Confocal microscopy images of isolated microparticles from platelets activated with HIT sera, thrombin, and calcium ionophore.

Microparticles were identified using platelet-specific primary antibody (mAb anti-GPIb and anti-GPIIb/IIIa) and a fluorescent secondary antibody (TR-conjugated goat antimouse). (A-D) Isolated microparticles following centrifugation of the platelet reaction over a sucrose layer. Very few microparticles were isolated from control reactions, in which platelets were incubated with patient serum that tested negative for (A) heparin-induced thrombocytopenia or heparin alone (data not shown). Microparticles isolated from platelets incubated with (B) heparin-induced thrombocytopenia serum, (C) thrombin, and (D) ionophore were less than 0.1 to 1.0 μm in diameter and demonstrated a similar degree of size heterogenosity and staining intensity as microparticles in unfractionated platelet reactions (not shown). The results of a representative experiment are shown.