The pathogenesis of natural and experimental arthropathies of sheep

The pathogenesis of natural and experimental arthropathies in sheep is poorly understood. The aims of the work described in this thesis were: 1) to determine the expression of immunologically relevant molecules in synovial tissues from sheep at different stages of development from the foetus to the adult, and sheep infected with Maedi-Visna virus (MVV), a non-oncogenic retrovirus: 2) study the kinetics of inflammatory cell turnover in synovial tissues and trafficking into the draining lymph node in sheep with experimental antigen-induced arthritis (AIA)

Immunohistlogical analysis of the synovial lining and flow cytometric analysis of cells in synovial fluid (SF) from sheep of different ages showed that there was a significant increase in the proportion of cells expressing MHC class II antigens during the first few months of fife. Very few lymphoid cells were found in tissues from sheep of any age.

Immunopathological studies of synovial tissues from clinically arthritic MVV-infected sheep showed that the inflammatory infiltrate was characterised by large numbers of large mononuclear cells and T lymphocytes, of which the CD8+ subset predominated over CD4+ and y5 T lymphocyte subsets. Large numbers of cells in the synovial lining expressed MHC class II and CD1 antigens. CD8+ T lymphocytes were found at a significantly higher density in some synovial tissues from MW-infected sheep with no clinical signs of arthritis compared to tissues from control sheep. Additionally, the proportion of MHC class Il-expressing cells in the subintima of these tissues was significantly higher than in tissues from control sheep.

To characterise the progression of an inflammatory arthritis in a more controlled way, an AIA was generated in a group of adult sheep. Immunopathological studies of synovial tissues from sheep at defined time points following generation of arthritis showed that there were temporal differences in the proportions of individual cell types infiltrating these tissues. The CD4:CD8 T lymphocyte ratio was significantly higher, and the the T:B and afkyS T lymphocyte ratios were significantly lower in tissues from day 3 compared to day 30 following generation of arthritis. A large proportion of all three T lymphocyte subsets in SF were activated as judged by MHC class II and IL2 receptor expression. There was also temporal variation in the expression of some cell adhesion molecules by T lymphocytes in SF.

The feasibility of following inflammatory cell trafficking out of inflamed joints into the afferent lymphatics was assessed using the AIA model. Following cannulation of the popliteal pseudoafferent lymphatic duct in the hindlimb, AIA was generated in the tibiotarsal joint distal to the cannulation site. In a small number of sheep it was possible to monitor changes in the draining lymph following generation of arthritis or a flare reaction. In the acute stages of arthritis these changes were characterised by large numbers of neutrophils followed by increases in the concentration or output of lymphocytes and dendritic cells (DC). Temporal variation was observed in the expression of activation and other molecules by lymphocytes and DC in the draining lymph. Antigen uptake by different cell types in AL was demonstrated by generating arthritis using fluorescein-labelled antigen and the potential for DC to migrate from SF into the afferent lymphatics was investigated using DC labelled in vitro with a fluorescent dye. These results indicate that lymphatic cannulation could provide an important novel approach to studying the dynamics of the inflammatory process in joints.