Interferon treatment inhibits the replication of simian immunodeficiency virus at an early stage: evidence for a block between attachment and reverse transcription

Stage-specific IFN-induced and IFN gene expression reveal convergence of type I and type II IFN and highlight their role in both acute and chronic stage of pathogenic SIV infection

Interferons (IFNs) play a major role in controlling viral infections including HIV/SIV infections. Persistent up-regulation of interferon stimulated genes (ISGs) is associated with chronic immune activation and progression in SIV/HIV infections, but the respective contribution of different IFNs is unclear. We analyzed the expression of IFN genes and ISGs in tissues of SIV infected macaques to understand the respective roles of type I and type II IFNs. Both IFN types were induced in lymph nodes during early stage of primary infection and to some extent in rectal biopsies but not in PBMCs. Induction of Type II IFN expression persisted during the chronic phase, in contrast to undetectable induction of type I IFN expression. Global gene expression analysis with a major focus on ISGs revealed that at both acute and chronic infection phases most differentially expressed ISGs were inducible by both type I and type II IFNs and displayed the highest increases, indicating strong convergence and synergy between type I and type II IFNs. The analysis of functional signatures of ISG expression revealed temporal changes in IFN expression patterns identifying phase-specific ISGs. These results suggest that IFN-γ strongly contribute to shape ISG upregulation in addition to type I IFN.

Protective Efficacy of Nonpathogenic Nef-Deleted SHIV Vaccination Combined with Recombinant IFN-γ Administration against a Pathogenic SHIV Challenge in Rhesus Monkeys

We previously reported that a nef-deleted SHIV (SHIV-NI) is nonpathogenic and gave macaques protection from challenge infection with pathogenic SHIV-C2/1. To investigate whether IFN-gamma augments the immune response induced by this vaccination, we examined the antiviral and adjuvant effect of recombinant human IFN-gamma (rIFN-gamma) in vaccinated and unvaccinated monkeys. Nine monkeys were vaccinated with nef-deleted nonpathogenic SHIV-NI. Four of them were administered with rIFN-gamma and the other five monkeys were administered with placebo. After the challenge with pathogenic SHIV-C2/1, CD4(+) T-cell counts were maintained similarly in monkeys of both groups, while those of the unvaccinated monkeys decreased dramatically at 2 weeks after challenge. However, the peaks of plasma viral load were reduced to 100-fold in SHIV-NI vaccinated monkeys combined with rIFN-gamma compared with those in SHIV-NI vaccinated monkeys without rIFN-gamma. The peaks of plasma viral load were inversely correlated with the number of SIV Gag-specific IFN-gamma-producing cells. In SHIV-NI-vaccinated monkeys with rIFN-gamma, the number of SIV Gag-specific IFN-gamma-producing cells of PBMCs increased 2-fold compared with those in SHIV-NI-vaccinated monkeys without rIFN-gamma, and the NK activity and MIP-1alpha production of PBMCs were also enhanced. Thus, vaccination of SHIV-NI in combination with rIFN-gamma was more effective in modulating the antiviral immune system into a Th1 type response than SHIV-NI vaccination alone. These results suggest that IFN-gamma augmented the anti-viral effect by enhancing innate immunity and shifting the immune response to Th1.

Evidence for a different susceptibility of primate lentiviruses to type I interferons

Type I interferons induce a complex transcriptional program that leads to a generalized antiviral response against a large panel of viruses, including human immunodeficiency virus type 1 (HIV-1). However, despite the fact that interferons negatively regulate HIV-1 ex vivo, a chronic interferon state is linked to the progression of AIDS and to robust viral replication, rather than protection, in vivo. To explain this apparent contradiction, we hypothesized that HIV-1 may have evolved a partial resistance to interferon, and to test this hypothesis, we analyzed the effects of alpha interferon (IFN-α) on the infectivity of HIV-1, human immunodeficiency virus type 2 (HIV-2), and rhesus monkey simian immunodeficiency virus (SIVmac). The results we obtained indicate that HIV-1 is more resistant to an IFN-α-induced response than are HIV-2 and SIVmac. Our data indicate that the accumulation of viral DNA is more compromised following the infection of IFN-α-treated cells with HIV-2 and SIVmac than with HIV-1. This defect correlates with a faster destabilization of HIV-2 viral nucleoprotein complexes (VNCs), suggesting a link between VNC destabilization and impaired viral DNA (vDNA) accumulation. The differential susceptibilities to IFN-α of the primate lentiviruses tested here do not map to the capsid protein (CA), excluding de facto a role for human tripartite motif protein isoform 5 alpha (Trim5α) in this restriction; this also suggests that an additional restriction mechanism differentially affects primate lentivirus infection. The different behaviors of HIV-1 and HIV-2 with respect to IFN-α responses may account at least in part for the differences in pathogenesis observed between these two virus types.

Characterization of the alpha interferon-induced postentry block to HIV-1 infection in primary human macrophages and T cells

Type I interferon (IFN) inhibits virus replication by activating multiple antiviral mechanisms and pathways. It has long been recognized that alpha interferon (IFN-alpha) can potently block both early and late stages of HIV-1 replication. The mechanistic basis for the early block(s) to infection is unknown, as is the identity of the participating antiviral factor(s). Here, we define the effect(s) of IFN-alpha on HIV-1 infection of primary human macrophages and CD4(+) T cells, as well as several monocytic and T-cell lines. We demonstrate that IFN-alpha treatment of macrophages, THP-1 cells, and, to a lesser extent, primary CD4(+) T cells markedly inhibits infection, whereas the effects are minimal in CD4(+) T-cell lines. Virus entry is essentially unaffected by IFN-alpha, but substantial decreases (sometimes >99%) in nascent cDNA accumulation correlate closely with losses in infectivity. Interestingly, proteasome inhibitors rescue viral cDNA accumulation, revealing a link between the ubiquitin-proteasome system and IFN-alpha-induced viral restriction. We also found that diverse primate and nonprimate retroviruses were susceptible to suppression by IFN-alpha. Importantly, all the primary and immortalized cells used here are proficient at responding to IFN-alpha, as judged by the induced expression of numerous IFN-stimulated genes, including PKR and OAS1, indicating that a general deficiency in IFN-alpha responsiveness does not underlie IFN-alpha's inability to elicit an antiviral state in CD4(+) T-cell lines. Rather, we speculate that IFN-alpha fails to induce antiretroviral factors in these cells and that comparative transcriptional profiling with responsive cells, such as macrophages, invokes a strategy for identifying new host-encoded antiviral effectors.

Effect of type-I interferon on retroviruses

Type-I interferons (IFN-I) play an important role in the innate immune response to several retroviruses. They seem to be effective in controlling the in vivo infection, though many of the clinical signs of retroviral infection may be due to their continual presence which over-stimulates the immune system and activates apoptosis. IFN-I not only affect the immune system, but also operate directly on virus replication. Most data suggest that the in vitro treatment with IFN-I of retrovirus infected cells inhibits the final stages of virogenesis, avoiding the correct assembly of viral particles and their budding, even though the mechanism is not well understood. However, in some retroviruses IFN-I may also act at a previous stage as some retroviral LTRs posses sequences homologous to the IFN-stimulated response element (ISRE). When stimulated, ISREs control viral transcription. HIV-1 displays several mechanisms for evading IFN-I, such as through Tat and Nef. Besides IFN-α and IFN-β, some other type I IFN, such as IFN-τ and IFN-ω, have potent antiviral activity and are promising treatment drugs.

Human immunodeficiency virus, restriction factors, and interferon

Recent discoveries have revealed previously unappreciated complexity with which retroviruses interact with their hosts. In particular, we have become aware that many mammals, including humans, are equipped with genes encoding so-called "restriction factors," that provide considerable resistance to retroviral infection. Such antiretroviral genes are sometimes constitutively expressed, and sometimes interferon-induced. Thus they can be viewed as comprising an intrinsic immune system that provides a pre-mobilized defense against retroviral infection or, alternatively, as a specialized extension of conventional innate immunity. Antiretroviral restriction factors have evolved at an unusually rapid pace, particularly in primates, and some startling examples of evolutionary change are present in genes encoding restriction factors. Our understanding of the mechanisms by which restriction factors interfere with retroviral replication, and how their effects are avoided by certain retroviruses, is accruing, but far from complete. Such knowledge could allow for novel forms of therapeutic intervention in pathogenic retroviral infections, as well as the development of animal models of human disease.

Transcriptional profiling in pathogenic and non-pathogenic SIV infections reveals significant distinctions in kinetics and tissue compartmentalization

Simian immunodeficiency virus (SIV) infection leads to AIDS in experimentally infected macaques, whereas natural reservoir hosts exhibit limited disease and pathology. It is, however, unclear how natural hosts can sustain high viral loads, comparable to those observed in the pathogenic model, without developing severe disease. We performed transcriptional profiling on lymph node, blood, and colon samples from African green monkeys (natural host model) and Asian pigtailed macaques (pathogenic model) to directly compare gene expression patterns during acute pathogenic versus non-pathogenic SIV infection. The majority of gene expression changes that were unique to either model were detected in the lymph nodes at the time of peak viral load. Results suggest a shift toward cellular stress pathways and Th1 profiles during pathogenic infection, with strong and sustained type I and II interferon responses. In contrast, a strong type I interferon response was initially induced during non-pathogenic infection but resolved after peak viral load. The natural host also exhibited controlled Th1 profiles and better preservation of overall cell homeostasis. This study identified gene expression patterns that are specific to disease susceptibility, tissue compartmentalization, and infection duration. These patterns provide a unique view of how host responses differ depending upon lentiviral infection outcome.

Simian immunodeficiency virus (SIV) does not cause disease in African green monkeys (a natural host for the virus), whereas experimentally infected Asian macaques (a non-natural host) develop a progressive disease that is similar to that which occurs in HIV-infected humans. Insight into how HIV causes disease and leads to development of AIDS may therefore be gained by comparing the response of natural and non-natural hosts to SIV infection. To this end, we examined changes that occurred in gene expression levels over time and in multiple tissues derived from African green monkeys and Asian macaques experimentally infected with SIV. Infection leads to host-specific gene expression patterns in lymph nodes, blood, and colon. The natural and non-natural hosts differed with respect to the timing, intensity, and duration of infection-induced gene expression changes associated with inflammation and response to stress.

Implication of TRIM alpha and TRIMCyp in interferon-induced anti-retroviral restriction activities

Background

TRIM5α is a restriction factor that interferes with retroviral infections in a species-specific manner in primate cells. Although TRIM5α is constitutively expressed, its expression has been shown to be up-regulated by type I interferon (IFN). Among primates, a particular case exists in owl monkey cells, which express a fusion protein between TRIM5 and cyclophilin A, TRIMCyp, specifically interfering with HIV-1 infection. No studies have been conducted so far concerning the possible induction of TRIMCyp by IFN. We investigated the consequences of IFN treatment on retroviral restriction in diverse primate cells and evaluated the implication of TRIM5α or TRIMCyp in IFN-induced anti-retroviral activities.

Results

First, we show that human type I IFN can enhance TRIM5α expression in human, African green monkey and macaque cells, as well as TRIMCyp expression in owl monkey cells. In TRIM5α-expressing primate cell lines, type I IFN has little or no effect on HIV-1 infection, whereas it potentates restriction activity against N-MLV in human and African green monkey cells. In contrast, type I IFN treatment of owl monkey cells induces a great enhancement of HIV-1 restriction, as well as a strain-tropism independent restriction of MLV. We were able to demonstrate that TRIM5α is the main mediator of the IFN-induced activity against N-MLV in human and African green monkey cells, whereas TRIMCyp mediates the IFN-induced HIV-1 restriction enhancement in owl monkey cells. In contrast, the type I IFN-induced anti-MLV restriction in owl monkey cells is independent of TRIMCyp expression.

Conclusion

Together, our observations indicate that both TRIM5α and TRIMCyp are implicated in IFN-induced anti-retroviral response in primate cells. Furthermore, we found that type I IFN also induces a TRIMCyp-independent restriction activity specific to MLV in owl monkey cells.

Social stress enhances sympathetic innervation of primate lymph nodes: mechanisms and implications for viral pathogenesis

Behavioral processes regulate immune system function in part via direct sympathetic innervation of lymphoid organs, but little is known about the factors that regulate the architecture of neural fibers in lymphoid tissues. In the present study, we find that experimentally imposed social stress can enhance the density of catecholaminergic neural fibers within axillary lymph nodes from adult rhesus macaques. This effect is linked to increased transcription of the key sympathetic neurotrophin nerve growth factor and occurs predominately in extrafollicular regions of the paracortex that contain T-lymphocytes and macrophages. Functional consequences of stress-induced increases in innervation density include reduced type I interferon response to viral infection and increased replication of the simian immunodeficiency virus. These data reveal a surprising degree of behaviorally induced plasticity in the structure of lymphoid innervation and define a novel pathway by which social factors can modulate immune response and viral pathogenesis.

HIV type 1 inhibition by protein kinase C modulatory compounds

The dichotomous effects of the protein kinase C (PKC) modulatory compounds 12-myristate 13-acetate (PMA), prostratin, and ingenol 3-angelate (I3A) on HIV-1 infection were investigated. PKC modulatory compounds were shown to be potent activators of cells latently infected with HIV-1 (I3A > prostratin). Conversely, PKC modulatory compounds inhibited infection of indicator cells (MAGI) with CXCR4-tropic HIV-1 (PMA > I3A > prostratin), and I3A also inhibited infection with CCR5-tropic virus (AD8-1). Pretreatment with the PKC inhibitors prior to treatment with either I3A or PMA resulted in increased infection, indicating inhibition is PKC mediated. Cell infections suggested that I3A rapidly inhibited the virus from infecting cells at an early point in infection. This observation was supported by the demonstration of inhibition at or before the synthesis of early reverse transcription products, and the inability of these compounds to block vesicular stomatitis virus (VSV) pseudotyped HIV-1 particles. As has already been shown with prostratin, treatment with I3A resulted in down-regulation of the CD4 receptor and CXCR4 coreceptor suggesting that this was a contributor to the infection inhibition. Intriguingly, 48 h pretreatment of unstimulated peripheral blood mononuclear cells (PBMC) prior to infection resulted in abrogation of virus production at concentrations where receptor/ coreceptor levels were not significantly reduced. This result hints at the possibility of inhibition by a PKC modulatory compound of an early pathway of viral entry in PBMC.

Cytokine expression, natural killer cell activation, and phenotypic changes in lymphoid cells from rhesus macaques during acute infection with pathogenic simian immunodeficiency virus

We studied the innate and adaptive immune system of rhesus macaques infected with the virulent simian immunodeficiency virus isolate SIVmac251 by evaluating natural killer (NK) cell activity, cytokine levels in plasma, humoral and virological parameters, and changes in the activation markers CD25 (interleukin 2R ¿IL-2R alpha chain), CD69 (early activation marker), and CD154 (CD40 ligand) in lymphoid cells. We found that infection with SIVmac251 induced the sequential production of interferon-alpha/beta (IFN-alpha/beta), IL-18, and IL-12. IFN-gamma, IL-4, and granulocyte-macrophage colony-stimulating factor were undetected in plasma by the assays used. NK cell activity peaked at 1 to 2 weeks postinfection and paralleled changes in viral loads. Maximum expression of CD69 on CD3(-)CD16(+) lymphocytes correlated with NK cytotoxicity during this period. CD25 expression, which is associated with proliferation, was static or slightly down-regulated in CD4(+) T cells from both peripheral blood (PB) and lymph nodes (LN). CD69, which is normally present in LN CD4(+) T cells and absent in peripheral blood leukocyte (PBL) CD4(+) T cells, was down-regulated in LN CD4(+) T cells and up-regulated in PBL CD4(+) T cells immediately after infection. CD8(+) T cells increased CD69 but not CD25 expression, indicating the activation of this cellular subset in PB and LN. Finally, CD154 was transiently up-regulated in PBL CD4(+) T cells but not in LN CD4(+) T cells. Levels of antibodies to SIV Gag and Env did not correlate with the level of activation of CD154, a critical costimulatory molecule for T-cell-dependent immunity. In summary, we present the first documented evidence that the innate immune system of rhesus macaques recognizes SIV infection by sequential production of proinflammatory cytokines and transient activation of NK cytotoxic activity. Additionally, pathogenic SIV induces drastic changes in the level of activation markers on T cells from different anatomic compartments. These changes involve activation in the absence of proliferation, indicating that activation-induced cell death may cause some of the reported increase in lymphocyte turnover during SIV infection.

Abundant defective viral particles budding from microglia in the course of retroviral spongiform encephalopathy

A pathogenetic hallmark of retroviral neurodegeneration is the affinity of neurovirulent retroviruses for microglia cells, while degenerating neurons are excluded from retroviral infections. Microglia isolated ex vivo from rats peripherally infected with a neurovirulent retrovirus released abundant mature type C virions; however, infectivity associated with microglia was very low. In microglia, viral transcription was unaffected but envelope proteins were insufficiently cleaved into mature viral proteins and were not detected on the microglia cell surface. These microglia-specific defects in envelope protein translocation and processing not only may have prevented formation of infectious virus particles but also may have caused further cellular defects in microglia with the consequence of indirect neuronal damage. It is conceivable that similar events play a role in neuro-AIDS.

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

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

Interferon inhibits the replication of HIV-1, SIV, and SHIV chimeric viruses by distinct mechanisms

Interferon (IFN) treatment of lentivirus-infected cells substantially reduces virus replication in vitro. Although the replication of both HIV-1 and simian immunodeficiency virus (SIV) is inhibited, IFN blocks the replication of these viruses at different stages of the viral life cycle. We previously demonstrated that in HIV-1-infected cells, IFN blocks a late step in viral replication, leading to a decrease in viral protein stability and a deregulation of polyprotein processing. In contrast, in SIV-infected cells, IFN blocks an early step in viral replication, between virus binding and reverse transcription. Thus, the viral gene products targeted by IFN may be different for each of these viruses. To attempt to define which viral proteins are targeted by the IFN response, we examined the effects of IFN on the replication of two SIV/HIV-1 (SHIV) chimeric viruses, SHIV-4(vpu+) and SHIV-4(vpu-) in 174 x CEM cells. These viruses were grown from constructs in which the SIVmac239 env, tat, and rev genes have been replaced with those HIV-1. The use of SHIV-4(vpu+) allowed us to examine whether vpu, which is unique to HIV-1, might contribute to the differential effects of IFN on HIV-1 and SIV replication. Surprisingly, we found that IFN inhibited SHIV replication differently than the replication of either HIV-1 or SIV. IFN treatment of SHIV-infected cells resulted in a decrease in the level of viral RNA expression but had no apparent effect on the integration of proviral DNA. Nuclear runoff transcription assays indicated that the reduction of SHIV RNA expression in IFN-treated cells was not due to alterations in RNA polymerase II-mediated transcription, suggesting that IFN may block SHIV replication by promoting the increased degradation of viral RNA. The presence of absence of the vpu gene did not alter the effects of IFN on SHIV replication, indicating that Vpu is not responsible for the differential effect of IFN on HIV-1 and SIV replication. Thus the response of SHIVs to antiviral agents such as IFN may be unique from either HIV-1 or SIV. This may be an important consideration when using SHIVs to evaluate anti-HIV-1 therapies in animal models of AIDS.