Microvesicles.
Microvesicles (MVs) are small membrane particles of 0.1–1.0 μm shed by either activated or apoptotic cells (28) in response to a variety of stimulatory factors, and they can originate from platelets, among other cells (29), playing a important role on hemostasis and thrombosis (28). The data obtained in our study showed significant differences between HA patients and controls, with untreated patients having a lower amount of total MVs than the controls. We also observed a lower number of CD62+ MVs in patients, both in the baseline sample and after the infusion of FVIII in comparison to the controls. Our patients showed a lower amount of CD144+ microvesicles after the infusion of FVIIII, a decrease which was also observed in the study of Mobarrez et al. (30). It is likely that this decrease may be related to the inclusion of these MVs in the platelet thrombus.
Differences in the number of MVs with respect to age have also been described (31), but we did not observe statistically significant differences in the number of MVs according to the age of patients, except for a lower number of endothelial MVs in the younger patients before FVIII administration.
In our study we did not observe statistically significant differences in the number of total MVs and those of platelet origin between patients (before and after FVIII administration). The group of patients in our study was a homogeneous group with respect to their underlying disease, that is, they all have severe HA. Our results are in agreement with preliminary data that could not find differences in the number of platelet MVs in patients with severe HA (32-33). However, Artoni et al. (34) observed more platelet-derived MVs in patients with severe HA. In these three papers, the measurement of the MVs or the cytometer used was not specified, thus it is difficult comparing it with our results.