Persistently infected sheep used to generate antigen-specific T-cell lines were infected for greater than 3 years and did not show clinical signs of disease. follows: anti-p25 antibody, 1:400 to >1:3,200; anti-p16 antibody, 1:400 to 1 1:3,200; and anti-p14 antibody, 1:<100 to 1 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 threegagantigens were detected in persistently infected sheep peripheral blood Plumbagin 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 recombinantgagantigens 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 threegagantigens may therefore play a role in immune-mediated lesion formation in MVV disease by presentation on infected macrophages in lesions. Lentiviruses are a subfamily of theRetroviridae. They cause slow, chronic disease and eventually, death of the infected animal. The group comprises the immunodeficiency viruses (human, simian, feline, and bovine immunodeficiency viruses), equine infectious anemia virus, and the small-ruminant lentiviruses, maedi-visna virus (MVV) and caprine arthritis encephalitis virus (CAEV). All the viruses infect accessory cells of the immune system (macrophages and dendritic cells) with the immunodeficiency viruses all having an extended tropism for lymphocytes (15). The macrophage and dendritic cell infection which is seen in the small-ruminant lentiviruses (40,54) causes immune-mediated lesions to develop in a variety of organs. The lesions are caused by lymphocyte accumulations, which often organize into follicular structures. Other organ-specific changes, such as smooth muscle Rabbit polyclonal to CD47 hyperplasia in the lung or demyelination in the central nervous system, also occur (6). Virus is usually cell associated, with only low frequencies of infected cells being detected even Plumbagin in lesions that are well developed (8,35,47). How the virus persists has been under investigation for many years with both latent or restricted infection and infection of myeloid precursors put forward as strategies which may aid the virus to survive in the host (19,20,44). Immune evasion has also been suggested as a reason for virus persistence. This comes from data where the antibody response was found to be weak and poorly neutralizing, and only transient T-cell immune responses were seen after infection (30,39,47,57,59,64). However, when studied closely, both T-cell proliferative and cytotoxic T-lymphocyte responses are detected, but the virus epitopes stimulating these responses are unknown (5,52). We therefore expressed the matrix (p16gag), core (p25gag), and nucleocapsid (p14gag) antigens of MVV in a bacterial expression system using a histidine tag to purify all the proteins, and the proteins were then used to analyze the immune response to the individual antigens. We analyzed the antibody and T-cell proliferative responses to the antigens and also determined whether virally infected macrophages could present antigen to T-cell lines raised to the antigens. The results show that all threegagantigens induced antibody and T-cell proliferative responses after infection with MVV. Infected macrophages were able to present these antigens togag-specific T cells. Persistence of the virus does not appear to be caused by the lack of an immune response to viralgagantigens. However, accessory cells infected with MVV will present viral antigen to CD4 T cells, increasing lymphoproliferation and lesion formation around infected cells. Cytokines released by activated CD4 T cells may provide a further stimulus for MVV replication by enhancing the differentiation of monocytes to macrophages and so Plumbagin enhancing continued lesion formation. == MATERIALS AND METHODS == == Sheep. == Adult Finnish Dorset crossed sheep (MVV-free flock from the Moredun Research Institute, Edinburgh, United Kingdom) were uninfected or infected with 5 10550% tissue culture infectious doses (TCID50) MVV strain EV1 (55) subcutaneously. Persistently infected sheep used to generate antigen-specific T-cell lines were infected for greater than 3 years and did not show clinical signs.
