Interactions between simian immunodeficiency virus and Mycobacterium leprae in experimentally inoculated rhesus monkeys

Thirty-four rhesus monkeys were inoculated with Mycobacterium leprae inoculum isolated from sooty mangabey monkeys with leprosy. Later it was learned that one of the M. leprae-donor mangabeys was asymptomatically infected with simian immunodeficiency virus (SIV). Thus, five of the rhesus monkey were coinoculated with M. leprae and SIV. Three of the five became SIV-positive and developed signs of leprosy and an AIDS-like illness. Two animals remained healthy. The coinoculated leprosy-positive rhesus monkeys developed leprosy despite serologic response patterns to M. leprae antigens that usually indicate leprosy resistance. Three (60%) of the five SIV-positive rhesus monkeys developed leprosy compared with 21% of the animals who received SIV-free M. leprae inocula. Diminished lepromin skin test responses and decreasing T-helper cell percentages were observed in SIV-coinoculated rhesus monkeys with leprosy. These observations suggest that SIV increases the susceptibility of rhesus monkeys to leprosy, possibly related to loss of T-helper cell function.     

Pathology of dual Mycobacterium leprae and simian immunodeficiency virus infection in rhesus monkeys

Three rhesus monkeys were experimentally inoculated with sooty-mangabey-derived Mycobacterium leprae and were inadvertently infected with the simian immunodeficiency virus (SIV) as well. They died of an immunodeficiency syndrome, and at autopsy all had lesions caused by M. leprae. One monkey was inoculated twice with M. leprae, initially with an inoculum from a sooty mangabey that was not infected with SIV and, subsequently, with an inoculum from a mangabey that was SIV infected. The monkey did not develop clinical lesions and became strongly lepromin skin test (LST) positive after the first inoculation, but became infected with both agents and LST negative following the second inoculation. These observations suggest that SIV-infected rhesus monkeys have an increased susceptibility to M. leprae infection and, by analogy, imply that HIV-infected human beings may have an increased susceptibility as well.     

A humanized,nondepleting anti-CD4 antibody that blocks virus entry inhibits virus replication in rhesus monkeys chronically infected with simian immunodeficiency virus

Therapeutic approaches that interfere with viral entry hold promise in preventing or treating HIV infection. Hu5A8, a humanized monoclonal antibody against CD4, was previously shown to inhibit HIV and SIV replication in vitro and was safely administered to rhesus monkeys without depleting CD4(+) T cells. This antibody completely suppressed replication of six different SIVmac 251 primary isolates in vitro. Twice weekly administration of 3-mg/kg doses of hu5A8 for 2 to 4 weeks to SIV-infected rhesus monkeys resulted in sustained plasma antibody levels of > or =20 microg/ml during treatment and 5- to 50-fold decreases in plasma viremia, although suppression of viral replication was transient. Two of three treated monkeys developed antibody responses against the administered monoclonal antibody. Loss of antiviral effect was not temporally associated with anti-hu5A8 antibody responses or due to activation of CD4(+) T cells by hu5A8. However, SIV isolated after hu5A8 treatment was approximately 5-fold more resistant to suppression by hu5A8 than SIV isolates obtained from the same monkeys before treatment. The rapid development of resistance may have resulted from SIV variants that infect cells by a CD4-independent mechanism. These results support the overall concept of anti-CD4 monoclonal antibody treatment to suppress AIDS virus replication in vivo while demonstrating important issues as to its clinical feasibility.     

An early increase in somatostatin mRNA expression in the frontal cortex of rhesus monkeys infected with simian immunodeficiency virus.

Motor and cognitive impairment is common in human immunodeficiency virus disease in humans and simian immunodeficiency virus (SIV) disease in rhesus monkeys. We have examined peptide neurotransmitter expression in the frontal cortex of SIV-infected rhesus monkeys to identify alterations in cortical neurons that might explain this impairment. A 2-fold higher number of preprosomatostatin (SRIF) mRNA-positive interneurons was observed in layer IV of frontal cortex in two separate cohorts of SIV-infected animals compared to uninfected controls. Increased SRIF mRNA expression in layer IV was independent of clinical signs of immunodeficiency disease and was associated with both motor and cognitive impairment. Altered SRIF mRNA expression in deeper cortical layers was associated specifically with motor impairment. Increased SRIF mRNA expression occurred without detectable changes in cortical cell density. These data suggest two mechanisms for cortical dysfunction associated with lentivirus infection. Increased SRIF mRNA expression in layer IV may be due to altered patterns of activity in cortical afferents that project to layer IV, while increased SRIF mRNA expression in deeper cortical layers could reflect susceptibility to locally generated mediators in response to primate lentivirus infection of the brain. Altered function of somatostatinergic interneurons may contribute to primate lentivirus-induced encephalopathy.     

Early activation and proliferation of T cells in simian immunodeficiency virus-infected rhesus monkeys

To longitudinally determine T cell activation and turnover in early simian immunodeficiency virus (SIV) infection of macaques, immunological and virological parameters were monitored in 10 SIV-infected animals starting before infection until 40 weeks postinfection (wpi). Lymphocyte subsets in blood and lymph nodes (LNs) were characterized by three-color flow cytometry for expression of markers of activation, proliferation, and differentiation. As early as 1 wpi, CD69 expression was upregulated both on CD4+ and CD8+ T cells, indicative of an early activation of these cells. Whereas this activation led to increased proliferation, determined by expression of Ki-67, and absolute numbers of CD8+ T cells, CD4+ T cells showed a decreased expression of Ki-67 and reduced counts in blood at 2 wpi. Later, the percentage of Ki-67-expressing CD4+ T cells in blood and LNs increased again above preinfection levels in most animals but remained low in two monkeys progressing to AIDS. These findings suggest that T cells are activated after SIV infection, leading to increased T cell proliferation already in the early asymptomatic phase. In addition, we found a correlation between the capacity to regenerate CD4+ T cells by peripheral proliferation and the disease course. Moreover, our data indicate that the increased peripheral T cell proliferation during immunodeficiency virus infection is probably not caused by the effort of the immune system to maintain T cell homeostasis but may be a reflection of the ongoing immune response against the virus.     

Clinical measles after measles virus challenge in simian immunodeficiency virus-infected measles virus-vaccinated rhesus monkeys

Understanding the impact of human immunodeficiency virus (HIV) infection on the clinical manifestations and kinetics of measles virus (MV) replication in MV-vaccinated and unvaccinated individuals is important for developing successful vaccine strategies for measles eradication. To model the pathogenesis of MV infection in MV-vaccinated and unvaccinated individuals infected with HIV, previously vaccinated and unvaccinated rhesus monkeys infected with simian immunodeficiency virus (SIV) were challenged with MV and monitored for clinical, virologic, and immunologic sequelae of infection. The magnitude and duration of MV viremia were unchanged by SIV infection. Nevertheless, clinical manifestations of MV infection were altered in animals with significant CD4(+) T lymphocyte loss. Importantly, 2 of the 3 SIV-infected monkeys with high titers of vaccine-induced MV-neutralizing antibody developed clinical evidence of MV infection. Thus, in this experimental animal model, a high-titer vaccine-induced MV-neutralizing antibody response does not protect against clinical manifestations of measles in the setting of a chronic acquired immunodeficiency syndrome virus infection.     

Alcohol unmasks simian immunodeficiency virus-induced cognitive impairments in rhesus monkeys

BACKGROUND: Alcohol and human immunodeficiency virus (HIV) produce similar neuropathological profiles, including loss of neurons in the frontal cortex. Additionally, HIV-positive patients with a history of alcohol abuse have greater neurologic deficits, and chronic alcohol abuse produces electrophysiological deficits earlier in the HIV disease process. Few studies, preclinical or clinical, have examined whether alcohol administration exacerbates the neuropsychological deficits in subjects with lentiviruses such as HIV. METHODS: To examine the combined effects of alcohol and immunodeficiency viruses (IVs) on neuropsychological functioning, four groups of young adult rhesus monkeys trained to respond under two complex behavioral tasks were administered ethanol 4 days per week via an intragastric catheter for 3 months and then infected with simian immunodeficiency virus (SIV). Behavioral testing after SIV inoculation was conducted in each group (-ethanol [EtOH]/-SIV, -EtOH/+SIV, +EtOH/-SIV, and +EtOH/+SIV) on days when alcohol was not administered to avoid a direct confound and on several occasions when ethanol or sucrose was administered as a probe of the effect of alcohol alone and the effect of caloric supplementation on the food-maintained tasks, respectively. RESULTS: During the days of the week when ethanol was not administered, little or no disruption was observed in either response rate or the percentage of errors (accuracy) across the different treatment groups. In contrast, behavioral testing during alcohol administration revealed that subjects in the various treatment groups had different susceptibilities to ethanol administration. As expected, a two-way ANOVA (ethanol condition, SIV condition) indicated there were significant main effects of ethanol on both response rate and percent errors in both behavioral tasks, but it also indicated there was a significant interaction between ethanol administration and SIV infection on the accuracy of responding in the acquisition (learning) task. In addition, the main effect of SIV on percent errors was in the performance task. CONCLUSIONS: The fact that alcohol administration in SIV-infected monkeys produced greater behavioral deficits than either alcohol or SIV alone further strengthens the supposition that IVs adversely affect neural substrates involved in cognition and that the adverse effects of many central nervous system drugs may be enhanced in IV-infected individuals.     

Requirements for simian immunodeficiency virus antigen-specific in vitro proliferation of T cells from infected rhesus macaques and sooty mangabeys

The measurement of cell-mediated immunity against the etiologic agent of human AIDS (HIV) in the non-human primate model of AIDS (simian immunodeficiency virus, SIV) has been difficult. In general, culture of peripheral blood mononuclear cells from HIV-1- and SIV-infected humans and monkeys, respectively, with purified inactivated HIV and SIV virus preparations has given inconsistent or negative proliferative responses. However, we describe herein an assay which consists of coculturing monocytes that have been pulsed with inactivated SIVsmm with nylon-wool-purified autologous T cells, leading to antigen-specific T-cell proliferation. The proliferative response, which predominantly occurs in CD4+ T cells, is major histocompatibility complex (MHC) class II-restricted and requires antigen processing. This assay will greatly facilitate the identification of the immunodominant epitopes recognized by T cells in sooty mangabeys, which are naturally infected but remain clinically asymptomatic, and in rhesus macaques, in which experimental infection leads to clinical symptomatology similar to human AIDS, eventually resulting in death.     

Effect of mycobacterial infection on virus loads and disease progression in simian immunodeficiency virus-infected rhesus monkeys

The effect of a mycobacterial infection on AIDS disease was studied in the simian model. Monkeys were infected with the primary virulent isolate SIV/DeltaB670 and inoculated 90 days later with BCG, an attenuated strain of Mycobacterium bovis. All monkeys experienced a dramatic transient increase in plasma viremia and CCR5 expression on T lymphocytes after BCG inoculation. Only two of the four SIV+ animals had substantial proliferative responses to PPD, with poor responders developing disseminated BCG during the course of the experiment. BCG inoculation of SIV-infected long-term nonprogressor (LTNP) monkeys was also performed. Similar to the acutely infected animals, two of three LTNPs experienced increases in plasma viral levels and CCR5 expression. In the majority of animals studied, there was no accelerated progression to AIDS despite the concomitant transient stimulation of virus replication and CCR5 expression on T lymphocytes.     

Urinary neopterin concentrations in rhesus monkeys after infection with simian immunodeficiency virus (SIVmac 251)

Two rhesus monkeys were infected with SIVmac 251. Elevated urinary neopterin concentrations were observed as the first sign of infection. Virus-specific antibodies were detected 14 days after infection, when neopterin concentrations were already decreasing. The neopterin levels of one animal remained elevated and the virus was repeatedly isolated. Urinary or serum neopterin concentrations appear to be early markers for SIV infection and viremia in rhesus monkeys.     

Determination of simian immunodeficiency virus production by infected activated and resting cells

OBJECTIVE: To determine the relative amount of virus produced by activated and resting CD4+ T cells. DESIGN: The total quantity of virus produced by an activated cell relative to a resting cell in vivo was estimated from 'snap-shots' of virus production by infected cells at one time point. METHODS: Bayesian statistical methods were used to determine a credible interval for the desired ratio. RESULTS: The posterior mean of the ratio of virus produced by a typical activated cell to a typical resting cell is 0.82 to 4.28, depending on the half-lives of the resting infected cells. Simian immunodeficiency virus-infected resting cells could accordingly be responsible for 70 to 93% of peak virus production in the acute stage of infection. CONCLUSIONS: Whereas in 'snap-shots' the infected resting cells apparently produce much less virus than infected activated CD4+ T cells, the coincidence of peak SIV production with predominant infection of resting cells along with longer half-lives for productively infected resting cells point to a major contribution to virus production in early infection.     

Soluble human CD4 elicits an antibody response in rhesus monkeys that inhibits simian immunodeficiency virus replication.

Rhesus monkeys infected with the simian immunodeficiency virus of macaques (SIVmac) demonstrate significant virologic and clinical improvement as a result of treatment with human recombinant soluble CD4 (rsCD4). We show that human rsCD4 does not efficiently inhibit SIVmac replication in bone marrow macrophages of rhesus monkeys and does not significantly augment bone marrow hematopoietic colony formation in vitro. However, plasma of human rsCD4-treated rhesus monkeys does exhibit significant anti-SIVmac activity in vitro. Plasma of these animals efficiently blocks SIVmac replication in peripheral blood lymphocytes and bone marrow macrophages. It also increases granulocyte/macrophage colony formation in vitro by bone marrow cells of SIVmac-infected monkeys. This plasma and the IgG fraction of plasma from a rhesus monkey immunized with human rsCD4 in adjuvant demonstrate reactivity with a soluble form of the rhesus monkey CD4 molecule, exhibit binding to CD4+ but not CD8+ concanavalin A-activated rhesus monkey peripheral blood lymphocytes, and precipitate the CD4 molecule from surface-labeled activated rhesus monkey peripheral blood lymphocytes. Moreover, anti-viral activity is demonstrable in the IgG fraction of plasma from a human rsCD4-immunized monkey. These studies raise the possibility that a modified human CD4 molecule serving as an immunogen might elicit an antibody response that could potentially induce a beneficial therapeutic response in human immunodeficiency virus-infected individuals.     

Characterization of simian immunodeficiency virus-specific T-cell-mediated cytotoxic response of infected rhesus macaques

Four juvenile rhesus macaques were infected with simian immunodeficiency virus (SIV)MAC-Freshly isolated peripheral blood mononuclear cells (PBMC) from these SIVMAC-infected and from uninfected control macaques were assessed for cytotoxic T-lymphocyte (CTL) activity monthly for 7 consecutive months, beginning 2 months after infection. Target cells consisted of major histocompatibility complex (MHC) haploidentical parental PBMC which were stimulated with mitogen and then pulsed with heat-killed SIVMAC. CTL activity was demonstrated on all four infected animals. The effector cells are T cells which mediate cytotoxicity against SIVMAC-pulsed target cells in an MHC-restricted manner. Furthermore, the cytotoxicity is virus specific and predominantly, if not exclusively, mediated by CD8+ T cells; it is also MHC class-I restricted. Incubation of target cells with leupeptin prior to the cytotoxic assay inhibited target cell generation, suggesting that viral antigens are processed via an endocytic pathway.     

Clinical features and predictive markers of disease progression in cynomolgus monkeys experimentally infected with simian immunodeficiency virus.

OBJECTIVE: To study the pathogenicity of simian immunodeficiency virus (SIVsm) in cynomolgus monkeys in order to establish an animal model for human AIDS. METHODS: Thirty-three cynomolgus monkeys were monitored for more than 2 years following experimental infection with SIVsm. RESULTS: All the macaques became SIV-infected, as demonstrated by virus recovery from peripheral blood lymphocytes and by the appearance of viral antibodies. SIVsm was found to be pathogenic, killing 29 out of the 33 monkeys (88%) within 26 months. Clinically, infected monkeys developed lymphadenopathy, splenomegaly, diarrhoea, weight loss, neurological symptoms and a remarkably high incidence (39%) of malignant lymphomas. All lymphomas were high-grade malignant and of B-cell origin. Disease progression was associated with low CD4+ lymphocyte count, involution of initially hyperplastic follicular B-cell areas in lymph nodes, reappearance of viral antigen in serum, loss of anti-Gag antibodies and development of systemic giant cell disease in 55% of the monkeys. CONCLUSIONS: There are many similarities between SIVsm-induced AIDS in cynomolgus monkeys and human AIDS with regard to clinical, virological, immunological and pathological manifestations.     

Immunological studies of the basis for the apathogenicity of simian immunodeficiency virus from African green monkeys.

Potential reasons for the lack of pathogenicity of the simian immunodeficiency virus SIVagm in its natural host, the African green monkey (AGM, Cercopithecus aethiops), were investigated with respect to immunological mechanisms. The functional immune response of monkeys to infection was similar (though not identical) to that of humans to infection with human immunodeficiency virus type 1 (HIV-1). In the sera of infected animals, neutralizing antibodies were found to be low or absent, and in particular there was no neutralization of the various isolates by homologous sera. There was no detectable antibody/complement cytotoxicity, though AGM sera were able to initiate antibody-dependent cellular cytolysis of infected cells in the presence of healthy effector peripheral blood lymphocytes. As in the human/HIV system, macrophages from AGMs are readily infected by SIVagm. Two possibly important differences between the AGM/SIVagm system and the human/HIV system are (i) the low immune response of the AGMs to the core protein of SIVagm and (ii) the significantly lower inhibitory effect of SIVagm proteins on the proliferation of AGM lymphocytes.     

Lack of simian immunodeficiency virus (SIV) specific IgA response in the intestine of SIV infected rhesus macaques

BACKGROUND: Little is known about secretory immunity-the major defence mechanism at mucosal surfaces-in human immunodeficiency virus (HIV) infected patients, especially in the early stages of the disease. AIMS: The aim of the study was to analyse mucosal immunoglobulin production and simian immunodeficiency virus (SIV) specific antibody response in the intestinal mucosa during the course of SIV infection in comparison with serum and saliva. ANIMALS AND METHODS: IgG, IgA, and IgM concentrations were determined in supernatants of short term cultured duodenal biopsies, serum, and saliva from SIV infected rhesus macaques (n=8) and controls (n=2) by ELISA at defined times before and after infection. Specific antibodies to SIV were detected by western blot and/or dot blot analysis. In addition, rectal swabs from two uninfected and 12 SIV infected rhesus macaques (seven without and five with enteritis) were analysed for albumin and IgG concentrations. RESULTS: An increase in total intestinal IgG and a decrease in IgA were observed. SIV specific IgG or IgA responses were detectable as early as one week after SIV infection in the serum of seven of eight animals. In contrast, intestinal SIV specific IgG production was detected only four weeks after infection in six of eight animals, and intestinal SIV specific IgA was not produced in the intestine at any time point. In saliva, the secretory component on SIV specific IgA was only detected in one animal at week 24 after infection. Enteritis is frequent in SIV infected animals and results in a significant increase in albumin and IgG secretion into the intestinal lumen. CONCLUSION: Despite modest quantitative changes in mucosal immunglobulin production there was a total lack of SIV specific IgA synthesis in the intestine during SIV infection. This lack or disturbed secretory SIV specific IgA response at mucosal surfaces may explain the rapid and high HIV/SIV replication in this compartment. In addition, our investigations indicate secretion of serum proteins into intestinal fluids during SIV infection. Previous investigations using intestinal secretions or swabs for analysing quantitative and specific immunglobulins therefore should be interpreted with caution.     

Impact of simian immunodeficiency virus (SIV) infection on lymphocyte numbers and T-cell turnover in different organs of rhesus monkeys

HIV infection leads to reduced numbers and increased turnover of CD4(+) T cells in blood. However, blood represents only 2% of the total lymphocyte pool, and information about other organs is lacking, leading to controversy about the effects of HIV infection on T-cell homeostasis. Therefore, we have determined phenotype and turnover of lymphocyte subsets in various tissues of macaques. Infection with simian immunodeficiency virus (SIV) resulted in increased proliferation rates of T cells in all organs. Despite reduced CD4 counts in blood, absolute numbers of CD4(+) T cells were increased in spleen and lymph nodes and remained stable in nonlymphoid organs such as liver, lung, bone marrow, and brain during the asymptomatic phase, indicative for an altered tissue distribution. In animals killed with first signs of AIDS, total body CD4 counts and proliferation rates had returned to control levels, whereas thymocytes were almost completely absent. Our data show that a drastically increased turnover in the early stages of HIV infection, driven by a generalized immune activation rather than a homeostatic response to CD4(+) T-cell destruction, is followed by exhaustion of the regenerative capacity of the immune system.     

Permissiveness of Kupffer cells for simian immunodeficiency virus (SIV) and morphological changes in the liver of rhesus monkeys at different periods of SIV infection

The pathogenesis of liver injury, which remains unclear in the course of human immunodeficiency virus infection, can be investigated in simian immunodeficiency virus-infected macaques, which develop an immunodeficiency disease resembling human acquired immune deficiency syndrome (AIDS). We studied the livers of 21 monkeys infected with simian immunodeficiency virus (SIV,_mac251) for 4 days to 39 months and detected viral antigens in Kupffer cells, macrophages, and lymphocytes in 65% of the livers tested. Virus-containing cells were present in 5 out of 9 livers tested as early as 4 days postinoculation. The number of positive cells as well as their content in viral proteins substantially increased in sinusoidal cells with the progression of the disease. Morphological features and double immunolabeling indicated that Kupffer cells constituted the predominant cell type containing viral antigens. The presence of multinucleated giant cells displaying the ultrastructural features of resident liver macrophages was another sign of the productive infection of Kupffer cells in vivo, which was attested by the observation of budding, immature, and mature SIV particles. Kupffer cell hyperplasia and hypertrophy were evident and appeared to be related to the development of SIV infection, because a close correlation was found between antigenemia and the surface area occupied by these cells. The Kupffer cells contained apoptotic lymphocytes, indicating that resident liver macrophages could play a role in the uptake of such cells from the blood. The production of tumor necrosis factor a (TNFa) and, possibly, interferon-a by Kupffer cells, the expression of vascular adhesion molecule-1, (VCAM-1), intralobular and periportal inflammation, and the proliferation and expansion of bile duct cells were other signs of liver involvement in SIV infection.