Chimeric simian/human immunodeficiency virus that causes progressive loss of CD4+ T cells and AIDS in pig-tailed macaques

By animal-to-animal passage of simian/human immunodeficiency virus (SHIV) in pig-tailed macaques, we have developed a macaque model of human immunodeficiency virus type 1 (HIV-1) disease in humans. Passaging was begun with a chimeric virus containing the env gene of HIV-1 HXBc2 and the gag and pol genes of simian immunodeficiency virus SIVmac239. SHIV was passaged serially in cohorts of two macaques each, using bone marrow-to-bone marrow transfers at 5, 5, and 16 weeks for passages 2, 3, and 4, respectively. The fifth passage was done by using cell-free virus isolated from cerebrospinal fluid of a passage 4 macaque. The virus became more virulent with each passage. Virus replication was restricted in all three animals in passages 1 and 2 but not in five of the six animals in passages 3, 4, and 5. In these animals, intense virus replication in the lymphoid tissues resulted in almost total elimination of CD4+ T cells within weeks of inoculation, and three of these animals developed AIDS in less than 1 year. The more uniform virus-host interaction initiated by the cell-free virus in the passage 5 animals contrasted with a more variable pattern of disease initiated by infectious bone marrow cells during earlier passages. The virulent cell-free SHIV can now be used to screen the efficacy of vaccines directed against the envelope of HIV-1.

Lymphocyte-tropic simian immunodeficiency virus causes persistent infection in the brains of rhesus monkeys

Molecularly cloned SIVmac239 is the prototypical SIVmac lymphocyte-tropic virus that replicates productively in lymphocytes but poorly in macrophages. In macaques, the virus causes activation and productive infection of T lymphocytes which invade the central nervous system (CNS) early after infection in the animal. However, infected animals develop immunosuppression and AIDS but rarely overt neurological disease. In this study, we examined multiple regions of the brain and spinal cord for the presence of SIV env sequences and histological lesions in five macaques that had been infected with SIVmac239 for 1.7 to 2.25 years. Histopathological examination of the brain revealed no lesions consistent with encephalitis; however, viral DNA was found in all five brains. In one animal the virus caused infection in a widely disseminated pattern from the frontal cortex to the distal end of the spinal cord, whereas in the other four animals infection in the CNS occurred in a nonspecific, focal pattern. Sequence analyses were performed on gp120 sequences isolated from selected regions of the CNS and compared to gp120 sequences isolated from corresponding lymph nodes, a tissue known to support productive replication of SIVmac239. Examination of the viral sequences from the CNS tissue from two animals (macaques 10F and 14F) revealed a low mutation rate when compared to the sequences isolated from the lymph node tissues. The percentage change in the amino acid sequence was approximately 1% for CNS clones versus > or = 3% for clones isolated from the lymph node. The majority of the CNS viral sequences of macaques 10F and 14F had none of the genetic markers shown in a previous study to be associated with macrophage-tropic variants and indeed retained a nucleotide sequence of similar to the original lymphocyte-tropic virus used for inoculation despite almost 2 years of persistent infection in the animals. Construction of chimeric viruses with V1-V5 regions of selected macaque 10F and macaque 14F CNS-gp120 clones confirmed the predicted lymphocyte-tropic nature of these env genes. In contrast, the gp120 sequences isolated from the CNS tissue of one of the other three animals (macaque 13F) had a mutation rate comparable to that observed for the lymph node clones. The CNS clones from this animal had amino acid substitutions that were previously shown to be associated with macrophage tropism. Compared to the chimeric viruses constructed with V1-V5 sequences from macaques 10F and 14F, viruses constructed with the V1-V5 sequences of several macaque 13F brain clones did not yield infectious virus.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaction of virion protein Vpr of human immunodeficiency virus type 1 with cellular transcription factor Sp1 and trans-activation of viral long terminal repeat

Acquired immunodeficiency syndrome (AIDS) is a result of replication of the human immunodeficiency virus type 1 (HIV-1) predominantly in CD4+ T lymphocytes and macrophages. However, most of these cells in vivo are immunologically quiescent, a condition restricting HIV-1 replication. Vpr is an HIV-1 virion protein suspected to enhance HIV-1 replication in vivo. We demonstrate in this report that Vpr specifically activates HIV-1 long terminal repeat (LTR)-directed transcription. This effect is most pronounced on a minimal promoter from HIV-1 LTR containing the TATA box and binding motifs for the ubiquitous cellular transcription factor Sp1. Evidence is presented that Vpr interacts with Sp1 when Sp1 is bound to the Sp1 motifs within the HIV-1 LTR Both Vpr-Sp1 interaction and Vpr trans-activation require a central Leu/Ile-rich domain in Vpr. Our findings suggest that Vpr trans-activation through Sp1 is most critical for the immediate early transcription of HIV-1 when other positive regulators, such as NF-kappa B, are limited or inactive, a condition presumably present in vivo. By interacting with Sp1, Vpr also has the potential to influence cellular gene expression and cellular functions. Thus, therapeutic approaches directed toward blocking the Vpr trans-activation function could prove valuable in treating AIDS.

Force Fluctuations in Bead Packs

Experimental observations and numerical simulations of the large force inhomogeneities present in stationary bead packs are presented. Forces much larger than the mean occurred but were exponentially rare. An exactly soluble model reproduced many aspects of the experiments and simulations. In this model, the fluctuations in the force distribution arise because of variations in the contact angles and the constraints imposed by the force balance on each bead in the pile.

Early appearance of antibodies to simian immunodeficiency virus in saliva and serum of infected macaques

Simian immunodeficiency virus (SIV) infection in macaques is an important animal model for human immunodeficiency virus infection in humans. This study evaluated the temporal development of antibodies to SIV in the parotid saliva of macaques inoculated with the virus and compared these findings with the development of antibodies to SIV in the animals' sera. Three animals (ages, 14, 18, and 18 years) were inoculated with the macrophagetropic strain SIVmac239. Prior to inoculation and at consecutive weekly intervals during a four-week period following the initial virus inoculations, parotid saliva and serum were collected from each animal. A fourth animal (age, 9 years) served as a negative control, and the fifth and sixth animals (ages, 2 and 22 years) served as positive controls (6 and 18 months postinoculation, respectively) with SIVmac239. Saliva and serum samples were reacted against SIV antigen in Western blots (immunoblots) prepared in the standard fashion to determine the presence of antibodies. The reactions of these antigen-antibody complexes with biotinylated anti-human immunoglobulin A (IgA), IgM, and IgG and biotinylated anti-human secretory component (SC) determined the class of antibody present or the presence of SC in the original parotid saliva or serum samples. In infected animals, the IgM to SIV was detectable in serum and saliva at 13 days, and antiviral IgA and IgG in serum and saliva were detectable at 20 to 27 days postinoculation. The antibody to SC reacted to saliva from only two animals at 20 and 27 days, and long-term positive controls were positive for SC in saliva, indicating that either secretory IgA or secretory IgM was present in these samples. Antibodies to SIVmac239 antigens have therefore been detected in saliva as early as 13 days postinfection. Saliva may be as useful as serum as a diagnostic specimen and/or disease-monitoring method in this important animal model.

Pathogenesis of lymphocyte-tropic and macrophage-tropic SIVmac infection in the brain

SIVmac239 replicates productivity in activated CD4+ T lymphocytes, but inefficiently in macrophages from rhesus macrophages. Inoculation of the virus into animals results in an acute, highly productive burst of virus replication in activated T lymphocytes in lymphoid tissues and infected cells invade the central nervous system (CNS). This phase lasts a few weeks and is eventually followed by development of immunosuppression of different degrees of severity, opportunistic infections, and tumors related to the loss of T lymphocytes. On rare occasions, infected immunosuppressed animals develop encephalitis and/or interstitial pneumonia, syndromes that are associated with selection of mutant viruses that replicate efficiently in macrophages of these tissues. Usually, however, brains of animals dying with AIDS caused by SIVmac239 appear histologically normal. Is the brain infected with virus? We report here on a macaque dying with AIDS, a neuroinvasive tumor and interstitial pneumonia associated with macrophage-tropic virus. Except for focal infiltration of tumor cells, the brain was normal histologically. We examined the virus and viral DNA from different tissues and found that lymphocytes but not macrophages from lymph nodes and spleen yielded virus, whereas macrophages but not lymphocytes from the lung produced virus. No virus was recovered from the brain but small amounts of viral p27 were present in the brain homogenate. Viral sequences were present in the brain as determined by PCR from tissue DNA. Comparison showed that the viral sequences in the brain closely resembled those from the spleen. Presumably, the virus caused a minimally productive infection detectable by production of small amounts of p27, but was not accompanied by any histopathological changes. It is unclear why the macrophage-tropic virus in the lung failed to 'take-off' in the brain of this animal. To determine whether this virus had encephalitic potential, we inoculated the lung homogenate containing cell-free, macrophage tropic virus into a young pigtail macaque, a species known to be sensitive to primate lentiviral infections. This animal developed severe encephalitis 10 weeks later. Virus from the brain was very similar to the inoculum virus, proving its encephalitic potential. Possible reasons for the differences in neurovirulence of this virus between the two animals remain speculative.

Simian immunodeficiency virus SIVmac chimeric virus whose env gene was derived from SIV-encephalitic brain is macrophage-tropic but not neurovirulent

We inoculated four rhesus macaques with molecularly cloned simian immunodeficiency virus SIVmac239/17E env, a chimeric virus whose env gene was derived from the brain of an SIV-encephalitic macaque. Blood and lymphoid tissues had high frequencies of infected cells. The virus was neuroinvasive, but productive virus replication did not occur in the brain, and animals did not develop encephalitis.

The proteins of lymphocyte- and macrophage-tropic strains of simian immunodeficiency virus are processed differently in macrophages

Since the pathogenesis of SIVmac disease complex is thought to be explained by the tropism of the infecting virus for either CD4+ T-lymphocytes or macrophages or both types of cells, we compared the infection in primary macaque macrophages with molecularly cloned, lymphocyte-tropic SIVmac239 and a cloned, macrophage-tropic chimeric virus (SIVmac239/17E) whose env gene was derived from brain of a macaque (17E) dying from SIV-induced encephalopathy. SIVmac239/17E caused a productive, syncytial cytopathic infection accompanied by accumulation of virus particles within cytoplasmic vesicles of the macrophages. Pulse-chase and immune precipitation studies showed that both the viral glycoprotein precursor (gp160) and the gag precursor (p57) were cleaved into gp120 and p27, respectively, and both were released into the culture medium of infected cells, although most of the p27 remained cell associated. SIVmac239 also infected macrophages, but in comparison to SIVmac239/17E, minimal virus replication occurred. Immunocytostaining revealed that while occasional syncytia were observed in cultures, the majority of the infected cells were not associated with syncytium formation. Ultrastructural studies did not reveal the accumulation of virions within infected macrophages. Pulse-chase studies showed that both gp160 and p57 were produced but were cleaved inefficiently and only minimal amounts of gp120 and p27 were released into the culture medium, even after prolonged incubation times. The processing of proteins of the two viruses was indistinguishable in lymphocytes. Since these two viruses are identical except for changes within the env gene, these results indicate that efficient assembly and release of SIV from blood-derived macrophages is mediated by changes in the envelope glycoprotein.

Induction of protection against Borna disease by inoculation with high-dose-attenuated Borna disease virus

Borna disease is a chronic neurological disease caused by an enveloped negative-strand RNA virus (BDV). Experimental disease can be reproduced in rats with brain homogenates derived from infected animals or with virus derived from infected cells in culture. The virus replicates in cultured cells without evidence of cytopathic effect or production of significant levels of cell-free virus. Borna disease is caused by an immunopathological response to viral infection of neural cells. To further investigate the pathogenesis of Borna disease, rats were inoculated with different doses of BDV attenuated by culture in MDCK cells. Low doses of attenuated BDV (10(2)-10(4) TCID50) resulted in typical clinical disease and severe encephalitis; however, the lag period between inoculation and disease was considerably longer than that with virulent BDV. In contrast, animals inoculated with a high dose of attenuated BDV (10(5)-10(6) TCID50) did not develop clinical disease, although a mild encephalitic response was present that did not progress beyond the mild encephalitis. Animals inoculated with a high dose of BDV developed high titers of anti-BDV antibody and were protected against virulent challenge. Protection was correlated with the rapid induction of an immune response in the animals and the lack of any biologically detectable virus in the CNS.

Biochemical mechanism of HIV-1 Vpr function. Oligomerization mediated by the N-terminal domain

The human immunodeficiency virus, type 1 (HIV-1) genome encodes a 15-kDa accessory gene product, Vpr, that is essential for virus replication in primary monocytes/macrophages. Being present in the virion, Vpr is believed to function in the early phases of HIV-1 replication, including nuclear migration of the pre-integration complex and/or transcription of the provirus genome. By gel filtration analysis of highly purified Vpr protein and its mutants, we demonstrate that HIV-1 Vpr exists as an oligomer. The N-terminal domain of Vpr (amino acids (aa) 1-42) is sufficient for oligomerization; however, deletion of aa 36-76 from Vpr disrupts oligomerization, suggesting that aa 36-42 are critical for Vpr oligomerization. As a result of Vpr oligomerization, basic aa residues within Vpr aa 1-73 are highly resistant to trypsin digestion, while those within Vpr aa 74-96 are easily accessible. Mutations within the leucine-/isoleucine-rich domain (aa 60-81), which was previously identified to be involved in Vpr interaction with a host cellular protein, rendered Arg62 more susceptible to trypsin digestion. Thus, the Vpr oligomeric structure must be extended into this domain. These results suggest a novel feature of HIV-1 Vpr that may be important for its functions.

Intracerebral infusion of TNF-alpha and IL-6 failed to activate latent SIV infection in the brains of macaques inoculated with macrophage-tropic neuroadapted SIVmac

Lymphocyte-tropic (L-tropic) SIVmac predictably causes immunosuppression and AIDS in rhesus macaques. SIV encephalitis, on the other hand, is caused mainly by macrophage-tropic (M-tropic) SIVmac. We have previously described the derivation of M-tropic, neuroadapted SIVmac from molecularly cloned, L-tropic SIVmac239. In this report we show that inoculation of four macaques with neuroadapted virus resulted in L-tropic SIVmac-related diseases in all four but neurological disease in only two of the four animals. Because cocultivation of infected macrophages with CD4+ lymphocytes results in production of tumor necrosis factor alpha and interleukin-6, we asked whether infiltration of supernatant fluids containing these cytokines into the brains of macaques infected with neuroadapted virus would enhance the development of neurological disease. These procedures failed to promote productive virus replication in the brain. Thus, although different degrees of immunosuppression and AIDS could be induced predictably with L-tropic virus, induction of neurological disease was not predictable even when animals were inoculated with neuroadapted M-tropic virus and inflammatory cytokines were infiltrated into the brains of these animals.

Biochemical mechanism of HIV-I Vpr function. Specific interaction with a cellular protein

vpr is an accessory gene of human immunodeficiency virus I (HIV-I). Although unnecessary for viral replication in T cell lines, growing evidence suggests that it is essential for virus replication in monocytes/macrophages and for replication in vivo. We expressed HIV-I vpr in Escherichia coli and purified Vpr by affinity chromatography. In a coprecipitation assay, the purified Vpr interacted specifically with a cellular protein designated as Vpr-interacting protein, or RIP. Mutational analysis suggested that this interaction required a domain rich in leucine/isoleucine residues and highly conserved between HIV-I and SIVmac Vprs. During transient expression in mammalian cells, HIV-I Vpr was localized in the nucleus. However, mutational analysis failed to identify in Vpr a typical nuclear localization signal rich in basic amino acid residues. Instead, Vpr nuclear localization seemed to correlate with Vpr interaction with RIP. Mutations in the C-terminal 20-amino acid region containing a cryptic nuclear localization signal did not abolish Vpr nuclear localization or interaction with RIP, whereas point mutations in the leucine/isoleucine-rich domain abolished Vpr interaction with RIP and rendered Vpr unstable during transient expression. These results suggest that RIP may be involved in Vpr function.

Development of transgenic sheep that express the visna virus envelope gene

The ovine lentiviruses cause encephalitis, pneumonia, and arthritis in sheep worldwide. Visna virus is a prototype of this family and the pathogenesis and molecular biology of the virus has been well characterized. The envelope proteins of visna virus are responsible for binding of virus to host cells and for causing cell fusion. The surface glycoprotein also elicits cellular and humoral immune responses to the virus, the former being thought to be responsible for eliminating infected cells as well as causing inflammatory lesions. In this study, transgenic sheep were constructed that expressed the envelope genes of visna virus under the control of the visna LTR to investigate the role of the env gene in the pathogenesis of lentiviral disease in its natural host. Three transgenic lambs were identified that contain the env transgene and express the envelope glycoproteins. These transgenic animals have remained healthy and expression of the viral gene has had no obvious deleterious effect. Expression of the visna envelope protein was demonstrated by cell fusion mediated by the envelope gene as well as by immunoprecipitation of the envelope proteins with monoclonal antibodies and immunofluorescence analyses of Env protein in cells. The target cell for visna virus replication in infected animals is the monocyte/macrophage. In natural infection, the level of viral gene expression in these cells increases with cell maturation. In the transgenic sheep, monocytes did not express the envelope glycoproteins until they differentiated into macrophages in vitro. Expression of the env mRNA in macrophages was quantitated by an RNase protection assay. In addition to expression in macrophages, the transgene was expressed by fibroblasts isolated from skin of the transgenic sheep. Expression of both the Env and Rev proteins was detected by immunoprecipitation and immunofluorescence. Two of the three lambs responded immunologically to the expression of the transgene by producing binding antibodies to the envelope glycoproteins. Thus, these transgenic sheep provide a model to study whether a lentivirus glycoprotein will prevent infection or modulate disease in its natural host after virus challenge.

Pathogenesis of SIVmac infection in Chinese and Indian rhesus macaques: effects of splenectomy on virus burden

The spleen and lymph nodes are the predominant sites of viral replication in SIV and HIV infections. We studied splenectomized and control unsplenectomized rhesus macaques of both the Indian and the Chinese subspecies of Macaca mulatta. All animals were inoculated with SIVmac239, a molecularly cloned strain of SIV. Our data showed: (1) splenectomized animals, particularly among the Indian subspecies, had a lower virus burden and longer survival than unsplenectomized controls, (2) the Chinese macaques controlled virus replication more effectively than did the Indian animals, and (3) that a higher infectious virus burden was present in LN/spleen than in blood in both splenectomized and control animals.

Borna disease virus-specific T cells protect against or cause immunopathological Borna disease

In this report we show that passive immunization of Lewis rats with viable CD4+, Borna disease virus (BDV)-specific T cells before infection with BDV resulted in protection against BD, whereas inoculation of these T cells after BDV infection induced clinical disease with more rapid onset than seen in BDV control animals. The protective as well as encephalitogenic effector functions of BDV-specific CD4+ T cells were mediated only by viable BDV-specific T cells. The protective situation was obtained by passive transfer of BDV-specific T cells into animals inoculated later with virus, whereas the immunopathological situation was observed when virus-specific T cells developed normally or after adoptive transfer, and appeared on the scene after considerable virus replication in the brain.

Early activation of PBMC and appearance of antiviral CD8+ cells influence the prognosis of SIV-induced disease in rhesus macaques

We studied 15 macaques inoculated with SIV and identified three phases of infection. Phase 1 was characterized by activated lymphocytes in blood and infected cells in the CSF. In phase 2, activated cells were not detected but virus was recovered from mitogen-stimulated PBMC, while in phase 3, virus was recovered from mitogen-stimulated PBMC only after depletion of CD8+ lymphocytes, indicating effective control of the virus in peripheral blood. Early development of phase 3 status correlated with a longer period of clinical normalcy.

Simian immunodeficiency virus SIVsmmPBj 1.9 induces multinucleated giant cell formation in human peripheral blood monocytes

SIVsmmPBJ 1.9 is an extremely virulent clone of the simian immunodeficiency virus SIVsmmPBj 14 that causes an acute lethal disease in pigtail macaques, with death occurring 6 to 8 days after infection. The disease is characterized by bloody mucoid diarrhea, lymphoid hyperplasia, and giant cell pneumonia. We have developed an in vitro model for the production of multinucleated giant cells (MGCs) in which peripheral blood monocytes rapidly fuse to form MGCs when cultured in lymphocyte-conditioned medium and antibody against class II MHC. We have tested the effect of SIVsmmPBj on monocytes in our MGC model system. Peripheral blood mononuclear cells (PBMCs) from normal healthy human subjects, when cultured in the presence of anti-class II MHC monoclonal antibody and SIVsmmPBj 1.9, but not either alone, resulted in the formation of MGCs within 4 days. Experiments using Transwell chambers indicated that such MGCs are formed by fusion of monocytes, not by virus-induced fusion of lymphocytes. SIVsmmPBj 1.9 is unique in inducing MGC formation in that other SIV and HIV isolates do not induce MGCs. Whereas SIVsmmPBj 1.9 grown in PBMCs was a potent inducer of MGCs in the presence of anti-class II MHC antibody, SIVsmmPBj 1.9 grown in CEMx174 failed to do so. Antibodies against IFN-gamma and TNF-alpha significantly inhibited SIVsmmPBj/anti-class II-induced formation of MGCs. These results indicate that cytokines released in response to SIVsmmPBj 1.9, in conjunction with antibodies to class II MHC, caused fusion of monocytes.

A gene expression vector useful for protein purification and studies of protein-protein interaction

This report describes the development of a gene expression vector that adds three features to the C-terminus of the putative synthesized protein: (1) a protein kinase A recognition domain allowing the protein to be radio-labeled in vitro, (2) an epitope marker for immunocharacterization of the protein with a commercial monoclonal antibody, and (3) a (His)6 block facilitating purification of the protein by metal chelating affinity chromatography. These features make it convenient to perform biochemical and functional analysis of the protein of interest.