HIV induces synaptic hyperexcitation via cGMP-dependent protein kinase II activation in the FIV infection model.

Over half of individuals infected with human immunodeficiency virus (HIV) suffer from HIV-associated neurocognitive disorders (HANDs), yet the molecular mechanisms leading to neuronal dysfunction are poorly understood. Feline immunodeficiency virus (FIV) naturally infects cats and shares its structure, cell tropism, and pathology with HIV, including wide-ranging neurological deficits. We employ FIV as a model to elucidate the molecular pathways underlying HIV-induced neuronal dysfunction, in particular, synaptic alteration. Among HIV-induced neuron-damaging products, HIV envelope glycoprotein gp120 triggers elevation of intracellular Ca2+ activity in neurons, stimulating various pathways to damage synaptic functions. We quantify neuronal Ca2+ activity using intracellular Ca2+ imaging in cultured hippocampal neurons and confirm that FIV envelope glycoprotein gp95 also elevates neuronal Ca2+ activity. In addition, we reveal that gp95 interacts with the chemokine receptor, CXCR4, and facilitates the release of intracellular Ca2+ by the activation of the endoplasmic reticulum (ER)-associated Ca2+ channels, inositol triphosphate receptors (IP3Rs), and synaptic NMDA receptors (NMDARs), similar to HIV gp120. This suggests that HIV gp120 and FIV gp95 share a core pathological process in neurons. Significantly, gp95's stimulation of NMDARs activates cGMP-dependent protein kinase II (cGKII) through the activation of the neuronal nitric oxide synthase (nNOS)-cGMP pathway, which increases Ca2+ release from the ER and promotes surface expression of AMPA receptors, leading to an increase in synaptic activity. Moreover, we culture feline hippocampal neurons and confirm that gp95-induced neuronal Ca2+ overactivation is mediated by CXCR4 and cGKII. Finally, cGKII activation is also required for HIV gp120-induced Ca2+ hyperactivation. These results thus provide a novel neurobiological mechanism of cGKII-mediated synaptic hyperexcitation in HAND.

Variation in Intra-individual Lentiviral Evolution Rates: a Systematic Review of Human, Nonhuman Primate, and Felid Species.

Lentiviral replication mediated by reverse transcriptase is considered to be highly error prone, leading to a high intra-individual evolution rate that promotes evasion of neutralization and persistent infection. Understanding lentiviral intra-individual evolutionary dynamics on a comparative basis can therefore inform research strategies to aid in studies of pathogenesis, vaccine design, and therapeutic intervention. We conducted a systematic review of intra-individual evolution rates for three species groups of lentiviruses-feline immunodeficiency virus (FIV), simian immunodeficiency virus (SIV), and human immunodeficiency virus (HIV). Overall, intra-individual rate estimates differed by virus but not by host, gene, or viral strain. Lentiviral infections in spillover (nonadapted) hosts approximated infections in primary (adapted) hosts. Our review consistently documents that FIV evolution rates within individuals are significantly lower than the rates recorded for HIV and SIV. FIV intra-individual evolution rates were noted to be equivalent to FIV interindividual rates. These findings document inherent differences in the evolution of FIV relative to that of primate lentiviruses, which may signal intrinsic difference of reverse transcriptase between these viral species or different host-viral interactions. Analysis of lentiviral evolutionary selection pressures at the individual versus population level is valuable for understanding transmission dynamics and the emergence of virulent and avirulent strains and provides novel insight for approaches to interrupt lentiviral infections.IMPORTANCE To the best of our knowledge, this is the first study that compares intra-individual evolution rates for FIV, SIV, and HIV following systematic review of the literature. Our findings have important implications for informing research strategies in the field of intra-individual virus dynamics for lentiviruses. We observed that FIV evolves more slowly than HIV and SIV at the intra-individual level and found that mutation rates may differ by gene sequence length but not by host, gene, strain, an experimental setting relative to a natural setting, or spillover host infection relative to primary host infection.

Detection of feline immunodeficiency virus subtypes A and B circulating in the city of Buenos Aires.

Feline immunodeficiency virus (FIV), genus Lentivirus, is responsible for feline immunodeficiency syndrome in domestic cats. FIV has been classified into six subtypes: A, B, C, D, E and F, based on regions of the env gene as well as the gag gene. In Argentina, the circulation of subtypes B and E was reported more than two decades ago. The objective of this work was to study the FIV variants circulating presently in the city of Buenos Aires in naturally infected cats utilizing a nested PCR targeting the gag gene. A phylogenetic comparison with representative sequences of five previously published subtypes shows a clustering with subtypes A and B. This is the first report of FIV subtype A in Argentina.

[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.

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.

Feline immudeficiency virus subtypes B and A in cats from São Luis, Maranhão, Brazil.

Feline immunodeficiency virus (FIV) is a retrovirus of the genus Lentivirus that is distributed worldwide, with prevalence rates varying between 2.5% and 44%. FIV causes immunosuppression, with depletion of TCD4+ lymphocytes, with the majority of clinical signs caused by secondary and opportunistic infections. Blood samples were collected from nine domestic cats (Felis catus domesticus) from the city of São Luís, Maranhão State, Brazil. All samples were positive in a rapid immunochromatographic test (SNAP® Combo FeLV Ag/FIV Antibody Test) and in a polymerase chain reaction (PCR) assay. Phylogenetic analysis showed that six samples clustered within subtype B, one within subtype A, and two did not cluster with any known subtype. Five unique haplotypes (Hap-1, Hap-2, Hap-3, Hap-5 and Hap-6) and a shared haplotype (Hap-4) were found, this last one being the most frequent. This is the first report on the genetic diversity of FIV in the city of São Luís and the first report of subtype A in Brazil. New variations of the virus are also reported.

Central and peripheral reservoirs of feline immunodeficiency virus in cats: a review.

Infection with feline immunodeficiency virus (FIV), a lentivirus similar to human immunodeficiency virus (HIV), results in lifelong viral persistence and progressive immunopathology in the cat. FIV has the ability to infect and produce infectious virus in a number of different cell types. FIV provirus can also be maintained in a replication-competent but transcriptionally quiescent state, facilitating viral persistence over time. Immediately after the initial infection, FIV infection quickly disseminates to many anatomical compartments within the host including lymphoid organs, gastrointestinal tract and brain. Collectively, the anatomic and cellular compartments that harbour FIV provirus constitute the viral reservoir and contain foci of both ongoing viral replication and transcriptionally restricted virus that may persist over time. The relative importance of the different phenotypes observed for infected cells, anatomic compartment, replication status and size of the reservoir represent crucial areas of investigation for developing effective viral suppression and eradication therapies. In this review, we discuss what is currently known about FIV reservoirs, and emphasize the utility of the FIV-infected cat as a model for the HIV-infected human.

Sexually transmitted infections and mate-finding Allee effects.

Infectious diseases can seriously impact dynamics of their host species. In this study, we model and analyze an interaction between a sexually transmitted infection and its animal host population affected by a mate-finding Allee effect. Since mating drives both host reproduction and infection transmission, the Allee effect shapes the transmission rate of the infection which we show takes a saturating form. Our model combining sexually transmitted infections with the mate-finding Allee effect in the host produces quite rich dynamics, including oscillations, several multistability regimes, and infection-induced host extinction. However, many of these complex patterns are restricted to a relatively narrow parameter range. We find that the host extinction occurs at intermediate levels of infection virulence, as well as for Allee effect strengths much lower than when the infection is absent. In both cases, a sequence of events comprising destabilization of an endemic equilibrium, growth of oscillation amplitude, and a heteroclinic bifurcation forms an underlying mechanism. We apply our model to the feline immunodeficiency virus (FIV) in domestic cats.

Molecular survey of Bartonella henselae and Bartonella clarridgeiae in pet cats across Japan by species-specific nested-PCR.

Cats are known to be the main reservoir for Bartonella henselae and Bartonella clarridgeiae, which are the agents of 'cat-scratch disease' in humans. In the present study, we investigated the prevalence of the two Bartonella species on 1754 cat bloods collected from all prefectures in Japan during 2007-2008 by a nested-polymerase chain reaction (PCR) targeting the 16S-23S rRNA internal transcribed spacer region. Overall, Bartonella DNA was detected in 4·6% (80/1754) of the cats examined. The nested-PCR showed that 48·8% (39/80) of the positive cats were infected with B. henselae mono-infection, 33·8% (27/80) with B. clarridgeiae mono-infection and 17·5% (14/80) were infected with both species. The prevalence (5·9%; 65/1103) of Bartonella infection in the western part of Japan was significantly higher than that (2·3%; 15/651) of eastern Japan (P < 0·001). Statistical analysis of the cats examined suggested a significant association between Bartonella infection and FeLV infection (OR = 1·9; 95% CI = 1·1-3·4), but not with FIV infection (OR = 1·6; 95% CI = 1·0-2·6).

Feline immunodeficiency virus and feline leukemia virus: frequency and associated factors in cats in northeastern Brazil.

Our aims were to determine the frequencies of feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) in owned and stray cats in the northeastern region of Brazil, ascertain the status of FeLV infection, and investigate potential associated factors among the owned cats. Blood samples from 200 asymptomatic owned cats and 30 stray cats were processed using nested PCR and commercial immunochromatographic tests to diagnose infections. To evaluate the factors associated with FIV and/or FeLV in owned cats, a semi-structured interview was conducted with each owner about the animal's environment, and these data were subjected to unconditional logistic regression. The frequencies for owned cats were 6% (12/200) and 3% (6/200) for FIV and FeLV, respectively. No owned cat was positive for both viruses. Stray cats showed frequencies of 6.66% (2/30) and 0% (0/30) for FIV and FeLV, respectively. Contact with other cats and living in peri-urban areas were considered to be risk factors (P < 0.05) for FIV. We did not identify any factors associated with infections with FeLV. Our results confirm the presence of these two retroviruses in the region under study. Our use of different diagnostic techniques allowed us to determine the frequency of retroviruses in the feline population more accurately, particularly with regard to infections by FeLV, which have complex pathogenesis.

Processing, fusogenicity, virion incorporation and CXCR4-binding activity of a feline immunodeficiency virus envelope glycoprotein lacking the two conserved N-glycosylation sites at the C-terminus of the V3 domain.

The process of feline immunodeficiency virus (FIV) entry into its target cells is initiated by the association of the surface (SU) subunit of the viral envelope glycoprotein (Env) with the cellular receptors CD134 and CXCR4. This event is followed by the fusion of the viral and cellular membranes, which is mediated by the transmembrane (TM) subunit of Env. We and others have previously demonstrated that the V3 domain of the SU subunit of Env is essential for CXCR4 binding. Of note, there are two contiguous and highly conserved potential N-glycosylation sites ((418)NST(420) and (422)NLT(424)) located at the C-terminal side of the V3 domain. We therefore decided to study the relevance for Env functions of these N-glycosylation motifs and found that disruption of both of them by introducing the N418Q/N422Q double amino acid substitution drastically impairs Env processing into the SU and TM subunits. Moreover, the simultaneous mutation of these N-glycosylation sites prevents Env incorporation into virions and Env-mediated cell-to-cell fusion. Notably, a recombinant soluble version of the SU glycoprotein carrying the double amino acid replacement N418Q/N422Q at the V3 C-terminal side binds to CXCR4 with an efficiency similar to that of wild-type SU.

Viral diagnostic criteria for Feline immunodeficiency virus and Feline leukemia virus infections in domestic cats from Buenos Aires, Argentina.

A cross-sectional study was carried out on cats attending the Small Animal Hospital at the Faculty of Veterinary Sciences of the University of Buenos Aires to assess the prevalence and associated risk factors of Feline immunodeficiency virus (FIV) and Feline leukemia virus (FeLV) in the city of Buenos Aires, Argentina. Blood samples from 255 cats with symptoms compatible with FIV or FeLV infection, collected between 2009 and 2013 were analyzed by serology (immunochromatography, IA) and by hemi-nested PCR (n-PCR). The IA and n-PCR assays showed similar percentages of positivity for FIV while the n-PCR test was more sensitive for FeLV. Differences between the diagnostic tests and their choice according to the age of the animal are discussed. The clinical histories of ninety of the 255 cats showed blood profiles similar to others previously reported and revealed a higher risk of infection in male adult cats with outdoor access.

Error correction and statistical analyses for intra-host comparisons of feline immunodeficiency virus diversity from high-throughput sequencing data.

BACKGROUND: Infection with feline immunodeficiency virus (FIV) causes an immunosuppressive disease whose consequences are less severe if cats are co-infected with an attenuated FIV strain (PLV). We use virus diversity measurements, which reflect replication ability and the virus response to various conditions, to test whether diversity of virulent FIV in lymphoid tissues is altered in the presence of PLV. Our data consisted of the 3' half of the FIV genome from three tissues of animals infected with FIV alone, or with FIV and PLV, sequenced by 454 technology. RESULTS: Since rare variants dominate virus populations, we had to carefully distinguish sequence variation from errors due to experimental protocols and sequencing. We considered an exponential-normal convolution model used for background correction of microarray data, and modified it to formulate an error correction approach for minor allele frequencies derived from high-throughput sequencing. Similar to accounting for over-dispersion in counts, this accounts for error-inflated variability in frequencies - and quite effectively reproduces empirically observed distributions. After obtaining error-corrected minor allele frequencies, we applied ANalysis Of VAriance (ANOVA) based on a linear mixed model and found that conserved sites and transition frequencies in FIV genes differ among tissues of dual and single infected cats. Furthermore, analysis of minor allele frequencies at individual FIV genome sites revealed 242 sites significantly affected by infection status (dual vs. single) or infection status by tissue interaction. All together, our results demonstrated a decrease in FIV diversity in bone marrow in the presence of PLV. Importantly, these effects were weakened or undetectable when error correction was performed with other approaches (thresholding of minor allele frequencies; probabilistic clustering of reads). We also queried the data for cytidine deaminase activity on the viral genome, which causes an asymmetric increase in G to A substitutions, but found no evidence for this host defense strategy. CONCLUSIONS: Our error correction approach for minor allele frequencies (more sensitive and computationally efficient than other algorithms) and our statistical treatment of variation (ANOVA) were critical for effective use of high-throughput sequencing data in understanding viral diversity. We found that co-infection with PLV shifts FIV diversity from bone marrow to lymph node and spleen.

The oral and conjunctival microbiotas in cats with and without feline immunodeficiency virus infection.

The oral and conjunctival microbiotas likely play important roles in protection from opportunistic infections, while also being the source of potential pathogens. Yet, there has been limited investigation in cats, and the impact of comorbidities such as feline immunodeficiency virus (FIV) infection has not been reported. Oral and conjunctival swabs were collected from cats with FIV infection and FIV-uninfected controls, and subjected to 16S rRNA gene (V4) PCR and next generation sequencing. 9,249 OTUs were identified from conjunctival swabs, yet the most common 20 (0.22%) OTUs accounted for 76% of sequences. The two most abundant OTUs both belonged to Staphylococcus, and accounted for 37% of sequences. Cats with FIV infection had significantly lower relative abundances of Verrucomicrobia, Fibrobacteres, Spirochaetes, Bacteroidetes and Tenericutes, and a higher relative abundance of Deinococcus-Thermus. There were significant differences in both community membership (P = 0.006) and community structure (P = 0.02) between FIV-infected and FIV-uninfected cats. FIV-infected cats had significantly higher relative abundances of Fusobacteria and Actinobacteria in the oral cavity, and significantly higher relative abundances of several bacterial classes including Fusobacteria (0.022 vs 0.007, P = 0.006), Actinobacteria (0.017 vs 0.003, P = 0.003), Sphingobacteria (0.00015 vs 0.00003, P = 0.0013) and Flavobacteria (0.0073 vs 0.0034, P = 0.030). The feline conjunctival and oral microbiotas are complex polymicrobial communities but dominated by a limited number of genera. There is an apparent impact of FIV infection on various components of the microbiota, and assessment of the clinical relevance of these alterations in required.

Emergence of CD134 cysteine-rich domain 2 (CRD2)-independent strains of feline immunodeficiency virus (FIV) is associated with disease progression in naturally infected cats.

BACKGROUND: Feline immunodeficiency virus (FIV) infection is mediated by sequential interactions with CD134 and CXCR4. Field strains of virus vary in their dependence on cysteine-rich domain 2 (CRD2) of CD134 for infection. FINDINGS: Here, we analyse the receptor usage of viral variants in the blood of 39 naturally infected cats, revealing that CRD2-dependent viral variants dominate in early infection, evolving towards CRD2-independence with disease progression. CONCLUSIONS: These findings are consistent with a shift in CRD2 of CD134 usage with disease progression.

Neurosteroid-mediated regulation of brain innate immunity in HIV/AIDS: DHEA-S suppresses neurovirulence.

Neurosteroids are cholesterol-derived molecules synthesized within the brain, which exert trophic and protective actions. Infection by human and feline immunodeficiency viruses (HIV and FIV, respectively) causes neuroinflammation and neurodegeneration, leading to neurological deficits. Secretion of neuroinflammatory host and viral factors by glia and infiltrating leukocytes mediates the principal neuropathogenic mechanisms during lentivirus infections, although the effect of neurosteroids on these processes is unknown. We investigated the interactions between neurosteroid-mediated effects and lentivirus infection outcomes. Analyses of HIV-infected (HIV(+)) and uninfected human brains disclosed a reduction in neurosteroid synthesis enzyme expression. Human neurons exposed to supernatants from HIV(+) macrophages exhibited suppressed enzyme expression without reduced cellular viability. HIV(+) human macrophages treated with sulfated dehydroepiandrosterone (DHEA-S) showed suppression of inflammatory gene (IL-1ß, IL-6, TNF-α) expression. FIV-infected (FIV(+)) animals treated daily with 15 mg/kg body weight. DHEA-S treatment reduced inflammatory gene transcripts (IL-1ß, TNF-α, CD3ε, GFAP) in brain compared to vehicle-(ß-cyclodextrin)-treated FIV(+) animals similar to levels found in vehicle-treated FIV(-) animals. DHEA-S treatment also increased CD4(+) T-cell levels and prevented neurobehavioral deficits and neuronal loss among FIV(+) animals, compared to vehicle-treated FIV(+) animals. Reduced neuronal neurosteroid synthesis was evident in lentivirus infections, but treatment with DHEA-S limited neuroinflammation and prevented neurobehavioral deficits. Neurosteroid-derived therapies could be effective in the treatment of virus- or inflammation-mediated neurodegeneration.

Differential type 1 interferon-regulated gene expression in the brain during AIDS: interactions with viral diversity and neurovirulence.

The lentiviruses, human and feline immunodeficiency viruses (HIV-1 and FIV, respectively), infect the brain and cause neurovirulence, evident as neuronal injury, inflammation, and neurobehavioral abnormalities with diminished survival. Herein, different lentivirus infections in conjunction with neural cell viability were investigated, concentrating on type 1 interferon-regulated pathways. Transcriptomic network analyses showed a preponderance of genes involved in type 1 interferon signaling, which was verified by increased expression of the type 1 interferon-associated genes, Mx1 and CD317, in brains from HIV-infected persons (P<0.05). Leukocytes infected with different strains of FIV or HIV-1 showed differential Mx1 and CD317 expression (P<0.05). In vivo studies of animals infected with the FIV strains, FIV(ch) or FIV(ncsu), revealed that FIV(ch)-infected animals displayed deficits in memory and motor speed compared with the FIV(ncsu)- and mock-infected groups (P<0.05). TNF-α, IL-1ß, and CD40 expression was increased in the brains of FIV(ch)-infected animals; conversely, Mx1 and CD317 transcript levels were increased in the brains of FIV(ncsu)-infected animals, principally in microglia (P<0.05). Gliosis and neuronal loss were evident among FIV(ch)-infected animals compared with mock- and FIV(ncsu)-infected animals (P<0.05). Lentiviral infections induce type 1 interferon-regulated gene expression in microglia in a viral diversity-dependent manner, representing a mechanism by which immune responses might be exploited to limit neurovirulence.

Evaluation of leukocyte ratios as survival prognostic markers in feline retrovirus infections.

The utility of neutrophil-lymphocyte ratio (NLR), monocyte-lymphocyte ratio (MLR), and platelet-lymphocyte ratio (PLR) as prognostic markers in Feline Leukemia Virus (FeLV) and Feline Immunodeficiency Virus (FIV) infections has not yet been investigated. The aim of this study was to investigate these leukocyte ratios in retrovirus-positive cats and to evaluate their prognostic value for survival. This retrospective case-control study included 142 cats, 75 FIV-Antibodies (Ab)-positive, 52 FeLV-Antigen (Ag)-positive, and 15 FIV-Ab+FeLV-Ag-positive, and a control population of 142 retrovirus-negative age-, sex-, and lifestyle-matched cats. Signalment, complete blood count at the time of serological testing, and outcome were recorded. Leukocyte ratios were compared within the same case-control population, among the three retrovirus-seropositive populations, and were related to survival time. No significant difference was found in NLR, MLR, or PLR between FIV-Ab-positive and FIV-Ab+FeLV-Ag-positive cats and their cross-matched controls. In the FeLV-Ag-positive population, MLR was significantly lower than in the control population (0.05 and 0.14, respectively, P=0.0008). No ratio discriminated among the three infectious states. No ratio was significantly different between survivors and non-survivors in the population of FIV-Ab-positive cats. MLR at diagnosis was significantly higher in FeLV-Ag-positive cats that died 1-3 years after diagnosis than in FeLV-Ag-positive cats still alive at 3 years (P=0.0284). None of the three ratios could predict retroviruses-positive cats that would survive to the end of the study. Overall the results indicate that NLR, MLR, and PLR are not significantly different among retrovirus statuses evaluated and had a very limited prognostic value for the survival time in retrovirus-positive cats.

Feline immunodeficiency virus latency.

Despite highly effective anti-retroviral therapy, HIV is thought to persist in patients within long-lived cellular reservoirs in the form of a transcriptionally inactive (latent) integrated provirus. Lentiviral latency has therefore come to the forefront of the discussion on the possibility of a cure for HIV infection in humans. Animal models of lentiviral latency provide an essential tool to study mechanisms of latency and therapeutic manipulation. Of the three animal models that have been described, the feline immunodeficiency virus (FIV)-infected cat is the most recent and least characterized. However, several aspects of this model make it attractive for latency research, and it may be complementary to other model systems. This article reviews what is known about FIV latency and chronic FIV infection and how it compares with that of other lentiviruses. It thereby offers a framework for the usefulness of this model in future research aimed at lentiviral eradication.

Biophysical characterization and crystal structure of the Feline Immunodeficiency Virus p15 matrix protein.

BACKGROUND: Feline Immunodeficiency Virus (FIV) is a viral pathogen that infects domestic cats and wild felids. During the viral replication cycle, the FIV p15 matrix protein oligomerizes to form a closed matrix that underlies the lipidic envelope of the virion. Because of its crucial role in the early and late stages of viral morphogenesis, especially in viral assembly, FIV p15 is an interesting target in the development of potential new therapeutic strategies. RESULTS: Our biochemical study of FIV p15 revealed that it forms a stable dimer in solution under acidic conditions and at high concentration, unlike other retroviral matrix proteins. We determined the crystal structure of full-length FIV p15 to 2 Å resolution and observed a helical organization of the protein, typical for retroviral matrix proteins. A hydrophobic pocket that could accommodate a myristoyl group was identified, and the C-terminal end of FIV p15, which is mainly unstructured, was visible in electron density maps. As FIV p15 crystallizes in acidic conditions but with one monomer in the asymmetric unit, we searched for the presence of a biological dimer in the crystal. No biological assembly was detected by the PISA server, but the three most buried crystallographic interfaces have interesting features: the first one displays a highly conserved tryptophan acting as a binding platform, the second one is located along a 2-fold symmetry axis and the third one resembles the dimeric interface of EIAV p15. Because the C-terminal end of p15 is involved in two of these three interfaces, we investigated the structure and assembly of a C-terminal-truncated form of p15 lacking 14 residues. The truncated FIV p15 dimerizes in solution at a lower concentration and crystallizes with two molecules in the asymmetric unit. The EIAV-like dimeric interface is the only one to be retained in the new crystal form. CONCLUSION: The dimeric form of FIV p15 in solution and its extended C-terminal end are characteristic among lentiviral matrix proteins. Crystallographic interfaces revealed several interactions that might be involved in FIV replication. Further studies are needed to better understand their biological relevance in the function of FIV Gag during viral replication.