[show abstract][hide abstract] ABSTRACT: The antagonistic interaction with host restriction proteins is a major driver of evolutionary change for viruses. We previously reported that polymorphisms of the TRIM5α B30.2/SPRY domain impacted the level of SIVsmm viremia in rhesus macaques. Viremia in macaques homozygous for the non-restrictive TRIM5α allele TRIM5(Q) was significantly higher than in macaques expressing two restrictive TRIM5alpha alleles TRIM5(TFP/TFP) or TRIM5(Cyp/TFP). Using this model, we observed that despite an early impact on viremia, SIVsmm overcame TRIM5α restriction at later stages of infection and that increasing viremia was associated with specific amino acid substitutions in capsid. Two amino acid substitutions (P37S and R98S) in the capsid region were associated with escape from TRIM5(TFP) restriction and substitutions in the CypA binding-loop (GPLPA87-91) in capsid were associated with escape from TRIM5(Cyp). Introduction of these mutations into the original SIVsmE543 clone not only resulted in escape from TRIM5α restriction in vitro but the P37S and R98S substitutions improved virus fitness in macaques with homozygous restrictive TRIM(TFP) alleles in vivo. Similar substitutions were observed in other SIVsmm strains following transmission and passage in macaques, collectively providing direct evidence that TRIM5α exerts selective pressure on the cross-species transmission of SIV in primates.
[show abstract][hide abstract] ABSTRACT: Nonhuman primate/SIV models are powerful tools to study the pathogenesis of HIV-1 in the brain. Our laboratory recently isolated a neuropathogenic viral swarm, SIVsmH804E, a derivative of SIVsmE543-3, the result of sequential intravenous passage of virus isolated from the brain of rhesus macaques with SIV encephalitis. Animals infected with SIVsmH804E or its precursor (SIVsmH783Br) developed SIV meningitis and/or encephalitis at high frequencies. Since we observed macaques with a combination of meningitis and encephalitis as well as animals where meningitis or encephalitis was the dominant component, we hypothesized that distinct mechanisms could be driving those two pathological states. Therefore we assessed viral populations in the meninges and the brain parenchyma by laser capture microdissection. Viral RNA was isolated from representative areas of meninges and brain parenchyma, terminal plasma, cerebrospinal fluid (CSF) and the inoculum and the SIV envelope fragment was amplified by PCR. Phylogenetic analysis of envelope sequences from the conventional progressors revealed compartmentalization of viral populations between the meninges and the parenchyma. In one of these animals, viral populations in meninges were closely related to those from CSF and shared signature truncations in the cytoplasmic domain of gp41, consistent with a common origin. Apart from MRI and PET imaging, CSF is the most accessible assess to the central nervous system of HIV-1 infected patients. However, our results suggest that virus in the CSF may not always be representative of viral populations in the brain and that caution should be applied in extrapolating between the properties of virus in these two compartments.
[show abstract][hide abstract] ABSTRACT: Simian immunodeficiency virus (SIV) infection of macaques can result in central nervous system (CNS) disorders, such as meningitis and encephalitis. We studied ten animals inoculated with brain-derived virus from animals with SIV-encephalitis. Over half of the macaques developed SIV-induced neurologic disease. Elevated levels of systemic immune activation were observed to correlate with viral RNA in the cerebral spinal fluid but not with plasma viral load, consistent with a role in the pathogenesis of neurologic disease.
[show abstract][hide abstract] ABSTRACT: Previous studies demonstrated that the nef gene is a critical determinant of the pathogenicity of simian immunodeficiency virus (SIV) in macaques. In the present study, we evaluated the effect of a spontaneous frameshift mutation in the C-terminus of the nef gene of the minimally pathogenic SIVsmH4i clone. This clone exhibited a single nucleotide deletion in the nef gene relative to pathogenic SIV clones that resulted in a frameshift and addition of 46 amino acids to the C-terminus of Nef. We generated a corrected version of this clone, SIVsmH4i Nef+ that restored Nef protein expression. Inoculation of macaques with SIVsmH4i resulted in delayed and low levels of peak viremia. This contrasted with improved kinetics and robust peak viremia in macaques inoculated with the corrected version. Despite the restoration of in vivo replication ability, neither clone resulted in memory CD4+ T cell loss or disease in a period of two years.
[show abstract][hide abstract] ABSTRACT: African green monkeys (genus Chlorocebus) can be infected with species-specific simian immunodeficiency virus (SIVagm) but do not develop AIDS. These natural hosts of SIV, like sooty mangabeys, maintain high levels of SIV replication but have evolved to avoid immunodeficiency. Elucidating the mechanisms that allow natural hosts to coexist with SIV without overt disease may provide crucial information for understanding AIDS pathogenesis. Here we show that many CD4(+) T cells from African green monkeys downregulate CD4 in vivo as they enter the memory pool; that downregulation of CD4 by memory T cells is independent of SIV infection; that the CD4(-) memory T cells maintain functions that are normally attributed to CD4(+) T cells, including production of interleukin-2 (IL-2), production of IL-17, expression of forkhead box P3 and expression of CD40 ligand; that loss of CD4 expression protects these T cells from infection by SIVagm in vivo; and that these CD4(-) T cells can maintain major histocompatibility complex class II restriction. These data show that the absence of SIV-induced disease progression in natural host species may be partially explained by preservation of a subset of T cells that maintain CD4(+) T cell function while being resistant to SIV infection in vivo.
Nature medicine 07/2009; 15(8):879-85. · 27.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: The progressive decline of CD4(+) T cells is a hallmark of disease progression in human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infection. Whereas the acute phase of the infection is dominated by virus-mediated depletion of memory CD4(+) T cells, chronic infection is often associated with a progressive decline of total CD4(+) T cells, including the naïve subset. The mechanism of this second phase of CD4(+) T cell loss is unclear and may include immune activation-induced cell death, immune-mediated destruction, and regenerative or homeostatic failure. We studied patterns of CD4(+) T cell subset depletion in blood and tissues in a group of 20 rhesus macaques inoculated with derivatives of the pathogenic SIVsmE543-3 or SIVmac239. Phenotypic analysis of CD4(+) T cells demonstrated two patterns of CD4(+) T cell depletion, primarily affecting either naïve or memory CD4(+) T cells. Progressive decline of total CD4(+) T cells was observed only in macaques with naïve CD4(+) T cell depletion (ND), though the depletion of memory CD4(+) T cells was profound in macaques with memory CD4(+) T cell depletion (MD). ND macaques exhibited lower viral load and higher SIV-specific antibody responses and greater B cell activation than MD macaques. Depletion of naïve CD4(+) T cells was associated with plasma antibodies autoreactive with CD4(+) T cells, increasing numbers of IgG-coated CD4(+) T cells, and increased incidence of autoreactive antibodies to platelets (GPIIIa), dsDNA, and phospholipid (aPL). Consistent with a biological role of these antibodies, these latter antibodies were accompanied by clinical features associated with autoimmune disorders, thrombocytopenia, and catastrophic thrombotic events. More importantly for AIDS pathogenesis, the level of autoreactive antibodies significantly correlated with the extent of naïve CD4(+) T cell depletion. These results suggest an important role of autoreactive antibodies in the CD4(+) T cell decline observed during progression to AIDS.
[show abstract][hide abstract] ABSTRACT: A subset of simian immunodeficiency virus (SIV)-infected macaques progresses rapidly to disease with transient SIV-specific immune responses and high viral loads. Unique SIV variants with convergent Env mutations evolve in these rapid progressor (RP) macaques. To address the pathogenic significance of RP-specific variants, we generated infectious molecular clones from the terminal-phase plasma of an RP macaque. Inoculation of macaques with a representative clone, SIVsmH635FC, resulted in a persistent viremia, comparable to that produced by pathogenic SIVsmE543-3, and a chronic disease with progressive loss of CD4(+) T cells. However, SIVsmH635FC did not reproduce the rapid-disease phenomenon. Molecular analyses of viruses from these macaques revealed rapid reversion to the wild-type SIVsmE543-3 sequence at two RP-specific sites and slower reversion at another three sites. SIVsmH635FC infection was not sufficient to cause rapid progression even following coinoculation with SIVsmE543-3, despite acute depletion of memory CD4(+) T cells. SIVsmH635FC competed efficiently during primary infection in the coinoculated macaques, but SIVsmE543-3 predominated after the development of SIV-specific immune responses. These data suggest that the replication fitness of the RP variant was similar to that of SIVsmE543-3 in a naïve host; however, SIVsmH635FC was at a disadvantage following the development of SIV-specific immune responses. Consistent with these findings, neutralization assays revealed that SIVsmH635FC was highly sensitive to neutralization but that the parental SIVsmE543-3 strain was highly resistant. This study suggests that the evolution of RP-specific variants is the result of replication in a severely immunocompromised host, rather than the direct cause of rapid progression.
Journal of Virology 10/2007; 81(17):8891-904. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: Simian immunodeficiency virus (SIV) is known to result in an asymptomatic infection of its natural African monkey host. However, some SIV strains are capable of inducing AIDS-like symptoms and death upon experimental infection of Asian macaques. To further investigate the virulence of natural SIV isolates from African monkeys, pig-tailed (PT) macaques were inoculated intravenously with either of two recently discovered novel lentiviruses, SIVlhoest and SIVsun. Both viruses were apparently apathogenic in their natural hosts but caused immunodeficiency in PT macaques. Infection was characterized by a progressive loss of CD4(+) lymphocytes in the peripheral blood and lymph nodes, generalized lymphoid depletion, a wasting syndrome, and opportunistic infections, such as Mycobacterium avium or Pneumocystis carinii infections. However, unlike SIVsm/mac infection of macaques, SIVlhoest and SIVsun infections in PT macaques were not accompanied by high viral loads during the chronic disease stage. In addition, no significant correlation between the viral load at set point (12 weeks postinfection) and survival could be found. Five out of eight SIVlhoest-infected and three out of four SIVsun-infected macaques succumbed to AIDS during the first 5 years of infection. Thus, the survival of SIVsun- and SIVlhoest-infected animals was significantly longer than that of SIVagm- or SIVsm-infected macaques. All PT macaques maintained strong SIV antibody responses despite progression to SIV-induced AIDS. The development of immunodeficiency in the face of low viremia suggests that SIVlhoest and SIVsun infections of macaques may model unique aspects of the pathogenesis of human immunodeficiency virus infection in humans.
Journal of Virology 12/2005; 79(22):14044-56. · 5.08 Impact Factor