Peripheral blood and synovial fluid mononuclear cell phenotypes in lentivirus induced arthritis.

OBJECTIVE: To identify the phenotypes and activation status of peripheral blood (PB) and synovial fluid (SF) mononuclear cells associated with caprine arthritis encephalitis virus (CAEV) induced arthritis in goats.
METHODS: PB and SF mononuclear cells from 8 goats chronically infected with CAEV and 2 mock-infected goats were phenotyped by single immunofluorescence flow cytometry using a panel of monoclonal antibodies (Mab) to caprine leukocyte differentiation molecules. The activation status of mononuclear cell subsets was evaluated by dual immunofluorescence flow cytometry using Mab to major histocompatibility complex (MHC) class II molecules and the interleukin 2 receptor (IL-2R).
RESULTS: Three CAEV infected goats had chronic progressive arthritis, clinically evident by periarticular swelling of carpal joints with excessive SF containing inflammatory cells and radiographic changes indicating soft tissue swelling and erosion of articular surfaces. The other 5 infected goats and 2 mock-infected control goats did not exhibit criteria of arthritis. The composition of PB mononuclear cells (11.3 +/- 5.0% monocytes, 21.1 +/- 4.7% B cells, 29.6 +/- 5.4% CD4+ cells, 15.2 +/- 6.1% CD8+ cells, and 9.7 +/- 3.9% gamma delta T cells) was not significantly different between mock-infected and CAEV infected goats. In contrast, cells within the SF of arthritic carpal joints consisted of 71.9 +/- 7.9% CD8+ T cells, 13.3 +/- 5.9% CD4+ T cells and < 2% B cells. The proportions of SF macrophages (7.8 +/- 5.2%) and gamma delta T cells (6.5 +/- 1.3%) were not significantly different from PB. All SF mononuclear cells were activated with respect to class II determinants orthologous to HLA-DR, DP and DQ. IL-2R expression by CD4+ and CD8+ T lymphocytes in SF was reduced compared to PB.
CONCLUSION: Lymphocytes infiltrating the SF of arthritic carpal joints of CAEV infected goats consisted of a predominant subset of class II activated CD8+ T lymphocytes and a minority population of CD4+ T lymphocytes, both of which express very little IL-2R. These results parallel previous reports of the phenotypes and activation status of mononuclear cells in rheumatoid SF. A potential connection between T lymphocyte subset reactivity to CAEV and immunopathogenesis of arthritis is suggested.