Leukotriene B 4 and Thromboxane a 2 Are Essential Cofactors in Cd 18 Depeendent Neutrophil Diapedesis

Previous studies have indicated that thromboxane (Tx) and leukotriene (LT) B4 act synergistically to induce neutrophil (PMN) adhesion in the microvasculature. This study tests the ability of Tx to induce LTB4 synthesis which then leads to activation of PMN and endothelial adhesion receptors. Tx-mimic (U 46619, lM-g/ml) was administered into abraded skin chambers placed on the back of rabbits (n=6). After 3 h LTB4 was synthesized in the blister fluid, 385 pg/ml, a value higher than levels in saline treated blisters 10 pg/ml (p < 0.05). The LTB4 generation following Tx-mimic was correlated (p < 0.05, r=0.70) with neutrophil diapedesis. These averaged 645 PMN/mm, higher than saline values of 20 PMN/mm (p < 0.05). Intravenous (IV) treatment of other rabbits (n=4) with the lipoxygenase inhibitor diethylcarbamazine 60 mg/kg followed by 40 mg/kg/h prevented Tx-mimic induced LTB4 synthesis (10 pg/ml) and diapedesis (19 PMN/mm) (both p < 0.05). IV treatment of yet other rabbits (n=4) with the anti-CD 18 monoclonal antibody R 15.7, lmg/kg abolished Tx-induced diapedesis (3 PMN/mm) (p < 0.05). In contrast, local administration of the protein synthesis inhibitor actinomycin D 3 ng, to prevent expression of endothelial adhesion proteins, limited TNF but not Tx-induced diapedesis. The data indicate that Tx-induced diapedesis is mediated by the generation of LTB4 and activation of neutrophil CD 18 but not endothelial adhesion receptors.