Microparticles That Form Immune Complexes as Modulatory Structures in Autoimmune Responses

Figure 1

The main characteristics of secreted vesicles. (a) Cells under basal or activated states release vesicles from internal compartments such as multivesicular endosomes, also called late endosomes. Fusion among the endosomal membranes and the cell membrane leads to secretion of intravesicular bodies, which once released are called exosomes and may contain components such as TSG101 and endocytic tetraspanins (CD9 and CD63). (b) Activated cells may secrete vesicles by direct budding of the plasma membrane, called MPs, that contain various receptors, integrins, selectins, cytokines, and nucleic acids. These molecules can be located inside or on the surface of the MPs; however, a cell at rest or in response to physiological stimuli can also produce MPs, but upon activation it produces increased amounts. (c) Apoptotic cell death leads to the formation of apoptotic bodies and MPs, which may contain histones and nucleic acids. The aminophospholipid phosphatidylserine (PS) is exposed on the outer face of the cell membrane during apoptosis. MPs that express PS on their surface can also be generated by cleavage processes from apoptotic bodies.