The identification and functional significance of factor VIII components on normal platelets.
Factor VIII-related antigen (VIII R:Ag) has previously been identified on human platelets by fluorescein-labelled heterologous antibodies to factor VIII. However, it is not known whether these antibodies identify only VIII R:Ag or whether antigens associated with factor VIII coagulant activity (VIII:C Ag) are also present. The current studies utilize specific antibodies and their Fab' fragments to evaluate the presence of both VIII R:Ag and VIII:C Ag on human platelets and to study the functional role of the platelet-associated VIII R:Ag on ristocetin-induced platelet agglutination. Immunofluorescent studies demonstrate the presence of VIII R:Ag, but do not identify VIII:C Ag on platelets. The functional studies reveal that after incubation with either of the Fab' fragments, platelets retain their reactivity in the ristocetin cofactor assay. These results indicate that this population of VIII R:Ag is not essential for the ristocetin aggregation reaction and that no antigenic determinants for factor VIII coagulant activity (VIII:C) are detectable on human platelets by immunofluorescence.
D000941:Antigens / Q000276:immunology; D001792:Blood Platelets / Q000276:immunology*; D005169:Factor VIII / Q000276:immunology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007141:Immunoglobulin Fc Fragments / Q000276:immunology; D010974:Platelet Aggregation; D014841:von Willebrand Factor / Q000276:immunology
D000941:Antigens; D007140:Immunoglobulin Fab Fragments; D007141:Immunoglobulin Fc Fragments; D014841:von Willebrand Factor; D005169:Factor VIII