Interleukin-1 immunoreactive nerve fibres in rat joint synovium

The occurrence of interleukin-1 immunoreactive nerves in the synovial membrane of rat knee joints was investigated by immunohistochemistry. Synovial tissue sections from 11 rats consistently showed interleukin-1 positive nerve fibres. The majority of the fibres appeared in blood vessel walls. However, varicose interleukin-1 positive fibres were also seen to terminate amidst synoviocytes. The overall distribution resembled that of autonomic fibres previously identified in synovium. Further investigation by double staining disclosed the co-existence of interleukin-1 and neuropeptide Y in the synovial nerve fibres. It has been suggested that the nervous system is implicated in the pathogenesis of arthritis. Considering the role of the cytokine interleukin-1 in various immunogenic and inflammatory conditions, it may prove that neuronal interleukin-1 in the synovial membrane represents a pathway for mediating such effects in joint tissue.