Origin of microvesicles and exosomes from cells. A microvesicle arises from budding of the plasma membrane. Microvesicles are more irregular in shape and size and can contain cytoplasmic materials. Microvesicles express surface markers such as integrin-β, CD40 and selectins such as plasma selectins and/or proteins from the cells they originate from. Exosomes originate from the endosomal trafficking system and, therefore, are more regular in shape and size. Exosomes are more easily identifiable via cell surface markers such as CD81, CD9 and CD63 and may contain materials such as mitochondrial DNAs, mRNAs and miRNAs. ER: endoplasmic reticulum; miRNA: microRNA; TGN: trans-Golgi network; MVB: multi-vesicular bodies.