Sequential appearance of fibronectin and collagen fibres in experimental arthritis in rabbits

The sequential changes in the presence of fibronectin in the synovial membrane during the development of antigen-induced arthritis in rabbits were studied using an indirect immunoperoxidase technique on the tissue specimens fixed in formaldehyde, embedded in paraffin and pre-treated with pepsin and testicular hyaluronidase. The relation to the distribution of fibronectin and connective tissue fibres, demonstrated as either argyrophilic or red by van Gieson method, was studied. Initial after the induction of the arthritis the synoviocytes became increased in size and number. The subsynoviocytial tissue was invaded by granulocytes and the number of vessels was increased. Fibronectin in increased amount was seen around the lining cells. After 2-4 weeks a markedly reduced amount of granulocytes were seen together with an increase in the number of macrophages. At this stage, fibronectin was also found together with argyrophilic fibres in the subsynoviocytial connective tissue. After 8-13 weeks the synovial membrane was found hypertrophic and folded. The lining layer was unchanged, but in the subsynoviocytial tissue lymphocytes and plasma cells were more focally arranged. At that time fine fibres, stained by the van Gieson method, were present together with fibronectin and argyrophilic fibres in the subsynoviocytial tissue. The morphological change and the distribution of fibronectin in experimentally induced arthritis correlated temporally to the morphological change and the presence of fibronectin found in experimentally induced granulation tissue.