Active nuclear import of human immunodeficiency virus type 1 preintegration complexes.

After cell infection by the human immunodeficiency virus type 1 (HIV-1), nascent viral DNA in the form of a high molecular weight nucleoprotein preintegration complex must be transported to the nucleus of the host cell prior to integration of viral DNA with the host genome. The mechanism used by retroviruses for nuclear targeting of preintegration complexes and dependence on cell division has not been established. Our studies show that, after infection, the preintegration complex of HIV-1 was rapidly transported to the nucleus of the host cell by a process that required ATP but was independent of cell division. Functional HIV-1 integrase, an essential component of the preintegration complex, was not required for nuclear import of these complexes. The ability of HIV-1 to use host cell active transport processes for nuclear import of the viral preintegration complex obviates the requirement for host cell division in establishment of the integrated provirus. These findings are pertinent to our understanding of early events in the life cycle of HIV-1 and to the mode of HIV-1 replication in terminally differentiated nondividing cells such as macrophages (monocytes, tissue macrophages, follicular dendritic cells, and microglial cells).

Quiescent T lymphocytes as an inducible virus reservoir in HIV-1 infection.

To better understand the basis for human immunodeficiency virus type 1 (HIV-1) persistence and latency, the form in which viral DNA exists in the peripheral T lymphocyte reservoir of infected individuals was investigated. In asymptomatic individuals, HIV-1 was harbored predominantly as full-length, unintegrated complementary DNA. These extrachromosomal DNA forms retained the ability to integrate upon T cell activation in vitro. In patients with acquired immunodeficiency syndrome (AIDS), there was an increase in integrated relative to extrachromosomal DNA forms. By analysis of DNA from patient lymphocyte subpopulations depleted of human lymphocyte antigen-Dr receptor-positive cells, quiescent T cells were identified as the source of extrachromosomal HIV-1 DNA. Thus quiescent T lymphocytes may be a major and inducible HIV-1 reservoir in infected individuals.

HIV-1 replication is controlled at the level of T cell activation and proviral integration.

During progression of the Acquired Immune Deficiency Syndrome (AIDS), the human immunodeficiency virus type 1 (HIV-1) is harbored in CD4+ T cells, which act as the primary reservoir for the virus. In vitro, HIV-1 requires activated T cells for a productive infection; however, in vivo, the number of circulating T cells in the activated state that are potential targets for HIV-1 infection is low. We have investigated the ability of HIV-1 to infect resting T cells, and the consequences of such an infection. T cell activation was not required for HIV-1 infection; however, viral DNA was unable to integrate in resting T cells and was maintained extrachromosomally. Subsequent T cell activation allowed integration of extrachromosomal forms and led to a productive viral life cycle. Extrachromosomal forms of viral DNA were found to persist for several weeks after infection of resting T cells and, following T cell activation, these forms maintained their ability to integrate and act as a template for infectious virus. Several lines of evidence, including temporal analysis of HIV-1 replication and analysis of an HIV-1 integrase deletion mutant, indicated that extra-chromosomal HIV-1 DNA genomes were transcriptionally active. These results are compatible with a model whereby HIV-1 can persist in a non-productive extra-chromosomal state in resting T cells until subsequent antigen-induced or mitogen-induced T cell activation, virus integration and release. Thus agents that induce T cell activation may control the rate of HIV-1 replication and spread during AIDS progression.

Effect of cyclic AMP and cyclic GMP on the activity of interferon against herpes simplex virus types 1 and 2, and vesicular stomatitis virus.

The antiviral action of interferon (IFN) on herpes simplex virus (HSV) types 1 and 2, and vesicular stomatitis virus (VSV) was examined with respect to the intracellular levels of cyclic adenosine monophosphate (CAMP) and cyclic guanosine monophosphate (CGMP) in human fibroblast (HF) cultures. Interferon by itself increased the intracellular levels of CAMP, but had no effect on the CGMP levels. Inoculation of HF with HSV, however, decreased the CAMP levels. Also, HSV inoculation elevated the CGMP levels, but VSV did not alter the CGMP levels. When HSV and IFN were added to the HF cultures in various combinations, HSV inhibited the IFN-induced elevation of CAMP and increased the CGMP levels to that characteristically observed with HSV inoculation in the absence of IFN. In contrast, IFN antagonized the VSV-associated decrease in CAMP levels. Although the yields of VSV were unaltered by the presence of CAMP- or CGMP-enhancing compounds, the yields of HSV were decreased with CAMP enhancers and increased with CGMP enhancers. the combination of IFN and CAMP enhancers had an additive effect in reducing the yields of HSV. Neither the CAMP or CGMP enhancers affected the action of IFN on VSV. These studies suggest that the interactions observed between HSV and cyclic nucleotides might account for the relatively refractive nature of HSV, as compared to VSV, toward the antiviral activity of IFN.

Combined antiviral effect of interferon and acyclovir on herpes simplex virus types 1 and 2.

Acyclovir and human interferon displayed an additive to synergistic effect in reducing the number of herpes simplex viral plaque-forming units in Vero cells, suggesting a therapeutic potential for such combination therapy.

Cells infected with herpes simplex virus induce human monocyte-macrophages to produce interferon.

Human monocyte-macrophages (MO) produced interferon when incubated with human fibroblast, Vero cell, or rabbit kidney cell cultures infected with herpes simplex virus (HSV). Induction of MO interferon required a 12-hour incubation with the HSV-infected cultures. The interferon produced biologically resembled human leukocyte-derived rather than human fibroblasts-derived interferon.

Interaction between cyclic nucleotides and herpes simplex viruses: productive infection.

Infection of human fibroblasts and HEp-2 cells with herpes simplex virus type 1 (HSV-1) produced a decrease in the intracellular levels of cyclic adenosine 5'- monophosphate (cAMP) and a concomitant increase in the cyclic guanosine 5'- monophosphate (cGMP) levels. In both cell cultures, changes in cyclic nucleotide levels were first observed at 6 h after viral inoculation and were maximal at 12 h. In human fibroblasts, the addition of theophylline, dibutyryl cAMP, or papaverine (cAMP-enhancing compounds) decreased significantly the yield of HSV-1, whereas the addition of insulin or dibutyryl cGMP (cGMP-enhancing compounds) increased the viral yield. In HEp-2 cells, only theophylline decreased the yield of HSV-1, and the cGMP-enhancing compounds had no apparent effect. Cyclic nucleotide enhancing compounds exhibited their effect only if added to either cell culture within the first 3 h after inoculation with HSV-1.

Analysis of baby hamster kidney cells persistently infected with lymphocytic choriomeningitis virus.

Baby hamster kidney cells were persistently infected with lymphocytic choriomeningitis (LCM) virus (BHKpi cells). After 21 passages of the BHKpi cells infectious virus could no longer be detected; however, the cultures continued to produce LCM virus particles which interfered with the replication of infectious LCM virus in BHKpi cells and protected mice from a subsequent intracranial inoculation of infectious LCM virus. Cultures of BHKpi cells appeared to consist of three cell populations: uninfected cells, infected cells containing infectious LCM virus, and infected cells releasing interfering particles of LCM virus.

Comparison of RNA polymerase associated with Newcastle disease virus and a temperature-sensitive mutant of Newcastle disease virus isolated from persistently infected L cells.

An in vitro comparison was made of the RNA polymerase activity associated with Newcastle disease virus (NDVo) and three clones of the temperature-sensitive mutant (NDVpi) isolated from persistently infected L cells. Less polymerase activity was associated with the NDVpi clones. Also, compared to NDVo, an increase in incubation temperature from 32 to 37 or 42 C resulted in a marked decrease in polymerase activity for the temperature-sensitive mutants which coincided with their inability to replicate at 42 C.

Role of interferon in six cell lines persistently infected with rubella virus.

Presistent infections with rubella virus were established in baby hamster kidney, BSC-1, HeLa, RK-13, rabbit embryo chondrocyte, and Vero cell lines. All of the cultures except Vero continually produced rubella virus and interferon to which the virus was sensitive. Concurrently, only the Vero cells did not display interference against superinfection with Newcastle disease and vesicular stomatitis viruses. The addition of 1,000 U of exogenous interferon to the cultures cured only the rabbit embryo and Vero cells of the persistent infection. That the interferon is not required for the initiation and maintenance of rubella viral persistence in vitro is implied by the following. (1) Vero cells were persistently infected in the absence of interferon; (2) actinomycin D or cortisone inhibited interferon synthesis but not the rubella viral infection; and (3) cells continuously cultured in the presence of cortisone maintained a viral persistence without interferon synthesis. On the other hand, interferon seems to be responsible for the viral interference; Vero cells infected with rubella virus and cultures inoculated with rubella virus in the presence of actinomycin D or cortisone did not display interference against Newcastle disease or vesicular stomatitis viruses.

Effect of actinomycin D on the yield of lymphocytic choriomeningitis virus in baby hamster kidney cells.

Depending on the concentration of actinomycin D, the yield of lymphocytic choriomeningitis virus in baby hamster kidney cells was either enhanced or inhibited.

Effect of serum on the yield of lymphocytic choriomeningitis virus in baby hamster kidney cells.

The yields of the Armstrong and WE strains of lymphocytic choriomeningitis virus in baby hamster kidney (BHK) cells cultivated in either bovine, calf, fetal bovine, or horse serum were investigated. Lines of BHK cells were established in these sera. When the infected cell lines were observed by immunofluorescence, the per cent fluorescing cells for a given virus strain did not vary. However, for both strains, the extracellular virus yields per cell were significantly greater in the fetal bovine-cell line than in the other serum-cell lines.