Cell division in the synovial lining in experimental allergic arthritis: proliferation of cells during the development of chronic arthritis.

The synovial tissue in experimentally induced immune arthritis induced in the rabbit has been used as a model of rheumatoid arthritis to determine which cells may contribute to the growth of this tissue. Tissue from the challenged and from the unchallenged knee joints was taken, after the intra-articular injection of a small amount of tritiated thymidine, from rabbits up to 3 months after the arthritis was induced. DNA synthesis, as a measure of cell proliferative activity, was assessed firstly by measuring the labelling index in autoradiographs of sections of such tissue, and secondly by the DNA synthetic index obtained by Feulgen cytophotometry. These measurements were made separately on synoviocytes, on the structural cells of the stroma, on the cells lining the small blood vessels, and on the infiltrating inflammatory cells. The DNA synthetic activity of the synoviocytes, and of the stromal noninflammatory cells, was maximal between 3 and 7 days after challenge. The activity in the synoviocytes, in particular, remained raised for up to 84 days after the challenge. Thus these cells appear to be capable of contributing to the hyperplasia, but the contribution of other cells, deeper in the stroma, cannot be excluded.