[Contribution of animal models to HIV research]. / Apport des modèles animaux dans la recherche sur le VIH.

Even today, despite triple therapy, the epidemic of the human immunodeficiency virus (HIV) is a major public health problem. In this perspective, continuous research is essential for the development of curative and vaccinal approaches. Animal models contribute to the implementation of new therapeutic and preventive strategies. We present here the characteristics of major animal models of HIV, which are non-human primates (SIV or SHIV-infected macaques and natural hosts of SIV), as well as different humanized mouse models and their advances. We will also list how they have already allowed, and still allow today, to broaden our knowledge on the physiopathology of HIV infection, tissue distribution of the virus, viral reservoirs, immunological responses against the virus in the very early infection stages and at the tissue level, but also in the development of vaccine candidates (RhCMV, broad-spectrum antibodies, etc…) and clinical trials for a cure. The advantages and limitations of the different animal models will be described. While continuing research on alternative methods, refinement or reduction of the animal model, a good knowledge of the specificities of each animal model allows an adequate use in relation to the scientific questions addressed.

Applications of the FIV Model to Study HIV Pathogenesis.

Feline immunodeficiency virus (FIV) is a naturally-occurring retrovirus that infects domestic and non-domestic feline species, producing progressive immune depletion that results in an acquired immunodeficiency syndrome (AIDS). Much has been learned about FIV since it was first described in 1987, particularly in regard to its application as a model to study the closely related lentivirus, human immunodeficiency virus (HIV). In particular, FIV and HIV share remarkable structure and sequence organization, utilize parallel modes of receptor-mediated entry, and result in a similar spectrum of immunodeficiency-related diseases due to analogous modes of immune dysfunction. This review summarizes current knowledge of FIV infection kinetics and the mechanisms of immune dysfunction in relation to opportunistic disease, specifically in regard to studying HIV pathogenesis. Furthermore, we present data that highlight changes in the oral microbiota and oral immune system during FIV infection, and outline the potential for the feline model of oral AIDS manifestations to elucidate pathogenic mechanisms of HIV-induced oral disease. Finally, we discuss advances in molecular biology, vaccine development, neurologic dysfunction, and the ability to apply pharmacologic interventions and sophisticated imaging technologies to study experimental and naturally occurring FIV, which provide an excellent, but often overlooked, resource for advancing therapies and the management of HIV/AIDS.

Neurologic disease in feline immunodeficiency virus infection: disease mechanisms and therapeutic interventions for NeuroAIDS.

Feline immunodeficiency virus (FIV) is a lentivirus that causes immunosuppression through virus-mediated CD4+ T cell depletion in feline species. FIV infection is complicated by virus-induced disease in the nervous system. FIV enters the brain soon after primary infection and is detected as FIV-encoded RNA, DNA, and proteins in microglia, macrophages, and astrocytes. FIV infection activates neuroinflammatory pathways including cytokines, chemokines, proteases, and ROS with accompanying neuronal injury and loss. Neurobehavioral deficits during FIV infection are manifested as impaired motor and cognitive functions. Several treatment strategies have emerged from studies of FIV neuropathogenesis including the therapeutic benefits of antiretroviral therapies, other protease inhibitors, anti-inflammatory, and neurotrophic compounds. Recently, insulin's antiviral, anti-inflammatory, and neuroprotective effects were investigated in models of lentivirus brain infection. Insulin suppressed HIV-1 replication in human microglia as well as FIV replication of lymphocytes. Insulin treatment diminished cytokine and chemokine activation in HIV-infected microglia while also protecting neurons from HIV-1 Vpr protein-mediated neurotoxicity. Intranasal (IN) insulin delivery for 6 weeks suppressed FIV expression in the brains of treated cats. IN insulin also reduced neuroinflammation and protected neurons in the hippocampus, striatum, and neocortex of FIV-infected animals. These morphological and molecular effects of IN insulin were confirmed by neurobehavioral studies that showed IN insulin-treated FIV-infected animals displayed improved motor and cognitive performance compared to sham-treated FIV-infected animals. Thus, FIV infection of the nervous system provides a valuable comparative in vivo model for discovering and evaluating disease mechanisms as well as developing therapeutic strategies for NeuroAIDS in humans.

Systolic blood pressure, routine kidney variables and renal ultrasonographic findings in cats naturally infected with feline immunodeficiency virus.

Objectives Hypertension is a common cause of proteinuria in HIV-infected people. In cats, feline immunodeficiency virus (FIV) infection appears to be associated with proteinuria. Therefore, the results from systolic blood pressure (SBP) measurements in naturally infected FIV-positive cats were reviewed to assess whether hypertension contributes to the observed proteinuria in these cats. Ultrasonographic findings in FIV-positive cats were reviewed to complete renal assessment and to extend the scant knowledge on renal ultrasonography in cats. Methods Data from client-owned, naturally infected FIV-positive cats were retrospectively reviewed. To obtain a control group, records were reviewed from age-matched, privately owned, FIV-negative cats. Results Data from 91 FIV-infected and 113 control cats were compared. FIV-infected cats showed a significantly lower SBP ( P <0.0001) and significantly fewer FIV-infected cats were hypertensive (⩾160 mmHg) compared with control cats ( P = 0.025). The prevalence of renal azotaemia did not significantly differ between groups, although FIV-infected cats had significantly lower urine specific gravity (USG) ( P = 0.0273) and a higher incidence of USG below 1.035 ( P = 0.043). Urinary protein:creatinine ratio (UPC) was significantly higher in FIV-infected cats ( P = 0.0005) and proteinuria (UPC >0.4) occurred more frequently in FIV-infected cats ( P <0.001). Renal ultrasonography showed abnormalities in 60/91 FIV-infected cats, with hyperechogenic cortices in 39/91 and enlarged kidneys in 31/91. Conclusions and relevance Hypertension can be excluded as a common cause of renal damage leading to proteinuria in FIV-infected cats. Proteinuria and poorly concentrated urine are common in naturally infected FIV-positive cats, in contrast to azotaemia. Clinicians should cautiously interpret ultrasonographic abnormalities as these occur in over half of FIV-infected cats.

Immune-endocrine interactions in treated and untreated cats naturally infected with FIV.

Feline immunodeficiency virus (FIV) is a lentivirus that causes a progressive disruption of immune function in cats. The neuroendocrine and immune systems communicate bidirectionally, mediated by cytokines such as tumour necrosis factor-α (TNF), several interleukins (IL-1, IL-6, IL-10), and through signals induced by the ratio of IL-10 to IL-12. FIV can affect both pituitary adrenal and thyroid axis function. Twenty FIV-infected cats in similar stages of the disease were evaluated for six months. A cross-sectional study in which the twenty cats were divided into two groups was performed. Ten were treated with Zidovudine (ZDV: 5mg/kg/d, PO, q12h, for six months) and 10 were untreated. Plasma concentrations of adrenocorticotropic hormone (ACTH), cortisol, T4, FT4, T3, IL-10, IL-12 and viral load (VL) were evaluated after six months. ACTH was found in significantly lower concentrations (p<0.0001) in the treated group whereas cortisol did not show significant differences between the two groups. Both T4 and FT4 had high values in untreated individuals (p<0.001) compared with Zidovudine treated cats. T3 did not show significant differences between the two groups. Both IL-10 and IL-12 were found in significantly higher concentrations in ZDV treated cats (p<0.001). By contrast, the IL10/IL-12 ratio values were significantly lower in untreated cats. Viral load was significantly lower in the treated cats after six months of therapy, compared with values detected pre-treatment (p<0.002). Untreated cats showed a significant increase of VL (p<0.04) compared with the values at the beginning of the study. In treated cats, VL showed lower numbers of viral copies than in untreated cats (p<0.01). In summary, Zidovudine treatment appeared to contribute to the normalization of both the adrenal and thyroid axes. This effect could be attributed to the decrease observed in VL, resulting in a change in cytokine patterns.

Strain-specific viral distribution and neuropathology of feline immunodeficiency virus.

Feline immunodeficiency virus (FIV) is a naturally occurring lentivirus of domestic cats, and is the causative agent of feline AIDS. Similar to human immunodeficiency virus (HIV), the pathogenesis of FIV involves infection of lymphocytes and macrophages, and results in chronic progressive immune system collapse and death. Neuropathologic correlates of FIV infection have not yet been elucidated, and may be relevant to understanding HIV-associated neurologic disease (neuroAIDS). As in HIV, FIV strains have been shown to express differential tendencies towards development of clinical neuroAIDS. To interrogate viral genetic determinants that might contribute to neuropathogenicity, cats were exposed to two well-characterized FIV strains with divergent clinical phenotypes and a chimeric strain as follows: FIV(PPR) (PPR, relatively apathogenic but associated with neurologic manifestations), FIV(C36) (C36, immunopathogenic but without associated neurologic disease), and Pcenv (a chimeric virus consisting of a PPR backbone with substituted C36 env region). A sham inoculum control group was also included. Peripheral nerve conduction velocity, CNS imaging studies, viral loads and hematologic analysis were performed over a 12 month period. At termination of the study (350 days post-inoculation), brain sections were obtained from four anatomic locations known to be involved in human and primate lentiviral neuroAIDS. Histological and immunohistochemical evaluation with seven markers of inflammation revealed that Pcenv infection resulted in mild inflammation of the CNS, microglial activation, neuronal degeneration and apoptosis, while C36 and PPR strains induced minimal neuropathologic changes. Conduction velocity aberrations were noted peripherally in all three groups at 63 weeks post-infection. Pcenv viral load in this study was intermediate to the parental strains (C36 demonstrating the highest viral load and PPR the lowest). These results collectively suggest that (i) 3' C36 genomic elements contribute to viral replication characteristics, and (ii) 5' PPR genomic elements contribute to CNS manifestations. This study illustrates the potential for FIV to provide valuable information about neuroAIDS pathogenesis related to genotype and viral kinetics, as well as to identify strains useful to evaluation of therapeutic intervention.

Improved health and survival of FIV-infected cats is associated with the presence of autoantibodies to the primary receptor, CD134.

We analyzed antibody responses in sera from feline immunodeficiency virus (FIV)-infected and uninfected cats. A strong antiviral response to the viral surface glycoprotein (SU) was noted in both natural and experimental infections. In addition, 143 of 226 FIV-infected animals (63%) also expressed antibodies to the primary binding receptor, CD134, whereas cats infected with other feline RNA viruses, including calicivirus, coronavirus, herpesvirus, and feline leukemia virus, did not. Both affinity-purified anti-CD134 and anti-SU antibodies blocked FIV infection ex vivo. FACS analyses revealed that the anti-CD134 antibodies bound to a cryptic epitope on the receptor that was only exposed when SU bound to CD134. Anti-CD134 binding caused displacement of SU from the surface of the cell and inhibition of infection. The presence of antibodies to CD134 correlated with lower virus loads and a better overall health status in FIV(+) cats, whereas anti-SU antibodies were present independent of health status. The findings are consistent with a role for antireceptor antibodies in protection from virus spread and disease progression.

Lymphocyte migration through the blood-brain barrier (BBB) in feline immunodeficiency virus infection is significantly influenced by the pre-existence of virus and tumour necrosis factor (TNF)-alpha within the central nervous system (CNS): studies using an in vitro feline BBB model.

AIMS: In human immunodeficiency virus infection, macrophage-tropic and lymphotropic viruses exist in the host. Central nervous system (CNS) infection is an early and ongoing event, important to understand when developing strategies to treat infection. Some knowledge exists on macrophage-tropic virus interactions with the blood-brain barrier (BBB), and the aim of this study was to investigate lymphotropic lentivirus interactions with the BBB. METHODS: Interactions of the lymphotropic feline immunodeficiency virus (FIV) with an in vitro model of the feline BBB were evaluated in scenarios to mimic in vivo infections. RESULTS: Cell-free FIV crossed the BBB in very low quantities, and in the presence of tumour necrosis factor (TNF)-alpha, BBB integrity was unaffected. However, cell-associated FIV readily crossed the BBB, but BBB integrity was not significantly altered. Transmigration of uninfected and infected lymphocytes increased in response to TNF-alpha, accompanied by a moderate disruption of barrier integrity and an upregulation of vascular cell adhesion molecule-1 rather than intercellular adhesion molecule-1. Significant enhancement of migration and disruption of BBB tight junctions occurred when infected cells and TNF-alpha were added to the brain side of the BBB and this enhancement was not mediated through additional TNF-alpha production. CONCLUSIONS: Small quantities of virus in the brain together with TNF-alpha have the potential to stimulate greater cell and viral entry into the CNS and this is likely to involve important factors other than further TNF-alpha production. Lymphotropic lentivirus entry to the CNS is governed by many factors similar to macrophage-tropic strains.

Evaluation of feline monocyte-derived dendritic cells loaded with internally inactivated virus as a vaccine against feline immunodeficiency virus.

Dendritic cells are the only antigen-presenting cells that can present exogenous antigens to both helper and cytolytic T cells and prime Th1-type or Th2-type cellular immune responses. Given their unique immune functions, dendritic cells are considered attractive "live adjuvants" for vaccination and immunotherapy against cancer and infectious diseases. The present study was carried out to assess whether the reinjection of autologous monocyte-derived dendritic cells loaded with an aldithriol-2-inactivated primary isolate of feline immune deficiency virus (FIV) was able to elicit protective immune responses against the homologous virus in naive cats. Vaccine efficacy was assessed by monitoring immune responses and, finally, by challenge with the homologous virus of vaccinated, mock-vaccinated, and healthy cats. The outcome of challenge was followed by measuring cellular and antibody responses and viral and proviral loads and quantitating FIV by isolation and a count of CD4(+)/CD8(+) T cells in blood. Vaccinated animals exhibited clearly evident FIV-specific peripheral blood mononuclear cell proliferation and antibody titers in response to immunization; however, they became infected with the challenge virus at rates comparable to those of control animals.

Feline immunodeficiency virus infection is enhanced by feline bone marrow-derived dendritic cells.

In the pathogenesis of feline immunodeficiency virus (FIV) infection, feline dendritic cells (feDCs) are thought to play an important role. As with DCs in other species, feDCs are believed to transport virus particles to lymph nodes and transfer them to lymphocytes. Our investigation has focused on the ability of feDCs to influence the infection of syngeneic peripheral blood mononuclear cells (PBMCs) and allogeneic thymocytes. feDCs were derived from bone marrow mononuclear cells that were cultured under the influence of feline interleukin-4 and feline granulocyte-macrophage colony-stimulating factor. By using these feDCs in co-culture with resting PBMCs, an upregulation of FIV replication was shown. An enhancement of FIV infection was also detected when co-cultures of feDCs/feline thymocytes were infected. To obtain this enhancement, direct contact of the cells in the co-culture was necessary; transwell cultures showed that the involvement of only soluble factors produced by feDCs in this process is not likely. These feDCs were also able to induce the proliferation of resting thymocytes, which might explain the enhanced FIV replication observed. Together, these data suggest that feDCs have abilities similar to those shown for simian and human DCs in the interaction with leukocytes. This system is suitable for further investigations of the interplay of DC and T cells during FIV infection in vitro.

Seroepidemiological survey of infection by feline leukemia virus and immunodeficiency virus in Madrid and correlation with some clinical aspects.

A study of 180 healthy cats found that 15.6% were feline leukemia virus (FeLV) positive, 8.3% were feline immunodeficiency virus (FIV) positive, and 1.1% were FIV and FeLV positive, which corresponded to 30.4, 13.8, and 2.6, of 115 cats with FIV- and FeLV-related symptoms, respectively. Differences were seen in the sexes and ages of the populations studied. Anemia, leukopenia, and lymphopenia were the most frequent hematological abnormalities in infected cats.

Effects of multiple acute morphine exposures on feline immunodeficiency virus disease progression.

Drug abuse is a common method of human immunodeficiency virus type 1 transmission, but the role of opiates on lentivirus disease progression is not well understood. The feline immunodeficiency virus (FIV)/cat system was used to model the weekend opiate abuser: the nondependent, nonaddicted, and nontolerant person. Sixteen cats were placed into 4 groups: FIV only, morphine only, morphine/FIV, and controls. Multiple acute morphine exposure did not increase the severity of early lentivirus infection. On the contrary, it delayed or moderated the FIV-induced disease progression. Although the animals were exposed to only 1 injection of morphine per day for 2 consecutive days per week, the morphine-treated FIV-infected animals had a delayed onset of the FIV-induced lymphadenopathy, did not develop or had a significant delay in the FIV-induced effects on brain stem auditory evoked potentials, and demonstrated a trend toward decreased virus load.

Exogenous glucocorticoids alter parameters of early feline immunodeficiency virus infection.

Feline immunodeficiency virus (FIV), a lentivirus, causes progressive immunosuppression and neurologic dysfunction in cats. Glucocorticoids are common therapeutic agents that are also immunosuppressive, and their use might enhance the pathogenic effects of lentivirus infections. Methylprednisolone acetate, a long-acting glucocorticoid, was administered to cats before FIV inoculation, and the course of early infection was monitored. The humoral immune response to FIV was not affected by corticosteroid treatment, but CD8+ cell-mediated antiviral activity was poor in cultures from FIV-infected cats treated with methylprednisolone. Steroid-treated cats had higher plasma viral RNA levels than untreated cats during acute viremia. In contrast, FIV-associated changes in brain stem auditory-evoked potentials were slow to develop in the methylprednisolone-treated cats. Methylprednisolone treatment of cats with established FIV infections appeared to reverse these neurophysiologic changes. These results emphasize the complexity of host-lentivirus interactions and suggest potential advantages and drawbacks of using glucocorticoids in lentivirus infections.

Assessment of intestinal function in cats with chronic diarrhea after infection with feline immunodeficiency virus.

OBJECTIVE: To identify consistent relevant mechanisms of small intestinal dysfunction in cats with experimentally induced feline immunodeficiency virus infection (FIV) that developed chronic diarrhea during the time they were being used in studies of pathogenicity and transmission of FIV. ANIMALS: 10 cats. PROCEDURE: The following investigative tests and techniques were performed on each of the cats: routine hematologic and serum biochemical analyses; urinalysis; fecal parasitologic and microbiologic examinations; breath hydrogen lactulose (BH2LT) and xylose (BH2XT) tests; intestinal permeability test; endoscopic examination of the intestinal mucosa; bacteriologic culture of endoscopically collected small intestinal juice; and histologic examination of endoscopically obtained intestinal biopsy specimens. RESULTS: Neutrophilia was evident in 3 cats, and lymphopenia was detected in 2 cats. Serum biochemical abnormalities were not observed. Urinalysis results were unremarkable. Fecal bacteriologic and parasitologic results were normal, except for isolation of Campylobacter sp from 1 cat. Abnormal BH2XT values suggestive of D-xylose malabsorption were identified in 2 cats, and BH2LT values indicated evidence of small intestinal bacterial overgrowth in 1 cat. Finally, permeability test results, quantitation of bacterial flora from the proximal part of the small intestine and histologic examination of biopsy specimens did not reveal any abnormalities. CONCLUSIONS: Enteric pathogens did not account for the development of diarrhea in cats with experimentally induced FIV infection, and consistent relevant mechanisms of small intestinal dysfunction were not identified.

Feline immunodeficiency virus infection: an overview.

In 1987, Pedersen et al. (1987) reported the isolation of a T-lymphotropic virus possessing the characteristics of a lentivirus from pet cats in Davis, California. From the first report onwards, it was evident that in causing an acquired immunodeficiency syndrome in cats, the virus was of substantial veterinary importance. It shares many physical and biochemical properties with human immunodeficiency virus (HIV), and was therefore named feline immunodeficiency virus (FIV). This article reviews recent knowledge of the aetiology, epidemiology, pathogenesis, clinical signs, diagnosis, prevention, and treatment options of FIV infection.

Eight-year observation and comparative study of specific pathogen-free cats experimentally infected with feline immunodeficiency virus (FIV) subtypes A and B: terminal acquired immunodeficiency syndrome in a cat infected with FIV petaluma strain.

Three specific pathogen-free cats experimentally infected with feline immunodeficiency virus (FIV) strains Petaluma, TM1 and TM2, respectively were observed for over 8 years. Without showing any significant clinical signs of immunodeficiency syndrome (AIDS) for 8 years and 4 months of asymptomatic phase, the Petaluma-infected cat exhibited severe stomatitis/gingivitis, anorexia, emaciation, hematological and immunological disorders such as severe anemia, lymphopenia, thrombocytopenia, and decrease of CD4/CD8 ratio to 0.075, and finally died with hemoperitoneum at 8 years and 8 months post-infection. Histopathological studies revealed that the cat had systemic lymphoid atrophy and bone marrow disorders indicating acute myelocytic leukemia (aleukemic type). Plasma viral titer of the cat at AIDS phase was considerably high and anti-FIV antibody titer was slightly low as compared with the other FIV-infected cats. In addition, immunoblotting analysis using serially collected serum/plasma samples of these cats revealed that antibodies against FIV proteins were induced in all the infected cats, however in the Petaluma-infected cat anti-Gag antibodies disappeared during the asymptomatic period. These results suggested that plasma viral load and anti-FIV Gag antibody response correlated with disease progression, and supported FIV-infected cats as a suitable animal model of human AIDS.

Dynamics of two feline retroviruses (FIV and FeLV) within one population of cats.

We present a deterministic model of the dynamics of two microparasites simultaneously infecting a single host population. Both microparasites are feline retroviruses, namely Feline Immunodeficiency Virus (FIV) and Feline Leukaemia Virus (FeLV). The host is the domestic cat Felis catus. The model has been tested with data generated by a long-term study of several natural cat populations. Stability analysis and simulations show that, once introduced in a population, FIV spreads and is maintained, while FeLV can either disappear or persist. Moreover, introduction of both viruses into the population induces an equilibrium state for individuals of each different pathological class. The viruses never induce the extinction of the population. Furthermore, whatever the outcome for the host population (persistence of FIV only, or of both viruses), the global population size at the equilibrium state is only slightly lower than it would have been in the absence of the infections (i.e. at the carrying capacity), indicating a low impact of the viruses on the population. Finally, the impact of the diseases examined simultaneously is higher than the sum of the impact of the two diseases examined separately. This seems to be due to a higher mortality rate when both viruses infect a single individual.

Retrospective study of 60 cases of feline lymphosarcoma.

OBJECTIVE: To characterise epidemiological and clinical findings, and diagnostic procedures undertaken, in cats with lymphosarcoma at a veterinary teaching hospital. DESIGN: Retrospective case study. PROCEDURE: Hospital records were reviewed for 7159 cats, sick or healthy, examined during a 10-year period (1984 to 1994). Sixty cats with lymphosarcoma were identified and classified by anatomical location of the tumor. Data on breed, age, sex, clinical signs and diagnostic procedures were collated. RESULTS: The prevalence of feline lymphosarcoma in the hospital population was 0.84%. Siamese cats appeared predisposed to lymphosarcoma but other purebreds were not. Males were somewhat overrepresented amongst affected cats. Similar numbers of cases (12 to 18) were seen in each of the four anatomic categories (multicentric, mediastinal, alimentary and extranodal). Cats with mediastinal lymphosarcoma were mostly young and Siamese. Clinical signs in affected cats were varied, usually multiple and often nonspecific. Two of 22 cases tested positive for feline leukaemia virus antigen in blood and 6 of 13 were positive for feline immunodeficiency virus antibody. CONCLUSIONS: Extranodal lymphosarcoma seemed more prevalent in this study than reported elsewhere. Siamese cats in the study population may have had a genetic predisposition to lymphosarcoma. Limited evidence suggested feline leukaemia virus may be less important, and feline immunodeficiency virus more important, in the local population than indicated in overseas reports. Additional studies are needed to investigate breed predisposition and feline leukaemia virus and feline immunodeficiency virus status in Australian cats with lymphosarcoma.

The value of primate models for studying human immunodeficiency virus pathogenesis.

Research on human immunodeficiency virus (HIV) infection is compromised by the obvious limitation in having for study only virus-infected individuals or those exposed to the virus. Steps involved in transmission or pathogenesis require planned experimentation. The identification of animal models of acquired immunodeficiency syndrome (AIDS) has therefore been helpful for evaluating phases of HIV pathogenesis. Of the seven subgenera of lentiviruses now recognized, two share the characteristics with HIV of a T cell tropism and the associated loss of CD4+ cells in the host associated with disease: the feline immunodeficiency virus (FIV) and the simian immunodeficiency virus (SIV) (Table 1). The other animal lentiviruses grow best in macrophages and their infection generally reflects clinical sequellae of infection of this cell type. This review addresses those features of SIV, HIV, and SHIV infections of non-human primates that illustrate the importance of the animal models of AIDS.