The MHC-haplotype influences primary, but not memory, immune responses to an immunodominant peptide containing T- and B-cell epitopes of the caprine arthritis encephalitis virus Gag protein

Molecular characteristics and prevalence of small ruminant lentiviruses in goats in Japan

Small ruminant lentiviruses (SRLVs), which comprise caprine arthritis-encephalitis virus (CAEV) and maedi-visna virus (MVV), are prevalent in goats and sheep worldwide, including in Japan. However, little is known about the molecular characteristics of goat lentiviruses in Japan. In this study, a molecular and phylogenetic analysis of the long gag region was performed. The phylogenic tree demonstrated that all samples belonged to SRLV subtype B1. Two clusters were identified, with one cluster distinct from previously reported strains of subtype B1. In addition, several alterations in the amino acid sequence were detected in immunodominant epitopes of the gag region. To gain a deeper understanding of the genetic diversity of SRLVs in Japan, it will be necessary to increase the sample size and conduct a broader survey. The present report is important for establishing baseline information on the prevalence of SRLV in Japan and providing data to develop a new, more sensitive diagnostic test for effective control of SRLV.

Impaired Expression of Cytokines as a Result of Viral Infections with an Emphasis on Small Ruminant Lentivirus Infection in Goats

Knowing about the genes involved in immunity, and being able to identify the factors influencing their expressions, helps in gaining awareness of the immune processes. The qPCR method is a useful gene expression analysis tool, but studies on immune system genes are still limited, especially on the caprine immune system. Caprine arthritis encephalitis, a disease caused by small ruminant lentivirus (SRLV), causes economic losses in goat breeding, and there is no therapy against SRLV. The results of studies on vaccines against other viruses are promising. Moreover, the Marker-Assisted Selection strategy against SRLV is possible, as has been shown in sheep breeding. However, there are still many gaps in our knowledge on the caprine immune response to infection. All types of cytokines play pivotal roles in immunity, and SRLV infection influences the expression of many cytokines in different types of cells. This information encouraged the authors to examine the results of studies conducted on SRLV and other viral infections, with an emphasis on the expression of cytokine genes. This review attempts to summarize the results of studies on the expression of cytokines in the context of the SRLV infection.

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.

Retroviral infections in sheep and goats: small ruminant lentiviruses and host interaction

Small ruminant lentiviruses (SRLV) are members of the Retrovirus family comprising the closely related Visna/Maedi Virus (VMV) and the Caprine Arthritis-Encephalitis Virus (CAEV), which infect sheep and goats. Both infect cells of the monocyte/macrophage lineage and cause lifelong infections. Infection by VMV and CAEV can lead to Visna/Maedi (VM) and Caprine Arthritis-Encephalitis (CAE) respectively, slow progressive inflammatory diseases primarily affecting the lungs, nervous system, joints and mammary glands. VM and CAE are distributed worldwide and develop over a period of months or years, always leading to the death of the host, with the consequent economic and welfare implications. Currently, the control of VM and CAE relies on the control of transmission and culling of infected animals. However, there is evidence that host genetics play an important role in determining Susceptibility/Resistance to SRLV infection and disease progression, but little work has been performed in small ruminants. More research is necessary to understand the host-SRLV interaction.

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.

Diverse host–virus interactions following caprine arthritis-encephalitis virus infection in sheep and goats

Interspecies transmissions substantially contribute to the epidemiology of small ruminant lentiviruses (SRLVs), including caprine arthritis encephalitis virus (CAEV) and visna-maëdi virus. However, comprehensive studies of host–virus interactions during SRLV adaptation to the new host are lacking. In this study, virological and serological features were analysed over a 6 month period in five sheep and three goats experimentally infected with a CAEV strain. Provirus load at the early stage of infection was significantly higher in sheep than in goats. A broad antibody reactivity against the matrix and capsid proteins was detected in goats, whereas the response to these antigens was mostly type-specific in sheep. The humoral response to the major immunodominant domain of the surface unit glycoprotein was type-specific, regardless of the host species. These species-specific immune responses were then confirmed in naturally infected sheep and goats using sera from mixed flocks in which interspecies transmissions were reported. Taken together, these results provide evidence that SRLV infections evolve in a host-dependent manner, with distinct host–virus interactions in sheep and goats, and highlight the need to consider both SRLV genotypes in diagnosis, particularly in sheep.

The presence or absence of the gamma-activated site determines IFN gamma-mediated transcriptional activation in CAEV promoters cloned from the mammary gland and joint synovium of a single CAEV-infected goat

The caprine arthritis encephalitis virus (CAEV) long terminal repeat promoter was cloned and sequenced from mammary gland and carpal joint synovium isolated from a 15.5 year old, CAEV-infected Toggenburg doe with chronic mastitis and carpal arthritis. A deletion of the CAEV gamma activated site (GAS) was identified in the mammary gland but not the synovial isolate. Subsequent promoter-reporter gene construct experiments indicated that the GAS is necessary for interferon γ-mediated promoter activation. Utilizing a molecular clone of the classic isolate CAEV-CO, these findings were corroborated by a set of GAS mutant promoter-reporter constructs with and without the CAEV GAS. Results of experiments with U937 monocyte cell lines stably transfected with molecular clones of CAEV-CO GAS deletion mutants also indicated the GAS is necessary for IFNγ-mediated promoter activation. The mammary gland CAE viral isolate was propagated in caprine peripheral blood mononuclear cells and was assigned the name CAEV-MA. This is the first report describing two CAE viral isolates cloned from different anatomical locations in the same animal with and without the CAEV GAS, and is the first report detailing cytokine-induced CAEV promoter function in a naturally occurring ΔGAS promoter.

Phylogenetic analysis of SRLV sequences from an arthritic sheep outbreak demonstrates the introduction of CAEV-like viruses among Spanish sheep

Small ruminant lentiviruses (SRLVs) cause different clinical forms of disease in sheep and goats. So far in Spain, Maedi visna virus-like (MVV-like) sequences have been found in both species, and the arthritic SRLV disease has never been found in sheep until a recent outbreak. Knowing that arthritis is common in goats, it was of interest to determine if the genetic type of the virus involved in the sheep arthritis outbreak was caprine arthritis encephalitis virus-like (CAEV-like) rather than MVV-like. Alignment and phylogenetic analyses on nucleotide and deduced amino acid sequences from SRLV of this outbreak, allowed a B2 genetic subgroup assignment of these SRLV, compatible with a correspondence between the virus genetic type and the disease form. Furthermore, an isolate was obtained from the arthritic outbreak, its full genome was CAEV-like but the pol integrase region was MVV-like. Although its LTR lacked a U3 repeat sequence and had a deletion in the R region, which has been proposed to reduce viral replication rate, its phenotype in sheep skin fibroblast cultures was rapid/high, thus it appeared to have adapted to sheep cells. This outbreak study represents the first report on CAEV-like genetic findings and complete genome analysis among Spanish small ruminants.

A Gag peptide encompassing B- and T-cell epitopes of the caprine arthritis encephalitis virus functions as modular carrier peptide

Short synthetic peptides are important tools in biomedical research permitting to generate hapten specific polyclonal sera for analytical purposes or functional studies. In this paper we provide proof of principle that a peptide located in a highly conserved portion of the Gag protein of the caprine arthritis encephalitis virus and carrying an immunodominant T helper cell epitope functions as an efficient carrier peptide, mediating a strong antibody response to a peptidic hapten encompassing a well-characterized B cell epitope of Env. The carrier and hapten peptides were collinearly synthesized permutating their molecular arrangement. While the antibody response to the hapten was similar for both constructs, the antibody response to a B cell epitope overlapping the T helper cell epitope of the Gag carrier peptide was considerably different. This permits a modular use of the carrier peptide to generate antibody directed exclusively to the hapten peptide or a strong humoral response to both carrier- and hapten-peptide. Finally, we have mapped the epitopes involved in this polarized antibody response and discussed the potential immunological implications.

A synthetic peptide encompassing the G5 antigenic region of the rabies virus induces high avidity but poorly neutralizing antibody in immunized animals

The immunization of goats with a synthetic peptide encompassing the G5 antigenic site of the rabies virus surface glycoprotein induces a strong humoral immune response in the absence of a carrier protein. The immunized animals mounted high antibody titers and showed a strong avidity maturation of the B cell immune response to both the G5-peptide and purified surface glycoprotein G. This antibody weakly neutralized rabies virus carrying the G5 epitope but failed to neutralize escape mutants carrying a single point mutation in this epitope. A putative T helper cell epitope, functional in the context of different caprine MHC haplotypes, was identified by structure analysis of the G5-peptide. This striking dichotomy between high titers and antibody of high avidity to the glycoprotein G and poor neutralizing activity strongly suggests that antibody binding assays such as ELISA cannot always reliably predict the neutralizing activity of sera as measured in functional assays.

Vaccination with a T-cell-priming Gag peptide of caprine arthritis encephalitis virus enhances virus replication transiently in vivo

CD4+ T cells are involved in several immune response pathways used to control viral infections. In this study, a group of genetically defined goats was immunized with a synthetic peptide known to encompass an immunodominant helper T-cell epitope of caprine arthritis encephalitis virus (CAEV). Fifty-five days after challenge with the molecularly cloned CAEV strain CO, the vaccinated animals had a higher proviral load than the controls. The measurement of gamma interferon and interleukin-4 gene expression showed that these cytokines were reliable markers of an ongoing immune response but their balance did not account for more or less efficient control of CAEV replication. In contrast, granulocyte–macrophage colony-stimulating factor appeared to be a key cytokine that might support virus replication in the early phase of infection. The observation of a potential T-cell-mediated enhancement of virus replication supports other recent findings showing that lentivirus-specific T cells can be detrimental to the host, suggesting caution in designing vaccine candidates.

Localization of a TNF-activated transcription site and interactions with the gamma activated site within the CAEV U3 70 base pair repeat

The cytokines TNFalpha and IFNgamma have previously been shown to activate caprine arthritis encephalitis virus (CAEV) transcription. Increased viral titers correlate with increased lesion severity. Therefore, TNFalpha and IFNgamma may augment the caprine arthritis lesion by increasing viral titers. CAEV transcription is under the control of the viral promoter within the U3 region of the long terminal repeat. A set of U3 deletion mutants was generated and used to establish stably integrated, U937-based cell lines. These cell lines were utilized to define the required promoter sequences for cytokine-induced transcriptional activation. Here we have identified a novel 17 nucleotide TNF-activated site within the U3 region 70 bp repeat which is both required and sufficient in a minimal construct for TNFalpha-induced CAEV transcriptional activation. In contrast to the results of previous studies with IFNgamma, we found that multiple sequences within the U3 region 70 bp repeat were required for IFNgamma-activation of the CAEV promoter. The results identify previously unrecognized complexity in the CAEV promoter that may be relevant to viral replication and disease.