo transfection of three newborn lambs by intratracheal inoculation with pJSRV21 DNA complexed with cationic lipids showed that pJSRV21 is an infectious molecular clone. Viral DNA was detected in the peripheral blood mononuclear cells (PBMCs) of the transfected animals by a highly sensitive JSRV-U3 heminested PCR at various time points ranging from 2 weeks to 6 months posttransfection. In addition, proviral DNA was detected in the PBMCs, lungs, and mediastinal lymph nodes of two lambs sacrificed 9 months posttransfection, but no macroscopic or histological SPA lesion was induced. We prepared JSRV particles by transient transfection of 293T cells with a JSRV construct (pCMV2JS21) in which the upstream U3 was replaced with the cytomegalovirus early promoter. Four newborn lambs were inoculated with JSRV21 particles produced in this manner, and two of them showed the classical signs of SPA 4 months postinfection. The resulting tumors were positive for JSRV DNA and protein. Thus, JSRV21 is an infectious and pathogenic molecular clone and is necessary and sufficient to induce sheep pulmonary adenomatosis.

Novel endogenous type D retroviral particles expressed at high levels in a SCID mouse thymic lymphoma

A xenograft model of the human disease Langerhans cell histiocytosis (LCH) was investigated with severe combined immunodeficiency (SCID) mice. Transplantation of human LCH biopsy material into SCID mice resulted in the generation of mouse tumors resembling lymphomas. A thymoma cell line (ThyE1M6) was generated from one of these mice and found to display significant levels of Mg2+-dependent reverse transcriptase activity. Electron microscopy revealed particles with type D retroviral morphology budding from ThyE1M6 cells at a high frequency, whereas control cultures were negative. Reverse transcription-PCR of virion RNA with degenerate primers for conserved regions of various mouse, human, and primate retroviruses amplified novel sequences related to primate type D retroviruses, murine intracisternal A particles, Jaagsiekte sheep retrovirus, and murine long interspersed nuclear elements but not other retroviral classes. We demonstrate that these sequences represent a novel group of endogenous retroviruses expressed at low levels in mice but expressed at high levels in the ThyE1M6 cell line. Furthermore, we propose that the activation of endogenous retroviral elements may be associated with a high incidence of thymomas in SCID mice.

Improved Mg2+-based reverse transcriptase assay for detection of primate retroviruses

The reverse transcriptase (RT) assay is a simple, relatively inexpensive, widely used assay that can detect all retroviruses (known and novel retroviruses as well as infectious and defective retroviruses) on the basis of the divalent cation requirement of their RT enzyme, i.e., Mg2+ or Mn2+. Descriptions of various RT assays have been published; however, they cannot be directly applied to the analysis of biological products or clinical samples without further standardization to determine the lower limit of virus detection (sensitivity), assay variability (reproducibility), or ability to detect different retroviruses (specificity). We describe the detection of type E and type D primate retroviruses, which may be pathogenic for humans, by a new 32P-based, Mg2+-containing RT assay. The results show that the sensitivity of detection is <3.2 50% tissue culture infective doses (TCID50s) for human immunodeficiency virus type 1 (HIV-1) and <1 TCID50 for simian immunodeficiency virus isolated from a rhesus macaque (SIVmac). Analysis of recombinant HIV-1 RT enzyme indicated that 10(-5) U, which is equivalent to 4.25 x 10(4) virions, could be detected. Additionally, genetically distinct type D retroviruses such as simian AIDS retrovirus and squirrel monkey retrovirus were also detected in the assay with similar sensitivities. Thus, the improved RT assay can be used to detect genetically divergent Mg2+-dependent retroviruses of human and simian origin that can infect human cells and that therefore pose a potential health risk to humans.

Characterization of enzootic nasal tumor virus capsid antigen

The RT-PCR was carried out on tumor tissue from sheep with enzootic nasal tumor (ENT), using primers designed from conserved amino acid regions of related type D retroviruses. A 591 bp PCR fragment, corresponding to 90% of the capsid antigen was cloned, sequenced and expressed in E. coli. Alignment with ovine pulmonary carcinoma (OPC) virus showed 93% nucleotide and 96% amino acid homology. No amplification occurred when DNA from ovine fetal cell line was used as template. The recombinant protein, highly expressed in prokaryotic system, reacted in immunoblot with mouse antiserum to Mason Pfizer monkey virus (MPMV) p27, as well as sera from OPC and ENT diseased animals. Preliminary application of this antigen in ELISA suggested its potential use to detect seropositive animals in infected flocks.

Jaagsiekte retrovirus establishes a disseminated infection of the lymphoid tissues of sheep affected by pulmonary adenomatosis

Jaagsiekte retrovirus (JSRV) is an exogenous type D-related retrovirus specifically associated with a contagious lung cancer of sheep (sheep pulmonary adenomatosis; SPA). Recently, epithelial tumour cells in the lungs of SPA-affected sheep were identified as major sites of JSRV replication by immunological techniques and RT-PCR amplification of part of JSRV gag. JSRV was not detected outside the lungs and their draining lymph nodes. However, low levels of JSRV expression in non-respiratory tissues could have been masked by co-amplification of endogenous JSRV-related sequences, which were differentiated from JSRV by the lack of a Scal restriction site in the PCR product. To further investigate the pathogenesis of SPA, an exogenous virus-specific hemi-nested PCR was developed utilizing primers in the U3 region of JSRV LTR, where major differences between endogenous and exogenous sequences exist. This technique was shown to be > or = 10(5)-fold more sensitive than the previous gag PCR/ScaI digestion method. Using this new assay the tissue distribution of JSRV in sheep with natural and experimentally induced SPA was analysed. Proviral DNA and JSRV transcripts were found in all tumours and lung secretions of SPA-affected sheep (n = 22) and in several lymphoid tissues. The mediastinal lymph nodes draining the lungs were consistently demonstrated to be infected by JSRV (10/10). JSRV transcripts were also detected in spleen (7/9), thymus (2/4), bone marrow (4/8) and peripheral blood mononuclear cells (3/7). Proviral DNA was also detected in these tissues although in a much lower proportion of cases. JSRV was not detected in 27 samples from unaffected control animals (n = 15).

PCR-based detection and partial characterization of a retrovirus associated with contagious intranasal tumors of sheep and goats

A type D-related retrovirus has been demonstrated in enzootic nasal tumors (ENTs) of sheep and goats. This retrovirus, ENT virus (ENTV), has antigenic cross-reactivity with the jaagsiekte sheep retrovirus (JSRV), which is associated with a contagious lung tumor of sheep (sheep pulmonary adenomatosis). Here, we present the first report of nucleic acid sequence from ENTV which confirms, at the nucleic acid level, that this retrovirus is related to JSRV yet apparently distinct from it. Reverse transcription-PCR followed by restriction enzyme digestion specifically identified ENTV. By this technique, ENTV was demonstrated exclusively in tumor tissues and exudates of animals with ENT. Thus, there is a unique and consistent association between ENT and the retrovirus, just as there is between JSRV and sheep pulmonary adenomatosis. This gives further weight to the hypothesis that these retroviruses are the etiologic agents of the tumors.

Endogenous D-type (HERV-K) related sequences are packaged into retroviral particles in the placenta and possess open reading frames for reverse transcriptase

All primates studied to date produce retroviral-like particles in their placentae. We have purified these particles from two primate species, one Old World (human) and one New World (marmoset), and have identified the retroviral sequences which are packaged into these particles. Three families of sequences have been detected in these particles in human, all of which have the highest homology to B- and D-type retroviruses and to the human endogenous retrovirus HERV-K10. Previous studies have reported that the New World monkeys do not possess sequences with homology to HERV-K10. We have identified a new family of low-copy-number sequences which are present in New World monkeys and which possess 70% homology to the HERV-K family. Particles from both species possess reverse transcriptase activity and we have found that some of these retroviral particles package sequences which encode long open reading frames in pol, as revealed by expression cloning in Escherichia coli. These open reading frames could encode the reverse transcriptase enzyme activity found in the particles.

Distribution of endogenous type B and type D sheep retrovirus sequences in ungulates and other mammals

The jaagsiekte sheep retrovirus (JSRV), which appears to be a type B/D retrovirus chimera, has been incriminated as the cause of ovine pulmonary carcinoma. Recent studies suggest that the sequences related to this virus are found in the genomes of normal sheep and goats. To learn whether there are breeds of sheep that lack the endogenous viral sequences and to study their distribution among other groups of mammals, we surveyed several domestic sheep and goat breeds, other ungulates, and various mammal groups for sequences related to JSRV. Probes prepared from the envelope (SU) region of JSRV and the capsid (CA) region of a Peruvian type D virus related to JSRV were used in Southern blot hybridization with genomic DNA followed by low- and high-stringency washes. Fifteen to 20 CA and SU bands were found in all members of the 13 breeds of domestic sheep and 6 breeds of goats tested. There were similar findings in 6 wild Ovis and Capra genera. Within 22 other genera of Bovidae including domestic cattle, and 7 other families of Artiodactyla including Cervidae, there were usually a few CA or SU bands at low stringency and rare bands at high stringency. Among 16 phylogenetically distant genera, there were generally fewer bands hybridizing with either probe. These results reveal wide-spread phylogenetic distribution of endogenous type B and type D retroviral sequences related to JSRV among mammals and argue for further investigation of their potential role in disease.

The exogenous form of Jaagsiekte retrovirus is specifically associated with a contagious lung cancer of sheep

Sheep pulmonary adenomatosis ([SPA] ovine pulmonary carcinoma) is a transmissible lung cancer of sheep that has been associated etiologically with a type D- and B-related retrovirus (jaagsiekte retrovirus (JSRV]). To date it has been impossible to cultivate JSRV in vitro and therefore to demonstrate the etiology of SPA by a classical approach. In addition, the presence of 15 to 20 copies of endogenous JSRV-related sequences (enJSRV) has hampered studies at the molecular level. The aim of this study was to investigate whether the expression of exogenous JSRV was specifically associated with neoplasia in SPA-affected animals. Initially, we found that enJSRVs were transcribed in a wide variety of normal sheep tissues. Then, by sequencing part of the gag gene of enJSRV we established a ScaI restriction site in gag as a molecular marker for the exogenous form of JSRV. Restriction enzyme digestion of PCR products obtained from the amplification of cDNA from a total of 65 tissues collected from SPA-affected and unaffected control sheep revealed that the exogenous form of JSRV was exclusively and consistently present in tumor tissues and lung secretions of the affected animals. In addition, exogenous JSRV provirus was detected only in DNA from SPA tumors and not from nontumor tissues of the same animals. This study has demonstrated clearly that the exogenous form of JSRV is specifically associated with SPA tumors.

Transmissible retrovirus in Epstein-Barr virus-producer B95-8 cells

Epstein-Barr virus (EBV) released from the B95-8 marmoset cell line has served as a prototype for biologic and biochemical studies of EBV. Here we identify and characterize a retrovirus carried by many cultures of B95-8 cells. The experiments were stimulated by the isolation of a cDNA clone from B95-8 cells in which sequences from the EBV large internal repeat were linked to gag sequences similar to those of squirrel monkey retrovirus, human isolate, SMRV-H. However, among 413 amino acids predicted from the nucleotide sequence of the gag region of the B95-8 SMRV isolate there were 48 amino acid changes that distinguished this virus from SMRV-H originally isolated from a human lymphoid cell line by Oda et al. (1988, Virology 167, 468-476). Nucleic acid and antibody probes were developed for the B95-8 isolate of SMRV. Using such probes, we found that SMRV-B95-8 was readily transmissible, independent of EBV, as an infectious virus to human B and T cell lines. SMRV-B95-8 was highly fusogenic in the presence or absence of EBV. The ultrastructural appearance of the B95-8 retrovirus was characteristic of a type D retrovirus. Cells dually infected with EBV and SMRV-B95-8 did not demonstrate increased levels of lytic EB viral replication. SMRV-B95-8 did not by itself cause lymphocyte immortalization or enhance immortalization by EBV. Thus SMRV-B95-8 does not contribute to the major biologic properties of the B95-8 strain of EBV.

Identification of human type D retrovirus as a contaminant in a neuroblastoma cell line

In this report we describe a type D virus isolated from a human neuroblastoma cell line (Paju). The viral RNA was isolated, partially molecularly cloned and sequenced. Our clones were shown to be identical to a human D-type retrovirus previously isolated from a human lymphoblastoid cell line. However, we obtained no evidence for the virus in earlier passage of the Paju cell line and therefore we must consider this isolate a laboratory contamination. contamination.

Purification and biochemical characterization of squirrel monkey retrovirus-H produced in a human lymphoblastoid cell line

We found a type D retrovirus in a human lymphoblastoid cell line of B-cell lineage. Molecular cloning and nucleotide sequencing of the provirus genome revealed that this virus was closely related to squirrel monkey retrovirus (SMRV), and we designated this virus as SMRV-H. To investigate the relationship between these retroviruses, SMRV-H was purified from the virus-producing cells, and its biochemical properties were characterized. The cell-adhesive virus particles were successfully separated from the cell by a brief trypsin treatment and purified by velocity sedimentation. The purification of the virus was confirmed by electron microscopy. Major gag protein of the virus is phosphorylated, and has a molecular weight of 34 kDa. The virion-associated reverse transcriptase prefers Mg2+ to Mn2+. These properties of SMRV-H were almost the same as those of SMRV.