Recognition of platelet-associated fibrinogen by polyclonal antibodies: correlation with platelet aggregation.
Progressive decreases in platelet-bound fibrinogen accessibility to antibody and enzymes were recently reported to occur after adenosine diphosphate (ADP)-induced fibrinogen binding. Because previous studies also indicated that platelets that are activated but not aggregated by ADP in the presence of fibrinogen lose their ability to aggregate in a time-dependent manner despite negligible changes in fibrinogen binding, the present study examined the relationship between platelet aggregation and accessibility of platelet-bound fibrinogen to specific polyclonal antibody F(ab')2 fragments over a 60-minute time course. Although 125I-fibrinogen binding remained virtually unchanged, comparison of antifibrinogen antibody F(ab')2 binding and platelet aggregation 5 minutes and 60 minutes after platelet stimulation with ADP or thrombin showed decreases in F(ab')2 binding of 62% +/- 13% and 73% +/- 7% (mean +/- SD, n = 5), respectively, and decreases of 65% +/- 16% and 60% +/- 10% in platelet aggregation. In contrast, platelets stimulated with A23187 or chymotrypsin retained 87% +/- 16% and 76% +/- 12% of their ability to aggregate over the same time course, and lost only 39% +/- 14% and 36% +/- 12% of their ability to bind antifibrinogen antibody F(ab')2 fragments, respectively. Pretreatment of ADP-stimulated platelets with chymotrypsin largely prevented the progressive loss of platelet aggregability and the accompanying decreased recognition of bound fibrinogen by antifibrinogen F(ab')2 fragments. Preincubation of platelets with cytochalasin D (30 micrograms/mL) also inhibited the decrease in platelet aggregation after exposure of ADP-treated platelets to fibrinogen over a 60-minute time course. This was accompanied by only a 25% +/- 18% decrease in antifibrinogen antibody F(ab')2 binding. Present data support the hypothesis that qualitative changes in platelet-bound fibrinogen correlate with loss of the ability of platelets to aggregate, and implicate both the platelet cytoskeleton and chymotrypsin-sensitive surface membrane structures in modulating qualitative changes in bound fibrinogen on the platelet surface.
Peerschke
E I
EI
Department of Pathology, SUNY, Stony Brook 11794-7300.
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000527:Alprostadil / Q000494:pharmacology; D000906:Antibodies; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D000001:Calcimycin / Q000494:pharmacology; D002918:Chymotrypsin / Q000494:pharmacology; D015638:Cytochalasin D / Q000494:pharmacology; D005340:Fibrinogen / Q000032:analysis / Q000378:metabolism*; D006801:Humans; D007140:Immunoglobulin Fab Fragments; D066298:In Vitro Techniques; D007700:Kinetics; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology
D000906:Antibodies; D007140:Immunoglobulin Fab Fragments; D010980:Platelet Membrane Glycoproteins; D015638:Cytochalasin D; D000001:Calcimycin; D000244:Adenosine Diphosphate; D005340:Fibrinogen; D002918:Chymotrypsin; D013917:Thrombin; D000527:Alprostadil