Ultrastructural Studies of Rabbit Synovitis Induced by Autologous IgG Fragments: II. Infiltrating Cells in the Sublining Layer

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Abstract
The synovial sublining layer of rabbits with synovitis induced by intra-articular injection of cathepsin D digested autologous IgG fragments (Fab2) has been examined under the electron microscope. Twelve or more injections of autologous Fab2 led to chronic synovitis with dense mononuclear cell infiltrates containing lymphocytes, blastic cells, plasma cells and macrophages. In the infiltrates there was evidence that the lymphocytes had been activated prior to transformation into mature plasma cells. Indirect evidence suggests that T lymphocyte activation also occurred in these infiltrates. Cellular contacts between macrophages and lymphocytes or plasma cells as well as between M cells and lymphocytes were demonstrated. These contacts are tentatively interpreted as a feature of ongoing immune processes in the synovium.