Microparticles and their Roles in Inflammation: A Review

Microparticles (MPs) were long dismissed as “platelet-dust”, cell debris, with no functional significance. Theyare anucleated vesicles (0.1μm to 1μm), enclosed in a membrane, secretedinto the circulation by cells during cell activation or apoptosis. They have now emerged as mediators and markers of inflammatory diseases and autoimmune disorders. They are distinctly different from exosomes and apoptotic bodiesand are released from nearly every cell type, the most abundant being platelets, leukocytes and endothelial cells. MPs can be detected using flow cytometry and more recently by nanotechnology, which is more accuratein detecting, quantifying and phenotypingMPs. MPs are instrumental in the pathogenesis of various cardiovascular diseases (thrombotic and atherosclerotic) through their pro-inflammatory and pro-coagulant properties. Their levels are significantly elevated in chronic inflammatory disorders such as rheumatoid arthritis and multiple sclerosis. However, increasing evidence suggests they also possess antiinflammatory and anti-coagulant roles which could confer immunoprotection. MPs transport various lipids, proteins, mRNA and microRNA (miRNA) which may influence activities of receiving cells. Particularly the miRNAspecies delivered by MPs have been shown to modulate inflammation. In vitro and in vivo studies are being conducted to bioengineer MPs to facilitate delivery of therapeutic compounds to desired location safely, specifically and more effectively, with fewer side effects. More research is required to understand the composition, origin, mechanisms of formation and release as well as their clearance from the circulation to pave way for gaining greater pharmacological benefits by controlling MP-mediated cellular responses.