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Biomedical subjects

O Narayan

Publications and source records attributed to O Narayan.

At least 127 records · Page 7Linked to original sources
PubMed1992

Neutralizing antibodies modulate replication of simian immunodeficiency virus SIVmac in primary macaque macrophages.

Cultured macaque macrophages are permissive for the replication of SIVmac251, and inoculation with virus is followed by the production of viral p27. Neutralizing macaque polyclonal and murine monoclonal antibodies preincubated with the virus prevented infection but did not prevent cytopathic virus replication when added more than 3 days after inoculation with virus. However, application of the neutralizing antibodies to macrophages 24 h after inoculation with virus resulted in sustained, low-level production of viral antigen. Cell lysates and individual macrophages from treated cultures contained less viral protein by Western blot (immunoblot) and immunocytochemistry than untreated controls. In situ hybridization and polymerase chain reaction procedures for detecting and estimating relative amounts of viral RNA and DNA showed that both viral nucleic acids failed to increase beyond the levels obtained before the addition of neutralizing antibodies. The data suggest that macrophages may need to be infected with a minimum threshold of virus particles in order to reach their full potential for virus replication and that their exposure to neutralizing antibodies prior to reaching this threshold resulted in limited virus replication.

Animals↗
PubMed1992

Ovine lentivirus is macrophagetropic and does not replicate productively in T lymphocytes.

The lentiviruses of sheep, goats, and horses cause chronic multiorgan disease in which macrophages are highly permissive for viral replication. Monocytes, which mature into macrophages, are thought to be latently infected with lentivirus, but the extent to which other leukocytes are infected is unknown. Dendritic cells have not been studied separately from monocytes and T-cell subsets have not been examined in previous attempts to identify infected cells in peripheral blood mononuclear cells (PBMC). We found no evidence of T-cell tropism using an animal-passaged, pathogenic ovine lentivirus. Phytohemagglutinin-stimulated infectious PBMC produced 20-fold less virus than differentiated macrophages, and cocultivation of infectious PBMC with fresh, uninfected phytohemagglutinin blasts did not facilitate virus replication. Furthermore, central lymph cells, the best in vivo source of purified lymphocytes, lacked virus and did not yield virus upon in vitro cultivation. In contrast, cultivated blood-derived macrophages were highly permissive for viral replication. To identify the latently infected PBMC, PBMC from infected sheep were selectively depleted of monocytes and B cells by passage over nylon wool and then of nonadherent cells bearing CD4, CD8, T19, gamma delta T-cell receptor, CD45RA, or major histocompatibility complex class II antigens by panning. Removal of adherent monocytes and B cells or of adherent cells and the three major T-cell subsets (CD4+, CD8+, T19+) did not decrease the infectivity of PBMC. The richest sources of infected cells in fresh PBMC were CD45RA+ and major histocompatibility complex class II+ nonadherent cells, which are three characteristics of dendritic cells. Thus, the dendritic cell, and not the monocyte or the CD4+ cell, is probably the predominant infected cell type in blood.

Animals↗
PubMed1992

Derivation of neurotropic simian immunodeficiency virus from exclusively lymphocytetropic parental virus: pathogenesis of infection in macaques.

Neurological disease resulting from lentivirus (including human immunodeficiency virus) infections is usually caused by a strain of virus that replicates productively in microglia in vivo and in macrophage cultures in vitro. We undertook this study using the model of simian immunodeficiency virus in macaques (SIVmac) to test the hypothesis that macrophage tropism is a prerequisite for neurotropism of the virus. Using molecularly cloned SIVmac239, a virus which is lymphocyte- but not macrophagetropic, we showed that this virus failed to infect brain after intracerebral (i.c.) inoculation into two macaques. Rather, these inoculations resulted in disseminated infection in lymphoid organs and the bone marrow. Two sequential passages of infected bone marrow cells inoculated i.c. into new macaques resulted in severe neurological disease and classical neuropathological lesions. Virus obtained from affected brain answered the hypothetical question: it was neurotropic and macrophagetropic. New findings in the study were that both lymphocyte- and macrophage-tropic viruses were present in the animals, but the viruses localized in different tissues: the lymphotropic virus in the spleen, lymph nodes, and plasma and the macrophagetropic virus in the brain and lungs. To determine whether the brain virus was preferentially neurotropic and whether it had neuroinvasive properties, infectious brain homogenate was inoculated into one animal i.c. and into two others peripherally. The i.c. inoculated animal developed fatal encephalitis 5 months later, and examination of tissues showed cell-free virus only in brain homogenates. Only microglia were infected despite persistent viremia and infection in bone marrow cells. The two macaques inoculated peripherally remained healthy and were euthanized at 6 months. Virus replication was detected only in the bone marrow cells and peripheral blood mononuclear cells. No infection in any macrophage population in visceral organs was detected, and the virus did not invade the brain. The strictly microglial specificity of this virus suggested that different macrophage populations in the body may select specific phenotypes of lentivirus from the quasispecies of virus in the bone marrow. This could provide the basis for specific disease affecting different organ systems.

Adaptation, Biological↗
PubMed1992

Lentivirus induced arthritis in animals.

Retroviral arthritis in sheep and goats depends on persistent infection in the animals. Virus is latent in macrophage precursor cells and viral replication is initiated when these cells are induced to differentiate. Antiviral antibodies and cytokines modulate the efficiency of viral gene product expression. Specific cytokines induced during replication of the lentivirus in mononuclear cells are also responsible for directing infected cells from peripheral blood through the vascular endothelium to particular tissues. Cytokines induced by other infectious agents such as bacteria, mycoplasma or protozoa, may also contribute to this chemotactic process. Once in the tissue, macrophages interact with lymphocytes to induce an inflammatory cascade with further production of cytokines which enhances expression of class II major histocompatibility complex antigens and proliferation of B and CD8 lymphocytes. In addition, immune complexes between viral glycoproteins and immunoglobulins are produced locally and probably lead to further enhancement of pathological changes in the tissues.

Animal Diseases↗
PubMed1991

Rhesus monkey macrophages infected with simian immunodeficiency virus cause rapid lysis of CD4-bearing lymphocytes.

Inoculation of simian immunodeficiency virus into cultures of primary rhesus monkey macrophages or CD4-bearing transformed T lymphocytes resulted in persistent infection, with minimal virus replication in the macrophages and extensive replication in the lymphocytes. However, uninfected T cells added to infected macrophages underwent rapid fusion and lysis and were almost completely eliminated without the production of virus particles. Lysis required direct contact between the T cells and the infected macrophages, which enabled binding between CD4 on the former and viral gp120 on the latter to occur. This process was blocked by soluble CD4 and dextran sulphate. Neutralizing antibodies in the serum of an infected macaque prevented cell fusion by preventing infection of the macrophages. However, these antibodies did not prevent fusion when added to previously infected macrophages. Infected macrophages were incorporated into the syncytia of lymphocytes and continued incorporation of new lymphocytes into the syncytia required infected macrophages to be metabolically active. One inference from these studies is that infected macrophages in vivo could help mediate the well known depletion of T4 cells in patients with AIDS.

Animals↗
PubMed1991

Analysis of Borna disease virus-specific RNAs in infected cells and tissues.

Borna disease virus (BDV) is an infectious agent that causes profound disturbances in motor function and behaviour in a wide range of animal species and possibly humans. The infectious nature of BDV has long been established, but the aetiological agent has not been isolated or classified. Recently, we have reported the isolation of BDV-specific cDNA clones using subtractive libraries constructed from mRNA from infected material. Here we describe studies on one of these cDNA clones, B8, and confirm its specificity by in situ hybridization on sections of BDV-infected brain. The complete nucleotide sequence of BDV-specific clone B8 was determined. Oligonucleotides of positive and negative polarity synthesized from sequences from the 5' and 3' ends, as well as the central part, of clone B8 identified both positive- and negative-strand BDV-specific RNAs in infected rat brain. All B8 sequences used as oligonucleotide probes were found to be contained in the larger positive- and negative-strand RNAs. Thus, the structure of the BDV-specific RNAs appears to be a nested set of multiple, overlapping subgenomic positive- and negative-strand RNA transcripts.

Amino Acid Sequence↗
PubMed1991

Molecular and immunopathological studies of borna disease virus infection in rats.

Borna disease virus is an agent distinct from all known viruses. Pathogenesis of its infection is also unique. This review highlights several aspects of the biology of this viral infection and the preliminary characterization of the agent. BDV can be used to answer important questions in neurobiology. These include neuroinvasiveness and neurotropism of viral agents, CD4+ T cell-mediated immunopathology and tolerance in newborn animals to a persistent viral infection in the CNS and behavioral diseases and eating disorders induced by neurotropic viruses. This review is dedicated to Prof. Dr. Rott on occasion of his 65th birthday in recognition of his immense contributions to studies on Borna disease and also for his success focusing the attention of the scientific community to this still evolving unique viral disease.

Animals↗
PubMed1991

Recovery of the simian immunodeficiency virus (SIV) and depression of colony formation in in vitro infected progenitor cell-enriched rhesus bone marrow (BM).

Rhesus progenitor-enriched BM was exposed overnight to SIV and cultured in a limiting dilution assay where the potential for progenitor interaction with lymphocytes or macrophages was low. Virus was consistently isolated late in culture, detection being aided by coculture with CEM174 lymphoblasts. Although infected cells had reduced clonogenic activity, colonies were indistinguishable from those derived from uninfected BM with respect to proliferative potential, morphology, and longevity in culture. Primate immunodeficiency viruses, therefore, may infect immature BM populations, directly affecting hematopoietic activity.

Animals↗
PubMed1990

A borna virus cDNA encoding a protein recognized by antibodies in humans with behavioral diseases.

Borna disease virus (BDV) causes a rare neurological disease in horses and sheep. The virus has not been classified because neither an infectious particle nor a specific nucleic acid had been identified. To identify the genome of BDV, a subtractive complementary DNA expression library was constructed with polyadenylate-selected RNA from a BDV-infected MDCK cell line. A clone (B8) was isolated that specifically hybridized to RNA isolated from BDV-infected brain tissue and BDV-infected cell lines. This clone hybridized to four BDV-specific positive strand RNAs (10.5, 3.6, 2.1, and 0.85 kilobases) and one negative strand RNA (10.5 kilobases) in BDV-infected rat brain. Nucleotide sequence analysis of the clone suggested that it represented a full-length messenger RNA which contained several open reading frames. In vitro transcription and translation of the clone resulted in the synthesis of the 14- and 24-kilodalton BDV-specific proteins. The 24-kilodalton protein, when translated in vitro from the clone, was recognized by antibodies in the sera of patients (three of seven) with behavioral disorders. This BDV-specific clone will provide the means to isolate the other BDV-specific nucleic acids and to identify the virus responsible for Borna disease. In addition, the significance of BDV or a BDV-related virus as a human pathogen can now be more directly examined.

Amino Acid Sequence↗
PubMed1990

Physical studies on the membranes and lipids of plasmalogen-deficient Megasphaera elsdenii.

Membrane fluidity and thermotropic phase behavior in the wild-type and plasmalogen-deficient strains of Megasphaera elsdenii have been studied by means of diphenylhexatiene steady state fluorescence anisotropy in isolated membranes, and by 31P-NMR and X-ray diffraction of the isolated phospholipids. Compared to the wild-type plasmalogen content of greater than 75%, plasmalogen-deficient strains had less than 5% plasmalogen, consisting largely of phosphatidylethanolamine and phosphatidylserine. Steady state fluorescence anisotropy measurements yielded an order parameter which was 6% lower in the plasmalogen-deficient membranes from 10 degrees to 40 degrees C, indicating higher membrane lipid mobilities. Both 31P-NMR and X-ray diffraction revealed the formation of a hexagonal phase in the lipids from the wild-type strain starting above 30 degrees C. In general the transition was not complete by 80 degrees C. In contrast, phospholipids from plasmalogen-deficient strains appeared to form a relatively stable lamellar phase.

Cell Membrane↗
PubMed1990

Lentiviruses are etiological agents of chronic diseases in animals and acquired immunodeficiency syndrome in humans.

Lentiviruses are species-specific, exogenously transmitted retroviruses that have a unique ability to replicate continuously but at a restricted rate in host tissues. This property is thought to be related to the retroviral nature of the replication process (RNA to DNA to RNA) and to the ability of the viruses to do this in cells of the macrophage lineage. The viral genomes are expressed only in certain populations of macrophages and this is dependent on a number of interactive factors including the genus of the host, the age of the host, maturation/differentiation factors in macrophages, the strain of virus and regulatory factors in the virus and the regulatory factors in the virus and the macrophages. Macrophages permissive for virus replication are found in specific tissues and virus replication in the cells causes development of lesions in the particular tissues. The nature of the lesions varies from virus induced necrosis to immunopathology to possible toxic infects of monokines produced by the infected macrophages. Cats and primates have further complicating diseases caused by the remarkable sensitivity of their helper T lymphocytes to infection with their lentiviruses. Elimination of these cells leads to onset of various local and systemic diseases caused by opportunistic agents. Whereas equidae and small ruminant animals develop diseases related to infection in macrophage populations, felines, macaques and humans develop diseases related to both infection in their macrophages and elimination of their T lymphocytes.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Pathogenesis of ovine lentivirus-induced arthritis: phenotypic evaluation of T lymphocytes in synovial fluid, synovium, and peripheral circulation.

Sheep and goats develop a chronic, progressive arthritis reminiscent of rheumatoid arthritis, but caused by lentiviruses related to human immunodeficiency virus. The distribution of T lymphocytes in peripheral circulation of two infected sheep with arthritis, one infected sheep with interstitial pneumonia, three asymptomatic sheep, and three uninfected sheep was evaluated. Sheep with clinical disease have depressed ratios of CD4/CD8 lymphocytes in peripheral circulation compared to asymptomatic and uninfected animals. In one sheep, the depressed ratio was due to an absolute increase in CD8-positive lymphocytes. The predominant lymphocyte populations in both synovial fluid and synovium from this animal were also CD8 positive. Macrophages were the other predominant cell population in synovial fluid and were infected with lentivirus. Little cell-free virus was detected in the synovial fluid, although 1 in 400 cells was infected as determined by infectious center assays. Infected cells in the synovial fluid had a reduction in virus gene expression compared to infected cells in peripheral circulation. This reduction in virus gene expression may be due to the presence of interferon-like activity in the synovial fluid.

Animals↗
PubMed1989

Astrocytes and Schwann cells are virus-host cells in the nervous system of rats with Borna disease.

Borna disease virus (BDV) replicates only in cells in the central (CNS) and peripheral (PNS) nervous system in adult rats. Infection of the nervous system is associated with a transient, intense mononuclear meningoencephalitis and immunemediated loss of BDV-infected neurons. The identification of BDV antigen in neurons and the accompanying immunologically-specific lysis of these cells led to the prediction that the CNS would be virus-free after the animal had recovered from encephalitis. However, BDV infectivity and antigen persist for the lifetime of the animal. It appeared, therefore, that other neural cells might be hosts for viral replication and provide a reservoir for the virus. Morphological criteria were used to identify astrocytes and Schwann cells which expressed BDV antigens in vivo. Borna disease virus (BDV) infected astrocytes were identified by double labeling tissue sections with combined cell-specific and BDV-specific antibodies in an avidin-biotin immunocytochemical assay. Examination of serial I micrometer-thick cryosections of hippocampus and sciatic nerve preparations revealed several cells that expressed both glial and BDV antigens. Infectious virus was recovered from cultures of Schwann cells from infected rats. Borna disease virus-infected glial elements persisted beyond the period of inflammation and massive neuronal destruction, and represented a major class of infected cells during chronic disease.

Animals↗
PubMed1989

Preliminary studies on the biology of Borna disease virus.

Borna disease virus (BDV) is an unclassified agent that causes neurological disease in a wide range of animal species and possibly in humans. The infectious nature of BDV has been long established but, despite extensive progress on the pathogenesis of the infection, the aetiological agent is still uncharacterized. Recent studies have shown that BDV replicates productively in cultures of foetal rabbit glial cells (FRG) which produce a virus-specific protein that is easily detected immunocytochemically. This provides a marker for BDV infectivity. This cell culture system was used to investigate the replication cycle of BDV. The agent required at least 1 h to bind to and penetrate the cells and the antigen was detected 24 h later. Cycloheximide and actinomycin D inhibited production of the antigen in inoculated cells, indicating that both protein synthesis and a DNA-dependent function were required for the production of viral antigen. Cocultivation of BDV-infected FRG cells with Vero cells resulted in a persistent productive infection in the latter. Use of these cells showed that the infectious agent matured exclusively in the cytoplasm and within the plasma membrane of the cell. Antigen-laden nuclei did not have infectivity. These studies showed that BDV has the physical and replicative properties typical of conventional viruses but its mechanism of replication and site of morphogenesis may be unique.

Animals↗