Plasmid DNA encoding caprine interferon gamma inhibits antibody response to caprine arthritis-encephalitis virus (CAEV) surface protein encoded by a co-administered plasmid expressing CAEV env and tat genes

The Vif protein of caprine arthritis encephalitis virus inhibits interferon production

Caprine arthritis-encephalitis (CAE) is a chronic progressive infectious disease caused by caprine arthritis-encephalitis virus (CAEV) that seriously threatens the goat industry. Chronic infection and life-long multi-tissue inflammation are the typical features of the disease. Innate antiviral immunity is essential for the host defense system that rapidly recognizes and eliminates invading viruses. Interferon β (IFN-β) is important for innate immunity and regulates immunity against a broad spectrum of viruses. To investigate the details of the IFN-β response to CAEV infection, the effects of six viral proteins and the molecular mechanisms by which they affect IFN-β production were analyzed. Overexpression of DU and Vif promote virus proliferation and inhibit the production of IFN-β. qRT-PCR and luciferase reporter assays showed that overexpression of Vif inhibits the expression of luciferase under the control of the ISRE, NF-κB or IFN-β promoter but does not affect the expression of IFN-β activated by IRF3, indicating that Vif negatively regulates IFN-β production by affecting upstream signal transduction of IRF3. Amino acids 149-164 of Vif were found to be necessary for the inhibitory effect of IFN-β production. Our results indicate that CAEV evades surveillance and clearance by intracellular innate immunity by downregulating IFN-β production.

Immunogenetics of small ruminant lentiviral infections

The small ruminant lentiviruses (SRLV) include the caprine arthritis encephalitis virus (CAEV) and the Maedi-Visna virus (MVV). Both of these viruses limit production and can be a major source of economic loss to producers. Little is known about how the immune system recognizes and responds to SRLVs, but due to similarities with the human immunodeficiency virus (HIV), HIV research can shed light on the possible immune mechanisms that control or lead to disease progression. This review will focus on the host immune response to HIV-1 and SRLV, and will discuss the possibility of breeding for enhanced SRLV disease resistance.

Immunization against small ruminant lentiviruses

Multisystemic disease caused by Small Ruminant Lentiviruses (SRLV) in sheep and goats leads to production losses, to the detriment of animal health and welfare. This, together with the lack of treatments, has triggered interest in exploring different strategies of immunization to control the widely spread SRLV infection and, also, to provide a useful model for HIV vaccines. These strategies involve inactivated whole virus, subunit vaccines, DNA encoding viral proteins in the presence or absence of plasmids encoding immunological adjuvants and naturally or artificially attenuated viruses. In this review, we revisit, comprehensively, the immunization strategies against SRLV and analyze this double edged tool individually, as it may contribute to either controlling or enhancing virus replication and/or disease.

Small ruminant lentiviruses (SRLVs) break the species barrier to acquire new host range

Zoonotic events of simian immunodeficiency virus (SIV) from non-human primates to humans have generated the acquired immunodeficiency syndrome (AIDS), one of the most devastating infectious disease of the last century with more than 30 million people dead and about 40.3 million people currently infected worldwide. Human immunodeficiency virus (HIV-1 and HIV-2), the two major viruses that cause AIDS in humans are retroviruses of the lentivirus genus. The genus includes arthritis-encephalitis virus (CAEV) and Maedi-Visna virus (MVV), and a heterogeneous group of viruses known as small ruminant lentiviruses (SRLVs), affecting goat and sheep. Lentivirus genome integrates into the host DNA, causing persistent infection associated with a remarkable diversity during viral replication. Direct evidence of mixed infections with these two closely related SRLVs was found in both sheep and goats. The evidence of a genetic continuum with caprine and ovine field isolates demonstrates the absence of an efficient species barrier preventing cross-species transmission. In dual-infected animals, persistent infections with both CAEV and MVV have been described, and viral chimeras have been detected. This not only complicates animal trade between countries but favors the risk that highly pathogenic variants may emerge as has already been observed in the past in Iceland and, more recently, in outbreaks with virulent strains in Spain. SRLVs affecting wildlife have already been identified, demonstrating the existence of emergent viruses adapted to new hosts. Viruses adapted to wildlife ruminants may acquire novel biopathological properties which may endanger not only the new host species but also domestic ruminants and humans. SRLVs infecting sheep and goats follow a genomic evolution similar to that observed in HIV or in other lentiviruses. Lentivirus genetic diversity and host factors leading to the establishment of naturally occurring virulent versus avirulent infections, in addition to the emergence of new strains, challenge every aspect of SRLV control measures for providing efficient tools to prevent the transmission of diseases between wild ungulates and livestock.

Important mammalian veterinary viral immunodiseases and their control

This paper offers an overview of important veterinary viral diseases of mammals stemming from aberrant immune response. Diseases reviewed comprise those due to lentiviruses of equine infectious anaemia, visna/maedi and caprine arthritis encephalitis and feline immunodeficiency. Diseases caused by viruses of feline infectious peritonitis, feline leukaemia, canine distemper and aquatic counterparts, Aleutian disease and malignant catarrhal fever. We also consider prospects of immunoprophylaxis for the diseases and briefly other control measures. It should be realised that the outlook for effective vaccines for many of the diseases is remote. This paper describes the current status of vaccine research and the difficulties encountered during their development.

Use of B7 costimulatory molecules as adjuvants in a prime-boost vaccination against Visna/Maedi ovine lentivirus

RNA transcripts of the B7 family molecule (CD80) are diminished in blood leukocytes from animals clinically affected with Visna/Maedi virus (VMV) infection. This work investigates whether the use of B7 genes enhances immune responses and protection in immunization-challenge approaches. Sheep were primed by particle-mediated epidermal bombardment with VMV gag and env gene recombinant plasmids together with plasmids encoding both CD80 and CD86 or CD80 alone, boosted with gag and env gene recombinant modified vaccinia Ankara virus and challenged intratracheally with VMV. Immunization in the presence of one or both of the B7 genes resulted in CD4+ T cell activation and antibody production (before and after challenge, respectively), but only immunization with CD80 and CD86 genes together, and not CD80 alone, resulted in a reduced number of infected animals and increased early transient cytotoxic T lymphocytes (CTL) responses. Post-mortem analysis showed an immune activation of lymphoid tissue in challenge-target organs in those animals that had received B7 genes compared to unvaccinated animals. Thus, the inclusion of B7 genes helped to enhance early cellular responses and protection (diminished proportion of infected animals) against VMV infection.

Mucosal immunization against ovine lentivirus using PEI-DNA complexes and modified vaccinia Ankara encoding the gag and/or env genes

Sheep were immunized against Visna/Maedi virus (VMV) gag and/or env genes via the nasopharynx-associated lymphoid tissue (NALT) and lung using polyethylenimine (PEI)-DNA complexes and modified vaccinia Ankara, and challenged with live virus via the lung. env immunization enhanced humoral responses prior to but not after VMV challenge. Systemic T cell proliferative and cytotoxic responses were generally low, with the responses following single gag gene immunization being significantly depressed after challenge. A transient reduction in provirus load in the blood early after challenge was observed following env immunization, whilst the gag gene either alone or in combination with env resulted in significantly elevated provirus loads in lung. However, despite this, a significant reduction in lesion score was observed in animals immunized with the single gag gene at post-mortem. Inclusion of IFN-gamma in the immunization mixture in general had no significant effects. The results thus showed that protective effects against VMV-induced lesions can be induced following respiratory immunization with the single gag gene, though this was accompanied by an increased pulmonary provirus load.

Mucosal immunization of sheep with a Maedi-Visna virus (MVV) env DNA vaccine protects against early MVV productive infection

Gene gun mucosal DNA immunization of sheep with a plasmid expressing the env gene of Maedi-Visna virus (MVV) was used to examine the protection against MVV infection in sheep from a naturally infected flock. For immunization, sheep were primed with a pcDNA plasmid (pcDNA-env) encoding the Env glycoproteins of MVV and boosted with combined pcDNA-env and pCR3.1-IFN-gamma plasmid inoculations. The pcDNA plasmid used in the control group contained the lacZ coding sequences instead of the env gene. Within a month post-challenge, the viral load in the vaccinated group was lower (p < or = 0.05) and virus was only detected transiently compared with the control group. Furthermore, 2 months later, neutralizing antibodies (NtAb) were detected in all the control animals and none of the vaccinated animals (p < or = 0.01). These results demonstrated a significant early protective effect of this immunization strategy against MVV infection that restricts the virus replication following challenge in the absence of NtAb production. This vaccine protective effect against MVV infection disappeared after two years post-challenge, when active replication of MVV challenge strain was observed. Protection conferred by the vaccine could not be explained by OLA DRB1 allele or genotype differences. Most of the individuals were DRB1 heterozygous and none was totally resistant to infection.

Antibody response to the surface envelope of caprine arthritis-encephalitis lentivirus: disease status is predicted by SU antibody isotype

This study evaluated the hypothesis that the disease status of Saanen goats infected with caprine arthritis-encephalitis lentivirus (CAEV) is associated with the focus of immune responses to viral antigens, particularly the surface envelope glycoprotein (SU). Specifically, we have proposed that Th2 responses promote progressive immune-mediated arthritis, whereas Th1 responses restrict virus replication and development of clinical disease. The present study determined the isotype of SU antibodies associated with progressor and long-term nonprogressor (LTNP) status. We show that chronically infected goats that develop clinical arthritis have predominantly IgG1 antibodies to SU during both preclinical and clinical stages of disease, whereas SU antibodies of LTNP goats are relatively biased toward IgG2. Additional studies determined the isotype of SU antibodies induced initially by CAEV infection. These experiments show that initial IgG1-dominated responses to SU are associated with subsequent development of preclinical inflammatory joint lesions, whereas lack of joint pathology is associated with an IgG2 bias of initial responses to SU. Our results using the CAEV model suggest that isotype bias of SU antibodies is a reliable indicator of clinical disease caused by lentiviruses. Isotype analysis may be a useful method to screen candidate lentiviral vaccines intended to prevent disease progression.

Prime-boost vaccination with plasmid DNA encoding caprine-arthritis encephalitis lentivirus env and viral SU suppresses challenge virus and development of arthritis

This study evaluated the efficacy of prime-boost vaccination for immune control of caprine arthritis-encephalitis virus (CAEV), a macrophage tropic lentivirus that causes progressive arthritis in the natural host. Vaccination of Saanen goats with pUC-based plasmid DNA expressing CAEV env induces T helper type 1 (Th1) biased immune responses to vector-encoded surface envelope (SU), and the plasmid-primed Th1 response is expanded following boost with purified SU in Freund's incomplete adjuvant (SU-FIA) (J. C. Beyer et al., 2001, Vaccine 19, 1643-1651). Four goats vaccinated with env expression plasmids and boosted with SU-FIA were challenged intravenously with 1 x 10(4) TCID(50) of CAEV at 428 days after SU-FIA boost and evaluated by immunological, virological, and disease criteria. Controls included two goats primed with pUC18 and eight unvaccinated goats. Goats receiving prime-boost vaccination with CAEV env plasmids and SU-FIA became infected but suppressed postchallenge virus replication, provirus loads in lymph node, and development of arthritis for at least 84 weeks.

Temporal effects of gamma interferon deficiency on the course of Friend retrovirus infection in mice

The current studies demonstrate complex and seemingly contradictory effects by gamma interferon (IFN-gamma) on Friend virus (FV) infection. Both temporal and tissue-specific effects were observed. During the first week of infection, IFN-gamma-deficiency caused increased levels of FV infection in multiple tissues. Surprisingly, however, by 2 weeks postinfection, IFN-gamma-deficient mice had significantly lower levels of infection in both the spleen and bone marrow compared to wild-type mice. The rapid reduction of virus in the IFN-gamma-deficient mice correlated with a more rapid virus-neutralizing antibody response than was observed in the wild-type mice. Furthermore, the virus-neutralizing antibody response in wild-type mice could be accelerated by ablation of their IFN-gamma response. Although the IFN-gamma-deficient mice developed an accelerated virus-neutralizing antibody response, they did not class-switch to immunoglobulin G class immunoglobulins nor could they maintain long-term virus-neutralizing antibody titers. Eventually, all of the IFN-gamma-deficient mice failed to keep persistent virus in check and developed fatal FV-induced erythroleukemia.