Tissue factor-enriched vesicles are taken up by platelets and induce platelet aggregation in the presence of factor VIIa
Irene Lopez-Vilchez
1
Servicio de Hemoterapia y Hemostasia, Hospital Clinic, Centre de Diagnostic Biomedic, IDIBAPS, Universidad de Barcelona, Spain;
,
Gines Escolar
1
Servicio de Hemoterapia y Hemostasia, Hospital Clinic, Centre de Diagnostic Biomedic, IDIBAPS, Universidad de Barcelona, Spain;
,
Maribel Diaz-Ricart
1
Servicio de Hemoterapia y Hemostasia, Hospital Clinic, Centre de Diagnostic Biomedic, IDIBAPS, Universidad de Barcelona, Spain;
,
Berta Fuste
1
Servicio de Hemoterapia y Hemostasia, Hospital Clinic, Centre de Diagnostic Biomedic, IDIBAPS, Universidad de Barcelona, Spain;
,
Ana M. Galan
1
Servicio de Hemoterapia y Hemostasia, Hospital Clinic, Centre de Diagnostic Biomedic, IDIBAPS, Universidad de Barcelona, Spain;
,
James G. White
2
Department of Laboratory and Clinical Medicine and Pediatrics, University of Minnesota, Minneapolis, Minnesota, USA
› InstitutsangabenFinancial support: This work has been partially supported by grants SAF2006–08003 (from the Ministerio de Educación y Ciencia, Spain), SGR2005–00952 (from the Generalitat de Catalunya), FIS PI040887 and FIS CP04–00112 (both from the Ministerio de Sanidad, Spain).
We investigated the interactions of vesicles containing human tissue factor (TF) with platelets and evaluated responses induced by rFVIIa using standard aggregometry, ultrastructural and flow-cytometry techniques. Washed platelets were exposed to a preparation of placental human TF (pTF) or to a relipidated formulation of recombinant humanTF (rTF). Under stirring conditions, pTF induced reversible aggregation with platelets returning to their resting state after 5 minutes. This reversible response to pTF was partially inhibited by antibodies against CD62-P, but not by antithrombin agents, and was not observed with rTF. Sequential ultrastructural studies revealed uptake of both TF preparations by platelets involving traffic of vesicles through channels of the open canalicular system (OCS). Immunocytochemical studies on cryosections identified TF in the OCS, and occasionally in the alpha-granules of the platelets. These processes were faster with pTF than with rTF, but bothTF preparations accumulated in platelets at the end of incubation periods. Flow cytometry studies revealed the presence of other cellular antigens (CD62-P, CD14 and CD45) associated to the pTF. Addition of rFVIIa to washed platelets exposed to pTF or rTF, caused a thrombin dependent irreversible platelet aggregation. Our studies demonstrate that platelets possess mechanisms to capture and incorporate TF-rich vesicles. These processes are accelerated by the presence of other cellular antigens in the vesicles. Our findings may explain the hemostatic action of rFVIIa in severely hemodiluted patients, but are also relevant for the understanding of potential implications of TF-associated to platelets in the propagation of thrombus.
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