Objective. There is relatively little direct evidence for the roles of interleukin-1 (IL-1) and tumor necrosis factor α (TNFα) in activating endothelium in vivo. The aim of this study was to use in vitro and in vivo models to investigate the contribution of these cytokines to both E-selectin expression and the recruitment of polymor-phonuclear cells (PMN) in monosodium urate monohydrate (MSU) crystal-induced inflammation.
Methods. MSU crystals were incubated with freshly isolated mononuclear cells, after which the harvested supernatants were tested for their ability to induce E-selectin expression during coculture with human umbilical vein endothelial cells. Subsequent experiments were performed with the addition of neutralizing anticytokine antibodies/antisera. The role of TNFα was then studied in an MSU crystal-induced monarthritis model, in the presence or absence of anti-TNFα (5 mg/kg intravenously). 99mtechnetium (99mTc)-labeled PMN cells and 111indium (111In)-labeled anti-E-selectin monoclonal antibody (MAb) 1.2B6 were intravenously administered 4 hours after intraarticular injection to quantify PMN recruitment and E-selectin expression in inflamed joints.
Results. MSU crystals were a potent stimulus for IL-1 and TNFα production by monocytes in vitro, and these cytokines fully accounted for MSU crystalstimulated, monocyte-mediated endothelial activation. In the MSU crystal-induced monarthritis model, TNFα blockade was very effective in suppressing both E-selectin expression and PMN emigration into the inflamed joints, as judged by gamma-camera image analysis and postmortem tissue counting following the intravenous injection of 99mTc-PMN and 111In-anti-E-selectin MAb.
Conclusion. IL-1 and TNFα appear to be the only factors released by monocytes following incubation with MSU crystals, which induce E-selectin expression in vitro. Anti-TNFα is effective in suppressing endothelial activation and PMN recruitment in vivo E-selectin imaging can be used to assess the endothelial response to therapy and may prove useful for clinical studies.