Binhua Ling

Sivmac pathogenesis in rhesus macaques of Chinese and Indian origin compared with primary Hiv infections in humans

ObjectiveTo develop a SIV–rhesus macaque (Rh) model of AIDS that more closely approximates HIV pathogenesis in humans. DesignThe pathogenesis of SIV was compared in two different types of Rh, the Chinese (Ch) and Indian (Ind) subspecies. MethodsCh Rh and Ind Rh origin were identified genetically and infected with the SIVmac239 molecular clone. Plasma viral loads, depletion of intestinal lymphocytes with memory phenotype, humoral immune responses and CD4/CD8 cell ratios were compared during acute and steady-state periods of infection. ResultsPlasma viral loads from 7 days after infection through 240 days were significantly lower in Rh of Ch origin compared with Ind Rh. Viral loads in Ch Rh were closer to viral loads observed in untreated humans infected with HIV-1. Depletion of intestinal effector cells was less evident in SIV-infected Ch Rh compared with Ind Rh. An index of intestinal pathogenesis was devised that closely paralleled viral load and severity of infection. There were no rapid progressors to AIDS among 10 Ch Rh. In contrast, three of four Ind Rh progressed rapidly to AIDS. ConclusionsCompared with Ind Rh, SIVmac pathogenesis in Ch Rh was closer to HIV-1 infections in untreated adult humans. The differences were statistically significant. The Ch Rh subspecies is a suitable AIDS model and may have advantages over the rapid and highly pathogenic Ind Rh model. Moreover, Ind Rh supplies are limited and use of Ch Rh provides a new resource.

Classic AIDS in a Sooty Mangabey after an 18-Year Natural Infection

ABSTRACT 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.

Differential CD4+ T-Lymphocyte Apoptosis and Bystander T-Cell Activation in Rhesus Macaques and Sooty Mangabeys during Acute Simian Immunodeficiency Virus Infection

ABSTRACT In contrast to pathogenic lentiviral infections, chronic simian immunodeficiency virus (SIV) infection in its natural host is characterized by a lack of increased immune activation and apoptosis. To determine whether these differences are species specific and predicted by the early host response to SIV in primary infection, we longitudinally examined T-lymphocyte apoptosis, immune activation, and the SIV-specific cellular immune response in experimentally infected rhesus macaques (RM) and sooty mangabeys (SM) with controlled or uncontrolled SIV infection. SIVsmE041, a primary SIVsm isolate, reproduced set-point viremia levels of natural SIV infection in SM but was controlled in RM, while SIVmac239 replicated to high levels in RM. Following SIV infection, increased CD8+ T-lymphocyte apoptosis, temporally coinciding with onset of SIV-specific cellular immunity, and elevated plasma Th1 cytokine and gamma interferon-induced chemokine levels were common to both SM and RM. Different from SM, SIV-infected RM showed a significantly higher frequency of peripheral blood activated CD8+ T lymphocytes despite comparable magnitude of the SIV-specific gamma interferon enzyme-linked immunospot response. Furthermore, an increase in CD4+ and CD4−CD8− T-lymphocyte apoptosis and plasma tumor necrosis factor-related apoptosis-inducing ligand were observed only in RM and occurred in both controlled SIVsmE041 and uncontrolled SIVmac239 infection. These data suggest that the “excess” activated T lymphocytes in RM soon after SIV infection are predominantly of non-virus-specific bystander origin. Thus, species-specific differences in the early innate immune response appear to be an important factor contributing to differential immune activation in natural and nonnatural hosts of SIV infection.

Early restoration of mucosal CD4 memory CCR5 T cells in the gut of SIV-infected rhesus predicts long term non-progression

Objectives:To use SIVmac-infected Chinese-origin rhesus macaques (Ch Rh) to characterize the immunopathology of the long term non-progressor (LTNP) state. The key questions addressed were whether or not LTNP experience an early and rapid loss of mucosal CD4 T cells during the acute infection and the mechanisms by which they maintain the LTNP state. Methods:Ch Rh were infected with SIVmac239. Polychromatic flow cytometry was used to analyze T lymphocyte subsets from blood, lymph nodes and gut tissues during SIV infection. Plasma viral loads were monitored by bDNA assay. Two LTNP were treated with anti-CD8 antibody to deplete CD8 cells in vivo. Results:Thirty-one percent (5/16) of SIVmac239-infected ChRh having low viral loads for as long as 6 years were LTNP. Both LTNP and progressors had similar levels of gut memory CD4/CCR5 T cells (target cells) before infection and there was an early and profound depletion of target cells in both groups. LTNP were distinguished by gradual restoration of mucosal target cells which was evident by 6 months post infection. In vivo CD8 depletion in two LTNP induced AIDS in one LTNP (V542) post anti-CD8 treatment and the other (AJ07) remained healthy after a transient spike in viremia. Conclusions:Early destruction of target cells was equivalent in LTNP and progressors and did not predict clinical outcome. Restoration of target cells in the gut is associated with long term non-progression. CD8 T cells may play a critical role on maintaining the LTNP state.

Noninvasive Detection of New Simian Immunodeficiency Virus Lineages in Captive Sooty Mangabeys: Ability To Amplify Virion RNA from Fecal Samples Correlates with Viral Load in Plasma

ABSTRACT The sooty mangabey (SM) (Cercocebus atys) is the natural host of a simian immunodeficiency virus, termed SIVsm, which gave rise to human immunodeficiency virus type 2. Data on the geographic distribution, prevalence, and genetic diversity of SIVsm in the wild remains limited. To address this issue, noninvasive strategies based on screening SM fecal and urine specimens for SIVsm-specific antibodies and virion RNA (vRNA) were developed, and the results were correlated with viral loads in plasma. Twenty-three SIVsm-infected and 27 uninfected SMs were evaluated. Time-matched urine, fecal and plasma samples were collected over a 2-month period from 16 captive naturally infected SMs. The remaining 7 infected and 27 uninfected SMs were sampled once. Each specimen was subjected to enhanced chemiluminescence-Western blot analysis and nested reverse transcriptase (RT) PCR. The results showed that urine was highly sensitive (96%) and specific (100%) for detection of SIVsm antibodies, while fecal detection was much less sensitive (16%). Conversely, vRNA detection was more sensitive in feces (50%) than in urine (2%) samples. Fecal-vRNA detection correlated with viral loads in plasma (P < 0.002). SMs with detectable fecal vRNA had a mean viral load in plasma of 458,006 copies/ml, while those with undetectable fecal vRNA had a mean viral load in plasma of 29,428 copies/ml. Moreover, for every log increase in the viral load in plasma, the odds of detecting virus in fecal samples increased 87-fold. Genetic diversity of SIVsm in the SM colony was characterized by sequencing partial gag (846 bp) and gp43 (439 bp) fragments. Surprisingly, four new SIVsm lineages were identified, two of which were initially detected by fecal RT-PCR. This study documents the suitability of noninvasive methods for the detection and molecular characterization of new SIV variants. These assays will be useful for studying the phylogeny and epidemiology of SIVsm infections in the wild, and they hold promise as tools for investigating natural SIV infections in endangered nonhuman primates.

Detection and partial characterization of simian immunodeficiency virus SIVsm strains from bush meat samples from rural Sierra Leone.

ABSTRACT Human immunodeficiency virus type 2 (HIV-2) originated from simian immunodeficiency viruses (SIVs) that naturally infect sooty mangabeys (SMs; Cercocebus atys). In order to further investigate the relationship between HIV-2 and SIVsm, the SIV specific to the SM, we characterized seven new SIVsm strains from SMs sold in Sierra Leone markets as bush meat. The gag, pol, and env sequences showed that, while the viruses of all seven SMs belonged to the SIVsm-HIV-2 lineage, they were highly divergent viruses, in spite of the fact that most of the samples originated from the same geographical region. They clustered in three lineages, two of which have been previously reported. Two of the new SIVsm strains clustered differently in gag and env phylogenetic trees, suggesting SIVsm recombination that had occurred in the past. In spite of the fact that our study doubles the number of known SIVsm strains from wild SMs, none of the simian strains were close to the groups in which HIV-2 was epidemic (groups A and B).

Decreased CCR5 Expression on CD4+ T Cells of SIV-Infected Sooty Mangabeys

Sooty mangabeys are the natural host of simian immunodeficiency virus (SIVsm). When injected into rhesus macaques, SIVsm infection results in progressive declines in CD4(+) T cells, opportunistic infections, and AIDS. In contrast, SIV-infected sooty mangabeys do not develop disease and live an apparently normal life span in captivity, despite maintaining high levels of virus in plasma throughout their lives. Determining the mechanisms by which sooty mangabeys have evolved to resist disease progression and AIDS may be useful in designing effective vaccine and therapeutic strategies to combat HIV-1 infection in humans. This article demonstrates that SIV-infected sooty mangabeys have significantly reduced CCR5 expression on their CD4(+) T cells compared with uninfected mangabeys or rhesus macaques. In contrast, no differences in CCR5 coexpression are found on CD8(+) T cells. Moreover, no differences in absolute numbers of CD4(+) T cells or rates of CD4(+) T cell proliferation were detected between SIV-infected and uninfected mangabeys. Combined, this suggests that either CD4(+) T cells downregulate CCR5 expression, or that CCR5(+)CD4(+) T cells are lost and not replenished in early SIV infection of sooty mangabeys. Regardless of the mechanism involved, significantly lower levels of CCR5 expression on CD4(+) T cells of SIV-infected mangabeys may play a major role in the diminished immune responses and the lack of disease progression in this natural host species.

Boosting of SIV-Specific T Cell Responses in Rhesus Macaques That Resist Repeated Intravaginal Challenge with SIVmac251

Despite repeated high-risk exposure to infectious HIV-1, some individuals remain HIV-1 seronegative and apparently uninfected. The use of nonhuman primate model systems to study SIVmac transmission may help to elucidate the factors responsible for protection in exposed, seronegative (ESN) humans. In an earlier vaccination study, three control rhesus macaques that were exposed to three sequential intravaginal challenges with pathogenic SIVmac251 failed to show evidence of infection after 5 years of observation. 51Cr release assay results suggested that these animals had low-level cytotoxic T lymphocyte responses to SIVmac proteins. We hypothesized that these responses might be an important component of protection from mucosal challenge. We performed an additional intravaginal challenge of all three macaques and monitored SIV-specific T cell responses in peripheral blood, using the sensitive enzyme-linked immunospot (ELISpot) assay. After the fourth challenge, one animal became infected; this animal did not mount a strong SIV-specific T cell response. Two other macaques remained uninfected as determined by peripheral blood mononuclear cell (PBMC) coculture, polymerase chain reaction (PCR), and branched DNA (bDNA) analysis of peripheral blood and lymphoid tissues, but demonstrated boosting of SIV-specific T cell responses after challenge. These results support a protective role for SIVmac-specific T cells in repeatedly exposed, persistently seronegative rhesus macaques.

Comparative susceptibility of rhesus macaques of Indian and Chinese origin to vaginal SHIV transmission as models for HIV prevention research

Historically, Indian rhesus macaques (iRMs) have been preferred for simian immunodeficiency virus (SIV)/HIV prevention, pathogenesis, and treatment studies, yet their supply is limited. Chinese rhesus macaques (cRMs) are currently more available, yet little is known regarding the relative susceptibility of this subspecies to vaginal transmission of SIV or simian-human immunodeficiency virus (SHIV). In this study, we compared the susceptibility of 40 cRMs and 21 iRMs with a single vaginal challenge with SHIVsf162P. Our results showed that cRMs have comparable primary SHIV infection as iRMs, underscoring their equal importance in studies of HIV transmission and prevention.