Immunopathology of chronic lentivirus-induced arthritis

This study evaluated histopathology and mononuclear cell phenotypes in synovial lesions of chronic arthritis induced by experimental infection of Saanen goats with caprine arthritis-encephalitis lentivirus. Histological examination of carpal joint synovium of three infected goats with clinical arthritis revealed progressive lesions consisting of membrane villus hypertrophy with extensive angiogenesis and mononuclear cell infiltration and degenerative changes of membrane villus necrosis associated with loss of vasculature and infiltrates. Changes in synovial tissue of five age-matched infected goats without clinical arthritis were limited to moderate synovial membrane hyperplasia also noted in an age-matched uninfected goat. Immunohistochemistry identified CD45R+ CD5- B lymphocytes as the principal component of most perivascular infiltrates in arthritic synovium. Other mononuclear cells included perivascular CD4+ and CD8+ T lymphocytes and macrophages with a prominent accumulation of CD8+ T lymphocytes at the lining surface of inflamed villi. T lymphocytes and macrophages as well as synovial lining cells were activated with respect to MHC class II but not for interleukin-2 receptors. Inflamed villi also contained lymphoid aggregates comprised of B cell germinal centers and activated T-cell mantles. B cells expressing immunoglobulin occurred around follicles and throughout inflamed villi. These findings indicate that memory immune responses that favor expansion and maturation of B cells and immunoglobulin production contribute to the immunopathology of chronic arthritis.