ANTIINFLAMMATORY EFFECT OF LIPOCORTIN-1 IN EXPERIMENTAL ARTHRITIS

The glucocorticoid-induced antiinflammatory protein lipocortin I is pr esent in arthritic synovium but its ability to regulate joint inflamma tion has not previously been studied. We investigated the role of lipo cortin 1 in the antiinflammatory activity of glucocorticoids in an acu te arthritis model induced by intraarticular injection of carrageenan. Compared to control joints (0.09 +/- 0.08 x 10(6) synovial fluid cell count), carrageenan injected joints exhibited marked infiltration of PMN (10.2 +/- 0.7 x 10(6), p < 0.001). Both intraperitoneal (1.0 mg/kg ) and intraarticular administration (5 mu g) of dexamethasone (DEX) si gnificantly suppressed arthritis severity (p < 0.001 and 0.005, respec tively), and the effects of DEX were significantly prevented by intra- articular injection of antilipocortin 1 mAb (p < 0.05). Carrageenan ar thritis was also significantly inhibited by intraarticular administrat ion of the N-terminal lipocortin 1 peptide Ac2-26 at doses of 1 or 2 m g/kg (p < 0.01). Intraarticular injection antilipocortin 1 mAb in the absence of DEX also significantly exacerbated arthritis severity (p < 0.005). In vitro treatment of PMN with DEX was associated with signifi cant inhibition of phagocytosis (p < 0.005) and reactive oxygen specie s (ROS) generation (p < 0.001). Antilipocortin 1 mAb significantly red uced the inhibitory effects of DEX (p < 0.01 and 0.005, respectively). These results demonstrate that lipocortin 1 mediates the effects of e xogenous glucocorticoids on neutrophil migration in carrageenan-induce d acute arthritis, exerts an endogenous antiinflammatory influence, an d mediates glucocorticoid inhibition of neutrophil activation.