HOMOTYPIC LEUKOCYTE AGGREGATION TRIGGERED BY A MONOCLONAL-ANTIBODY SPECIFIC FOR A NOVEL EPITOPE EXPRESSED BY THE INTEGRIN BETA-1 SUBUNIT - CONVERSION OF NONRESPONSIVE CELLS BY TRANSFECTING HUMAN INTEGRIN ALPHA-4 SUBUNIT CDNA

The monoclonal antibody 33B6 was found to be specific for the beta1 integrin subunit. Treatment of leukocytes with this antibody induced a vigorous homotypic aggregation that had similar physiologic conditions as aggregation induced by a monoclonal antibody specific for the alpha4 subunit. Expression of a beta1 subunit on the cell surface was not sufficient for mAb 33B6-mediated aggregation to occur, since cells of the K562 erythroleukemia line failed to respond even though they expressed the beta1 subunit and the 33B6 epitope. However, after transfection with cDNA encoding the alpha4 subunit, K562 cells acquired the ability to aggregate in response to mAb 33B6 binding. By contrast, mAb 33B6 blocked cell binding to the endothelial surface protein vascular cell adhesion molecule-1 and the extracellular matrix protein fibronectin. These results suggest that the beta1 epitope defined by mAb 33B6 may play a novel role in regulating leukocyte adhesive interactions.