INTEGRIN ALPHA(4)BETA(7) MEDIATES HUMAN EOSINOPHIL INTERACTION WITH MADCAM-1, VCAM-1 AND FIBRONECTIN

We have investigated the contribution of integrin alpha(4) beta(7) to human peripheral blood eosinophil adhesive interactions. Immunofluores cence and flow cytometry demonstrated constitutive expression of alpha (4) beta(7) by eosinophils. Expression of alpha(4) beta(1) or alpha(4) beta(7) was not enhanced by eosinophil activation with platelet-activ ating factor (PAF). Expression of alpha(4) beta(7) was confirmed by im munoprecipitation of I-125-labelled lysates analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Approximately 20% of unstimulated eosinophils were adherent to L1-2 cells transfect ed with vascular cell adhesion molecule-1 (VCAM-1) cDNA, while very fe w resting eosinophils adhered to mouse mucosal adressin cell adhesion molecule-1 (MAdCAM-1) transfectants. Binding of unstimulated eosinophi ls to VCAM-1 transfectants was inhibited by HP1/2 (an antibody that bl ocks both alpha(4) beta(1) and alpha(4) beta(7) functions), but not Ac t-1, an alpha(4) beta(7) monoclonal antibody (mAb). PAF stimulation re sulted in increased binding of eosinophils to MAdCAM-1 transfectants, which was inhibited by both HP1/2 and Act-1. In contrast, PAF did not enhance binding to VCAM-1 transfectants, although binding of PAF-stimu lated eosinophils to VCAM-1 could be partially inhibited by Act-1. Sti mulation of eosinophils with the beta(1)-activating mAb TS2/16 resulte d in enhanced binding of eosinophils to both VCAM-1 and MAdCAM-1 trans fectants. The increased binding was largely alpha 4 beta(7)-dependent. Unstimulated eosinophils bound to soluble recombinant human (rh)VCAM- 1 and fibronectin (Fn), coated on 96-well plates in a dose-dependent m anner. Binding was inhibited by HP1/2 and 4b4, an anti-beta(1) mAb, bu t not by Act-1. TS2/16 treatment increased adherent cell numbers and t his enhanced binding was inhibited by Act-1. We have therefore confirm ed that alpha(4) beta(1) is functionally active on unstimulated eosino phils. In contrast, PAF-induced enhancement of eosinophils binding to VCAM-1 or MAdCAM-1 was alpha(4) beta(7)-dependent. In addition, treatm ent with TS2/16 resulted in a alpha(4) beta(7)-dependent enhancement o f eosinophil binding to VCAM-1, MAdCAM-1 and Fn. We therefore hypothes ize that alpha(4) beta(7) may have an important role in eosinophil loc alization in diseases such as asthma and inflammatory bowel disease.