Plasma membrane-derived vesicles (PMVs) are released into circulation in response to normal and stress/pathogenic conditions. They are of tremendous significance for the prediction, diagnosis, and observation of the therapeutic success of many diseases. Knowledge of their molecular characteristics and therefore functional properties would contribute to a better understanding of the pathological mechanisms leading to various diseases in which their levels are raised.
Schematic presentation of modes of emission of PMVs vs. Exosomes. This figure shows the formation of an endosome by invagination. By inward blebbing of the endosomal membrane, intraluminal vesicles are formed. Endosomes containing intraluminal vesicles are called multivesicular bodies (MVBs). Cells release the contents of their MVB when the membrane of the MVB fuses with the plasma membrane and in contrast to exosomes, PMVs are formed by major structural rearrangements of the cytoskeleton and are ‘budded’ off from the outer cell membrane.
PMVs shed from both normal and cancerous cells may serve as a means of intercellular communication as they carry proteins, lipids and nucleic acids derived from the host cell. Their isolation and analysis from blood samples has the potential to provide information about the state and progression of malignancy in terms of cancer. PMVs are also likely to prove of great clinical importance as biomarkers for a variety of disease states in other words of potential diagnostic value as well as a therapeutic tool. However, a standardized protocol for isolation has not yet been agreed upon. It is often unclear what the content of the isolates are and whether the isolated PMVs, were present in vivo or whether they were created during the isolation procedure. Vesicular structures, which are sized from 1 μm down to 50 nm, are present in isolates of many body fluids. Isolates of PMVs sometimes contain different populations that differ in size and shape, which indicates that methods of isolation and determination of the number of PMVs in the peripheral blood need to be elaborated and improved upon.