Rubella arthritis in adults. Isolation of virus, cytology and other aspects of the synovial reaction.

Rubella virus was isolated from three consecutive samples of synovial fluid after 1 to 4 days of arthritis in adults with typical naturally acquired rubella. In the two samples suitably prepared, cells in the synovial fluid were mononuclear, with numerous monocytes and macrophages. Detailed studies in one case revealed a close similarity in all respects to the illness caused by Ross River virus, another member of the Togaviridae. Cells in the synovial exudate of this patient showed intense phagocytosis. A fine nodular cytoplasmic distribution of virus antigen was detected by immunofluorescence in 45% of the cells. There was no depletion of the complement components C'3 and C'4 in serum or synovial fluid, and no evidence of excessive immune complexes in the circulation or of immune-complex uptake by cells in the synovial exudate or intima. Synovial intima from the suprapatellar region merely showed slight hyperplasia without cellular infiltration, indicating that the lodgement of virus and the inflammatory cellular reaction to it can be confined to limited regions of the synovial lining, at least in the early stages.