Immune activation and viral burden in acute disease induced by simian immunodeficiency virus SIVsmmPBj14: correlation between in vitro and in vivo events

Immune profiling of pregnant Toxoplasma-infected US and Colombia patients reveals surprising impacts of infection on peripheral blood cytokines

In North America (NA) and Europe, the majority of toxoplasmosis cases are benign and generally asymptomatic, whereas in South America (SA) toxoplasmosis is associated with much more severe symptoms in adults and congenitally infected children. The reasons for these differences remain unknown; currently, there is little information from patients in either region on how the immune system responds to infection with Toxoplasma gondii. Here, we report the relative abundance of 51 serum cytokines from acute and chronic toxoplasmosis cohorts of pregnant women from the United States, where approximately one-half of clinical isolates are Type II, and Colombia, where clinical isolates are generally "atypical" or Type I-like strains. Surprisingly, the results showed notably lower levels of 23 cytokines in acutely infected patients from the United States, relative to uninfected US controls. In acutely infected Colombian patients, however, only 8 cytokine levels differed detectably with 4 being lower and 4 higher relative to uninfected controls. Strikingly, there were also differences in the cytokine profiles of the chronically infected patients relative to uninfected controls in the US cohort. Hence, Toxoplasma appears to specifically impact levels of circulating cytokines, and our results may partly explain region-specific differences in the clinical spectrum of toxoplasmosis.

The cytokine network of acute HIV infection: a promising target for vaccines and therapy to reduce viral set-point?

Cytokines play a central role in the pathogenesis of many diseases, including HIV infection. However, the role of the cytokine network in early HIV infection is only now starting to be elucidated. A number of studies conducted in recent years have indicated that cytokines of the acute/early stages of HIV and SIV infection can impact viral set-point months later, and this is of critical importance since viral set-point during chronic HIV infection affects virus transmission and disease progression. This raises the question whether modulating the cytokine environment during acute/early HIV infection can be a target for novel approaches to develop a vaccine and therapeutics. In this review we focus on the kinetics and function of cytokines during acute HIV and SIV infection and how these may impact viral set-point. We also discuss unresolved questions that are essential for our understanding of the role of acute infection cytokines in HIV infection and that, if answered, may suggest novel therapeutic and vaccine strategies to control the worldwide HIV pandemic.

Mutation of a diacidic motif in SIV-PBj Nef impairs T-cell activation and enteropathic disease

Background

The non-pathogenic course of SIV infection in its natural host is characterized by robust viral replication in the absence of chronic immune activation and T cell proliferation. In contrast, acutely lethal enteropathic SIVsmm strain PBj induces a strong immune activation and causes a severe acute and lethal disease in pig-tailed macaques after cross-species transmission. One important pathogenicity factor of the PBj virus is the PBj-Nef protein, which contains a conserved diacidic motif and, unusually, an immunoreceptor tyrosine-based activation motif (ITAM).

Results

Mutation of the diacidic motif in the Nef protein of the SIVsmmPBj abolishes the acute phenotype of this virus. In vitro, wild-type and mutant PBj (PBj-Nef202/203GG) viruses replicated to similar levels in macaque PBMCs, but PBj-Nef202/203GG no longer triggers ERK mitogen-activated protein (MAP) kinase pathway including an alteration of a Nef-associated Raf-1/ERK-2 multiprotein signaling complex. Moreover, stimulation of IL-2 and down-modulation of CD4 and CD28 were impaired in the mutant virus. Pig-tailed macaques infected with PBj-Nef202/203GG did not show enteropathic complications and lethality as observed with wild-type PBj virus, despite efficient replication of both viruses in vivo. Furthermore, PBj-Nef202/203GG infected animals revealed reduced T-cell activation in periphery lymphoid organs and no detectable induction of IL-2 and IL-6.

Conclusions

In sum, we report here that mutation of the diacidic motif in the PBj-Nef protein abolishes disease progression in pig-tailed macaques despite efficient replication. These data suggest that alterations in the ability of a lentivirus to promote T cell activation and proliferation can have a dramatic impact on its pathogenic potential.

Analysis of Jembrana disease virus replication dynamics in vivo reveals strain variation and atypical responses to infection

Jembrana disease virus (JDV) is an acute lentiviral infection of Bali cattle in Indonesia. Data generated during a series of cattle infection experiments was examined and significant differences were identified in the mean plasma viral load on the first and second days of the febrile response in cattle infected with JDV(TAB/87) compared to those infected with JDV(PUL/01). The peak and total viral loads >or=10(6) genome copies/ml during the acute stage of the disease were significantly higher in JDV(TAB/87) infected cattle. JDV(PUL/01) infected cattle developed peak rectal temperatures earlier than the JDV(TAB/87) cattle but there were no differences in the duration of the febrile responses observed for the 2 groups of animals. The plasma viremia was above 10(6) genome copies/ml for almost 3 days longer in JDV(TAB/87) compared to JDV(PUL/01) infected cattle. Atypical responses to infection occurred in approximately 15% of experimentally infected animals, characterized by reduced viral loads, lower or absent febrile responses and absence of p26-specific antibody responses. Most of these cattle developed normal Tm-specific antibody responses between 4-12 weeks post-infection.

Delayed viral replication and CD4+ T cell depletion in the rectosigmoid mucosa of macaques during primary rectal SIV infection

Rectal infection of macaques by SIV is a model for rectal HIV transmission. We focus here on the digestive tract during days 7-14 of primary rectal infection by SIV in 15 rhesus macaques. Surprisingly, we did not detect productively infected cells in the rectosigmoid colon at early stages of viral dissemination. This strongly suggests that there is no massive viral amplification in the rectosigmoid colon prior to viral dissemination. As dissemination proceeds, productively infected T cells are observed in the rectosigmoid colon and small intestine, with rectosigmoid colon showing the heaviest viral load. Lymphoid follicles are infected prior to lamina propria at both sites. When viral dissemination is widespread, inflammatory infiltrates are visible in the rectosigmoid colon, but not in the small intestine. An important decrease in CD4(+) T cells is then observed in the lamina propria of the rectosigmoid colon only.

Patterns of gene expression in peripheral blood mononuclear cells of rhesus macaques infected with SIVmac251 and exhibiting differential rates of disease progression

Using the Affymetrix HuGeneFL GeneChip, the global expression patterns of genes in the peripheral blood mononuclear cells (PBMCs) of rhesus macaques, infected with SIVmac251 and exhibiting rapid, typical, or slow rates of disease progression, were examined. Assessments of the change in gene expression (fold change), the temporal coordination of gene expression (self-organizing map analysis), and the similarities and significant differences in gene expression across the groups were performed on samples taken before infection and 3 and 7 weeks postinfection. An upregulation of the p27 interferon-inducible gene and of genes associated with cellular activation and immune response was observed in all three groups. Rapidly progressing animals exhibited a modest number of genes with a change in expression of 3-fold or greater, typically progressing animals exhibited the greatest number, and slowly progressing animals exhibited the fewest. Self-organizing map cluster analysis indicated that rapidly progressing animals exhibited the least coordinated gene expression over the three study time points, typically progressing animals exhibited a moderate degree, and animals with slow progression exhibited the most coordinated gene expression. Mann-Whitney U analysis indicated that differences in gene expression were most pronounced between the rapidly and slowly progressing groups and least pronounced between the rapidly and typically progressing animals. These observations elucidate distinct features of gene expression in animals with different rates of disease progression.

Biologic studies of chimeras of highly and moderately virulent molecular clones of simian immunodeficiency virus SIVsmPBj suggest a critical role for envelope in acute AIDS virus pathogenesis

Previous studies identified three molecular clones of the acutely pathogenic SIVsmPBj strain that varied in terms of relative in vivo pathogenicity. One clone, SIVsmPBj6.6, reproducibly induced a rapidly fatal disease in pigtailed macaques. In contrast, a highly related clone (SIVsmPBj6.9) was only minimally pathogenic in macaques. PBj6.6 and PBj6.9 shared a tyrosine substitution at position 17 in the Nef protein that is a major determinant of virulence but differed at one residue in Vpx (C89R), three residues within the envelope (D119G, R871G, G872R), and a single residue in Nef (F252L). SIVsmPBj6.9 was less efficient in inducing proliferation of resting macaque peripheral blood mononuclear cells in vitro than SIVsmPBj6.6 and exhibited a marked reduction in infectivity relative to SIVsmPBj6.6. Chimeric viruses for each of these variable residues were constructed, and their biologic properties were compared to those of the parental strains. Differences in Vpx and Nef did not alter the basic biologic phenotype of the chimeras. However, the D119G substitution in the envelope of SIVsmPBj6.9 was associated with a marked reduction in the infectivity of this virus relative to SIVsmPBj6.6. An associated processing defect in gp160 of SIVsmPBj6.9 and chimeras expressing the D119G substitution suggests that a reduction in virion envelope incorporation is the mechanistic basis for reduced virion infectivity. In vivo studies revealed that substitution of the PBj6.9 amino acid into PBj6.6 (D119) abrogated the pathogenicity of this previously pathogenic virus. Introduction of the PBj6.9 G119, however, did not confer full virulence to the parental PBj6.9 virus, implicating one or all of the other four substitutions in the virulence of SIVsmPBj6.6.

Postinoculation PMPA treatment, but not preinoculation immunomodulatory therapy, protects against development of acute disease induced by the unique simian immunodeficiency virus SIVsmmPBj

The fatal disease induced by SIVsmmPBj4 clinically resembles endotoxic shock, with the development of severe gastrointestinal disease. While the exact mechanism of disease induction has not been fully elucidated, aspects of virus biology suggest that immune activation contributes to pathogenesis. These biological characteristics include induction of peripheral blood mononuclear cell (PBMC) proliferation, upregulation of activation markers and Fas ligand expression, and increased levels of apoptosis. To investigate the role of immune activation and viral replication on disease induction, animals infected with SIVsmmPBj14 were treated with one of two drugs: FK-506, a potent immunosuppressive agent, or PMPA, a potent antiretroviral agent. While PBMC proliferation was blocked in vitro with FK-506, pig-tailed macaques treated preinoculation with FK-506 were not protected from acutely lethal disease. However, these animals did show some evidence of modulation of immune activation, including reduced levels of CD25 antigen and FasL expression, as well as lower tissue viral loads. In contrast, macaques treated postinoculation with PMPA were completely protected from the development of acutely lethal disease. Treatment with PMPA beginning as late as 5 days postinfection was able to prevent the PBj syndrome. Plasma and cellular viral loads in PMPA-treated animals were significantly lower than those in untreated controls. Although PMPA-treated animals showed acute lymphopenia due to SIVsmmPBj14 infection, cell subset levels subsequently recovered and returned to normal. Based upon subsequent CD4(+) cell counts, the results suggest that very early treatment following retroviral infection can have a significant effect on modifying the subsequent course of disease. These results also suggest that viral replication is an important factor involved in PBJ-induced disease. These studies reinforce the idea that the SIVsmmPBj model system is useful for therapy and vaccine testing.

Pathogenicity and comparative evolution in vivo of the transitional quasispecies SIVsmmPBj8

During 14 months of infection of a pig-tailed macaque, the acutely lethal simian immunodeficiency virus SIVsmmPBj14 (SIV-PBj14) evolved from the minimally pathogenic strain SIVsmm9. The virus isolated at 8 months (SIV-PBj8) exhibited properties of both SIVsmm9 and SIV-PBj14, indicating that a phenotypic transition occurred between 6 and 10 months. To assess the influence that this new composition of biologic properties might have on pathogenicity, three pig-tailed macaques were inoculated intravenously with SIV-PBj8. Although no animals developed the severe acute disease syndrome typical of SIV-PBj14, all had high levels of viremia and died of AIDS at 4, 10. 5, and 32 months. Characterization of the SIV-PBj8-derived quasispecies that evolved in these macaques showed that at 4 days after inoculation, viruses from all three animals exhibited in vitro properties different from those of the inoculum. By 4 months, the initial phenotypic profiles had changed, with the quasispecies in plasma from the animal (J90232) that died at this time most closely resembling SIV-PBj14, not SIV-PBj8. Phylogenetic trees of the gp41/Nef region of viruses in 4-month plasma from J90232 revealed three distinct populations with high bootstrap values: one group branched with SIVsmm9, one with SIV-PBj14, and one with SIV-PBj8 (ratio of clones, 5:9:5). Nucleotide sequence analysis suggested that some members of the original SIV-PBj8 quasispecies may have been evolving toward a SIV-PBj14-like genotype at the time macaque J90232 died. The use of SIV-PBj8, which was more pathogenic than SIVsmm9, but less pathogenic than SIV-PBj14, may provide the optimal genetic background on which to identify the minimal, multigenic determinants of the SIV-PBj14 phenotype. The results of our studies on SIV-PBj14 indicate that in some, but not all, cases of primate lentivirus infection more pathogenic variants evolve, selectively proliferate, and more than likely contribute to disease progression.

Virus threshold determines disease in SIVsmmPBj14-infected macaques

Simian immunodeficiency virus (SIV) variant SIVsmmPBj14 is unique in producing an acutely lethal enteropathic syndrome in pigtail macaques. To determine whether the nature of the PBj14 disease would be attenuated by decreasing virus input and to relate tissue virus burden to the severity of disease, we infected pigtail macaques with serial 10-fold doses of SIVsmmPBj14 clone bcl.3 spanning 10(-2) through 10(4)TCID50. The results revealed a strikingly narrow difference between minimum infectious and fatal disease-inducing doses and a close association between enteric lymphoid tissue virus burden and disease. All animals infected with as much as 10(4) TCID50 through as little as 100 TCID50 of virus died of the lethal PBj14 syndrome between 7 and 13 days postinfection. Animals receiving 10(-1) TCID50 became infected (PCR+) but did not develop clinical disease. Animals receiving 10(-2) TCID50 did not become infected. The clinical syndrome was surprisingly similar in all affected macaques, although the time to disease onset and total survival time increased slightly as virus input decreased from 10(4) to 10 degrees TCID50. Highest terminal virus loads in plasma, gut-associated lymphoid tissue (GALT), and lymph nodes and greatest lesion severity were attained at intermediate levels of virus input (10(1) to 10(2) TCID50), probably owing to optimal time for virus amplification in target tissues. The present study reinforces others on the PBj14 system, suggesting that once a threshold level of virus replication is attained in intestinal lymphoid tissues, the cascade of events precipitating the lethal PBj14 syndrome is triggered irreversibly.

In vivo cell and tissue tropism of SIVsmmPBj14-bcl.3

To gain insight into the unique pathogenicity of simian immunodeficiency virus (SIV) variant PBj14, which produces an acutely lethal enteropathic syndrome in infected pigtail macaques, we investigated the cell and tissue tropisms of a highly pathogenic biologic clone (bcl.3) of SIVsmmPBj14. To compare the relative amount of viral antigen in lymphoid organs of infected macaques we used an objective semiquantitative immunohistochemistry (sQIHC) assay. We found that in all animals viral antigen load was greater in alimentary-associated lymphoid tissues (gut-associated lymphoid tissue [GALT], tonsil, mesenteric and retropharyngeal lymph nodes) than in non-alimentary-associated lymphoid tissues (spleen, thymus, inguinal and axillary lymph nodes). Moreover, in six of nine animals examined, virus load in GALT was greater than that in any other lymphoid tissue. To determine whether the acute pathogenicity and prolific replication of SIVsmmPBj14 might be explained by a broader in vivo cell tropism than is typical of SIVs, we used cell subset separation and nested PCR. We found that the primary target cells in mesenteric lymph node for SIVsmmPBj14 were CD4+ T lymphocytes. However, the virus also infected macrophages, as well as CD8+ T cells and B cells, albeit at low frequencies. These results suggest that alimentary lymphoid tissue localization rather than unusual cell phenotype tropism distinguishes the singular pathogenesis of SIVsmmPBj14.

Induction of fas ligand expression by an acutely lethal simian immunodeficiency virus, SIVsmmPBj14

Simian immunodeficiency virus strain PBj14, SIVsmmPBj14, is unique among primate lentiviruses in its ability to trigger the proliferation of resting simian lymphocytes and to cause the rapid death of experimentally inoculated pigtailed macaques. Severe enteropathy, immune activation, and extensive apoptosis, particularly within gut-associated lymphoid tissue, characterize the acute disease syndrome associated with SIVsmmPBj14 infection. In the present study, we examined whether the ability of this virus to cause widespread apoptosis might be linked to the up-regulation of Fas ligand (CD95L) expression in virally infected cells. In vitro studies revealed that expression of the viral Nef protein, in the absence of any other viral gene product, was sufficient to up-regulate the transcriptional activity of the CD95L promoter and to cause cell surface expression of Fas ligand. This up-regulation was NFAT dependent (inhibited by cyclosporin A) and did not occur in cells that expressed a mutated derivative of the viral Nef protein, lacking a previously defined immunoreceptor tyrosine-based activation motif. These findings were corroborated by analysis of tissue sections from virally infected macaques. Immunohistochemical staining revealed that Fas ligand expression was efficiently up-regulated in the GALT of animals that had been experimentally infected with wild-type SIVsmmPBj14 but not in animals that were infected with a nonacutely pathogenic viral mutant lacking the Nef ITAM. Taken together, these results suggest that the ability of SIVsmmPBj14 to cause acutely lethal disease and to up-regulate FasL expression may be linked. Additional studies will be required to determine whether the induction of FasL expression is in itself important for acute disease pathogenesis.

Activation of macrophages and B lymphocytes by an oligodeoxynucleotide derived from an acutely pathogenic simian immunodeficiency virus

Certain CpG-containing DNA sequences from bacteria, viruses, or invertebrates elicit responses in the vertebrate innate immune system. These responses also account for many nonspecific effects of oligodeoxynucleotides used for antisense approaches. Here we describe a sequence from an acutely pathogenic simian immunodeficiency virus (SIV) that induces release of cytokines from macrophages and B lymphocyte proliferation. Furthermore, several similar sequences in other immunodeficiency viruses were found that also activate macrophages. These results led to the question if CpG-containing DNA, which is thought to play an immunostimulatory role in bacterial infections, has a similar role in infections by immunodeficiency viruses.

Endogenous tumor necrosis factor-alpha contributes to lymphoproliferation induced by simian immunodeficiency virus variant, SIVsmmPBj14

The simian immunodeficiency virus (SIV) isolate, SIVsmmPBj14, contains an immunoreceptor tyrosine-based activation motif (ITAM) within its nef gene product and triggers efficient lymphoproliferation in vitro. In experimentally inoculated macaque monkeys, this virus causes acutely lethal enteropathy, which is accompanied by high levels of pro-inflammatory cytokines, including tumor necrosis factor (TNF)-alpha. Since TNF-alpha has been shown to possess weak comitogenic activity for antigen- or mitogen-induced human T-cell proliferation, experiments were conducted to examine whether TNF-alpha might also contribute to SIVsmmPBj14-induced lymphoproliferation. Addition of a dimeric soluble human TNF receptor (sTNFR):Fc fusion protein to SIVsmmPBj14-infected simian peripheral blood mononuclear cells (PBMC) resulted in a partial (> 50%) inhibition of virally-induced lymphoproliferation, but had no effect on the strong T-cell activation signal provided by phytohemagglutinin and interleukin-2. Finally, the addition of exogenous human TNF-alpha to simian PBMC infected with a non-mitogenic variant of SIVsmmPBj14 failed to result in detectable lymphoproliferation, suggesting that TNF-alpha alone is not sufficient to cause the proliferation of SIV infected T-cells. Taken together, the data suggest that endogenous TNF-alpha enhances SIVsmmPBj14-induced lymphoproliferation in simian PBMC cultures.

Costimulatory pathways in lymphocyte proliferation induced by the simian immunodeficiency virus SIVsmmPBj14

The PBj14 isolate of the simian immunodeficiency virus SIVsmmPBj14 is unique among primate lentiviruses in its ability to induce lymphocyte proliferation and acutely lethal disease. The studies reported here show that viral induction of T-cell proliferation requires accessory cells, such as primary monocytes or Raji B-lymphoma cells, as well as the presence of a putative immunoreceptor tyrosine-based activation motif within the viral Nef protein. Addition of CTLA4-immunoglobulin fusion protein or anti-B7 antibodies to virally infected T cells led to substantial, but not complete, inhibition of monocyte-costimulated T-cell proliferation-suggesting that both CD28/B7-dependent and non-CD28-dependent pathways may contribute to the costimulation of virally induced lymphoproliferation. Finally, cyclosporin A, a specific inhibitor of the calcium-calmodulin-regulated phosphatase activity of calcineurin, which influences activation of the transcription factor nuclear factor of activated T cells, was shown to block virally mediated T-cell proliferation. Taken together, these findings suggest that the effect of SIVsmmPBj14 on T-cell activation may be functionally analogous, at least in part, to the effect of engagement of the T-cell receptor.

Simian-human immunodeficiency virus (SHIV) containing the nef/long terminal repeat region of the highly virulent SIVsmmPBj14 causes PBj-like activation of cultured resting peripheral blood mononuclear cells, but the chimera showed No increase in virulence

SIVsmmPBj14 is a highly pathogenic lentivirus which causes acute diarrhea, rash, massive lymphocyte proliferation predominantly in the gastrointestinal tract, and death within 7 to 14 days. In cell culture, the virus has mitogenic effects on resting macaque T lymphocytes. In contrast, SIVmac239 causes AIDS in rhesus macaques, generally within 2 years after inoculation. In a previous study, replacement of amino acid residues 17 and 18 of the Nef protein of SIVmac239 with the corresponding amino acid residues of the Nef protein of SIVsmmPBj14 yielded a PBj-like virus that caused extensive activation of resting T lymphocytes in cultures and acute PBj-like disease when inoculated into pig-tailed macaques. This study suggested that nef played a major role in both processes. In this study, we replaced the nef/long terminal repeat (LTR) region of a nonpathogenic simian-human immunodeficiency virus (SHIV), SHIVPPc, with the corresponding region from SIVsmmPBj14 and examined the biological properties of the resultant virus. Like SIVsmmPBj14, SHIVPPcPBjnef caused massive stimulation of resting peripheral blood mononuclear cells (PBMC), which then produced virus in the absence of extraneous interleukin 2. However, when inoculated into macaques, the virus failed to replicate productively or cause disease. Thus, while these results confirmed that the nef/LTR region of SIVsmmPBj14 played a major role in the activation of resting PBMC, duplication of the cellular activation process in macaques may require a further interaction between nef and the envelope glycoprotein of simian immunodeficiency virus because SHIV, containing the envelope of human immunodeficiency virus type 1, failed to cause activation in vivo.

Structured-tree topology and adaptive evolution of the simian immunodeficiency virus SIVsm envelope during serial passage in rhesus macaques according to likelihood mapping and quartet puzzling

Species-specific strains of simian immunodeficiency virus (SIV) are nonpathogenic in African primates. The SIV strain most closely related to human immunodeficiency virus type 2 (HIV-2) is SIVsm, the strain specific to the sooty mangabey (Cercocebus atys). Infection of Asian primates with SIV causes AIDS and allows the study of the adaptive evolution of a lentivirus to replicate efficiently in a new host, providing a useful animal model of HIV infection and AIDS in humans. Serial passage of SIVsm from sooty mangabeys in rhesus macaques drastically shortened the time of disease progression from 1.5 years to 1 month as the retrovirus adapted to these Asian hosts. In the present study we analyzed the quasispecies nature of the SIVsm envelope gene (env) during serial population passage in rhesus macaques. We asked ourselves if phylogenetic evidence could be provided for the structured topology of the SIVsm env tree and subsequently for the adaptive evolution of SIVsm env. Likelihood mapping showed that phylogenetic reconstruction of the passage was possible because a high percentage of the sequence data had a "tree-like" form. Subsequently, quartet puzzling was used and produced a phylogeny with a structure parallel to the known infection history. The adaptation of SIVsm to Asian rhesus macaques appears to be an ordered process in which the env evolves in a tree-like manner, particularly in its constant regions.

The U3 promoter and the nef gene of simian immunodeficiency virus (SIV) smmPBj1.9 do not confer acute pathogenicity upon SIVagm

Two chimeric proviruses comprising the U3 promoter and the nef gene of simian immunodeficiency virus (SIV) smmPBj1.9 in addition to other genomic regions of SIVagm3mc from African green monkeys (Cercopithecus aethiops) were constructed. The derived chimeric viruses (SIVagm3mc/SIVsmmPBj1.9) were both able to replicate in nonstimulated peripheral blood leukocytes from pig-tailed macaques (Macaca nemestrina), a biological property often correlated with acute pathogenicity. However, only one of the chimeric viruses was acutely pathogenic, inducing a rapid depletion of the peripheral CD4+ T cells in two infected pig-tailed macaques within 10 days after infection in a manner similar to infection with SIVsmmPBj1.9 itself. The other chimeric virus actively replicated during the first 8 weeks after experimental infection of two pig-tailed macaques but induced neither acute disease nor CD4+ T-cell depletion for 113 weeks after infection. Thus, the U3 promoter and the nef gene of SIVsmmPBj1.9 alone appear to be insufficient to confer acute pathogenicity to SIVagm3mc.

Down-modulation of the ZAP-70 protein tyrosine kinase in macaque T lymphocytes infected with SIVsmmPBj14

The simian immunodeficiency virus SIV-PBj14 is the most virulent primate lentivirus identified to date. Other SIV strains, including the parental SIVsmm9, require mitogen-activated peripheral blood mononuclear cells (PBMC) for replication in vitro; however, SIV-PBj14 replicates in quiescent pig-tailed macaque PBMC and induces cellular proliferation, consistent with its in vivo pathogenesis. To identify mechanisms involved in SIV-PBj14-induced T-cell proliferation, kinases important in early T-cell receptor-mediated activation pathways were studied. Immunoblot analyses showed that ZAP-70 protein, a tyrosine kinase, was downregulated, primarily in CD8+ T cells, as early as 30 minutes after in vitro infection of quiescent macaque PBMC with SIV-PBj 14. Furthermore, this downregulation required the presence of either CD4+ T cells or adherent cells or both cell populations. In agreement with the in vitro results, ZAP-70 expression was downregulated in macaque PBMC, spleen, and rectal lymph node cells as early as 2 days after rectal inoculation of pig-tailed macaques with SIV-PBj14. This phenomenon, however, was not observed in cells obtained from distal lymph nodes to which the virus had not disseminated, implying that the presence of SIV-PBj14 is necessary to induce downregulation of ZAP-70.

Severe combined immunodeficient mice engrafted with macaque peripheral blood leukocytes support replication of SIVsmm

Peripheral blood leukocytes (PBLs) from normal pigtail macaques were engrafted into severe combined immunodeficient C.B-17 scid/scid (SCID) mice to develop a small animal model in which to study and identify genetic determinants responsible for the acutely lethal disease syndrome induced by SIVsmmPBj14 (SIV-PBj14) in pigtail macaques. In vivo infection of macaques with SIV-PBj14 results in acute disease in all animals and death of most animals, depending on the route of infection, due to immune activation and production of inflammatory cytokines. A small animal model in which a similar acute disease syndrome was induced would facilitate screening of virus variants to identify regions of the SIV-PBj14 genome responsible for the unique phenotype. Although intraperitoneal inoculation of SCID mice with SIV-PBj14-infected PBLs or uninfected PBLs followed by cell-free SIV-PBj14 produced chimeric mac-PBL-SCID mice that supported SIV replication, obvious clinical signs of disease were not observed. SIV-infected macaque PBLs were recovered from spleen, bone marrow, peripheral blood, and the peritoneal cavity; cell-free SIV was recovered from peritoneal lavage fluid and serum or plasma. PBLs that were mitogen stimulated and SIV-PBj14 infected in vitro migrated rapidly and were recovered from the spleen and bone marrow as early as 1 day after inoculation of mice. The mac-PBL-SCID model may be useful for screening potential drug or immunomodulatory therapies before testing in macaques.

A lymph node-derived cytopathic simian immunodeficiency virus Mne variant replicates in nonstimulated peripheral blood mononuclear cells

Lymph nodes (LNs) are sites of active human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) replication and disease at both early and late stages of infection. Consequently, variant viruses that replicate efficiently and subsequently cause immune dysfunction may be harbored in this tissue. To determine whether LN-associated SIVs have an increased capacity to replicate and induce cytopathology, a molecular clone of SIV was isolated directly from DNA extracted from unpassaged LN tissue of a pig-tailed macaque (Macaca nemestrina) infected with SIVMne. The animal had declining CD4+ T-lymphocyte counts at the time of the LN biopsy. In human CD4+ T-cell lines, the LN-derived virus, SIVMne027, replicated with relatively slow kinetics and was minimally cytopathic and non-syncytium inducing compared to other SIVMne clones. However, in phytohemagglutinin-stimulated pig-tailed macaque peripheral blood mononuclear cells (PBMCs), SIVMne027 replicated efficiently and was highly cytopathic for the CD4+ T-cell population. Interestingly, unlike other SIVMne clones, SIVMne027 also replicated to a high level in nonstimulated macaque PBMCs. High-level replication depended on the presence of both the T-cell and monocyte/macrophage populations and could be enhanced by interleukin-2 (IL-2). Finally, the primary determinant governing the ability of SIVMne027 to replicate in nonstimulated and IL-2-stimulated PBMCs mapped to gag-pol-vif. Together, these data demonstrate that LNs may harbor non-syncytium-inducing, cytopathic viruses that replicate efficiently and are highly responsive to the effects of cytokines such as IL-2.

Detection of simian T cell leukemia virus type I infection in seronegative macaques

Simian species of Asian and African origin are naturally infected with the simian T cell leukemia virus type I (STLV-I). Like the closely related human T cell leukemia virus type I (HTLV-I), STLV-I is primarily cell associated, and typical infections exhibit low viral burdens. Four macaques experimentally inoculated with a new STLV-I strain isolated from a sooty mangabey monkey were examined over extended periods of time for signs of infection by (1) commercial enzyme immunoassay and immunoblot assay for cross-reactive serum antibodies to HTLV-I, (2) commercial HTLV-I p24gag antigen-capture assay on supernatants from cocultures of macaque peripheral blood mononuclear cells (PBMCs) with human PBMCs, and (3) nested PCR amplification of proviral sequences in macaque PBMC DNA. The nested PCR assay was 100% specific and detected a single STLV-I copy in 150,000 PBMCs. In addition, our data show that experimental infection of macaques with STLV-I can be serologically silent for more than 43 months.

Simian immunodeficiency viruses containing mutations in the long terminal repeat NF-kappa B or Sp1 binding sites replicate efficiently in T cells and PHA-stimulated PBMCs

The long terminal repeats (LTRs) of primate lentiviruses contain conserved binding sites for the NF-kappa B and Sp1 cellular transcription factors. In order to study the role that these sites play in simian immunodeficiency virus (SIV) replication, we have introduced mutations that disrupt either the NF-kappa B or Sp1 binding sites in the LTR of an infectious molecular clone of SIVmac239. An additional mutation also disrupted the SF3 transcription factor binding site that overlaps the NF-kappa B site. Viruses containing point mutations or deletions of the NF-kappa B, SF3, or Sp1 binding sites retained the ability to replicate efficiently in the CEMx174 and MT4 cell lines, as well as in PHA-stimulated primary rhesus macaque peripheral blood mononuclear cells (PBMCs). Efficient replication of SIVs mutated in either NF-kappa B or Sp1 binding sites suggests that the SIV LTR promoter contains multiple functionally redundant elements capable of supporting sufficient transcription to allow productive viral replication.

Increased in vitro tetanus-induced production of HIV type 1 following in vivo immunization of HIV type 1-infected individuals with tetanus toxoid

We have previously demonstrated that immunization of HIV-1-infected individuals with the common recall antigen, tetanus, induced transient increases in plasma viremia as well as an increased ability to isolate virus from CD8+ T cell-depleted peripheral blood mononuclear cells (PBMCs) under minimally stimulated culture conditions (IL-2 plus IL-4) postimmunization. In this study, HIV-1-infected individuals were immunized with tetanus toxoid and PBMCs were examined at multiple time points following immunization. Tetanus-induced production of virus was defined as an increased ability to isolate HIV-1 from CD8+ T cell-depleted PBMCs in vitro in the presence of tetanus antigen as opposed to no antigen or control antigen alone. Following immunization, in vitro tetanus-induced production of HIV-1 was observed in 8 of 13 (62%) patients compared to 2 of 13 (15%) patients prior to immunization. In four of these patients, virus could also be isolated from CD8+ T cell-depleted PBMCs in the presence of tetanus without the addition of any exogenous IL-2. Furthermore, virus could be isolated from the unfractionated PBMCs of two patients when tetanus antigen alone was added to the culture in the absence of added PHA or PHA blasts. HIV-1 was isolated predominantly from CD4+ T cells with a CD45RO+, CD25+ phenotype and was associated with a trend to elevated levels in culture supernatants of IFN-gamma, IL-6, TNF-alpha, and IL-4. These findings have important implications with regard to the role of ongoing antigen-specific immune responses in the induction of HIV-1 expression in vivo.

Role of dendritic cells in immunopathogenesis of human immunodeficiency virus infection

The role of dendritic cells (DC) in the pathogenesis of human immunodeficiency virus (HIV) disease has been a subject of considerable interest for several years. Initial studies focused on the infection, dysfunction, and depletion of DC in HIV-infected individuals. More recent studies have begun to identify the functional role of DC in the initiation and propagation of viral replication in T cells in HIV-infected individuals. This review discusses recent data regarding the role of DC in HIV disease with the aim of delineating basic immunopathogenic principles of infection and the development of therapeutic strategies.

Loss of the SIVsmmPBj14 phenotype and nef genotype during long-term survival of macaques infected by mucosal routes

The ability of the simian immunodeficiency virus SIVsmmPBj14 (SIV-PBj14) to activate and induce proliferation of quiescent peripheral blood lymphocytes from macaques is an in vitro correlate of its acutely lethal in vivo phenotype. SIV-PBj14 differs from other SIV strains by encoding tyrosine at amino acid 17 (Y17) in Nef, which generates an activation motif important for signal transduction. Although intravenous inoculation of pig-tailed macaques with SIV-PBj14 uniformly leads to death within 2 weeks, inoculation by mucosal routes results in persistent infections that progress to AIDS. In the present study, we determined whether viruses in long-term survivors retained not only the Nef Y17 residue but also the biologic properties associated with rapid disease-and death. Viruses reisolated at early and late times after mucosal infection of macaques with SIV-PBj14 were tested in vivo for acute lethality and in vitro for the ability to replicate in and induce activation and proliferation of quiescent macaque lymphocytes. In addition, the coding sequence for the first 55 amino acids in Nef was amplified from proviral DNA or plasma virion RNA by PCR or RT-PCR, respectively, and nucleotide sequences were obtained. The results showed that the majority of the quasispecies that persisted as disease progressed not only lost biological properties unique to SIV-PBj14, but also lost through mutation either Y17 or Y28 in Nef, which together were part of the activation motif. In the case of Y17, these mutations were stepwise to histidine then arginine, the amino acid encoded in this position in other SIV strains. We conclude, therefore, that replicative properties of the acutely lethal virus provide no selective advantage during long-term infections with SIV-PBj14 and that disruption of the activation motif in Nef is associated with loss of the acutely lethal phenotype.

Dynamics and modulation of human immunodeficiency virus type 1 transcripts in vitro and in vivo

The dynamics of human immunodeficiency virus type 1 (HIV-1) transcription was analyzed in vitro and in vivo by using a specific molecular approach which allows accurate quantitation of the different classes of viral mRNAs. Unspliced (US) and multiply spliced (MS) HIV-1 transcripts were assayed by competitive reverse transcription (cRT)-PCR, using a single competitor RNA bearing in tandem internally deleted sequences of both template species. Acute HIV-1 infection of primary peripheral blood mononuclear cells (PBMCs), monocytes/macrophages cells, and the A3.01 T-lymphocyte-derived cell line was studied; both classes of HIV-1 mRNAs increased exponentially (r2 > 0.98) at days 1 to 3 and 1 to 4 postinfection in HIV(IIIB)-infected A3.01 cells and PBMCs, respectively, whereas monocytes/macrophages infected with monocytotropic HIV(BaL) exhibited a linear (r2 = 0.81 to 0.94) accumulation of US and MS transcripts. Following induction of chronically infected ACH-2 cells, MS transcripts increased 2 h postinduction and peaked at 5 h (doubling time, 58 min), while at 24 h, US mRNAs increased 3,053-fold compared with basal time (doubling time, 137 min). To address the biopathological significance of HIV-1 expression pattern during infection progression, pilot cross-sectional and longitudinal analyses were carried out with samples from untreated and treated HIV-1-infected patients. In almost all untreated (recently infected, long-term nonprogressor, and progressor) patients, MS transcript levels followed the general trend of systemic HIV-1 activity. In patients under treatment with powerful antiretroviral compounds, viral MS transcripts rapidly fell to undetectable levels, indicating that in vivo, levels of MS mRNAs in PBMCs are closely associated with the number of newly infected cells and suggesting a new role for the quantitative analysis of HIV-1 transcription in infected patients.

Simian immunodeficiency virus infection of CD8+ lymphocytes in vivo

To determine the lymphoid target cells of simian immunodeficiency virus (SIV) in vivo, peripheral blood lymphocytes (PBL) and lymph node lymphocytes (LNL) were positively selected (>97% purity) for surface expression of CD4, CD8, or CD20 and then analyzed for SIV provirus using semiquantitative DNA amplification. We found provirus in CD4+ and CD8+ lymphocytes but none in CD20+ lymphocytes. During acute SIV infection (< or = 214 days postinoculation), the percentage of PBL and LNL CD4+ cells containing proviral DNA ranged from 0.2 to 20% and from 0.2 to 2%, respectively. Proviral burden in the CD8+ population of either PBL or LNL ranged from 0.01 to 0.2%. Virus isolation by cocultivation was positive for both CD4+ and CD8+ purified populations. No difference in proviral burden was observed between PBL and LNL subsets during acute SIV infection. Up to 19.4% of positively selected CD8+ cells also expressed CD4, and thus the provirus may reside within a dual-positive population. This dual-positive population may represent activated lymphocytes that are particularly susceptible to infection and may provide an opportunity for virus entry into the CD8+ CD4- lymphocytes in vivo.

Effect of immunization with a common recall antigen on viral expression in patients infected with human immunodeficiency virus type 1

BACKGROUND

Activation of the immune system is a normal response to antigenic stimulation, and such activation enhances the replication of human immunodeficiency virus type 1 (HIV-1). We studied the effect of immunization with a common recall antigen on viral expression in HIV-1-infected patients, on the ability to isolate virus, and on the susceptibility to HIV-1 infection of peripheral-blood mononuclear cells (PBMCs) from control subjects not infected with HIV-1.

METHODS

Thirteen HIV-1-infected patients and 10 uninfected adults were given a 0.5-ml booster dose of tetanus toxoid. Studies were performed to evaluate changes in the degree of plasma viremia, proviral burden, the ability to isolate HIV-1, and the susceptibility of PBMCs to acute infection in vitro. Two patients underwent sequential lymph-node biopsies for the assessment of viral burden in these tissues.

RESULTS

All 13 HIV-1-infected patients had transient increase in plasma viremia after immunization, and the proviral burden increased in 11. These changes did not correlate with the base-line CD4+ T-cell counts. The lymph-node tissue also had increases in the proviral burden and viral RNA after immunization. The virus was more easily isolated from PBMCs from nine of the patients after immunization than before immunization. Despite considerable variability in the results, PBMCs from 7 of the 10 normal subjects were more easily infected in vitro with HIV-1 after immunization than before immunization.

CONCLUSIONS

Activation of the immune system by an ongoing antigen-specific immune response to an exogenous stimulus transiently increases the expression of HIV-1 and may enhance the susceptibility of uninfected subjects to HIV-1.

Interleukin 1 beta, interleukin 6, tumor necrosis factor alpha, and interleukin 10 responses in peripheral blood mononuclear cells of cynomolgus macaques during acute infection with SIVmac251

HIV infection ultimately leads to AIDS, despite the immune responses elicited soon after infection. In addition to the observed changes in lymphoid cell subsets, alteration of the cytokine network most likely accompanies and/or contributes to the lack of protective immune responses. In an attempt to delineate the early events in the immune response to lentivirus infection, we have sequentially monitored levels of proinflammatory (IL-1 beta, IL-6, and TNF-alpha) and antiinflammatory (IL-10) cytokine mRNAs in PBMCs of cynomolgus macaques during primary SIVmac infection. Eight monkeys were infected i.v. with 4 AID50 of cell-free SIVmac251. All monkeys seroconverted between days 16 and 21 postinfection (p.i.), and had detectable peripheral viremia. The viral load peaked between days 12 and 16 p.i., and fell sharply thereafter. A marked increase in the expression of IL-6 mRNA was observed in all macaques during the first weeks following infection. An increase in the levels of expression of IL-1 beta, TNF-alpha, and IL-10 mRNA was also determined in six, six, and five of the eight monkeys, respectively. While IL-6, TNF-alpha, and IL-10 increased transiently, increased levels of IL-1 beta mRNA expression were sustained over 44 days in most monkeys.

The efficiency of acute infection of CD4+ T cells is markedly enhanced in the setting of antigen-specific immune activation

Human immunodeficiency virus (HIV) disease in sub-Saharan Africa generally differs from that observed in the United States and other developed countries in that the risk of seroconversion after exposure is greater and the rate of disease progression to AIDS and death is faster. One theory that could in part explain this difference is the increased state of immune activation associated with a relatively high rate of parasite infestation and other infections among inhabitants of these regions. Using a model based on the cellular microenvironment of lymphoid organs, the role of exposure to HIV during a state of antigen-specific immune activation was investigated. Dendritic cells and CD4+ T cells are the major cellular components of the paracortical region of lymphoid tissue, the primary site of HIV replication. We analyzed cocultures of HIV-pulsed dendritic cells that had matured in the presence of tetanus toxoid and CD4+ T cells before and after inducing an antigen-specific response by in vivo immunization with tetanus toxoid. During antigen-specific immune activation, 100 times less HIV was needed to initiate a productive infection. These findings provide a model system to further delineate the relationship between immune activation and the propagation of HIV infection and suggest a mechanism for the epidemiologic observations of an increased ease of developing HIV infection and faster progression for HIV disease in geographic areas where immune activation is prevalent.

Simian immunodeficiency virus variants: threat of new lentiviruses

Infection in humans with the lentivirus HIV-1 typically results in the development of a chronic disease state characterized by the slow decline of CD4+ lymphocytes, the development of immunosuppression, and the development of opportunistic infections, ultimately leading to death. Although the average course of disease runs approximately 10 years, shorter and longer progression times have been noted. These alterations are presumed to be, at least partially, a factor of viral variation. The simian immunodeficiency viruses (SIVs) are the nonhuman primate counterparts to HIV. Several of these isolates, including SIV from sooty mangabey monkeys, induce a remarkably similar disease in Asian macaques. Recently, variants of SIV from sooty mangabey monkeys and SIV from African green monkeys have been described, which are increasingly more pathogenic. As in HIV-1 infections, this is probably due to genetic variation. On the basis of these findings, atypical viruses with tremendous pathogenic potential can arise from apathogenic or moderately pathogenic viruses.

AIDS-like disease following mucosal infection of pig-tailed macaques with SIVsmmPBj14

Following exposure of the rectal or vaginal mucosa to cell-free SIVsmmPBj14, four male and two female pig-tailed macaques developed a characteristic acute disease, including mucoid diarrhea, lymphopenia, and anorexia. Two macaques infected by the rectal route died within 14 days, and one female died of an AIDS-like disease at five months after inoculation. The three other animals have survived more than nine months, but all are exhibiting lymphadenopathy, thrombocytopenia, and progressive declines in percentages and numbers of CD4+ lymphocytes.

Molecular and biological analyses of quasispecies during evolution of a virulent simian immunodeficiency virus, SIVsmmPBj14

A prototypic simian immunodeficiency virus (SIVsmm9), isolated from a naturally infected sooty mangabey (Cercocebus atys), was passaged in vivo in a pig-tailed macaque (Macaca nemestrina) having the identifier PBj. When PBj died of a typical AIDS-like syndrome 14 months after infection, the virus isolated from its tissues was subsequently shown to differ from SIVsmm9 genetically and biologically. Most notably, this isolate, SIVsmmPBj14 (SIV-PBj14), is the most virulent primate lentivirus known: it induces acute disease and death within 6 to 10 days after intravenous inoculation into pig-tailed macaques. Between the time of infection with SIVsmm9 and isolation of SIV-PBj14, isolates were obtained periodically from peripheral blood mononuclear cells of PBj. To establish the temporal relationship between evolution of new biologic properties and fixation of specific mutations in the virus population, these sequential SIV-PBj isolates were characterized for unique properties of SIV-PBj14 that appeared to correlate with acute lethal disease. These properties included the ability to replicate in quiescent macaque peripheral blood mononuclear cells, to activate and induce proliferation of CD4+ and CD8+ cells, and to exhibit cytopathicity for mangabey CD4+ lymphocytes. Consistent with earlier studies, a major change in biologic properties occurred between 6 (SIV-PBj6) and 10 (SIV-PBj10) months, with the SIV-PBj8 quasispecies exhibiting properties of both earlier and later isolates. Multiple biologic clones derived from the 6-, 8-, and 10-month isolates also exhibited diverse phenotypes. For example, one SIV-PBj10 biologic clone resembled SIVsmm9 phenotypically, whereas three other biologic clones resembled SIV-PBj14. To evaluate genetic changes, proviral DNA of the biologic clones generated from SIV-PBj6, -PBj8, and -PBj10 was amplified by PCR in the U3 enhancer portion of the long terminal repeats (LTR) and the V1 region of env, where the greatest nucleotide diversity between SIVsmm9 and SIV-PBj14 resided. Nucleotide sequence data indicated that all biologically cloned viruses are distinct and that insertions/duplications of 3 to 27 nucleotides (in multiples of three) had accumulated stepwise in the env V1 region, beginning with SIV-PBj8. In addition, one of four SIV-PBj8 biologic clones had a 22-bp duplication in the LTR which is characteristic of SIV-PBj14. When virus mixtures containing different proportions of two SIV-PBj10 biologic clones with opposite phenotypes were tested, the SIV-PBj14 phenotype was clearly dominant, since mixtures with as few as 10% of the viruses being SIV-PBj14-like exhibited all the properties of the lethal isolate.(ABSTRACT TRUNCATED AT 400 WORDS)

Developing animal models for AIDS research--progress and problems

Tremendous advances in our understanding of the human immunodeficiency viruses (HIVs) have been made through the use of animal models. However, there are limitations inherent in many of the current models that use either nonhuman primates, or viruses other than HIV-1. Researchers continue to search for improved models using small-animal model alternatives and different viruses. Animal models will remain an important tool in our continued search for vaccines and therapeutic agents.

Enhanced responsiveness to nuclear factor kappa B contributes to the unique phenotype of simian immunodeficiency virus variant SIVsmmPBj14

Infection with a variant of simian immunodeficiency virus, SIVsmmPBj14, leads to severe acute disease in macaques. This study was designed to investigate the functional significance of previously described mutations in the viral long terminal repeat (LTR) and to elucidate their contribution to the unique phenotype of SIVsmmPBj14. LTR-directed transcription was measured by using luciferase reporter constructs that were transiently transfected into cultured cells. In a wide range of cell types, the basal transcriptional activity of the LTR from SIVsmmPBj14 was found to be 2- to 4.5-fold higher than that of an LTR from a non-acutely pathogenic strain. These LTRs differ by five point mutations and a 22-bp duplication in SIVsmmPBj14, which includes a nuclear factor kappa B (NF kappa B) site. Transcriptional differences between these LTRs were further enhanced by two- to threefold upon treatment of cells with phorbol ester or tumor necrosis factor alpha or by cotransfection with plasmids expressing NF kappa B subunits. Mutagenesis studies, and the use of a reporter construct containing an enhancerless promoter, indicate that these transcriptional effects are due principally to the 22-bp sequence duplication and the NF kappa B site contained within it. Finally, infectious virus stocks that were isogenic except for the LTR were generated. The LTR from SIVsmmPBj14 was found to confer an increase in the kinetics of virus replication in cultured cells. Inclusion of this LTR in recombinant SIVs also resulted in a two- to threefold rise in the extent of cellular proliferation that was induced in quiescent simian peripheral blood mononuclear cells. These studies are consistent with the hypothesis that LTR mutations assist SIVsmmPBj14 in responding efficiently to cellular stimulation and allow it to replicate to high titers during the acute phase of viral infection.