Platelets Factor 4, complexes with heparin

Stuckey JA, St Charles R, Edwards BF. A model of the platelet factor 4 complex with heparin. Proteins 1992 14 277-87. 

The second type of heparin-induced thrombocytopenia is severe and may be associated with a platelet count below 100,000/mm and thrombosis. ° ° The platelet count generally begins to decline 5 to 10 days after the start of heparin therapy (sooner in patients previously treated with heparin). Thrombocytopenia and thrombosis may develop with low-dose heparin, heparin-coated catheters, or even heparin flushes. Historically, the reaction was thought to be mediated by the formation of antibodies to the platelet-heparin complex. However, evidence suggests a complex interaction between heparin, platelet factor 4 (PF4), platelet membrane Fc receptors, and possibly heparin-like molecules on the surface of endothehal cells (Fig. 102-6). Circulating heparin reacts with PF4 to produce a... 

Heparin-induced thrombocytopenia (HIT). Most frequent antibody-mediated drug-induced thrombocytopenia. Occurs in 1-2% of patients treated with heparin intravenously for longer than four days. Mediated by antibodies to complexes formed between heparin and the endogenous platelet factor 4 (PF4). 

Heparin continues to be used as a ligand and a wide variety of proteins may be purified on affinity columns prepared from this material. Perhaps its most important use is in the purification of proteins involved in, or associated with, the complex process of blood-clotting e.g. anti-thrombin III, platelet factor 4, factor XI and factor XII ). Other proteins purified using heparin include an oestradiol receptor, arginine-rich high density lipoprotein as well as a number... 

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