Molecular basis of the pathobiology of lentiviruses

Small ruminant lentiviruses: immunopathogenesis of visna-maedi and caprine arthritis and encephalitis virus

The small ruminant lentiviruses include the prototype for the genus, visna-maedi virus (VMV) as well as caprine arthritis encephalitis virus (CAEV). Infection of sheep or goats with these viruses causes slow, progressive, inflammatory pathology in many tissues, but the most common clinical signs result from pathology in the lung, mammary gland, central nervous system and joints. This review examines replication, immunity to and pathogenesis of these viruses and highlights major differences from and similarities to some of the other lentiviruses.

Identification of cellular proteins interacting with equine infectious anemia virus S2 protein

The macrophage-tropic lentivirus, equine infectious anemia virus (EIAV), encodes the small auxiliary protein S2 from a short open reading frame that overlaps the amino terminus of env EIAV S2 is dispensable for virus replication in cultured cells but is required for disease production. S2 is approximately 7 kDa and has no overall amino acid sequence homology to other cellular or viral proteins. Therefore it is likely that S2 plays a role as an adaptor protein. To further investigate S2 function we performed a yeast-2-hybrid screen to identify cellular proteins that interact with EIAV S2. The screen identified two human cellular proteins, amplified in osteosarcoma (OS-9) and proteasome 26S ATPase subunit 3 (PSMC3) that interact with S2. The equine homologues of these proteins were cloned and their interactions with S2 confirmed using co-immunoprecipitation assays. We identified two OS-9 isoforms that interact with S2 and a third splice variant that does not, indicating a region of OS-9 apparently required for the S2 interaction. The roles of these cellular proteins during EIAV infection have not been determined.

A deletion in the R region of long terminal repeats in small ruminant lentiviruses is associated with decreased pathology in the lung

A particular variant of the maedi visna virus (MVV) that although present in blood causes no clinical signs in infected sheep has been described. This variant carries a 13-14 nucleotide deletion in the R region of the proviral long terminal repeats. The hypothesis that this specific deletion may be associated with low pathogenicity has been investigated by comparing the distribution of proviral sequences, the histopathological lesions and the expression of viral proteins in the brain, lungs and udders of sheep naturally infected with viral strains carrying the deletion. Provirus could be demonstrated in most of the tissues examined from sheep infected with either type of virus, and the tissue-derived virus carried the typical deletion in the study flock animals. Histopathological analysis revealed that the lungs were significantly less affected in the animals infected with virus carrying the deletion. Concomitantly, viral expression was significantly reduced in the lungs of these animals. The findings suggest that the reduced pathogenicity of MVV with the specific deletion in the R region is not due to a restriction in the availability of specific tissues to infection, but is associated with a reduced capacity for viral expression in the lungs.

Detection of maedi-visna virus in the liver and heart of naturally infected sheep

Maedi-visna virus (MVV) in sheep, which infects mainly cells of the monocyte/macrophage lineage, produces changes in the lung, mammary gland, brain and joints. In this study, however, the liver and heart of six naturally infected sheep were examined for the presence of the virus. MVV proviral DNA was demonstrated by polymerase chain reaction (PCR) analysis, and immunohistochemical examination revealed viral antigens in the cytoplasm of hepatocytes and cardiac myocytes. Although histopathological examination showed mild to moderate, chronic lymphocytic cholangiohepatitis and myocarditis and the presence of small lymphoid aggregates, the typical maedi lymphoproliferative lesions (lymphoid follicle-like structures of considerable size with germinal centres) were not seen in the liver and heart. These novel findings suggest that, although the macrophage is the main cell for productive viral replication, the liver and heart represent additional MVV targets.

Lentivírus de pequenos ruminantes (CAEV e Maedi-Visna): revisão e perspectivas

Os lentivírus de pequenos ruminantes (SRLV), cujos protótipos são os vírus da Artrite-Encefalite Caprina (CAEV) e Maedi-Visna, são patógenos amplamente distribuidos, os quais causam doenças degenerativas progressivas lentas em caprinos e ovinos, determinando importantes perdas econômicas. Estes vírus causam infecções persistentes com período de incubação longo e causam inflamatórias e degenerativas. As lesões são induzidas em tecidos específicos do hospedeiro como articulações, pulmões, CNS e glandulas mamárias devido à replicação viral em células da linhagem monocítico-fagocitária que são as principais células-alvo. A infecção ocorre principalmente durante os primeiros meses de vida, através da ingestão de vírus no leite ou colostro de cabras ou ovelhas infectadas. A indução da resposta imunológica é variável e não protege contra a infecção. O diagnóstico é baseado primariamente na detecção de anticorpos para SRLV, geralmente por imunodifusão em gel de agar (AGID) e enzyme linked immunosorbent assay (ELISA). O diagnóstico e separação ou descarte dos animais soropositivos associado ao uso de certas práticas de manejo, especialmente das crias, são os principais meios implementados para prevenir a disseminação de SRLV, uma vez que ainda não existe vacina contra o vírus. As estratégias adotadas pelos SRLV para enfrentar o sistema imune dificultam o diagnóstico da infecção, controle ou prevenção da disseminação de SRLV. Esta revisão apresenta alguns aspectos das lentivíroses de pequenos ruminantes baseadas em estudos filogenéticos de amostras isoladas, aspectos clínicos e imunopatológicos.

Functional correction of fanconi anemia group C hematopoietic cells by the use of a novel lentiviral vector

Lentiviral vectors transduce nondividing hematopoietic cells more efficiently than other currently available vector systems. Here we report the results of human hematopoietic cell gene transfer using lentiviral vectors based upon human immunodeficiency virus (HIV-1) and equine infectious anemia virus (EIAV). EIAV is a nonprimate lentivirus and is severely restricted in its host range to horses and closely related equines. We employed the EIAV vector system to test for gene transfer to human Fanconi anemia (FA) hematopoietic cells by comparison with HIV-1- and Moloney murine leukemia virus-based systems. Fanconi anemia is characterized by bone marrow failure secondary to stem cell dysfunction. Fanconi anemia group C EBV-transformed lymphoblasts were transduced with all three viral vectors. Phenotypic correction of FA cells, as measured by mitomycin C drug resistance, was observed with a similar efficiency in all vector systems. This is the first description of lentiviral correction of FA cells and suggests that lentiviral vectors may be useful for FA gene transfer.

Isolamento e identificação pela imunofluorescência direta e reação em cadeia de polimerase do vírus da artrite-encefalite caprina

Amostras do vírus da artrite-encefalite caprina (CAEV) de animais dos estados de Minas Gerais e Pernambuco foram isoladas a partir de explantes de membrana sinovial (MS) (amostras BrMg 1-01, BrMg 2-01, BrMg 2-02, BrMg 2-03 e BrPe 1-01) ou de co-cultivo de leucócitos com MS (BrMg 1-02). As amostras foram identificadas pelo efeito citopático-ECP (formação de sincícios), imunofluorescência direta (IFD) e reação em cadeia de polimerase (PCR) aperfeiçoada para amplificação de parte do gene gag da amostra CAEV Cork. O estudo do ECP revelou a presença de amostras pouco (BrMg 1-01 e BrMg 1-02) ou fortemente indutoras de ECP (BrMg 2-01, BrMg 2-02, BrMg 2-03 e BrPe 1-01). A IFD mostrou resultado positivo em células de todas as monocamadas infectadas pelas amostras isoladas e em células de referência (CAEV Cork e visna/maedi K 1514). A PCR do DNA de células infectadas resultou na amplificação específica de um fragmento de DNA de 286pb da amostras testadas, exceto do visna/maedi K 1514.

Demonstration that orf2 encodes the feline immunodeficiency virus transactivating (Tat) protein and characterization of a unique gene product with partial rev activity

The long PCR technique was used to amplify the three size classes of viral mRNAs produced in cells infected by feline immunodeficiency virus (FIV). We identified in the env region a new splice acceptor site that generated two transcripts, each coding for an 11-kDa protein, p11(rev), whose function is unknown. The small-size class of mRNAs included two bicistronic orf2/rev mRNAs and two rev-like mRNAs, consisting only of the second exon of rev and coding for a 15-kDa protein, p15(rev). p15(rev) contained the minimal effector domain of Rev and was sufficient to mediate partial Rev activity. The bicistronic mRNAs encoded two distinct proteins, one of 23 kDa corresponding to Rev and a 9-kDa protein encoded by the orf2 gene. The orf2 gene product is a protein of 79 amino acids with characteristics similar to those of the Tat (transactivator) proteins of the ungulate lentiviruses. Transient expression assays, using the FIV long terminal repeat (LTR) to drive transcription of the bacterial gene for chloramphenicol acetyltransferase demonstrated that the orf2 gene transactivates gene expression an average of 14- to 20-fold above the basal level. Deletion mutants of the FIV LTR were generated to locate sequences responsive to transactivation mediated by the orf2 gene. A 5' deletion mutant that removed the AP1 site resulted in residual low-level transactivation by orf2. Further experiments using LTR mutants with internal deletions identified three regions located between positions -126 and -47 relative to the cap site that were important for orf2-directed transactivation. These regions include the AP1 site, a C/EBP tandem repeat, and an ATF site.

In vivo functions of the auxiliary genes and regulatory elements of feline immunodeficiency virus

Feline immunodeficiency virus (FIV) is a widespread lentivirus of domestic cats that causes an acquired immunodeficiency syndrome (AIDS)-like disease similar to human AIDS caused by human immunodeficiency virus. FIV has a complex genome structure including structural, enzymatic and auxiliary genes and regulatory elements. In this article, we review the in vivo roles of some of these FIV auxiliary genes and regulatory elements, especially focusing on the dUTPase, vif, and ORF-A genes and AP-1 binding site in the enhancer region of the long terminal repeat, by comparison with those of other non-primate lentiviruses. These genes and elements are considered to be important for viral replication, immunological response and pathogenesis in cats.

Simian immunodeficiency viruses containing mutations in the long terminal repeat NF-kappa B or Sp1 binding sites replicate efficiently in T cells and PHA-stimulated PBMCs

The long terminal repeats (LTRs) of primate lentiviruses contain conserved binding sites for the NF-kappa B and Sp1 cellular transcription factors. In order to study the role that these sites play in simian immunodeficiency virus (SIV) replication, we have introduced mutations that disrupt either the NF-kappa B or Sp1 binding sites in the LTR of an infectious molecular clone of SIVmac239. An additional mutation also disrupted the SF3 transcription factor binding site that overlaps the NF-kappa B site. Viruses containing point mutations or deletions of the NF-kappa B, SF3, or Sp1 binding sites retained the ability to replicate efficiently in the CEMx174 and MT4 cell lines, as well as in PHA-stimulated primary rhesus macaque peripheral blood mononuclear cells (PBMCs). Efficient replication of SIVs mutated in either NF-kappa B or Sp1 binding sites suggests that the SIV LTR promoter contains multiple functionally redundant elements capable of supporting sufficient transcription to allow productive viral replication.

Roles of the auxiliary genes and AP-1 binding site in the long terminal repeat of feline immunodeficiency virus in the early stage of infection in cats

To examine the roles of auxiliary genes and the AP-1 binding site in the long terminal repeat of feline immunodeficiency virus (FIV) in vivo, three mutant viruses, which are defective in the vif gene ([delta]vif), ORF-A gene (deltaORF-A), and AP-1 binding site (deltaAP-1), and wild-type virus as a positive control were separately inoculated into three specific-pathogen-free cats. These cats were assessed by measuring the number of proviral DNA copies in peripheral blood mononuclear cells (PBMCs), the CD4/CD8 ratio and antibody responses to FIV for 16 weeks and then examining histological changes at necropsy. Although viral DNAs were detected in PBMCs from all 12 cats to various degrees until 16 weeks postinoculation, no virus was recovered from PBMCs of cats infected with (delta)vif virus during the observation period. However, a very weak antibody response was induced in one cat infected with the (delta)vif virus. In contrast, despite the successful recovery of virus from both groups of cats infected with deltaORF-A and deltaAP-1 virus, antibody responses and decrease in the CD4/CD8 ratio in the groups were milder than those in cats infected with wild-type virus. Furthermore, the numbers of proviral DNA copies in PBMCs from the two groups were not able to reach the level in cats infected with wild-type virus during the observation period. From these results, we conclude that these mutant viruses are still infectious for cats but failed in efficient viral replication and suggest that these auxiliary genes and enhancer element are important or essential to full viral replication kinetics and presumably to full pathogenicity during the early stage of infection in vivo.

A single mutation within the V3 envelope neutralization domain of feline immunodeficiency virus determines its tropism for CRFK cells

Feline immunodeficiency virus (FIV) isolates differ in the ability to replicate in Crandell feline kidney (CRFK) cells. The difference in tropism between two variants of the Dutch isolate FIV-UT113 was studied by using molecular clones which contained the envelope genes of the variants in a background of the FIV-14 Petaluma sequence. Virus produced from clone pPET-113Th replicated in thymocytes, whereas virus from pPET-113Cr propagated in both thymocytes and CRFK cells, thereby reflecting the phenotypes of the parental variants. Exchange of envelope gene fragments showed that a 464-bp surface protein (SU)-encoding fragment encompassing the third variable region (V3) determines CRFK cell tropism. Sequence analysis of the exchanged fragments demonstrated two amino acid changes that led to an increase of the overall charge of the V3 domain: a G-->R transition at position 397 and a E-->K change at position 407. Mutational analysis of these residues revealed that the E-->K shift was responsible for the change in tropism, while the G-->R mutation improved the replication kinetics in CRFK cells. Mapping of a tropism determinant for FIV to a region which is also a major neutralization domain is reminiscent of human immunodeficiency virus type 1, in which a similar colocation was found.