Related Experiment Videos
Activation of human platelets by exposure to a monoclonal antibody, PM6/248, to glycoprotein IIb-IIIa
E J Hornby1, S Brown, J M Wilkinson
1Department of Peripheral Pharmacology, Glaxo Group Research, Ware, Hertfordshire.
Abstract:
Monoclonal antibody PM6/248, which recognizes the GPIIb-IIIa complex on human platelets, causes platelet aggregation in platelet-rich plasma or in gel-filtered platelet suspensions. Aggregation follows a concentration-dependent lag phase and reaches a maximum at 8 micrograms/ml. High concentrations of antibody (less than 30 micrograms/ml) produce complete inhibition of the aggregation response. Aggregation is accompanied by serotonin secretion and thromboxane A2 synthesis, neither of which are inhibited by high concentrations of antibody, and by the mobilization of intracellular Ca2+. The F(ab')2 fragment of PM6/248 does not cause platelet activation and pre-incubation of platelets with this fragment inhibits all platelet responses stimulated by the whole antibody. Pre-incubation with the F(ab')2 fragment of the anti-Fc gamma RII Mab, IV. 3, also inhibits all responses to PM6/248. These data indicate that platelet activation stimulated by PM6/248 is caused by cross-linking of GPIIb-IIIa to the Fc gamma RII which stimulates signal transduction across the plasma membrane through a conformational change in the Fc gamma RII.
Insights
Monoclonal antibody PM6/248 triggers human platelet aggregation by linking GPIIb-IIIa to Fc gamma RII. This interaction activates signaling pathways, leading to platelet activation and serotonin release.
Area of Science:
- Immunology
- Hematology
- Cell Biology
Background:
- The GPIIb-IIIa complex is crucial for platelet aggregation.
- Fc gamma RII (CD32) is a receptor expressed on platelets.
- Understanding the role of Fc gamma RII in platelet activation is important for thrombosis research.
Purpose of the Study:
- To investigate the mechanism by which monoclonal antibody PM6/248 induces platelet activation.
- To determine the role of GPIIb-IIIa and Fc gamma RII in PM6/248-mediated platelet aggregation.
Main Methods:
- Platelet aggregation assays using platelet-rich plasma and gel-filtered platelets.
- Measurement of serotonin secretion and thromboxane A2 synthesis.
- Use of F(ab')2 fragments of PM6/248 and anti-Fc gamma RII antibody (IV.3) for inhibition studies.
- Intracellular calcium mobilization assays.
Main Results:
- Monoclonal antibody PM6/248 induced concentration-dependent platelet aggregation, serotonin secretion, thromboxane A2 synthesis, and intracellular Ca2+ mobilization.
- The F(ab')2 fragment of PM6/248 did not induce activation but inhibited responses to the whole antibody.
- Pre-incubation with an anti-Fc gamma RII antibody fragment also inhibited PM6/248-induced platelet responses.
- High concentrations of PM6/248 inhibited aggregation but not secretion or thromboxane synthesis.
Conclusions:
- Platelet activation by PM6/248 is mediated by the cross-linking of GPIIb-IIIa to Fc gamma RII.
- This cross-linking initiates signal transduction via Fc gamma RII, leading to platelet activation.
- The findings elucidate a novel mechanism of platelet activation involving Fc gamma RII signaling.