Intratracheal inoculation as an efficient route of experimental infection with maedi–visna virus

The lesions caused by maedi-visna virus (MVV) are known to be immune mediated with a presumed contribution by the response to viral antigens. However, very little is known about the T-cell response to individual viral proteins. We have therefore expressed the three individual gag antigens of MVV strain EV1 (p16, p25, and p14) in a bacterial expression system and used the purified recombinant proteins to analyze the antibody and CD4؉ T-cell response to MVV. Plasma samples were taken from sheep after 1 year of infection with MVV. The titers for antibodies in these samples were determined by indirect enzyme-linked immunosorbent assays and were as follows: anti-p25 antibody, 1:400 to >1:3,200; anti-p16 antibody, 1:400 to 1:3,200; and anti-p14 antibody, 1:<100 to 1:3,200. When the induction of antibodies was followed over time postinfection (p.i.), samples positive for anti-p25 were seen by day 24 p.i., followed by anti-p16 by day 45 p.i., and lastly anti-p14 by day 100 p.i. T-cell proliferative responses to all three gag antigens were detected in persistently infected sheep peripheral blood lymphocytes. The antigens were therefore used to raise T-cell lines from persistently infected sheep. These T-cell lines were shown to be specific for the recombinant gag antigens and for viral antigen expressed on infected macrophages. The proliferative response was restricted to major histocompatibility complex class II HLA-DR and so was due to CD4 ؉ T lymphocytes. All three gag antigens may therefore play a role in immune-mediated lesion formation in MVV disease by presentation on infected macrophages in lesions.

Section: Discussionmentioning

confidence: 99%

Immune Response to Individual Maedi-Visna VirusgagAntigens

Singh

McConnell

Blacklaws

2006

“…This was demonstrated only after lower lung instillation of infected cells, suggesting that the upper respiratory tract is relatively insensitive to cell-associated VMV, as is the case for cell-free VMV (46). As the site of particle deposition in the lung is related to particle size, with larger particles (Ͼ10 m) being preferentially deposited in the Evidence for a lack of cell migration from the lung airspace to the draining lymph nodes was based on two observations.…”

Section: Discussionmentioning

confidence: 99%

Role of Alveolar Macrophages in Respiratory Transmission of Visna/Maedi Virus

McNeilly

Baker

Brown

et al. 2008

A major route of transmission of Visna/maedi virus (VMV), an ovine lentivirus, is thought to be via the respiratory tract, by inhalation of either cell-free or cell-associated virus. In previous studies, we have shown that infection via the lower respiratory tract is much more efficient than via upper respiratory tissues (T. N. In this study, we use an experimental in vivo infection model that allowed the infection of specific segments of the ovine lung. We demonstrate that resident AMs are capable of VMV uptake in vivo and that this infection is associated with a specific up-regulation of AM granulocyte-macrophage colony-stimulating factor mRNA expression (P < 0.05) and an increase in bronchoalveolar lymphocyte numbers (P < 0.05), but not a generalized inflammatory response 7 days postinfection. We also demonstrate that both autologous and heterologous VMV-infected AMs are capable of transmitting virus after lower, but not upper, respiratory tract instillation and that this transfer of virus appears not to involve the direct migration of virus-infected AMs from the airspace. These results suggest that virus is transferred from AMs into the body via an intermediate route. The results also suggest that the inhalation of infected AMs represents an additional mechanism of virus transmission.Visna/maedi virus (VMV) is a member of the lentivirus subgroup of retroviruses that cause lymphoid interstitial pneumonia, encephalitis, arthritis, and mastitis in sheep (40,41). The main routes of transmission of VMV are thought to be through the ingestion of infected colostrum and/or milk or through the inhalation of infected respiratory secretions (6, 34). We recently have demonstrated that a major route of respiratory transmission is likely via the uptake of cell-free VMV in the lower respiratory tract (33), although the initial target cells for cell-free VMV at this site were not identified.

“…Icelandic sheep, 6 months old, were infected intratracheally with 1.0 ml of 10 4 50% tissue culture infective doses. Virus was injected into the trachea with a needle (23 gauge) under sedation with xylazinum (Xylapan; 0.2 ml intravenously) (34).…”

Section: Methodsmentioning

confidence: 99%

Simultaneous Mutations in CA and Vif of Maedi-Visna Virus Cause Attenuated Replication in Macrophages and Reduced Infectivity In Vivo

Gudmundsson

Jónsson

Ólafsson

et al. 2005

Maedi-visna virus (MVV) is a lentivirus of sheep sharing several key features with the primate lentiviruses.The virus causes slowly progressive diseases, mainly in the lungs and the central nervous system of sheep. Here, we investigate the molecular basis for the differential growth phenotypes of two MVV isolates. One of the isolates, KV1772, replicates well in a number of cell lines and is highly pathogenic in sheep. The second isolate, KS1, no longer grows on macrophages or causes disease. The two virus isolates differ by 129 nucleotide substitutions and two deletions of 3 and 15 nucleotides in the env gene. To determine the molecular nature of the lesions responsible for the restrictive growth phenotype, chimeric viruses were constructed and used to map the phenotype. An L120R mutation in the CA domain, together with a P205S mutation in Vif (but neither alone), could fully convert KV1772 to the restrictive growth phenotype. These results suggest a functional interaction between CA and Vif in MVV replication, a property that may relate to the innate antiretroviral defense mechanisms in sheep.