Quantitative analysis of immunohistological changes in the synovial membrane of sheep infected with Maedi-Visna virus.

We have carried out a quantitative immunohistological analysis of synovial membrane from the joints of clinically arthritic sheep naturally infected with Maedi-Visna virus (MVV) and compared the results to subclinically affected joints (carpal and tarsal) from infected sheep and to joints from a control population. Significantly elevated numbers of all three T lymphocyte subsets (CD4+, CD8+ and gamma delta) were found in the synovia from clinically arthritic sheep compared to controls. There was also a significant increase in the number of CD8+ T lymphocytes in the carpal synovium of subclinically arthritic animals. In both clinically arthritic and subclinical disease states CD8+ T cells predominated over CD4+ T cells and T cells bearing the gamma delta T cell receptor. Significant increases were also observed in the numbers of cells staining for MHC class II antigens in the synovial lining cell layer and subintimal cell populations of synovia from clinically arthritic sheep. These increases were apparent in the subintimal cell population at the subclinical stage of disease. Macrophage-like cells staining for the viral core protein p15 were observed in some of the most inflamed samples. The data are thus consistent with a disease process driven by chronic viral antigen presentation to infiltrating T cells, and could serve as a model for elucidating the mechanisms underlying some types of inflammatory joint disease in man.