Basement membrane transmigration is an important step in tissue recruitment of eosinophils into inflamed tissue. Recent reports showed that this phenomenon is modulated by platelet-activating factor (PAF) in combination with cytokines and proteinases. We investigated the in vitro efficacy of 5-oxo-6,8,11, 14-eicosatetraenoic acid (5-oxo-ETE), a metabolite of arachidonic acid and known as a potent eosinophil chemotactic factor, in promoting the transmigration of blood eosinophils from normal and asthmatic subjects through a Matrigel basement membrane. 5-Oxo-ETE proved to be a more potent (> 10-fold) inducer of eosinophil transmigration than PAF, and this effect was similar in cells from normal and asthmatic subjects (82.0 +/- 3.7% and 88.1 +/- 3.7%, respectively). Moreover, 5-oxo-ETE was active in the absence of interleukin (IL)-5, although this cytokine amplified the effect of 5-oxo-ETE from 61.3 +/- 3.3% to 92.8 +/- 1.8% (p = 0.003). The membrane receptor for urokinase plasminogen activator (CD87), a serine protease, was observed on eosinophils, and its expression was increased by IL-5. The inhibition of both metalloproteinases (MMP) and plasmin/plasminogen complex with inhibitor or monoclonal antibodies decreased cell transmigration by about 50%. Combination of an MMP inhibitor with anti-CD87 antibodies had no additive effect. These data show that 5-oxo-ETE is an efficient promoter of eosinophil transmigration in vitro, and is much more potent in this respect than PAF. The data suggest that 5-oxo-ETE could play an important role in eosinophil recruitment in vivo. Moreover, they demonstrate that in addition to MMP, the plasmin/plasminogen system could be involved in eosinophil transmigration.

The effect of eotaxin, a potent eosinophil chemotactic factor, on eosinophil transmigration through a reconstituted basal membrane (Matrigel®) was evaluated. Eotaxin induced significant eosinophil transmigration in the presence of 10% fetal bovine serum (FBS) and interleukin-5. Its effect was optimal at 0.01 μM, and it plateaued at 18 h. Eotaxin's effect was greater with eosinophils from asthmatic subjects (61.1 ± 3.4%) than with eosinophils from normal subjects (38.7 ± 4.2%) (P < 0.001). Inhibition of metalloproteinases decreased eotaxin-induced transmigration by ≤10.4%, whereas inhibition of the plasminogen-plasmin system decreased eotaxin's effect by ≤44.4% (P = 0.0002). Moreover, eotaxin-induced transmigration was largely diminished in medium with low concentrations of serum [0.5% FBS: 6.1 ± 2.4%; 10% FBS: 40.2 ± 5.8% (P = 0.0001)] but returned to its initial level with the addition of plasminogen (2 U/mL) to 0.5% FBS (43.1 ± 6.5%). These data show that eotaxin is an efficient promoter of eosinophil transmigration in vitro, that it is more potent with cells from asthmatics than with normal cells, and that its effect depends predominantly on the activation of the plasminogen-plasmin system.