What is the underlying mechanism of heparin-induced thrombocytopenia (HIT)?

HIT is an iatrogenic disorder usually mediated by IgG antibodies that target multimolecular complexes of PF4 and heparin, leading to platelet activation, generation of procoagulant platelet-derived microparticles and activation of white blood cells and endothelial cells. The net result is a profoundly hypercoagulable state.