MOLECULAR-IDENTIFICATION OF THE CROSS-REACTING EPITOPE ON ALPHA(M)BETA(2) INTEGRIN-I DOMAIN RECOGNIZED BY ANTI-ALPHA(IIB)BETA(3) MONOCLONAL-ANTIBODY 7E3 AND ITS INVOLVEMENT IN LEUKOCYTE ADHERENCE

The monoclonal antibody (mAb) 7E3 directed to the platelet integrin al pha(IIb)beta(3) was tested for its cross-reactivity with the homologou s leukocyte integrin alpha(M)beta(2),. Nested recombinant fragments of alpha(M) I domain were expressed as glutathione S-transferase fusion proteins and analyzed for antibody recognition. In enzyme-linked immun osorbent assay, mAb 7E3 bound alpha(M) I domain fragments containing t he amino-terminal sequence Cys(128)-Ser(172) whereas the carboxyl-term inal region Leu(173)-Pro(291) was ineffective. A synthetic peptide des ignated R1.1 and duplicating the alpha(M) sequence G(127)CPQEDSDIAFLID GSGSIIPHDF(150) bound mAb 7E3, In contrast, the adjacent alpha(M) regi on F(150)RRMKEFVSTVMEQLKKSKTLFS(172) or a control peptide with a scram bled R1.1 sequence was not recognized by mAb 7E3, Binding of mAb 7E3 t o alpha(M) I domain blocked monocyte and neutrophil adhesion to immobi lized fibrinogen and fibrinogen-dependent leukocyte-endothelium bridgi ng, indistinguishably from bona fide anti-beta(2) mAb IB4. In contrast , leukocyte binding to stable transfectants expressing intercellular a dhesion molecule-1 was not affected by mAb 7E3, Balloon-mediated injur y of iliofemoral arteries in rabbits resulted in prominent deposition of fibrinogen and increased monocyte adhesion to the injured vessel, i n a reaction inhibited by mAb 7E3, but unaffected by control mAb 14E11 . Through its cross-reactivity between alpha(IIb)beta(3) and alpha(M)b eta(2), mAb 7E3 may initiate a new class of integrin antagonists, capa ble of simultaneously targeting platelet and leukocyte adhesion mechan isms in vascular injury.