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.