EOSINOPHIL ADHESION TO VASCULAR CELL-ADHESION MOLECULE-1 ACTIVATES SUPEROXIDE ANION GENERATION

Adhesion to the adhesion protein, VCAM-1, on vascular endothelium is p roposed to be an important factor in the selective accumulation of eos inophils at sites of allergic inflammation. To determine whether eosin ophil adhesion to VCAM-1 is also associated with an alteration of eosi nophil function, human peripheral blood eosinophils were isolated from allergic donors and incubated in VCAM-1-coated wells. Spontaneous adh erence of isolated eosinophils to VCAM-1-coated wells was greater than cells incubated in FCS-treated control wells (38.0 +/- 1.6% vs 17.1 /- 1.9%, n = 16, p < 0.0001). In addition, eosinophils incubated in VC AM-1-coated wells spontaneously generated modest but significant amoun ts of superoxide anion (O-2(-); 2.0 +/- 1.3 vs 0.5 +/- 0.5 nmol/5 x 10 (5) cells, n = 9, p = 0.029). Moreover, when 100 nM FMLP was added to eosinophils in the presence of VCAM-1, significantly greater O-2(-) ge neration occurred (7.2 +/- 0.9 vs 5.4 +/- 1.0 (FCS control) nmol/5 x 1 0(5) cells, n = 9, p = 0.009). Adhesion, as well as the spontaneous an d enhanced O-2(-) generation to FMLP activation, was blocked by the mo noclonal anti-alpha(4) integrin Ab, HP 1/2, implying involvement of an alpha(4) integrin-VCAM-1 interaction. In contrast, the anti-CD18 mAb, L130, inhibited the spontaneous and enhanced O-2(-) generation to FML P without affecting adhesion, suggesting an involvement of CD18 molecu le(s) only in VCAM-1-enhanced respiratory burst. Finally, 1 mu M genis tein, a tyrosine kinase inhibitor, suppressed the VCAM-1-enhancing eff ect on eosinophil O-2(-) generation and VCAM-1-induced tyrosine phosph orylation, suggesting a role for tyrosine phosphorylation in this eosi nophil functional up-regulation. Our observations suggest that eosinop hil adhesion to VCAM-1 may be an important step in determining the eve ntual functional activity of these cells as they migrate from the circ ulation to the airways and contribute to the allergic inflammatory pro cess.