GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR REGULATES THE FUNCTIONAL ADHESIVE STATE OF VERY LATE ANTIGEN-4 EXPRESSED BY EOSINOPHILS

As very late antigen-4 (VLA-4) can exist in different functional state s, we have sought to determine whether a cytokine expressed by inflame d endothelium (i.e., granulocyte-macrophage CSF (CM-CSF)) could regula te the functional state of VLA-4 expressed by eosinophils. Using a mic ropipette single cell adhesion assay able to measure the strength of a dhesion forces, eosinophils exhibited low levels of basal adhesion to unstimulated endothelium (separation force, 0.022 +/- 0.003 mdynes), I n contrast, individual eosinophils bound to IL-1 beta-stimulated endot helium (0.49 +/- 0.02 mdynes), TNF-stimulated endothelium (0.62 +/- 0. 05 mdynes), or IL-4-stimulated endothelium (0.11 +/- 0.01 mdynes) with increased avidity as assessed by separation force, Eosinophil binding to IL-4-stimulated endothelium was significantly inhibited by neutral izing Abs to either vascular cell adhesion molecule (VCAM) or YLA-4. T he strength of eosinophil adhesion to VCAM (0.31 +/- 0.02 mdynes) or t o connecting segment-1 (CS-1) (0.18 mdynes) was greater than the stren gth of eosinophil adhesion to unstimulated endothelium (0.02 mdynes), but was less than the strength of eosinophil adhesion to IL-1. beta-st imulated endothelium (0.49 +/- 0.02 mdynes). After incubating eosinoph ils for 30 min with GM-CSF, the mean adhesion strength of eosinophils to CS-1 and VCAM increased significantly by 84 and 54%, respectively, compared with that of controls. This increased binding of eosinophils to VCAM or CS-1 was not due to alterations in VLA-4 receptor number (a ssessed by FAGS analysis) or alterations in VLA-4 receptor distributio n (assessed by confocal microscopy), These studies suggest that endoth elial-derived cytokines such as GM-CSF have the potential to alter the functional state of eosinophil-expressed VLA-4 from a low affinity st ate to a high affinity state.