ROLE OF TNF-ALPHA IN THE INDUCTION OF ANTIGEN-INDUCED ARTHRITIS IN THE RABBIT AND THE ANTIARTHRITIC EFFECT OF SPECIES-SPECIFIC TNF-ALPHA NEUTRALIZING MONOCLONAL-ANTIBODIES

Objective-To investigate the role of tumour necrosis factor alpha (TNF alpha) in the development of antigen induced arthritis (ALA) in rabbi ts. Methods-Monoclonal antibodies to rabbit TNF alpha were developed i n rats and were used to detect TNF alpha in synovial fluid by enzyme l inked immunosorbent assay and to localise it in tissue sections of syn ovium and cartilage from rabbits up to 21 days after induction of AIA. An antibody which neutralised TNF alpha activity in vitro was injecte d into rabbits to block TNF alpha action in vivo in ALA. Joint swellin g, leucocyte infiltration into synovium and proteoglycan loss from car tilage were measured and compared with a control group, which were inj ected with sterile saline. Results-Monoclonal antibodies to purified r abbit TNF alpha were prepared in rats and two were selected which were able to neutralise rabbit TNF alpha in a cytotoxicity bioassay. TNF a lpha was detected in significant concentrations (21.7 (SE 0.5) pg/ml) in the arthritic joint fluid of rabbits with AZA only at one day after induction and it was then also sparsely localised in cells of the syn ovium, but from day 3 onwards it was localised more strongly in the de ep zone of articular cartilage. Injection of anti-TNF monoclonal antib ody R6 over three days into rabbits with AIA reduced joint swelling an d leucocyte infiltration into joint fluid and decreased the expression of CD11b and CD18 on cells in the joint fluid. However, there was no significant reduction in the loss of proteoglycan from articular carti lage, although the joint fluid at three days contained a lower glycosa minoglycan content. The antibody R6 gave most effect at a dose of 0.6 mg/kg and there was-no increase in its effectiveness at a fivefold gre ater dose (3.0 mg/kg). Treatment over 10 days gave a more complete sup pression of joint swelling, but did not result in any less proteoglyca n loss from cartilage. Treatment for five days with a 16 day follow up gave a significant reduction in swelling for several days beyond the treatment, but the swelling then slowly returned, until by day 21 ther e was no significant difference in joint swelling and there was also n o recovery of cartilage proteoglycan content. A rabbit anti-rat immuno globulin response was detected at 21 days, which may have limited the long term effectiveness of the antibody. Conclusions-In AIA in rabbits , TNF alpha was only detected in synovial fluid at one day after induc tion and there was only limited cellular localisation of TNF alpha in synovium and cartilage from three days. However, neutralising TNF alph a with a monoclonal antibody was effective in suppressing inflammatory changes in the joint during the acute onset of AIA, but it had little effect on the loss of proteoglycan from cartilage. The results sugges t that blocking inflammation and synovitis with anti-TNF alpha may be more easily achieved than preventing damage to articular cartilage.