Production of interleukin 1 in the joint during the development of antigen-induced arthritis in the rabbit.

Antigen-induced arthritis in the rabbit closely resembles rheumatoid arthritis. The levels of interleukin 1 (IL-1) in the synovial fluid and the synthesis of IL-1 by infiltrating cells in synovial fluid and by the synovial lining from control and inflamed joints has been assessed during the first month of this disease. A number of biological assays have been used to measure rabbit IL-1. Of these, only the assay using the murine thymoma cell line (EL-4 NOB-1) was able to detect IL-1 activity in the synovial fluid of arthritic joints, which was present only in the very early lesion. The leucocytes infiltrating the synovial cavity produced little IL-1 ex vivo in the acute lesion but released large amounts when arthritis was established. A similar finding was made with respect to the production of IL-1 by the synovial lining.