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Heparin-induced thrombocytopenia: laboratory studies
J G Kelton1, D Sheridan, A Santos
1Department of Medicine, McMaster University Medical Centre, Hamilton, Ontario, Canada.
Blood
|September 1, 1988
Summary
Heparin-induced thrombocytopenia is an IgG-heparin immune complex disorder. This involves both the Fab and Fc portions of the IgG molecule, impacting platelet function.
Area of Science:
- Immunology
- Hematology
- Pathophysiology
Background:
- Heparin-induced thrombocytopenia (HIT) is a serious complication of heparin therapy.
- The exact mechanisms underlying HIT pathophysiology require further elucidation.
Purpose of the Study:
- To investigate the pathophysiology of heparin-induced thrombocytopenia.
- To determine the role of IgG antibodies and their components in HIT.
Main Methods:
- Studied IgG fractions from HIT patients.
- Utilized radiolabeled serotonin release assays to measure platelet activation.
- Employed monoclonal antibodies against platelet Fc receptors and tested various IgG fragments.
- Examined platelet reactivity in patients with specific glycoprotein deficiencies.
Main Results:
- IgG from HIT patients induced heparin-dependent platelet serotonin release.
- Both Fc and Fab portions of IgG were necessary for platelet activation.
- Platelet Fc receptors (identified by IV.3 antibody) were crucial for the reaction.
- Monocytes and neutrophils inhibited the reaction, suggesting Fc receptor affinity differences.
- Platelet release was independent of glycoproteins Ib/IX and IIb/IIIa.
Conclusions:
- HIT is an IgG-heparin immune complex disorder.
- The Fab portion of IgG binds heparin, forming immune complexes.
- These complexes activate platelets via Fc receptors, involving both Fab and Fc portions of IgG.