The role of human immunodeficiency virus type 1 envelope glycoproteins in virus infection.
Explore the source record for details and available documents.
CD4 Antigens↗
Biomedical subjects
M A Martin
Publications and source records attributed to M A Martin.
Rapid induction of apoptosis by cell-to-cell transmission of human immunodeficiency virus type 1.
The kinetics of human immunodeficiency virus type 1 (HIV-1)-induced cell death were investigated in cell-to-cell and cell-free models of virus transmission. Cocultivation of HIV-1 chronically infected H9 donor cells with uninfected H9 recipient cells resulted in rapid induction of programmed cell death. Within 8 h, apoptotic chromatin condensation was identified by histologic staining. In addition, many single cells with apoptotic nuclei were observed, indicating that stable cell fusion was not a requirement for apoptosis to occur. By 12 to 18 h of coculture, a DNA fragmentation ladder characteristic of apoptosis was detected by agarose gel electrophoresis. Quantitation of apoptosis by measurement of nuclear DNA content revealed that at least 20 to 30% of the nuclei were undergoing apoptosis by 24 h after cocultivation. The appearance of condensed nuclei and fragmented DNA occurred as HIV reverse transcription was completed, and it was not inhibited by zidovudine, suggesting that induction of apoptosis did not require new HIV replication. Soluble CD4 inhibited apoptosis, demonstrating that Env-CD4 interactions were required for apoptosis. In contrast to that in cell-to-cell transmission, apoptosis in cell-free HIV infections was markedly inefficient and was not observed until 70 to 90 h after infections were initiated. These findings indicate that HIV-1 induction of programmed destruction of the nucleus is initiated at the time of cell-cell cocultivation by a mechanism which requires CD4-Env interactions but not new HIV replication.
Acquired Immunodeficiency Syndrome↗
p6Gag is required for particle production from full-length human immunodeficiency virus type 1 molecular clones expressing protease.
The human immunodeficiency virus type 1 (HIV-1) Gag protein precursor, Pr55Gag, contains at its C-terminal end a proline-rich, 6-kDa domain designated p6. Two functions have been proposed for p6: incorporation of the HIV-1 accessory protein Vpr into virus particles and virus particle production. To characterize the role of p6 in the HIV-1 life cycle and to map functional domains within p6, we introduced a number of nonsense and single and multiple amino acid substitution mutations into p6. Following the introduction of the mutations into the full-length HIV-1 molecular clone pNL4-3, the effects on Gag protein expression and processing, virus particle production, and virus infectivity were analyzed. The production of mutant virus particles was also examined by transmission electron microscopy. The results indicate that (i) p6 is required for efficient virus particle production from a full-length HIV-1 molecular clone; (ii) a Pro-Thr-Ala-Pro sequence, located between residues 7 and 10 of p6, is critical for virus particle production; (iii) mutations outside the Pro-Thr-Ala-Pro motif have little or no effect on virus assembly and release; (iv) the p6 defect is manifested at a late stage in the budding process; and (v) mutations in p6 that severely reduce virion production in HeLa cells also block or significantly delay the establishment of a productive infection in the CEM (12D-7) T-cell line. We further demonstrate that mutational inactivation of the viral protease reverses the p6 defect, suggesting a functional linkage between p6 and the proteolytic processing of the Gag precursor protein during the budding of progeny virions.
Amino Acid Sequence↗
Multiple effects of mutations in human immunodeficiency virus type 1 integrase on viral replication.
The integration of a DNA copy of the human immunodeficiency virus type 1 (HIV-1) genome into a chromosome of an infected cell is a pivotal step in virus replication. Integration requires the activity of the virus-encoded integrase, which enters the cell as a component of the virion. Results of numerous mutagenesis studies have identified amino acid residues and protein domains of HIV-1 integrase critical for in vitro activity, but only a few of these mutants have been studied for their effects on HIV replication. We have introduced site-directed changes into an infectious DNA clone of HIV-1 and show that integrase mutations can affect virus replication at a variety of steps. We identified mutations that altered virion morphology, levels of particle-associated integrase and reverse transcriptase, and viral DNA synthesis. One replication-defective mutant virus which had normal morphology and protein composition displayed increased levels of circular viral DNA following infection of a T-cell line. This virus also had a significant titer in a CD4-positive indicator cell assay, which requires the viral Tat protein. Although unintegrated viral DNA can serve as a template for Tat expression in infected indicator cells, this level of expression is insufficient to support a spreading viral infection in CD4-positive lymphocytes.
Base Sequence↗
Integration is required for productive infection of monocyte-derived macrophages by human immunodeficiency virus type 1.
Certain human immunodeficiency virus type 1 (HIV-1) isolates are able to productively infect nondividing cells of the monocyte/macrophage lineage. We have used a molecular genetic approach to construct two different HIV-1 integrase mutants that were studied in the context of an infectious, macrophage-tropic HIV-1 molecular clone. One mutant, HIV-1 delta D(35)E, containing a 37-residue deletion within the central, catalytic domain of integrase, was noninfectious in both peripheral blood mononuclear cells and monocyte-derived macrophages. The HIV-1 delta D(35)E mutant, however, exhibited defects in the assembly and/or release of progeny virions in transient transfection assays, as well as defects in entry and/or viral DNA synthesis during the early stages of monocyte-derived macrophage infection. The second mutant, HIV-1D116N/8, containing a single Asp-to-Asn substitution at the invariant Asp-116 residue of integrase, was also noninfectious in both peripheral blood mononuclear cells and monocyte-derived macrophages but, in contrast to HIV-1 delta D(35)E, was indistinguishable from wild-type virus in reverse transcriptase production. PCR analysis indicated that HIV-1D116N/8 entered monocyte-derived macrophages efficiently and reverse transcribed its RNA but was unable to complete its replication cycle because of a presumed block to integration. These data are consistent with the hypothesis that integration is an obligate step in productive HIV-1 infection of activated peripheral blood mononuclear cells and primary human macrophage cultures.
Amino Acid Sequence↗
Staphylococcus aureus septic arthritis in patients on hemodialysis treatment.
We retrospectively reviewed hospital discharge diagnoses of septic arthritis over an 11-year period (1982 through 1992) at 3 medical centers; 11 episodes of septic arthritis were identified in patients on hemodialysis treatment. Of the 11 episodes, 9 were caused by Staphylococcus aureus; in 8 of 9, the blood cultures were positive for the organism and the infection was monoarticular. Concurrent infection of the dialysis access site occurred in 4 cases. Two patients died (22%). We postulate that repeated skin trauma and contact with health care personnel and facilities result in a high rate of nasal carriage of S aureus and, hence, an increased risk of bacteremia with its attendant complications such as septic arthritis. The use of mupirocin nasal ointment is reported to eradicate or suppress carriage in a high percentage of patients; some studies report that long-term suppressive therapy reduces the frequency of S aureus bacteremia.
Administration, Intranasal↗
The AIDS epidemic: 'it ain't over yet'.
Explore the source record for details and available documents.
Acquired Immunodeficiency Syndrome↗
Amino acid substitutions in the human immunodeficiency virus type 1 gp120 V3 loop that change viral tropism also alter physical and functional properties of the virion envelope.
The third variable (V3) region within the gp120 envelope glycoprotein of the human immunodeficiency virus type 1 (HIV-1) has been reported to be an important determinant of viral tropism. In this study a series of isogenic recombinant HIV-1 viruses, containing V3 regions from fresh isolates, were examined to ascertain if a relationship exists between viral tropism and specific properties of the virion-associated envelope. All of the viruses were able to infect CD4+ primary lymphocytes, although with different infection kinetics. Several recombinants, however, were unable to infect a continuous CD4+ T-cell line permissive for the parental virus and exhibited a marked decrease in the kinetics of virion-associated gp120 binding to a soluble form of CD4. A known macrophage-tropic HIV-1 isolate, also unable to infect the T-cell line, bound CD4 with similarly slow reaction kinetics. Although the inability to infect T-cell lines is a commonly observed property of macrophage-tropic isolates of HIV-1, the loss of T-cell line tropism by the V3 recombinants was not accompanied by a substantial infectivity for monocyte-derived macrophages, as monitored by reverse transcriptase production. Additional analyses of the recombinant virion gp120s indicated that most of the V3 substitutions increased the inherent stability of the virion gp120-gp41 envelope complex. These results indicate that V3-induced alterations in viral tropism are associated with changes in physical and functional properties of the virion envelope.
Amino Acid Sequence↗
Lectin reactivities as intermediate biomarkers in premalignant colorectal epithelium.
Normal colonic epithelial cells undergo maturation as they traverse the crypt to the lumenal surface. The binding of lectins to goblet cell mucins and other glycoconjugates changes as the cells migrate and differentiate. Additional stepwise modifications in glycoconjugate expression occur in premalignant and malignant neoplasms that may be detected by lectin binding studies. The lectins Dolichos biflorus agglutinin (DBA) and soybean agglutinin (SBA) have been developed as markers of differentiation in normal-appearing colonic epithelium. Using a quantitative biometric system to score tissues, reduced levels of lectin binding have been found in rectal tissue from patients with familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer. The lectin Amaranthus caudatus agglutinin (ACA) binds to a cytoplasmic glycoconjugate expressed at the base of the colonic crypt and serves as a possible proliferation marker in the distal, but not proximal, colon. ACA binding increases in tandem with increased levels of proliferation (using BrdU incorporation) in neoplastic tissues. Binding by the peanut lectin (PNA) occurs late in the adenoma-to-carcinoma sequence--in larger adenomas and in cancers--and serves as a marker of advancing neoplasia. Lectins identify the stepwise changes that occur during normal differentiation, proliferation and in advancing neoplasia. By selecting the appropriate probe, biomarkers may be developed for early, intermediate, and late events in colorectal cancer.
Biomarkers↗
Molecular characterization of a polymerase mutant human immunodeficiency virus.
Explore the source record for details and available documents.
Amino Acid Sequence↗
Kinetics of HIV-1 interactions with sCD4 and CD4+ cells: implications for inhibition of virus infection and initial steps of virus entry into cells.
The mechanisms of human immunodeficiency virus (HIV-1) entry into CD4+ cells and HIV-1 inactivation by sCD4 were studied by analyzing the kinetics of inhibition of viral infection by sCD4 and the kinetics of fusion of CD4+ cells with intact virions labeled with the lipid fluorophore octadecylrhodamine (R18). sCD4 inhibited HIV-1 infection much more effectively when preincubated with virus prior to interaction with CD4+ cells than when mixed simultaneously with virions and cells. The kinetics of inhibition of infection was much slower at 4 degrees and at low sCD4 concentrations than at 37 degrees and at high sCD4 concentrations. In the absence of sCD4, attachment of virus to cells leading to productive infection occurred within 10-30 min. Fusion of the virions with cells started after a 1-2 min lag time and was complete within 15 min. In high-density cell suspensions (5 x 10(7) cells/ml), even very high sCD4 concentrations (100 micrograms/ml) failed to block viral infection during simultaneous mixing of cells, sCD4 and HIV-1. We conclude that the kinetics of sCD4-virus interaction and the competition of sCD4 with the cell surface associated CD4 for the virus are crucial factors in the inhibition of HIV-1 infection by sCD4. These results provide insight into mechanisms of viral penetration into cells and should be considered when designing new approaches for AIDS therapy.
Binding, Competitive↗
Antiendotoxin monoclonal antibodies for gram-negative sepsis: guidelines from the IDSA.
Explore the source record for details and available documents.
Antibodies, Monoclonal↗
Gram-negative sepsis and the adult respiratory distress syndrome.
Gram-negative sepsis has dramatically increased in frequency throughout the twentieth century in the United States. Currently, approximately 200,000 patients develop gram-negative sepsis each year in this country. Of these, about one-quarter develop the adult respiratory distress syndrome (ARDS). Among these critically ill patients, mortality is estimated at 60%-90%. In the complex series of events leading to acute lung injury in gram-negative sepsis, endotoxin is the proximal mediator. Although endotoxin may be capable of causing direct injury to the pulmonary endothelium, its primary role is as a trigger activating inflammatory agents, including complement, neutrophils, and platelets, and inducing the production of cytokines and arachidonic acid metabolites. The end results are impairment of the endothelial barrier, diffusely increased capillary permeability, and adherence of neutrophils to the endothelium with subsequent migration into the tissues. The consequent clinical syndrome is one of acute respiratory distress with pulmonary edema, poorly compliant lungs, and refractory hypoxemia. Endothelial injury often becomes widespread, leading to the failure of multiple organs, including the kidneys, brain, intestine, and liver. Conventional therapy consists of supplemental oxygen, positive end-expiratory pressure, inotropic agents, fluid management, and antibiotics aimed at the offending pathogen. Recent discoveries regarding the mediators of sepsis as well as the expansion of the biotechnological armamentarium have provided clinicians with a plethora of new tools with which to manipulate the host's inflammatory response. The challenge for the next decade will be to ensure the safety, efficacy, and cost-effective use of these expensive but potentially lifesaving immunomodulators, singly or in combination, as adjuvant therapy.
Endotoxins↗
Evaluation of the integrity of the blood-brain barrier after meningeal trauma.
RATIONALE AND OBJECTIVES: The authors used magnetic resonance imaging (MRI) techniques to examine the effect of meningeal trauma produced by cisterna magna puncture on the integrity of the blood-cerebrospinal fluid barrier (BCB) in a rat model. METHODS: Intravenous gadolinium-DTPA (Gd-DTPA), a relaxation rate modifier which normally does not cross the BCB, was used as a probe to follow leakage of fluid across the BCB. After Gd-DTPA injection, cerebrospinal fluid (CSF) serial samples were obtained through the needle used to create the experimental trauma. These samples were subsequently examined in vitro by MRI to obtain their T1 relaxation rates and assayed by mass spectrometry for gadolinium and elemental iron concentrations. RESULTS: The iron levels reflected the severity of puncture-related subarachnoid hemorrhage. Rats with ongoing meningeal damage showed significantly higher CSF levels of gadolinium and significantly higher CSF T1 relaxation rates than controls at all samples times over 1 hour after the puncture. Blood in the CSF could not explain these changes because the CSF iron levels did not significantly differ from control levels. CONCLUSIONS: Intravenously administered Gd-DTPA can gain access to the subarachnoid space through minor defects in the BCB and cause significant increases in CSF T1 relaxation rates.
Animals↗
Human immunodeficiency virus type 1 Vpu protein regulates the formation of intracellular gp160-CD4 complexes.
Intracellular transport and processing of the human immunodeficiency virus type 1 (HIV-1) envelope precursor glycoprotein, gp160, proceeds via the endoplasmic reticulum and Golgi complex and involves proteolytic processing of gp160 into the mature virion components, gp120 and gp41. We found that coexpression of gp160 and human CD4 in HeLa cells severely impaired gp120 production due to the formation of intracellular gp160-CD4 complexes. This CD4-mediated inhibition of gp160 processing was alleviated by coexpression of the HIV-1-encoded Vpu protein. The coexpression of Vpu and CD4 in the presence of gp160 resulted in increased degradation of CD4. Although the precise mechanism(s) responsible for the Vpu effect is presently unclear, our findings suggest that Vpu may destabilize intracellular gp160-CD4 complexes.
CD4 Antigens↗
Human immunodeficiency virus type 1 Vpu protein induces rapid degradation of CD4.
CD4 is an integral membrane glycoprotein which is known as the human immunodeficiency virus (HIV) receptor for infection of human cells. The protein is synthesized in the endoplasmic reticulum (ER) and subsequently transported to the cell surface via the Golgi complex. HIV infection of CD4+ cells leads to downmodulation of cell surface CD4, due at least in part to the formation of stable intracellular complexes between CD4 and the HIV type 1 (HIV-1) Env precursor polyprotein gp160. This process "traps" both proteins in the ER, leading to reduced surface expression of CD4 and reduced processing of gp160 to gp120 and gp41. We have recently demonstrated that the presence of the HIV-1-encoded integral membrane protein Vpu can reduce the formation of Env-CD4 complexes, resulting in increased gp160 processing and decreased CD4 stability. We have studied the effect of Vpu on CD4 stability and found that Vpu induces rapid degradation of CD4, reducing the half-life of CD4 from 6 h to 12 min. By using a CD4-binding mutant of gp160, we were able to show that this Vpu-induced degradation of CD4 requires retention of CD4 in the ER, which is normally accomplished through its binding to gp160. The involvement of gp160 in the induction of CD4 degradation is restricted to its function as a CD4 trap, since, in the absence of Env, an ER retention mutant of CD4, as well as wild-type CD4 in cultures treated with brefeldin A, a drug that blocks transport of proteins from the ER, is degraded in the presence of Vpu.
Antiviral Agents↗
Functional characterization of a U5 ribozyme: intracellular suppression of human immunodeficiency virus type 1 expression.
We have designed a ribozyme that cleaves human immunodeficiency virus type 1 (HIV-1) RNA in U5 (at nucleotide +115). This ribozyme was tested in vitro and was found to give efficient and specific digestion of RNA containing the HIV-1 U5 sequence. When the U5 ribozyme was placed into the HIV-1 genome, virus replication was suppressed in tissue culture. Introduction of this ribozyme into cells by using an amphotropic retrovirus vector significantly reduced expression of U5-containing RNA in cells chronically infected with HIV-1. Naive T cells were cocultivated with packaging cells that produce defective amphotropic retroviruses containing the U5 ribozyme. These lymphocytes were found to be partially protected from HIV-1 infection.
Base Sequence↗
A comparison of the effectiveness of three regimens in the prevention of Pneumocystis carinii pneumonia in human immunodeficiency virus-infected patients.
BACKGROUND: Pneumocystis carinii pneumonia (PCP) is a major cause of morbidity and the leading cause of death in patients with the acquired immunodeficiency syndrome. The prevention of the occurrence and recurrence of PCP is a cornerstone in the treatment of patients infected with the human immunodeficiency virus. There are few studies comparing PCP prophylactic regimens. METHODS: The efficacy of three regimens for prophylaxis against PCP was assessed in a retrospective chart review of 211 human immunodeficiency virus-infected patients at risk for the disease. Over the course of the 2-year study period, 133 patients were prescribed trimethoprim-sulfamethoxazole (one double-strength tablet twice a day, thrice weekly) for a mean of 7.4 months (range, 1 to 25 months). Seventy-seven patients received dapsone (50 mg daily) for a mean of 5.7 months (range, 1 to 23 months), and 125 patients received aerosolized pentamidine (300 mg via nebulizer once monthly) for a mean of 9.3 months (range, 1 to 21 months). The majority of patients (62%) received primary prophylaxis; 38% had one or more previous episodes of PCP; and 73% were receiving concomitant antiretroviral therapy. RESULTS: Pneumocystis carinii pneumonia did not develop in any patient receiving trimethoprim-sulfamethoxazole in 981 patient-months. Five patients receiving dapsone for 437 patient-months and 17 patients receiving aerosolized pentamidine for 1166 patient-months developed PCP. Fifty-six percent of the trimethoprim-sulfamethoxazole group and 55% of the dapsone group changed drug due to adverse reactions, while only 2% in the aerosolized pentamidine group required drug change. CONCLUSION: Despite its adverse reaction profile, trimethoprim-sulfamethoxazole is the most effective agent to prevent the occurrence and recurrence of PCP.
Acquired Immunodeficiency Syndrome↗