Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.49 (reverse transcriptase)
31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mononuclear phagocytes can be infected with the human immunodeficiency virus type 1 (HIV-1). Although these cells express CD4 antigen, which is the recognized cellular receptor for HIV, additional cell surface proteins such as the Fc receptor, might serve as receptors for infection. In order to study this possibility we used the U937 monocytic cell line as a target for HIV infection. Flow cytometry of U937 showed that 97% of cells expressed CD4, 33% expressed the high affinity 72 kD Fc receptor (FcRI), and 74% expressed the low-affinity 40 kD Fc receptor (FcRII). Virus neutralization tests were performed by preincubating heat-inactivated human anti-HIV sera with HIV-1, IIIB strain, and then challenging U937. After 13 days in culture, productive HIV-1 infection was monitored by reverse transcriptase activity. High concentrations of certain sera (10(-1)-10(-3) dilutions) neutralized HIV-1, but at subneutralizing concentrations (10(-4)-10(-6) dilutions), five of these sera enhanced viral infection approximately two- to threefold. This enhancement of HIV-1 infection was totally blocked by 1 microgram/ml recombinant soluble CD4 (rCD4) or by 0.5 microgram/ml anti-CD4 Leu3a monoclonal antibody. These results suggest that serum enhancement of HIV-1 infection, thought to be due to binding to the monocyte Fc receptor, requires HIV-1 binding to CD4, since rCD4 or Leu3a blocked this phenomenon.
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PMID:Inhibition of serum-enhanced HIV-1 infection of U937 monocytoid cells by recombinant soluble CD4 and anti-CD4 monoclonal antibody. 236 Oct 75

Human immunodeficiency virus (HIV) infection was studied by means of CD4-expressing human-murine T-cell hybrids, containing a variable amount of human chromosomes. Fusion of the HPRT- murine cell line BW5147 with human T-cell acute lymphoblastic leukemia or normal human blood cells resulted in a panel of human-murine T-cell hybrids. For this study, we used four hybrids containing all or several human chromosomes, which all expressed the CD4 antigen, as assessed by different anti-CD4 monoclonal antibodies (e.g., OKT4A, Leu-3a, and MT151) and, in addition, a variable number of other human T-cell antigens. For infection, HTLV-IIIB-infected H9 cells, pretreated with mitomycin C, and cell-free concentrated supernatants from these cells were used. In cells of inoculated cultures of the CD4+ T-cell hybrids, no viral antigen could be demonstrated. Culture supernatants of inoculated hybrids, except for an initial rise due to the virus inoculum, never showed reverse transcriptase activity above background. Cocultivation of these cell cultures with H9 cells did not result in detectable virus replication. Cocultivation of CD4-expressing hybrid cells with HIV-infected cells did not result in syncytium formation. Moreover, these hybrids were resistent to infection with vesicular stomatitis virus (VSV)-HIV pseudotypes. These findings imply that expression of the CD4 antigen on the cell surface is not sufficient for productive infection with HIV. The infectivity block observed in these hybrids seems to occur at the level of virus penetration, presumably at the stage of membrane fusion events.
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PMID:Human immunodeficiency virus infection studied in CD4-expressing human-murine T-cell hybrids. 246 72

The addition of monosialoganglioside GM1 to serum-free culture medium efficiently and specifically inhibited CD4 antigen expression on normal T lymphocytes from peripheral blood or thymus as well as on cells from H9 and Molt-3 lines; other molecules such as CD3, CD2 and CD8 were not affected. Subsequent addition of fetal calf serum or bovine and human serum albumin blocked GM1 action on CD4 expression, most likely through the formation of ganglioside-albumin complexes. Removal of GM1 from the medium was followed by the prompt reappearance of CD4 on the cell surface. GM1 treatment of H9 and Molt-3 cells greatly reduced HIV-1 infectivity, which was evaluated by reverse transcriptase activity levels in culture supernatants and p24 detection on target cells. GM1 also inhibited syncytial formation in Molt-3 cells even when treatment was initiated 24h after infection. The GM1 effect on HIV-1 infectivity, however, was not long-lasting since removal of the compound was followed by a rapid increase in viral replication, probably due to CD4 re-expression and HIV-1 propagation from a few initially infected cells.
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PMID:CD4 modulation and inhibition of HIV-1 infectivity induced by monosialoganglioside GM1 in vitro. 247 63

Cell lines originally derived from malignant tumours of the brain were infected by diverse human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2) isolates. By surface immunofluorescence it was shown that susceptible cells did not bear the CD4 antigen. They were also non-permissive for the formation of plaques by vesicular stomatitis virus pseudotypes and did not form syncytia with HIV-producing cells. Virus production was of low titre, and reverse transcriptase and the p24 antigen were consistently undetectable in the culture supernatants. Output virus could be detected by cocultivation with a sensitive T cell line, C8166, by the culture of supernatant medium with T cells and by detection of proviral HIV DNA after amplification. A higher multiplicity of input virus was required to establish a brain cell infection than was required for T lymphocytes or monocytes. Some HIV-susceptible brain cells contained mRNA for CD4 but infection was not blocked by anti-CD4 antibodies. Apparently HIV infection of these cells does not involve CD4 as the cellular receptor.
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PMID:Infection of brain cells by diverse human immunodeficiency virus isolates: role of CD4 as receptor. 267 35

The expression of CD4 antigen on the surface of LeuM3-positive human blood monocytes was found to be variable with 65 to 90% of cells from 46 normal human volunteers being positive by dual staining flow cytometry. When monocytes adhered to plastic (but not when cultured on Teflon), a marked decrease in CD4 expression was observed between 1 and 24 h post-adherence. CD4 expression could not be detected in macrophages adhered to plastic for 5 days by using four anti-CD4 monoclonal antibodies in flow cytometry or direct immunofluorescence. Conversely an increasing proportion of adherent cells expressed LeuM3 and OKM5 surface antigens over the 5 days. CD4 mRNA levels were measured by slot-blot and Northern hybridization, and total cellular CD4 protein levels by immunoprecipitation. Both cellular mRNA and CD4 levels remained constant throughout the 5 day period but membrane CD4 protein levels were greatly reduced indicating that the down-regulation of CD4 was post-translational. Infection with two of six fresh human immunodeficiency virus (HIV) isolates showed different kinetic patterns when tested on purified monocytes recently adhered to plastic and macrophages adherent for 5 days. HIV antigen and reverse transcriptase levels in infected monocyte cultures remained high for 3 to 4 weeks before detachment and necrosis of the cells occurred. Infection of macrophages generated much lower levels of antigen and reverse transcriptase which declined to very low or undetectable levels over 2 weeks, leaving persisting viable macrophages. One week after infection HIV nucleic acid was detected in 69 +/- 7% of monocytes and 6 +/- 3% of macrophages by in situ hybridization. Blocking experiments with anti-Leu3a monoclonal antibody suggested that HIV infection of 5 day adherent macrophages occurred mainly by a mechanism other than binding to CD4.
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PMID:Variations in CD4 expression by human monocytes and macrophages and their relationships to infection with the human immunodeficiency virus. 267 36

The effect of 3'-azido-2',3'-dideoxythymidine (AZT) on the human immunodeficiency virus (HIV)-associated giant cell formation was studied in vitro. For this purpose we developed a coculture system using Molt-4 and its virus-producing cell, Molt-4/HTLV-III, which induced syncytia very efficiently. Treatment of the cocultures with 1 and 5 microM of AZT did not inhibit induction of multinucleated giant cells, although only 0.1 microM AZT resulted in almost complete inhibition of HIV replication in Molt-4 cells by cell-free virus infection. This was also evidenced by the assays for viral antigen-positive cells, reverse transcriptase activity, and virus particles released from cell cultures after AZT treatment. When the cocultures were treated with 1% neutralizing antibody (NA) from HIV-infected individuals alone, giant cell formation was inhibited to some extent. However, the concomitant treatment of culture with AZT and NA resulted in much stronger inhibition of giant cell formation. The amount of CD4 antigens on the surface of cells was reduced greatly in the HIV producer cells (Molt-4, H9, and MT-4 cells) as compared to their HIV-free counterparts. These data suggest that (1) both CD4 antigen and viral antigens on the surface of cells play central roles in the induction of multinucleated giant cells and (2) AZT is more effective in inhibition of viral spread in patients with higher NA, probably at an earlier stage of the disease than in patients with lower NA titer.
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PMID:Effect of 3'-azido-2',3'-dideoxythymidine (AZT) and neutralizing antibody on human immunodeficiency virus (HIV)-induced cytopathic effects: implication of giant cell formation for the spread of virus in vivo. 311 Oct 83

We have examined for synergy between the IIIB strain of HIV-1 and Epstein-Barr virus (EBV) during infection of a homogeneous cell type. In order to obtain a cell population consisting of a homogeneous cell type, CD19-positive B lymphocytes were purified from human tonsils by flow cytometry. CD19-positive lymphocytes did not express detectable surface CD4 antigen. However, CD4 mRNA could be detected in CD19-positive lymphocytes by reverse transcription coupled to polymerase chain reaction and by dot blot hybridization using an antisense riboprobe. Transcription of CD4 mRNA in CD19-positive lymphocytes was suppressed by infection with the B95-8 strain of EBV and lost in B95-8-transformed lymphoblastoid cell lines. In contrast, the P3HR-1K strain of EBV had no effect on the level of CD4 mRNA. HIV-1 could infect CD19-sorted B cells as measured by accumulation of reverse transcriptase and syncytia induction after coculture with SupT1 cells. HIV-1 infection of CD19-bearing lymphocytes was blocked by OKT4a antibodies. The ability of HIV-1 to replicate in CD19-positive B lymphocytes declined following preinfection with B95-8 but not with P3HR-1K. These results as well as results with an EBNA-2 expression vector suggest that down-regulation of both CD4 mRNA and HIV-1 infection in human B cells is a function of EBV nuclear antigen EBNA-2. The fact that native CD19-positive B lymphocytes express sufficient CD4 receptor mRNA to allow HIV-1 infection strengthens the possibility that HIV-1 replication in B cells directly participates in AIDS pathogenesis. In addition, infection with EBV may modulate the ability of HIV-1 to infect and establish a latent infection in B lymphocytes in co-infected individuals.
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PMID:CD4 mRNA expression in CD19-positive B cells and its suppression by the Epstein-Barr virus. 750 84

Recent data on the phenotype of nef-defective HIV-1 in vitro indicate a new function of the Nef gene product: enhancement of viral infectivity. Single-cycle replication studies have suggested that Nef enhances the efficiency of an early step during viral replication, a step that leads to the establishment of viral DNA. To test this interpretation, the accumulation of low-molecular-weight (unintegrated) viral DNA was measured in cells following exposure to wild-type and nef-defective viruses. nef-defective virus accumulated less DNA than the wild type. This difference was observed after as little as 5 hr of exposure to virus. However, the reverse transcriptase activities of wild-type and nef-defective viruses were equal when measured in cell-free assays using either exogenous or endogenous templates. In addition, the abilities of these viruses to bind and enter cells were not significantly different. Together, these data suggest that Nef optimizes postentry events that are required for efficient synthesis of viral DNA. To determine if these effects were related to the property of Nef-mediated downregulation of CD4, growth curves of these viruses were determined using cells that express a CD4 molecule unable to respond to Nef. nef-defective virus remained attenuated in these cells, indicating that Nef-mediated downregulation of CD4 is not required for Nef-mediated enhancement of viral propagation in vitro.
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PMID:The growth advantage conferred by HIV-1 nef is determined at the level of viral DNA formation and is independent of CD4 downregulation. 757 14

In the present study, the expression of the CD4 molecule on murine egg plasma membrane was confirmed by the indirect immunofluorescence (IIF) method. The full-length CD4 cDNA from murine eggs was synthesised by the reverse transcriptase-polymerase chain reaction (RT-PCR) method and its authenticity verified by Southern blot hybridisation using an end-labelled internal oligonucleotide. The results of DNA sequencing showed that the nucleotide sequence of the cDNA of CD4 from murine egg mRNA was identical to that of immune T cells. To demonstrate the direct interaction of CD4 from murine egg with murine sperm cells bearing MHC (major histocompatibility complex) class II molecule, we employed a baculovirus expression system to generate CD4 on the surface of Spodoptera frugiperda (Sf9) cells. Expression of CD4 on Sf9 cells infected with Autographa californica nuclear polyhedrosis virus (AcNPV)-CD4 was demonstrated by IIF and immunoblotting. The CD4-expressing Sf9 cells adhered to MHC class II-bearing sperm cells since the adhesion was specifically blocked by anti-CD4 monoclonal antibody (mAb) or anti-monomorphic region of MHC class II mAb. Taking our previous and present experimental results together, they strongly suggest that intercellular membrane adhesion between two gametes at the fusion step in fertilisation is mediated by the MHC class II molecule located on the posterior region of the sperm head and the CD4 molecule on egg plasma membrane.
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PMID:Molecular structure and function of CD4 on murine egg plasma membrane. 761 76

Infection of adherent primary monocytes with HIV-1Ba-L is significantly suppressed in the presence of human saliva. By reverse transcriptase (RT) levels, saliva, although present for only 1 h during monocyte viral exposure, inhibited HIV-1 infectivity for 3 wk after infection, whereas human plasma and synovial fluid failed to inhibit HIV-1 infectivity. Antiviral activity was identified in the saliva soluble fraction, and to determine the factor(s) responsible, individual saliva proteins were examined. Of those proteins examined, only secretory leukocyte protease inhibitor (SLPI) was found to possess anti-HIV-1 activity at physiological concentrations. SLPI anti-HIV-1 activity was dose dependent, with maximal inhibition at 1-10 micrograms/ml (> 90% inhibition of RT activity). SLPI also partially inhibited HIV-1IIIB infection in proliferating human T cells. SLPI appears to target a host cell-associated molecule, since no interaction with viral proteins could be demonstrated. However, SLPI anti-HIV-1 activity was not due to direct interaction with or downregulation of the CD4 antigen. Partial depletion of SLPI in whole saliva resulted in decreased anti-HIV-1 activity of saliva. These data indicate that SLPI has antiretroviral activity and may contribute to the important antiviral activity of saliva associated with the infrequent oral transmission of HIV-1.
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PMID:Secretory leukocyte protease inhibitor: a human saliva protein exhibiting anti-human immunodeficiency virus 1 activity in vitro. 761 18


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