ANALYSIS OF THE INFLAMMATORY CYTOKINE NETWORK AMONG TNF-ALPHA, IL-1-BETA, IL-1 RECEPTOR ANTAGONIST, AND IL-8 IN LPS-INDUCED RABBIT ARTHRITIS

We investigated the cytokine network in rabbit lipopolysaccharide (LPS )-induced arthritis, using inhibitors against homologous TNF alpha, IL -1 beta, and IL-8. Rabbits were intraarticularly injected with LPS (10 ng) and cytokine inhibitors (10 mu g each), and the concentrations of each cytokine in the synovial fluids were measured. Maximum levels of TNF alpha and IL-8 were detected at 2 hours after LPS-injection, wher eas IL-1 beta and IL-1 receptor antagonist (IL-1Ra) were detected at 6 and 9 hours, respectively. By immunohistochemistry, synovial lining c ells were positive for TNF alpha and IL-8, and infiltrating leukocytes were positive for IL-1 beta and IL-1Ra. The effects of cytokine inhib itors on the release of each cytokine were then investigated. The maxi mum levels of TNF alpha and IL-8 were not affected by blocking the act ivities of other cytokines. In contrast, the peak concentration of IL- 1 beta was reduced by anti-TNF alpha monoclonal Ab (mAb), IL-1Ra or an ti-IL-8 IgG. Peak concentrations of IL-l Ra were reduced by anti-TNF a lpha mAb or anti-IL-8 IgG. Anti-TNF alpha mAb, IL-1Ra, and anti-IL-8 I gG reduced the recruitment of leukocytes into the joint cavity, and th e effect of anti-IL-8 IgG was less than that of anti-TNF alpha mAb plu s IL-1Ra. The initial phase of the leukocyte influx was not inhibited. These results provide new evidence that IL-8 as well as TNF alpha are the most proximal cytokines and induce subsequent production of IL-1 beta and IL-1Ra. The data also raise the possibility that factor(s) ot her than IL-8 may be involved in the leukocyte influx in LPS-induced a rthritis.