Involvement of growth-related protein in lipopolysaccharide-induced rabbit arthritis: cooperation between growth-related protein and IL-8, and interrelated regulation among TNFalpha, IL-1, IL-1 receptor antagonist, IL-8, and growth-related protein.

We investigated the functional role of a CXC chemokine, growth-related protein (GRO), in the recruitment of neutrophils in lipopolysaccharide (LPS)-induced rabbit arthritis. The amounts of GRO in the synovial fluids (SF) reached the first peak (major) at 2 hours and the second peak (minor) at 9 hours after injection of LPS into the knee joints. Administration of anti-GRO mouse monoclonal antibody inhibited 54% of the peak leukocyte accumulation at 9 hours (neutrophils greater than 95%), which was similar to the inhibition by anti-IL-8 IgG (48%). Co-administration of these inhibitors increased the inhibition up to 70% at 9 hours and also inhibited 65% of the initial phase of leukocyte infiltration at 2 hours (neutrophils greater than 99%), which was not affected by a single administration of each inhibitor. The amounts of GRO in SF at 2 hours were not altered by either anti-TNFalpha mAb or anti-IL-8 IgG, but reduced by rabbit recombinant IL-1 receptor antagonist (rrlL-1Ra) by 39%. The inhibition by rrlL-1 Ra was augmented further to 59% with coadministered anti-TNFalpha mAb. In contrast, the amounts of GRO at 9 hours were reduced by rrlL-1Ra by 67%. There was no additional reduction in the amounts of GRO at 9 hours by either combination of rrlL-1Ra with anti-TNFalpha mAb or anti-IL-8 IgG. Administration of anti-GRO mAb did not alter TNFalpha or IL-8 contents in SF at their peak (2 hours), but reduced the amounts of IL-1beta at 6 hours and IL-1Ra at 9 hours by 42% and 49%, respectively. These results provide evidence for the following: (a) GRO as well as IL-8 are important mediators involved in the recruitment of neutrophils both in the early and the late phase of LPS-induced arthritis, (b) IL-1 produced in the early phase stimulates GRO production, (c) GRO plays a role in the later induction of IL-1beta and IL-1Ra, and (d) induction of GRO is not regulated by IL-8.

Production and regulation of monocyte chemoattractant protein-1 in lipopolysaccharide- or monosodium urate crystal-induced arthritis in rabbits: roles of tumor necrosis factor alpha, interleukin-1, and interleukin-8.

The production of monocyte chemoattractant protein-1 (MCP-1) and its regulation by TNFalpha, IL-1, and IL-8 were investigated in two rabbit models of arthritis induced by intra-articular injection of lipopolysaccharide (LPS) or monosodium urate (MSU) crystals. We first prepared recombinant rabbit MCP-1 and antibodies and then developed an immunoassay. The immunoassay detected 3 pg/ml rabbit MCP-1 and did not cross-react with other rabbit chemokines such as IL-8 or GRO. MCP-1 was first detected in synovial fluid (SF) at 1 hour, and peaked at 4 or 2 hours after the injection of LPS or MSU crystals, respectively. Immunohistochemically, MCP-1 was detected in synovial lining cells and infiltrating neutrophils. The amounts of MCP-1 detected in SF from neutrophil-depleted rabbits were similar to those in normal rabbits, suggesting that synovial lining cells were the main source of MCP-1 detected in SF. The peak level of MCP-1 in SF after LPS-injection was inhibited by 57% with anti-TNFalpha mAb and by 41% with IL-1 receptor antagonist (IL-1Ra). Coadministration of anti-TNFalpha mAb and IL-1Ra inhibited 90% of MCP-1 production. In contrast, the peak level of MCP-1 in SF after MSU crystal-injection was not affected by any cytokine inhibitor, but was reduced by 52% with coadministration of anti-TNFalpha mAb and IL-1Ra. Anti-IL-8 IgG had no effect on the production of MCP-1 in either model. Thus, the production of MCP-1 in LPS-induced arthritis was mostly regulated by TNFalpha and IL-1, whereas half the extent of MCP-1 production in MSU crystal-induced arthritis was independent of TNFalpha or IL-1. IL-8 does not seem to regulate the production of MCP-1 in SF either directly or indirectly. Finally, administration of neutralizing anti-MCP-1 antibody inhibited LPS- and MSU crystal-induced monocyte infiltration by 58.4% and 44.9%, respectively, suggesting that synovial production of MCP-1 plays an important role in the recruitment of monocytes in these arthritis models.

Analysis of the cytokine network among tumor necrosis factor alpha, interleukin-1beta, interleukin-8, and interleukin-1 receptor antagonist in monosodium urate crystal-induced rabbit arthritis.

In the present study, we analyzed the cytokine network among TNFalpha, IL-1beta, IL-8, and IL-1 receptor antagonist (IL-1Ra) in a rabbit experimental model of acute gout. The production of TNFalpha in synovial fluids reached the peak at 2 hours after the intra-articular injection of monosodium urate (MSU) crystals. The production of IL-1beta and IL-8 reached the first peak at 2 hours and the second peak at 9 and 12 hours, respectively. The production of endogenous IL-1Ra reached the peak at 9 hours. The source of TNFalpha and the first phase of IL-8 was synovial cells, whereas infiltrating leukocytes were the source of the second phase of IL-8 and also of IL-1beta and IL-1Ra. The production of TNFalpha was not altered by either anti-lL-8 IgG or IL-1Ra. The first IL-1beta peak was reduced only with a combination of anti-TNFalpha mAb and anti-lL-8 IgG, whereas the second peak was significantly reduced by either inhibitor. The first IL-8 peak was not altered with anti-TNFalpha mAb or IL-1 Ra, whereas the second IL-8 peak was reduced with IL-1Ra. Anti-TNFalpha mAb or anti-lL-8 IgG significantly reduced the peak level of endogenous IL-1Ra. These cytokine inhibitors also attenuated the maximal leukocyte accumulation at 9 hours, but not the initial phase, which occurred within 2 hours. These results provide evidence that IL-8 and TNFalpha were responsible for the production of IL-1beta and IL-1Ra, and that IL-1beta was responsible for the second phase of IL-1beta and IL-8 production. Our data also suggest that the initial and the maximal phases of leukocyte influx are differently regulated. Finally, the intravenous injection of colchicine inhibited neutrophil infiltration without affecting the production of TNFalpha or the first peak of IL-8, suggesting that colchicine inhibits MSU crystal-induced arthritis by directly inhibiting the migration of neutrophils.

Production of IL-1 and IL-1 receptor antagonist and the pathological significance in lipopolysaccharide-induced arthritis in rabbits.

Injection of lipopolysaccharide (LPS) into rabbit knee joints provoked leucocyte infiltration and loss of proteoglycan (PG) from the cartilage. We investigated the role of IL-1 and IL-1 receptor antagonist (IL-1Ra) and its significance in the pathogenesis of LPS-arthritis. Production of IL-1 beta peaked at 6 h (196.7 +/- 89.4 pg/joint) after injection of 10 ng of LPS, while IL-1Ra peaked at 9 h (34.5 +/- 13.4 ng/joint). The amount of IL-1Ra was 180-200-fold molar excess of IL-1, and a large amount of IL-1Ra was sustained for 1 week. Both IL-1 beta and IL-1Ra were mainly produced by synovial exudate cells. Arthritis was reproduced by rabbit IL-1 beta. LPS-induced leucocyte infiltration was inhibited 70-75% by rabbit IL-1Ra. Loss of PG in LPS-arthritis was prevented by IL-1Ra and also by neutrophil elastase inhibitor, and superoxide dismutase. In leucopenic rabbits, injection of LPS induced neither production of IL-1 beta nor loss of PG. Direct injection of inflammatory exudated cells in leucopenic rabbits reproduced loss of PG, and there was only a partial recovery by IL-1Ra. These results suggest that LPS-initiated IL-1 acts as a key mediator in LPS-arthritis and that endogenous IL-1Ra may suppress a part of IL-1 activity at the site, but its amount was too low for suppression of the produced IL-1. Loss of PG is a sequela of infiltrated leucocytes and leucocyte-derived elastase, and superoxide anion may play a pivotal role in the destruction of cartilage.