Infection of rhesus and cynomolgus macaques with a rapidly fatal SIV (SIVSMM/PBj) isolate from sooty mangabeys

Breaking Barriers to an AIDS Model with Macaque-Tropic HIV-1 Derivatives

The development of an animal model of human immunodeficiency virus type 1 (HIV-1)/AIDS that is suitable for preclinical testing of antiretroviral therapy, vaccines, curative strategies, and studies of pathogenesis has been hampered by the human-specific tropism of HIV-1. Although simian immunodeficiency virus (SIV) or HIV-1/SIV chimeric viruses (SHIVs)-rhesus macaque models are excellent surrogates for AIDS research, the genetic differences between SIV or SHIV and HIV-1 limit their utility as model systems. The identification of innate retro viral restriction factors has increased our understanding about blockades to HIV-1 replication in macaques and provided a guide for the construction of macaque-tropic HIV-1 clones. However, while these viruses replicate in macaque cells in vitro, they are easily controlled and have not caused AIDS in host animals, indicating that we may not fully understand the restrictive barriers of innate immunity. In this review, we discuss recent findings regarding HIV-1 restriction factors, particularly as they apply to cross-species transmission of primate lentiviruses and the development of a macaque model of HIV-1/AIDS.

Integrin alpha4beta7 is downregulated on the surfaces of simian immunodeficiency virus SIVmac239-infected cells

Simian immunodeficiency virus (SIV) and human immunodeficiency virus (HIV) infection results in an early and enduring depletion of intestinal CD4(+) T cells. SIV and HIV bind integrin alpha4beta7, thereby facilitating infection of lymphocytes that home to the gut-associated lymphoid tissue (GALT). Using an ex vivo flow cytometry assay, we found that SIVmac239-infected cells expressed significantly lower levels of integrin alpha4beta7 than did uninfected cells. This finding suggested a potential viral effect on integrin alpha4beta7 expression. Using an in vitro model, we confirmed that integrin alpha4beta7 was downregulated on the surfaces of SIVmac239-infected cells. Further, modulation of integrin alpha4beta7 was dependent on de novo synthesis of viral proteins, but neither cell death, the release of a soluble factor, nor a change in activation state was involved. Downregulation of integrin alpha4beta7 may have an unappreciated role in the CD4 depletion of the mucosal-associated lymphoid compartments, susceptibility to superinfection, and/or immune evasion.

HIV/AIDS: in search of an animal model

AIDS is among the most devastating diseases of our time, claiming the lives of approximately 3 million people per year. The primary cause of AIDS, human immunodeficiency virus type 1 (HIV-1), is a pathogen that is highly specific for humans and generally does not infect or cause disease in other species. This property complicates the generation of animal models that are urgently needed to test new antiretroviral therapies and vaccines. The most practical animal models developed to date consist of infection of rhesus macaques with a simian immunodeficiency virus (SIV) or chimeric HIV/SIV viruses. Although these models are useful for particular applications, the fact that SIV is a distinct virus compared with HIV-1 represents a significant limitation to their use. Here, we discuss the uses and limitations of existing models and recent advances that might lead to better animal models for HIV/AIDS.

Classic AIDS in a sooty mangabey after an 18-year natural infection

Prevailing theory holds that simian immunodeficiency virus (SIV) infections are nonpathogenic in their natural simian hosts and that lifelong infections persist without disease. Numerous studies have reported that SIV-infected sooty mangabeys (SMs; Cercocebus atys) remain disease free for up to 24 years despite relatively high levels of viral replication. Here, we report that classic AIDS developed after an 18-year incubation in an SM (E041) with a natural SIVsm infection. Unlike that described in previous reports of SIV-related disease in SMs, the SIVsm infecting E041 was not first passaged through macaques; moreover, SM E041 was simian T-cell leukemia virus antibody negative. SM E041 was euthanized in 2002 after being diagnosed with severe disseminated B-cell lymphoma. The plasma virus load had been approximately the same for 16 years when a 100-fold increase in virus load occurred in years 17 and 18. Additional findings associated with AIDS were CD4(+)-cell decline, loss of p27 core antibody, and loss of control of SIVsm replication with disseminated giant cell disease. These findings suggest that the time to development of AIDS exceeds the average lifetime of SMs in the wild and that the principal adaptation of SIV to its natural African hosts does not include complete resistance to disease. Instead, AIDS may develop slowly, even in the presence of high virus loads. However, a long-term relatively high virus load, such as that in SM E041, is consistent with AIDS development in less than 18 years in humans and macaques. Therefore, the results also suggest that SMs have a special mechanism for resisting AIDS development.

Comparison of SIVmac239(352-382) and SIVsmmPBj41(360-390) enterotoxic synthetic peptides

To characterize the active domain of the simian immunodeficiency virus (SIV) surface unit (SU) enterotoxin, peptides corresponding to the V3 loop of SIVmac239 (SIVmac) and SIVsmmPBj41 (SIVpbj) were synthesized and examined for enterotoxic activity, alpha-helical structure, and interaction(s) with model membranes. SIVmac and SIVpbj induced a dose-dependent diarrhea in 6-8-day-old mouse pups similar to full-length SU. The peptides mobilized [Ca(2+)](i) in HT-29 cells with distinct oscillations and elevated inositol triphosphate levels. Circular dichroism analyses showed the peptides were predominantly random coil in buffer, but increased in alpha-helical content when placed in a hydrophobic environment or with cholesterol-containing membrane vesicles that are rich in anionic phospholipids. None of the peptides underwent significant secondary structural changes in the presence of neutral vesicles indicating ionic interactions were important. These data show that the SIV SU enterotoxic domain localizes in part to the V3 loop region and interacts with anionic membrane domains on the host cell surface.

In vivo inactivation of Nef ITAM motif of chimeric simian/human immunodeficiency virus SHIVsbg-YE correlates with absence of increased virulence in Chinese rhesus macaques

SHIVsbg, expressing Vpu, Tat, Rev, and Env proteins of HIV-1 Lai, was shown to be infectious for rhesus macaques. In this study, we mutated SHIVsbg Nef amino acids 17-18 from RQ to YE, conferring to SHIVsbg-YE the ability to replicate in vitro in unstimulated macaque PBMC. Juvenile macaques inoculated intravenously or orally with SHIVsbg-YE developed persistent infection. All macaques lost weight during the first 17 weeks but recovered afterward. All animals developed a strong HIV-specific humoral immune response. Viruses isolated 2 years postinoculation lost the ability to replicate in unstimulated macaque PBMC. Point mutations or 33-bp-wide deletions in the nef ITAM motif were responsible for this phenotype and correlated with clinical improvement of the infected macaques. These data demonstrate that the ITAM domain is inactivated in animals developing an acute antiviral immune response and may be detrimental to viral replication, perhaps by interfering with other well-conserved functions of SIV Nef protein.

Simian immunodeficiency viruses from multiple lineages infect human macrophages: implications for cross-species transmission

Zoonotic transfer of simian immunodeficiency virus (SIV) from chimpanzees and sooty mangabeys to humans has been documented on at least seven occasions. Several recently identified SIV isolates have also been shown to replicate efficiently in human peripheral blood mononuclear cells (PBMCs) in vitro, indicative of the potential for additional cross-species transmission via T cell infection. Although SIV predominantly uses the macrophage-tropic HIV chemokine coreceptor CCR5, little is known about the ability of SIV to infect human macrophages. In this study, 16 SIV isolates belonging to five different primate lentivirus lineages were tested for their ability to infect human monocyte-derived macrophages (MDMs). Twelve of the viruses were capable of infecting MDMs, and 11 of these were also able to replicate in human PBMCs. The replication capacity of the isolates differed within and between the various families and was dependent on particular donor macrophages. Our results suggest that most simian lentiviruses characterized to date not only have the ability to infect primary human T lymphocytes but also replicate efficiently in macrophages, thereby increasing the potential for cross-species transmission into the human population. Comparative studies using these isolates may facilitate the identification of characteristics that contribute to virus infectivity and pathogenicity.

Species-specific variation in SIV disease progression between Chinese and Indian subspecies of rhesus macaque

The shortage of rhesus macaques of Indian origin for acquired immune deficiency syndrome (AIDS) research has prompted a search for an alternate species. As rhesus macaques of Chinese origin are more readily obtainable, we have defined the parameters of infection in seven members of this subspecies with the primary virulent isolate, SIV/delta B670. Viremic peaks and set points as determined by real time polymerase chain reaction were, in general, lower than that observed in Indian origin rhesus macaques. As expected, these values were associated with maintenance of CD4+ lymphocytes and significantly longer survival, with six of seven Chinese origin animals living significantly longer than Indian origin rhesus macaques. Interestingly, these findings were associated with a selective amplification of one of two major phylogenetic groups found within the inoculum. This observation is in contrast to Indian origin animals where both phylogenetic groups are commonly identified. Together, these data suggest prudence in the design of experimental protocols using rhesus macaques of Chinese origin where survival and rapid loss of CD4+ lymphocytes are desired endpoints.

Simian immunodeficiency virus infection of monkeys as a model system for the study of AIDS pathogenesis, treatment, and prevention

As presented in this review, there are a number of different models of both natural and experimental infection of monkeys with primate lentiviruses. There are numerous different viruses and multiple different monkey species, making for a potentially large number of different combinations. The fact that each different combination of virus isolate and host macaque species may show different behavior underscores the need to understand the different models and their key features. On the one hand, this diversity of systems underscores the need to provide some standardization of the systems used for certain kinds of studies, such as vaccine evaluations, in order to facilitate the comparison of results obtained in different experiments, but in essentially the same experimental system. On the other hand, the rich diversity of different systems, with different features and behaviors, represents a tremendous resource, among other things allowing the investigator to select the system that best recapitulates particular aspects of human HIV infection for study in a relevant nonhuman primate model. Such studies have provided, and may be expected to continue to provide, important insights to guide HIV treatment and vaccine development in the future.

Isolation and partial characterization of a lentivirus from talapoin monkeys (Myopithecus talapoin)

We have identified a novel lentivirus prevalent in talapoin monkeys (Myopithecus talapoin), extending previous observations of human immunodeficiency virus-1 cross-reactive antibodies in the serum of these monkeys. We obtained a virus isolate from one of three seropositive monkeys initially available to us. The virus was tentatively named simian immunodeficiency virus from talapoin monkeys (SIVtal). Despite the difficulty of isolating this virus, it was readily passed between monkeys in captivity through unknown routes of transmission. The virus could be propagated for short terms in peripheral blood mononuclear cells of talapoin monkeys but not in human peripheral blood mononuclear cells or human T cell lines. The propagated virus was used to infect a naive talapoin monkey, four rhesus macaques (M. mulatta), and two cynomolgus macaques (M. fascicularis). All animals seroconverted and virus could be reisolated during a short period after experimental infection. A survey of SIVtal-infected captive talapoin monkeys revealed a relative decrease in CD4(+) cell numbers in chronically (>2 years) infected animals. No other signs of immunodeficiency were observed in any of the infected animals. PCR amplification followed by DNA sequencing of two fragments of the polymerase gene revealed that SIVtal is different from the presently known lentiviruses and perhaps most related to the SIV from Sykes monkeys.

The importance of lymphocyte trafficking in regulating blood lymphocyte levels during HIV and SIV infections

In humans, blood is commonly monitored to provide surrogates of disease progression and assess immune status. However, the varied, rapid and atypical alterations in lymphocyte subsets which may occur in blood in response to pathogens, are not predictive of changes in the bulk of the immune system. A hallmark of human and simian immunodeficiency virus (SIV) infections is the profound loss of blood CD4(+) lymphocytes, a feature widely accepted as being a consequence of direct or indirect viral killing of CD4(+) cells throughout the body. However, in recording declining CD4 counts and CD4/8 ratios in the blood, little attention has been paid to migratory behaviour or the composition and tissue distribution of various lymphocyte subsets. This article compares the lymphocyte subsets in blood and various tissues in normal and virus-infected individuals prior to and following drug treatment and indicates an absence of selective CD4(+) cell decreases or increases, highlighting the importance of lymphocyte trafficking and compartmentalization in regulating blood T cell levels and suggesting a reevaluation of the currently favoured paradigm.

Limited protection from a pathogenic chimeric simian-human immunodeficiency virus challenge following immunization with attenuated simian immunodeficiency virus

Two live attenuated single-deletion mutant simian immunodeficiency virus (SIV) constructs, SIV239Deltanef and SIVPBj6.6Deltanef, were tested for their abilities to stimulate protective immunity in macaques. During the immunization period the animals were examined for specific immune responses and virus growth. Each construct generated high levels of specific immunity in all of the immunized animals. The SIV239Deltanef construct was found to grow to high levels in all immunized animals, with some animals remaining positive for virus isolation and plasma RNA throughout the immunization period. The SIVPBj6.6Deltanef was effectively controlled by all of the immunized animals, with virus mostly isolated only during the first few months following immunization and plasma RNA never detected. Following an extended period of immunization of over 80 weeks, the animals were challenged with a pathogenic simian-human immunodeficiency virus (SHIV) isolate, SIV89. 6PD, by intravenous injection. All of the SIV239Deltanef-immunized animals became infected with the SHIV isolate; two of five animals eventually controlled the challenge and three of five animals, which failed to check the immunizing virus, progressed to disease state before the unvaccinated controls. One of five animals immunized with SIVPBj6.6Deltanef totally resisted infection by the challenge virus, while three others limited its growth and the remaining animal became persistently infected and eventually died of a pulmonary thrombus. These data indicate that vaccination with attenuated SIV can protect macaques from disease and in some cases from infection by a divergent SHIV. However, if animals are unable to control the immunizing virus, potential damage that can accelerate the disease course of a pathogenic challenge virus may occur.

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.

Isolation and characterization of a neuropathogenic simian immunodeficiency virus derived from a sooty mangabey

Transfusion of blood from a simian immunodeficiency virus (SIV)- and simian T-cell lymphotropic virus-infected sooty mangabey (designated FGb) to rhesus and pig-tailed macaques resulted in the development of neurologic disease in addition to AIDS. To investigate the role of SIV in neurologic disease, virus was isolated from a lymph node of a pig-tailed macaque (designated PGm) and the cerebrospinal fluid of a rhesus macaque (designated ROn2) and passaged to additional macaques. SIV-related neuropathogenic effects were observed in 100% of the pig-tailed macaques inoculated with either virus. Lesions in these animals included extensive formation of SIV RNA-positive giant cells in the brain parenchyma and meninges. Based upon morphology, the majority of infected cells in both lymphoid and brain tissue appeared to be of macrophage lineage. The virus isolates replicated very well in pig-tailed and rhesus macaque peripheral blood mononuclear cells (PBMC) with rapid kinetics. Differential replicative abilities were observed in both PBMC and macrophage populations, with viruses growing to higher titers in pig-tailed macaque cells than in rhesus macaque cells. An infectious molecular clone of virus derived from the isolate from macaque PGm (PGm5.3) was generated and was shown to have in vitro replication characteristics similar to those of the uncloned virus stock. While molecular analyses of this virus revealed its similarity to SIV isolates from sooty mangabeys, significant amino acid differences in Env and Nef were observed. This virus should provide an excellent system for investigating the mechanism of lentivirus-induced neurologic disease.

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.

Didanosine but not high doses of hydroxyurea rescue pigtail macaque from a lethal dose of SIV(smmpbj14)

It has been previously reported that hydroxyurea (HU) displays anti-HIV-1 activity and potentiates the antiviral effects of didanosine (ddI) in vitro. To assess the antiviral efficacy of HU in an animal model, the effects of HU and ddI, either individually or as combination therapy, were tested in a model using infection of pigtail macaque with the acutely fatal variant SIV(smpbj14). At the high dosage used (100 mg/kg/day), HU monotherapy failed to protect the exposed animals from viral infection and death, which occurred within 10 days postinoculation. However, both of the ddI-treated animals (5 mg/kg/day) survived the SIV(smmpbj14) lethal dose and displayed a reduction in viral load (undetectable SIV RNA or p27gag) in the primary phase of infection. Of the animals treated with the combination of drugs, one died at day 18 after infection and failed to seroconvert to viral antigens. These data suggest that a high dose of HU monotherapy does not protect against death induced by SIV(mmpbj14). However, lower doses of HU as monotherapy or combination therapy deserve further evaluation for their therapeutic effects.

Characteristics of the CD8+ lymphocytosis during primary simian immunodeficiency virus infections

OBJECTIVE

To investigate the source of the expanded blood CD8+ subsets during an acute primary simian immunodeficiency virus (SIV) infection of macaques and the potential role of these cells in disease progression.

DESIGN AND METHODS

The primary CD8+ lymphocytosis, which occurs at 1-2 weeks following infection with SIVsmm/PBj-14, was examined in rhesus and cynomolgus macaques. Extensive subset analysis of the expanded blood CD8+ cell pool in a rhesus macaque was compared phenotypically with those in thymus, lymph nodes, spleen, ileum and lung washouts obtained at necropsy during blood lymphocytosis. The influence of the primary CD8+ cells expansion on disease progression was assessed at days 175-679 post-infection in long-term PBj-14 survivors staged according to immunological, virological and histopathological changes in their lymphoid organs.

RESULT

The very rapid and transient blood lymphocytosis following infection consisted of two distinct CD45RA(low), CD8+ and CD28-, lymphocyte function-associated antigen (LFA)-1(high), CD45RA(high), CD8+ populations. These populations were present in low levels in thymus, lymph and spleen but were highly represented in mucosal tissues, such as long washout, in which CD28- LFA-1(high) CD45RA(high) CD8+ cells comprised 86% of CD8+ cells, and gut, which was predominantly CD45RA(low) CD28- CD8+ cells. A comparison of progressor and non-progressor PBj-14-infected rhesus and cynomolgus macaques also indicated that the existence or magnitude of a blood CD8+ lymphocytosis during the acute phase of infection did not by itself appear to influence or be predictive of disease progression.

CONCLUSION

The marked blood CD8+ lymphocytosis observed during acute SIV infection did not result from expansion of virus-specific precursors in peripheral lymph node and did not appear to influence the rate of disease progression. The findings provide a novel explanation for the primary CD8+ cell lymphocytosis and invoke a mechanism whereby virus-induced cytokine/chemokine production in mucosal sites initiate the transient migration of a pre-existing CD8+ population into the blood from compartments such as lung and gut. Such results suggest that the magnitude of lymphocytosis may depend on the level of viral replication in mucosal tissues and the presence of other infections, for example, cytomegalovirus.

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.

Genomic characterization of the region between HLA-B and TNF: implications for the evolution of multicopy gene families

The major histocompatibility complex (MHC) contains genes which confer susceptibility to numerous diseases and must be important in primate evolution. In some instances, genes have been mapped to the region between human histocompatibility leukocyte antigen (HLA)-B and tumor necrosis factor (TNF) but precise localization has proven difficult especially since this region is subject to insertions, deletions, and duplications. Utilizing computer similarity searches and coding prediction programs, we have identified several potential coding sequences between HLA-B and TNF. Three of these sequences, PERB11.2, PERB15, and PERB 18, are similar to members of multicopy gene families that are located in other regions of the MHC. The identification of numerous fragmented and intact retroelements (L1, Alu, LTR, and THE sequences) flanking the PERB11 and PERB15 genes suggests that these retroelements are involved in the duplication process. The evaluation of candidate genes for disease susceptibility within the MHC is complicated by their similarity to other members of multicopy gene families. The determination of sequence differences within and between species provides a strategy with which to investigate the candidate genes between HLA-B and TNF.

Requirements for lymphocyte activation by unusual strains of simian immunodeficiency virus

When residues 17 and 18 in nef of simian immunodeficiency virus strain SIVmac239 were changed from RQ to YE, the resultant virus was able to replicate in peripheral blood mononuclear cell cultures without prior lymphocyte activation and without the addition of exogenous interleukin-2, caused extensive lymphocyte activation in these cultures, and produced an acute disease in rhesus and pigtail macaques (Z. Du, S. M. Lang, V. G. Sasseville, A. A. Lackner, P. 0. Ilyinskii, M. D. Daniel, J. U. Jung, and R. C. Desrosiers, Cell 82:665-674, 1995). These properties are similar to those of the acutely lethal pathogen SIVpbj14 but dissimilar to those of the parental SIVmac239. We show here that the single change of R to Y at position 17 in nef of SIVmac239 is sufficient to confer the full, unusual phenotype. Conversely, the lymphocyte-activating properties of SIVpbj14 were lost by the single change of Y to R at position 17 of nef. The change of R17F or Q18E in SIVmac239 nef did not confer the unusual in vitro properties. Since SIVpbj14 has a duplication of the NF-kappaB binding sequence in the transcriptional control region, we also constructed and tested strains of SIVmac239/Rl7Y with zero, one, and two NF-kappaB binding elements. We found no difference in the properties of SIVmac239/R17Y, either in cell culture or in vivo, whether zero, one, or two NF-kappaB binding sites were present. Thus, tyrosine at position 17 of nef is absolutely necessary for the unusual phenotype of SIVpbj14 and is sufficient to convert SIVmac239 to a virus with a phenotype like that of SIVpbjl4. Multiple NF-kappaB binding sites are not required for the in vitro properties or for acute disease.

Deletion of the nef gene abrogates the ability of SIV smmPBj to induce acutely lethal disease in pigtail macaques

Simian immunodeficiency virus (SIV) infection in macaque species is typically associated with the development of a progressive immunodeficiency disease, similar to human AIDS, resulting in death of animals in months to years after infection. In contrast, a variant virus, termed SIVsmmPBj, induces an acute disease in macaques, resulting in death in 5 to 14 days after infection. Previously, we have shown that several viral determinants contribute to the pathogenesis of this disease. The present study was undertaken to evaluate the role of Nef in the pathogenesis of SIVsmmPBj-induced acute disease. A molecular clone of SIVsmmPBj was generated that contains a deletion in the nef coding region (PBj6.6 delta nef). Virus derived from this molecular clone was tested with the parental virus, PBj6.6, in replication studies in pigtail macaque and rhesus macaque peripheral blood mononuclear cells (PBMCs). In general, PBj6.6 delta nef displayed markedly reduced replication abilities when compared with PBj6.6; the only exception being in stimulated pigtail macaque PBMCs, where replication kinetics were nearly identical. In addition, PBj6.6 delta nef was unable to induce the proliferation of peripheral blood mononuclear cells (PBMCs) in vitro, a unique characteristic of acutely pathogenic SIVsmmPBj. Inoculation of this virus into pigtail macaques resulted in infection, but did not result in any detectable acute disease. These studies suggest that Nef is an important viral determinant in the pathogenesis of SIVsmmPBj-induced disease, and further suggest that Nef plays a significant role in viral replication in vivo.

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.

Recent advances in the understanding of Jembrana disease

Jembrana disease is a severe and acute clinical disease in Bali (Bos javanicus) cattle with a case fatality rate of about 20%, and a mild sometimes subclinical disease in other cattle types and buffalo. The aetiological agent has been identified as a lentivirus, designated as Jembrana disease virus (JDV). Preliminary sequence analysis has confirmed the identity of JDV as a lentivirus and has shown that it is distinguishable from BIV. There is antigenic cross-reactivity between the capsid protein of JDV and the previously identified bovine lentivirus designated bovine immunodeficiency virus (BIV). Serological tests that detect antibody to the capsid protein of JDV or BIV would not differentiate between antibody due to infection by either virus. The diseases induced by BIV and JDV infection in cattle are very different, and the pathogenesis of JDV infection in Bali cattle is unusual for a lentivirus infection.

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.

Induction of AIDS by simian immunodeficiency virus from an African green monkey: species-specific variation in pathogenicity correlates with the extent of in vivo replication

Previous studies suggested that simian immunodeficiency viruses isolated from African green monkeys (SIVagm) are relatively nonpathogenic. The report describes the isolation and biologic and molecular characterization of a pathogenic SIVagm strain derived from a naturally infected African green monkey. This virus induced an AIDS-like syndrome characterized by early viremia, frequent thrombocytopenia, severe lymphoid depletion, opportunistic infections, meningoencephalitis, and death of five of eight macaques within 1 year after infection. An infectious clone derived from this isolate reproduced the immunodeficiency disease in pig-tailed (PT) macaques, providing definitive proof of the etiology of this syndrome. Although the virus was highly pathogenic in PT macaques, no disease was observed in experimentally infected rhesus macaques and African green monkeys despite reproducible infection of the last two species. Whereas infection of PT macaques was associated with a high viral load in plasma, peripheral blood mononuclear cells, and tissues, low-level viremia and infrequent expression in lymph nodes of rhesus macaques and African green monkeys suggest that differences in pathogenicity are associated with the extent of in vivo replication. The availability of a pathogenic molecular clone will provide a useful model for the study of viral and host factors that influence pathogenicity.

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.

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

The simian immunodeficiency virus SIVsmmPBj14 (SIV-PBj14) is an atypical lentivirus that causes acute disease and death in pig-tailed macaques and in vitro replicates efficiently in resting macaque lymphocytes and activates and induces proliferation of lymphocytes. The present study was conducted to test the hypothesis that production of large quantities of SIV-PBj14 induces widespread immune activation and elaboration of cytokines which lead directly to the death of infected pig-tailed macaques. Following intravenous inoculation of pig-tailed macaques with SIV-PBj14, acute disease developed and was characterized by high levels of plasma viremia, p27gag antigenemia, tumor necrosis factor alpha, and interleukin-6 (IL-6). All animals died within 10 days of infection, at which time some animals had as many as 100% CD4+ cells in the periphery and lymphoid tissues infected. During the last few days before death, titers of infectious virus in blood increased as much as 10(5)-fold. By using dual-label immunofluorescence assays for detection of cell surface activation markers, both CD4+ and CD8+ lymphocytes were shown to express the IL-2 and transferrin receptors following either in vivo or in vitro infection with SIV-PBj14. Furthermore, in vitro infection of quiescent macaque lymphocytes by SIV-PBj14 was accompanied by proliferation of both CD4+ and CD8+ lymphocyte subsets, as measured by incorporation of [3H]thymidine. Increases in numbers of activated lymphocytes and levels of proinflammatory cytokines in plasma coincided with increased amounts of detectable virus in vivo. Clinical signs of disease and pathologic findings were most consistent with death from a shock-like syndrome, in which acute-phase inflammatory cytokines are known to play a major role. Tumor necrosis factor alpha, IL-2, and IL-6 were detected in some cultures infected with SIV-PBj14, but this finding was not consistent. When cytokines were detected, their concentrations were essentially no different from those found in control cultures infected with SIVsmm9, a prototypic strain from which SIV-PBj14 was derived. The in vivo results suggest a synergistic cycle of activation of lymphocytes and monocytes, elaboration of cytokines, and virus production that accelerates uncontrolled and culminates in death. The observed correlations between in vivo and in vitro activation events following SIV-PBj14 infection validate the use of in vitro studies to clarify lentivirus-lymphocyte interactions that may contribute to the virulence of SIV-PBj14.

Intercellular adhesion molecules (ICAM)-1 ICAM-2 and ICAM-3 function as counter-receptors for lymphocyte function-associated molecule 1 in human immunodeficiency virus-mediated syncytia formation

It has been previously demonstrated that lymphocyte function-associated molecule 1 (LFA-1) plays a major role in human immunodeficiency virus (HIV)-mediated syncytia formation. In the present study we investigated the involvement of intercellular adhesion molecule-1 (ICAM-1), ICAM-2 and ICAM-3 in the process. The ability of monoclonal antibodies (mAb) directed against ICAM-1, ICAM-2 and ICAM-3 to block syncytia was analyzed either in phytohemagglutinin (PHA)-activated lymphocytes infected in vitro with primary or laboratory strains of HIV or by coculturing a T cell line stably expressing HIV envelope with PHA-activated lymphocytes. Complete inhibition of syncytia formation was observed only by the simultaneous addition to the cell cultures of all (i.e. anti-ICAM-1, anti-ICAM-2 and anti-ICAM-3) mAb. These results indicate that the interaction between LFA-1 and ICAM is a critical step in HIV-mediated syncytia formation, and that ICAM-1, ICAM-2 and ICAM-3 are the receptor molecules for the LFA-1-dependent syncytia formation.

An acutely lethal simian immunodeficiency virus stimulates expansion of V beta 7- and V beta 14-expressing T lymphocytes

SIVsmmPBj14, a variant simian immunodeficiency virus isolated from a pig-tailed macaque, stimulates the proliferation of macaque T lymphocytes in vitro and induces an acutely lethal disease in macaques characterized, in part, by lymphadenopathy and splenomegaly. To determine whether SIVsmmPBj14 exhibits superantigen-like activity, in vitro and in vivo studies of T-cell receptor V beta repertoire were undertaken using PCR-based quantitative methods. Whereas in vitro phytohemagglutinin stimulation of macaque peripheral blood lymphocytes did not cause a perturbation of T-cell receptor V beta repertoire, SIVsmmPBj14 stimulated the expansion of both CD4+ and CD8+ T-lymphocyte subpopulations expressing the V beta 7 and V beta 14 gene families. Such V beta 7 and V beta 14 expansions could be confirmed by a multiple RNase protection assay. Furthermore, the expansion of the same lymphocyte subpopulations was also detected in peripheral blood lymphocytes and lymph node cells of virus-infected macaques. These observations suggest that SIVsmmPBj14-mediated V beta expansion may contribute to the induction of an acutely lethal disease in macaques.

Characterization of simian immunodeficiency virus (SIV) infected AA-2 cells by SEM and immunoelectron microscopy

The ultrastructural features of AA-2 cells infected with either of two strains of simian immunodeficiency virus (SIVMne-E11S or SIVSMM-PBj) were examined by scanning electron microscopy (SEM). Transformed CD4+ human B lymphocytes (AA-2) were inoculated with SIV and observed at 2, 4, and 7 days post-inoculation (dPI). Infected AA-2 cells were distinguished by the progressive loss of microvilli, and variable numbers of free or protruding spherical particles measuring 90-120nm in diameter along the cell surface. Syncytial cell formation (complexes of fused cells) and necrotic cells were evident at each time point with the most numerous observations at 7 dPI. While the distribution and severity of the viral induced changes increased with time and affected virtually all cells by 7 dPI, the alterations were detected sooner and were more pronounced in SIVSMM-PBj infected cells. This finding is consistent with the in vivo data from primate studies using the same strains of SIV. Syncytial cells exhibited slight to moderate indentations which appeared to coincide with the boundaries of individual cells forming the complex. The plasma membrane of syncytial cells was relatively smooth and lacked microvilli. Spherical particles and buds protruding from the plasma membrane were predominate features of syncytial cell surfaces. By the employment of antisera generated against whole SIVMne-E11S, both transmission and scanning immunoelectron microscopy confirmed the identity of the spherical structures as free and budding SIV virions.

Immunological and virological changes associated with decline in CD4/CD8 ratios in lymphoid organs of SIV-infected macaques

The decline in CD4/CD8 ratios in lymph nodes (LNs) of SIV macaques and HIV-infected individuals occurs later than that in blood. In a previous study, long-term SIV-infected macaques were delineated into two groups: (1) those whose LNs had normal CD4/CD8 ratios and (2) those whose LNs had low CD4/CD8 ratios. In the present investigation, LNs, spleens, and blood from these groups have been further analyzed to ascertain the cellular and virological events, particularly those involving CD8+ cells, that occur concomitantly with LN CD4% decline. An increase in the percent of CD69-, IL-2R(p75)-, CD45RA1o CD8+ cells was the most constant event observed in lymphoid tissue from mid- to late-stage SIV-infected monkeys. Such cells were sometimes observed in LNs prior to any other immunological or morphological changes. However, decline in LN CD4/CD8 ratios and the associated degeneration of follicular dendritic cells (FDCs) in the germinal centers (GCs) of these nodes were observed only when both CD8+ cell infiltration of GCs and accumulation of viral antigens within the FDC network could be demonstrated. These dramatic changes were also associated with significantly reduced responsiveness to mitogens throughout the lymphoid compartment. In terms of viral burden, immunological and structural collapse of LNs was not always associated with increased viral DNA levels. Despite the CD4+ cell decline in blood during HIV and SIV infections, the immunological and architectural collapse of the lymphoid compartment, which comprises the bulk of the lymphocytes in the body, appears to be a critical event leading to the onset of AIDS. The present findings suggest that increased CD8+ cell activity as well as decrease in CD4+ cell function both contribute to this process.

Unique lentivirus--host interactions: SIVsmmPBj14 infection of macaques

The most virulent primate lentivirus identified to date, the simian virus SIVsmmPBj14 (SIV-PBj14), is unique not only because it causes acute disease and death within days instead of months or years, but also because of its replicative and cellular activation properties. The acute disease syndrome has many features in common with primary HIV-1 disease, but differences in the respective outcomes of these two acute lentiviral infections appear to be linked to the rapidity with which SIV-PBj14 replicates and the high titers of virus that subsequently accumulate in lymphoid tissues. The most prominent pathologic feature of SIV-PBj14 is extensive lymphoid hyperplasia of T-cell zones, especially in the gut-associated lymphoid tissue. These expanded T-cell zones contain a high proportion of lymphoblasts, activated macrophages and syncytial cells, which are positively correlated with high numbers of SIV antigen-positive cells. Replication of the virus to high titers, accompanied by extensive cellular activation and proliferation, leading to high levels of cytokines, such as interleukin-6 and tumor necrosis factor-alpha, are consistent with acute inflammatory disease. The pathogenesis of SIV-PBj14 also appears to correlate most directly with some of its unique biologic properties, such as the ability to replicate in resting peripheral blood mononuclear cells, to activate lymphocytes, and to induce lymphocyte proliferation. Biologically and molecularly cloned viruses derived from SIV-PBj14 and isolates obtained from macaque PBj at earlier times, are being used to identify viral determinants that influence biologic and pathogenic properties of SIV-PBj14. Further characterization of this virus should provide new insights into lentivirus-cell interactions and their contributions to disease.

Viral genetic determinants in SIVsmmPBj pathogenesis

A variant simian immunodeficiency virus (SIV) from sooty mangabeys, SIVsmmPBj, induces an acutely lethal disease in pigtailed macaques (Macaca nemestrina). This study further characterizes the viral genetic determinants involved in this acutely lethal disease. We have generated chimeric molecular clones constructed between SIVsmmPBj and either SIVsmH4 or SIVsmm9 to analyze the role of the 5' half of the genome and the envelope gene in the induction of acute disease. These studies suggest that the gag and gp40 of SIVsmmPBj are required for the development of lethal disease, and an additional determinant in the central regulatory gene region of the SIVsmmPBj genome is also required.

Adaptation of HIV-1 to pigtailed macaques

In vitro infectivity experiments were performed to assess the susceptibility of cells from various monkey species to HIV-1. T lymphocytes from pigtailed macaques, but not those from rhesus or cynomolgus monkeys, were susceptible to infection, but virus expression was limited. The majority of HIV-1 isolates were unable to productively infect pigtailed macaque cells. Inoculation of autologous, HIV-1 expressing cells led to establishment of persistent infection in pigtailed macaques as evidenced by recovery of infectious virus and development of virus-specific antibody responses.

SIVsmmPBj14: an atypical lentivirus

SIV-PBj14 is atypical for a lentivirus in that infection of pig-tailed macaques usually does not result in long-term progressive disease; however, this model may potentially provide valuable information about the pathogenesis of HIV and the development of AIDS. By capitalizing on some of the unique properties of the virus and the model system discussed above, new insights may be gained in: (a) understanding pathogenic mechanisms of acute lentiviral infections, (b) dissecting lentivirus-host cell interactions, (c) evaluating the role(s) of cytokines in lentivirus-induced disease, (d) rapidly assessing therapeutic and prophylactic benefits of new drugs and vaccines, and (e) identifying regions of the viral genome that influence specific biological properties. While it is unlikely, but possible, that HIV-1 variants as virulent as SIV-PBj14 will become a threat to humans, SIV-PBj14 may possess properties important to the development of lentivirus-induced disease. An understanding of all possible virus-host interactions, from the most virulent to the most benign, may be required to make a significant, positive impact on the HIV-1 pandemic.

Association of interleukin-6 in the pathogenesis of acutely fatal SIVsmm/PBj-14 in pigtailed macaques

Infection with a variant of simian immunodeficiency virus (SIVsmm/PBj-14) causes death in juvenile pigtailed macaques within 8 days of infection. The primary pathology is localized to the lymphoid tissues of the gut and spleen. Although the virus is present, the lesions are most consistent with acute reactive inflammation. We studied the serum and tissues for evidence of acute cytokine production often associated with acute inflammation. One factor, IL-6, was found to be significantly increased (> 1000-fold) over all other measured cytokines in all the pigtailed macaques who died acutely. Increased levels of IL-6 were found both in the serum and in the inflamed tissues. mRNA for IL-6 was found in the tissues with the highest protein levels of IL-6. The marked increase in IL-6 and IL-6 mRNA correlated with the virus levels in the tissues and serum as determined by viral isolation, immunohistochemistry, and Northern blot analysis. These findings suggest that the underlying pathogenesis of primary tissue damage, necrosis, and death by PBj-14 is the induction of cytokine production. Although the presence of the virus may be critical for the initiation of these events, the intense inflammatory reaction is associated with the cause of death.

Decline in the CD4+ lymphocyte population in the blood of SIV-infected macaques is not reflected in lymph nodes

Although loss of CD4+ lymphocytes in peripheral blood is a standard criterion for evaluating the course of HIV disease, little is known about changes within lymphoid organs, which contain the bulk (> 50%) of the body's lymphocytes. Because such studies are feasible only by using non-human primates, we have examined lymph nodes (LNs), spleen, and blood from monkeys infected with two isolates of simian immunodeficiency virus (SIV). During both the acute and chronic phases of these infections, characteristic reductions in the blood CD4+ cell levels are not reflected in LN, where the CD4+ pool remains within normal levels. However, when circulating CD4/CD8 ratios have consistently fallen to approximately 0.5, striking decreases in the percentage of CD4 cells (CD4%) and CD4/CD8 ratios in LN occur concomitantly with dramatic increases in viral antigen expression on follicular dendritic cells within LN germinal centers (GCs). The data suggest that loss from the total T cell pool in minimal until the final stages of SIV and HIV disease and that the immunological deterioration of LN is the event that precipitates the increased susceptibility to infections and progression to AIDS.

Multiple viral determinants contribute to pathogenicity of the acutely lethal simian immunodeficiency virus SIVsmmPBj variant

Simian immunodeficiency virus (SIV) induces an immunodeficiency syndrome similar to human AIDS. Although the disease course of SIV-induced immunodeficiency is generally measured in months to years, a disease syndrome that results in death in 5 to 14 days has been described in pig-tailed macaques infected with the SIVsmmPBj (PBj) strain. The purpose of this study was to derive an acutely lethal PBj molecular clone in order to study viral genes involved in pathogenesis. Six infectious molecular clones were generated; acutely fatal disease was induced by experimental inoculation of pig-tailed macaques with virus stocks derived from either of two clones, PBj6.6 or PBj14.6. Molecular chimeras were constructed by exchange of regions of the genome of PBj6.6 and a nonlethal, related clone, SIVsmH4. Only a chimera expressing the PBj genome under the control of a SIVsmH4 long terminal repeat induced death soon after inoculation. These studies suggest that multiple viral genes of PBj are critical for development of acute disease. More specifically, the env gene but not the long terminal repeat PBj was required for acute disease induction; however env must act in concert with another gene(s) of the PBj genome.