Electron microscopic observations of Visna virus-infected cell cultures

Phenotypic and ultrastructural characteristics of bronchoalveolar lavage cells of lentivirus-infected lambs treated with recombinant ovine IFN-tau

Ovine lentivirus (OvLV) belongs to the family Retroviridae and closely resembles the human immunodeficiency virus (HIV). Pulmonary lesions in OvLV-infected sheep consist of lymphoid interstitial pneumonia (LIP) and lymphocytic alveolitis. Similar pulmonary lesions occur in up to 40% of HIV-infected children and in some adults with AIDS. Interferon-tau (IFN-tau), a type I IFN, is produced by trophectoderm of ruminant conceptuses and is the pregnancy recognition signal in these species. To evaluate changes in phenotypes of bronchoalveolar lavage (BAL) cells of OvLV-infected lambs treated with recombinant ovine IFN-tau (rOvIFN-tau), 24 lambs were randomly allocated to one of four groups (n = 6 per group): 1, no virus + placebo (NVP); 2, no virus + rOvIFN-tau (NVI); 3, virus + placebo (VP); 4, virus + rOvIFN-tau (VI). The BAL cells from 3 lambs in each group were labeled with monoclonal antibodies (mAb) to cell surface markers at 16 weeks of treatment, and cells from the remaining 3 lambs in each group were labeled with mAb at 34 weeks of treatment. After labeling, BAL cells were analyzed by flow cytometry. The morphology of BAL cells from all experimental lambs was examined by transmission electron microscopy (TEM). At week 16, no differences in the relative proportions of BAL cell phenotypes were detected among the experimental groups. At week 34, VI lambs had higher proportions of CD8(+), gammadelta(+), MHC class II(+), and L-selectin (LS(+)) BAL cells compared with VP lambs. Higher proportions of CD14(+) and CD44(+) cells were found in VP lambs compared with NVP lambs at 34 weeks. OvLV-like particles were detected only in bronchoalveolar macrophages of VP lambs. In this study, rOvIFN-tau increased the proportions of primary antiviral gammadelta(+) and CD8(+) immune cells in OvLV-infected lambs. This may represent a cellular mechanism to explain the antiviral and therapeutic efficacy of this cytokine, in addition to its direct antiviral effect. However, because the actual number of cells labeled with mAb CD8 was low and some subsets of gammadelta cells may coexpress the CD8 marker, further studies are necessary to better define the role of rOvIFN-tau in the modulation of these cells in vivo.

Ovine lentivirus (maedi-visna virus) protein expression in sheep alveolar macrophages

The expression of gag (p15, p25) and env gene products in ovine lentivirus-infected cells was studied in 20 adult Texel ewes seropositive to maedi-visna virus and 10 seronegative matched controls. Bronchoalveolar lavage was performed to recover alveolar cell pools from which cytocentrifuge preparations were made. Single and double immunocytochemical techniques were applied to study viral replication and coexpression of viral markers with markers for macrophages, lymphocytes, and major histocompatibility complex (MHC) class II. Aveolar macrophages of eight of 20 infected sheep (40%) were positive for viral protein expression. The percentage of positive macrophages varied from < 1% to 12% of the total population of macrophages. Viral protein expression was not detected in lymphocytes or other cell types. A relationship between virus-replicating macrophages and differential expression of MHC class II molecules, upregulated in ovine lentivirus infection, could not be established. Pathology was evaluated in nine infected ewes. Animals with the highest levels of positive cells had moderate or severe lymphoid interstitial pneumonia. However, sheep with similar degrees of lesions had lower percentages of positive macrophages or were negative for viral protein detection. These results support the idea that a partial or even a complete loss in the restriction mechanism of maedi-visna virus in lungs can occur in some individuals.

The biology of maedi-visna virus--an overview

This review aims to summarize the current understanding of the biology of maedi-visna virus (MVV), the prototype virus of the family lentivirinae. The paper provides a short overview of the historical background to the discovery of MVV. Detailed descriptions of the structure and organization of the MVV genome and of the virion encoded polypeptides are given and the MVV life cycle in vitro and in vivo are compared and contrasted and the tropism of the virus discussed. The clinical consequences of infection are considered and the mode of transmission, immune response to the virus and possible mechanisms of pathogenesis are discussed.

Isolation and preliminary characterisation of a novel retrovirus isolated from a leukaemic dog

A novel canine retrovirus was isolated from mononuclear cells of the peripheral blood of a leukaemic dog. The main clinical and pathological findings in this dog were lethargy, anorexia, weakness, dyspnoea, severe anaemia, thrombocytopenia and a high white blood cell count, practically all of which were lymphoblasts. The virus was isolated from mononuclear cells obtained from the blood, cocultivated with indicator cells. The virus particles encode a reverse transcriptase with Mg++ preference, have a density in sucrose gradients of 1.16 g ml-1, and induce syncytia in permissive cell cultures such as Himalayan tahr ovary and canine fetal thymus lines. This agent replicates to high titres. The virus exhibits a morphogenesis and morphology typical of lentiviruses. Immunoblotting and competitive radioimmunoassays failed to detect immunological crossreactivity with other representative lentiviruses and oncoviruses of the retrovirus family.

Potential human health risks associated with animal retroviruses: some hypotheses

Several studies have demonstrated the existence of morphological, biological, genetic and antigenic correlations between human and animal retroviruses. Furthermore, some agents of bovine and feline origin can also be considered useful comparative models for the pathogenetic study of human diseases such as leukaemia, acquired immunodeficiency syndrome (AIDS) and multiple sclerosis (MS). In spite of the existence of data suggesting a possible role of some animal retroviruses (e.g. the bovine leukosis virus, BLV) in the etiology and epidemiology of human leukaemia and MS, the true zoonotic potential of such agents remains unknown, but their genetic and antigenic linkages with some human lentiviruses (such as the human immunodeficiency virus-1, HIV 1) can make them hypothetically responsible for a certain number of false-positive serological reactions in man, especially in those subjects who are professionally exposed to animal lentiviruses. In the present paper particular reference is made to this last hypothesis which, if confirmed, would suggest a larger scale-utilization of more specific diagnostic tests for HIV infection in man, such as the immunoblotting techniques.

Human T-cell lymphotropic virus type III shares sequence homology with a family of pathogenic lentiviruses

The etiologic agent of the acquired immune deficiency syndrome, human T-cell lymphotropic virus type III (HTLV-III), has recently been shown to morphologically resemble and share sequence homology with visna virus, a pathogenic lentivirus. Molecular hybridization, heteroduplex mapping, and DNA sequence analyses were used to compare HTLV-III to other lentiviruses of domestic animals, including visna, caprine arthritis encephalitis, and equine infectious anemia viruses. Hybridization results showed that a substantial amount of sequence homology exists between each of these viruses and HTLV-III. In addition, a closer relationship was found between visna and caprine arthritis encephalitis viruses than for any of the other lentiviruses studied. These results, along with nucleotide and amino acid sequence comparisons, have been used in a comprehensive effort to derive a systematic relationship for lentiviruses and to provide further evidence for classifying HTLV-III with the Lentivirinae subfamily of retroviruses. This relationship predicts that similarities in biology and disease process can be expected between HTLV-III and other Lentivirinae members.

Isolation of visna-maedi virus from the choroid plexus of an apparently healthy sheep in Italy

In this paper, the presence of visna-maedi in Italy, reported to exist since 1982 on clinical grounds, and the presence of anti-visna-maedi antibody is confirmed by the isolation of the viral agent from choroid plexus cells of an apparently healthy sheep. Gel diffusion test antigen, prepared from the explanted choroid plexus cells and from normal choroid plexus cells infected with the isolated agent, gave a positive reaction with one or two identity lines with reference antigens. The isolated agent gave both a characteristic cytopathic effect and a cytoplasmic fluorescence starting 24 hours after infection in normal choroid plexus cell cultures. Fluorescence was observed neither in control normal choroid plexus cells nor in infected normal choroid plexus cells incubated with a visna-maedi negative serum. By electron microscopy, budding forms arising from the cell membrane and extracellular particles of two distinct types were observed. One type was characterized by an electron-dense central core and a single membrane, and ranged from 80 to 110 nm, while the other had elongated bar-like cores and a double wall, and ranged from 100 to 140 nm. The characteristics observed for the isolated agent are identical to those reported by various authors for visna-maedi virus.

Sequence homology and morphologic similarity of HTLV-III and visna virus, a pathogenic lentivirus

A study was conducted of the genetic relation between human T-cell lymphotropic retroviruses and visna virus. The human T-cell lymphotropic viruses include those associated with T-cell malignancies (HTLV-I and HTLV-II) as well as the etiologic agent of the acquired immune deficiency syndrome (HTLV-III). Visna virus, a slowly replicating and pathogenic but nononcogenic retrovirus of sheep, is a member of the subfamily Lentivirinae. Results obtained by molecular hybridization and heteroduplex analysis indicated that a greater extent of nucleotide sequence homology exists between HTLV-III and visna virus than between HTLV-III and any of the other viruses. The homology observed under conditions of low stringency spanned the entire genome, but was strongest in the gag/pol region. The morphogenesis and fine structure of HTLV-III and visna virus also demonstrated striking similarities. The data provide strong evidence for a close taxonomic and thus evolutionary relation between HTLV-III and the Lentivirinae subfamily.

Characterisation, experimental infection and serological response to caprine retrovirus

A virus (151) isolated from synovial membrane explant cultures from a goat with arthritis-synovitis was characterised with respect to cytopathic effect in synovial membrane cell cultures, virus morphology, buoyant density and presence of RNA dependent DNA polymerase. Virus 151 was shown to be a retrovirus with similar properties to caprine arthritis-encephalitis virus in the United States of America. Inoculation of the virus into uninfected goats caused the development of arthritis-synovitis lesions and the virus was recovered from affected joints and lung 361 days post-inoculation. The development of antibody to virus 151 was detected using an enzyme linked immunosorbent assay (ELISA). Other goats with arthritis-synovitis, progressive pneumonia or viral leukoencephalomyelitis all had antibody that reacted in this ELISA. Viruses similar to virus 151 were recovered from a number of cases. Goats inoculated with one of the viruses produced serum antibody that cross-reacted in ELISA using maedi-visna virus and virus 151 as antigens.

Morphological and immunological comparison of caprine arthritis encephalitis and ovine progressive pneumonia viruses

Caprine arthritis encephalitis virus (CAEV) causes a variety of pathological conditions ranging from mild to very severe and from acute to chronic, depending upon the age of initial infection and other variables. Although the virus has been reported to have properties of characteristic of retroviruses and to be related to maedi-visna virus (also called progressive pneumonia virus [PPV]), relatively little information about its morphological and immunological characteristics has been reported. We describe the morphological features of CAEV replicating in cultured caprine cells. Although the virus replicates slowly and very little virus is released from productively infected cells, it is apparent that the morphogenesis of CAEV is strikingly similar to that of maedi-visna. After the transmission of CAEV to a more permissive permanent cell line derived from Himalayan tahr ovary, it was possible to grow and purify enough virus to initiate biochemical characterization. The structural proteins of CAEV are generally very similar to those of PPV, suggesting that the two viruses are closely related but not identical. This was substantiated by showing that serum from a CAEV-infected goat immunoprecipitated both CAEV and PPV virion structural antigens from extracts of radiolabeled virus and also precipitated putative nonstructural viral antigens from extracts of both CAEV- and PPV-infected cells.

Goat visna virus: isolation of a retrovirus related to visna virus of sheep

Choroid plexus (GCP-3) cell cultures were prepared from an adult goat with symptoms of visna. The GCP-3 cell layer had partly fused into large multinucleated giant cells and electronmicrographs showed virus particles morphologically indistinguishable from sheep visna virus (SVV). A virus, designated goat visna virus (GVV), was subsequently purified from the GCP-3 cultures. The virus particles have a density of 1.15 g/ml and a high molecular weight RNA similar in size to that of SVV. A virion-associated DNA polymerase was identified which is stimulated to the same extent as the SVV polymerase by different synthetic RNA and DNA template-primer combinations and which shows the same Mg2+ and Mn2+ stimulation optima. Polypeptide analysis by SDS-PAGE revealed that the virion proteins of GVV and SVV had similar molecular weights. By immunodiffusion tests it was demonstrated that the major internal proteins of GVV and SVV are related. Consequently, we conclude that GVV should be classified as a retrovirus and that it is closely related to visna virus of sheep.

Ultrastructural studies on Maedi-Visna virus

Ultrastructural studies of Maedi-Visna virus (MVV) particles isolated from tissue culture fluids of MVV-infected cells as well as cultured cells infected with MVV were performed. MVV particles aree bounded by an envelope with projections loosely attached to its surface. Virions contain a core (sometimes two or more) of conical or ovoid shape enclosing an electron-dense nucleoid which is much smaller in diameter than the core and which can only be seen in ultrathin sections. A distinct core shell is to be found in most of the ultrasectioned particles. Cores, liberated from the virions by detergent treatment, exhibited the same shape as their enveloped counterparts. Budding structures with crescents underlying the cell membrane without an intermediate space seem to be bordered on their cell side by an electron-dense thin layer. Particles obviously representing intervenig stages of viral maturation showing parts of the crescents at the viral membrane and empty core shells could be found in single cases.

Maedi-visna in Canadian sheep

Lesions of maedi-visna were seen in sheep from the institutional research flock of the Animal Research Institute, Research Branch, Agriculture Canada in Ottawa. Viral particles demonstrated by electron microscopy in tissue culture cells and serological results confirm the diagnosis of maedi-visna. The extent of the problem in this flock will be described in a future paper.

Characterization of visna virus envelope neuraminic acid

Visna virus particles inhibit influenza virus hemagglutination in an assay for neuraminic acid-containing viruses. Pretreatment of visna virus with neuraminidase abolished hemagglutination inhibition activity but did not significantly affect attachment, infectivity, or virus-induced cell fusion in sheep choroid plexus cell monolayers.

Properties of Visna Virus Particles Harvested at Short Time Intervals: RNA Content, Infectivity, and Ultrastructure

The major RNA component of Visna virus harvested at short intervals of time (5 min) is not the 60 to 70 S RNA but a molecule of higher electrophoretic mobility. This RNA has been isolated and characterized. Its sedimentation coefficient is identical to that of 30 to 40 S RNA subunits obtained by heat denaturation of the 60 to 70 S RNA. In 1.8% acrylamide gels without agarose the electrophoretic mobility of 30 to 40 S RNA subunits present in rapidly harvested virus is slightly lower than that of the subunits obtained by denaturation of the 60 to 70 S RNA; after heat denaturation the mobilities are identical. These free RNA subunits present in early virus particles assemble into a 60 to 70 S RNA complex as shown by following the RNA content of early virus incubated at 37 C for various lengths of time. The rate of this maturation process is slow. There is no difference between the infectivity of immature and mature virus particles. Both particles have a dense core when examined in sections of virus pellets.

Visna virus infection of American lambs

Random-bred fetal and 4-week-old American lambs, inoculated intracerebrally with visna virus, developed a persistent infection in the brain and sometimes in the lung. The pathologic changes present in these lambs were similar to the early lesions of visna in Icelandic sheep, thus providing a possible model for the study of virus-induced demyelinating disease.

Ultrastructural studies of a visna-like syncytia-producing virus from cattle with lymphocytosis

A virus structurally similar to viruses associated with maedi, progressive pneumonia, and visna of sheep has been isolated from buffy coat cells of cattle with chronic lymphocytosis. Electron microscope studies revealed three variants of the virion: (i) an intracytoplasmic form 98 to 116 nm in diameter when occurring in a nonlaminated form, (ii) a budding form 120 to 130 nm in diameter, and (iii) an extracellular form 80 to 130 nm in diameter and containing a 30 to 43 nm eccentrically located electron-dense core.

Polyadenylic acid in Visna virus RNA

Visna virus 70S RNA contains long stretches of polyadenylic acid [poly(A)]. The homogeneity in length of poly(4) regions is observed in 70S RNA from visna virus and all RNA tumor viruses tested, and not with other types of RNA. By this criterion visna virus resembles RNA tumor viruses.

Antigenic and morphological similarities of progressive pneumonia virus, a recently isolated "slow virus" of sheep, to visna and maedi viruses

Progressive pneumonia virus, the causative agent of a slow, pulmonary disease of Montana sheep, was shown to be antigenically related to two other slow viruses of sheep, visna and maedi. Electron microscopic examination of infected cells revealed that the virus matures by a budding process and that the budding particles as well as the mature, extracellular virions bear striking resemblances to the oncogenic ribonucleic acid (RNA) viruses. Recent findings of an RNA-dependent deoxyribonucleic acid polymerase associated with the virions of this group of slow viruses lend further support to the notion that they may tentatively be classified with the oncogenic RNA tumor viruses.

DNA polymerase activities in varions of visna virus, a causative agent of a "slow" neurological disease

The presence is reported of an RNA-instructed DNA polymerase in visna virus, the causative agent of a "slow" neurological disease in sheep. The product synthesized by the RNA-directed reaction has been shown to be a DNA heteropolymer by the following criteria: synthesis requires the presence of all four deoxyriboside triphosphates; the product is resistant to ribonuclease and alkali but is degraded by DNase; and the product has a density of 1.420 in Cs(2)SO(4) solution, characteristic of DNA.Visna virions, like those of the oncogenic RNA viruses, contain DNA polymerase activities that respond to a variety of double-stranded DNAs and to synthetic DNA.RNA hybrids.