Microparticles (MPs, also known as
microvesicules or ectosomes) are heterogeneous subcellular vesicular particles
(0.1-1.0 m in diameter) released constitutively from
cells and platelets undergoing cell activation or cell death by blebbing or
shedding. Platelet MPs are usually the most abundant type in blood.
The presence of basal levels of MPs is common
in healthy individuals, and is estimated, in peripheral blood, to range between
5 and 50 g/ml (105-106 MPs/ml). Numerous types of MPs have been
characterized with important physiologic effects by the detection of different
cell surface antigens reflecting their origin and activation method.
MPs represent distinct subcellular structures
and serve a prominent role in homeostasis and intercellular communication
including immune activation. They can transfer bioactive molecules from
parental to target cells, allowing for regulation and amplification of several
biological mechanisms such as activation, apoptosis, coagulation, and
proliferation.
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