FREEZING ADHESION MOLECULES IN A STATE OF HIGH-AVIDITY BINDING BLOCKSEOSINOPHIL MIGRATION

Leukocyte extravasation is mediated by multiple interactions of adhesi ve surface structures with ligands on endothelial cells and matrix com ponents. The functional role of beta1 (CD29) integrins (or very late a ntigen [VLA] proteins) in eosinophil migration across polycarbonate fi lters was examined under several in vitro conditions. Eosinophil migra tion induced by the chemoattractant C5a or platelet-activating factor was fully inhibited by monoclonal antibody (mAb) 8A2, a recently Chara cterized ''activating'' CD29 mAb. However, inhibition by mAb 8A2 was o bserved only under filter conditions that best reflected the in vivo s ituation, i.e., when the eosinophils migrated over filters preincubate d with the extracellular matrix (ECM) protein fibronectin (FN), or whe n the filters were covered with confluent monolayers of cultured human umbilical vein endothelial cells (HUVEC). When bare untreated filters were used, mAb 8A2 had no effect, whereas the C5a-directed movement w as prevented by CD18 mAb. Studies with alpha-subunit (CD49)-specific m Abs indicated that the integrins VLA-4 and -5 mediated migration acros s FN-preincubated filters, and VLA-2, -4, -5, and -6 were involved in eosinophil migration through filters covered with HUVEC. In contrast w ith the activating CD29 mAb 8A2, a combination of blocking CD49 mAbs o r the nonactivating but blocking CD29 mAb AIIB2 failed to inhibit comp letely eosinophil migration over FN-preincubated or HUVEC-covered filt ers. mAb 8A2 stimulated binding to FN but not to HUVEC. Moreover, eosi nophil migration over FN-preincubated or HUVEC-covered filters was sig nificantly inhibited by anti-connecting segment 1 (CS-1) mAbs, as well as the soluble CS-1 peptide (unlike migration across bare untreated f ilters). Thus, inhibition of eosinophil migration by mAb 8A2 depended upon the presence of ECM proteins and not upon the presence of HUVEC p er se. In conclusion, ''freezing'' adhesion receptors of the beta1 int egrin family into their high-avidity binding state by the activating C D29 mAb 8A2 results in a complete inhibition of eosinophil migration u nder physiological conditions. Hence, activation of beta1 integrin-med iated cell adhesion may represent a new approach to prevent influx of inflammatory cells.