2 INDEPENDENT SETS OF MONOCLONAL-ANTIBODIES DEFINE NEOEPITOPES LINKED TO SOLUBLE LIGAND-BINDING AND LEUKOCYTE ADHESION FUNCTIONS OF ACTIVATED ALPHA(M)BETA(2)

The integrin alpha(M) beta(2) mediates a variety of events, adhesive, phagocytic, and inflammatory. Evidence has suggested that the functional events may be mediated by the ''activated'' conformational forms of alpha(M) beta(2) produced by appropriate stimulation of myeloid and monocytic lineage. The activation of alpha(M) beta(2) may be associated with new epitopes on alpha(M) beta(2), sites that may be related to the acquired receptor functions. Monoclonal antibodies were produced that preferentially bind neoepitopes expressed by activated alpha(M) beta(2). These anti-neo antibodies each inhibited three activation-associated specific receptor alpha(M) beta(2) functions, though to different extents. One set of anti-neo antibodies inhibited in a concordant manner the binding of factor X and of fibrinogen by >90%, abolished the alpha(M) beta(2)-initiated cellular coagulant response, and inhibited monocyte adhesion to unstimulated endothelial monolayers. A second set of anti-neo antibodies only diminished factor X and fibrinogen binding by approximate to 40% to 50% but markedly suppressed Xa generation and only partially inhibited monocyte adherence to unstimulated endothelium. Concordance was observed between binding of factor X or fibrinogen and competence for leukocyte adhesion to unstimulated endothelium. Antibody competition assays segregated the anti-neo antibodies into the same two distinct sets, consistent with recognition of separate neoepitopes that are linked to alpha(M) beta(2) function. These data support the conclusion that the activated conformer of alpha(M) beta(2) that binds fibrinogen and factor X also mediates monocyte-endothelial interactions as well as the alternative cellular coagulation pathway.