Experimental allergic arthritis in the rabbit: alterations in the cellularity and the rate of cellular proliferation in the synovial linings of the challenged joints of rabbits immunized with antigen in Freund's incomplete adjuvant.

Rabbits have been immunized with ovalbumin in Freund's incomplete adjuvant (FIA) followed by the intra-articular injection of ovalbumin, in order to follow the development of inflammation in the synovial lining. The kinetics of cell proliferation have been investigated using tritiated thymidine (3HTdR) autoradiography and Feulgen cytophotometry. Unexpectedly, marked histological changes were found in the synovium, with hyperplasia of synoviocytes, and of the connective-tissue cells of the subintima, being seen as early as 3 days after challenge. Large numbers of inflammatory cells, including many plasma cells, were found in the synovium at between 5 and 11 days. Labelling of synoviocytes and connective-tissue cells reached a maximum at 3 days and declined thereafter, reaching normal levels at 14 days. Three weeks after challenge the synovium was normal in appearance.