(1) A very small particle, especially one that can pass through a filter of specified fineness. (2) A vesicle, ranging in size from 5 to 100 mcm, released from the membrane of a cell into the circulation. Microparticles are immunologically unique to their cells of origin and may play a role in antigen presentation. Increased numbers of certain kinds of microparticle may be found in the circulation in vascular and thrombotic disorders. [micro- + particle]
