Differential inhibition of fibrinogen binding to agonist- and RGDS peptide-activated states of GPIIb-IIIa by an anti-GPIIIa monoclonal antibody, PMA5.
Platelet agonists and RGD-containing peptides can convert platelet membrane glycoprotein (GP) IIb-IIIa from its resting state to an activated state competent to bind soluble fibrinogen. We examined the effects of two anti-GPIIb-IIIa monoclonal antibodies, PMA1 and PMA5, on fibrinogen binding to agonist- and RGD-activated GPIIb-IIIa. PMA1 abolished aggregation of both agonist- and RGDS peptide-activated fixed platelets, and inhibited the binding of 125I-fibrinogen to these platelets almost completely. PMA5 had the same effects on agonist-activated platelets, but had little effect on the aggregation of RGDS-activated fixed platelets, and inhibited fibrinogen binding to RGDS-activated fixed platelets by only 44%. PMA5 bound to agonist- and RGDS-activated platelets equally. Immunoblot analysis showed that PMA5 bound to intact GPIIIa, but not to a 66 kDa fragment of GPIIIa digested by chymotrypsin. Although PMA5 inhibited platelet adhesion to immobilized fibrinogen by 94%, 44% of the remaining adherent platelets were spread. In contrast, no platelet spreading was observed in the presence of PMA1. These findings indicate that PMA5 is a novel anti-GPIIIa monoclonal antibody with the ability to inhibit fibrinogen binding to agonist- and RGD-activated states of GPIIb-IIIa differentially, and suggest that binding of immobilized fibrinogen to RGD-activated GPIIb-IIIa is necessary for platelet spreading.
Nakatanl
S
S
Department of Internal Medicine 1, Ehime University School of Medicine, Japan.
Hato
T
T
Minamoto
Y
Y
Fujita
S
S
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D005340:Fibrinogen / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D009842:Oligopeptides / Q000494:pharmacology*; D015539:Platelet Activation / Q000187:drug effects*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000819:agonists / Q000276:immunology / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects
D000911:Antibodies, Monoclonal; D009842:Oligopeptides; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C047981:arginyl-glycyl-aspartic acid; D005340:Fibrinogen