Exosome composition

Exosome composition varies depending on the cell type of origin. Nevertheless, exo- somes contain a number of

common protein components (Thery et al., 2001). Several adhesion molecules such as intercellular adhesion molecule-1,

CD146, CD9, milk-fat-globule EGF-factor VIII (MFG-E8), CD18, CD11a, CD11b, CD11c, CD166 and LFA- 3/CD58

have also been identified in exosomal preparations ( Thery et al., 2001; Mears et al., 2004 ). In addition, several proteins

involved in apoptosis are present on exosomes including thioredoxin peroxidase II, Alix, 14-3-3 and galectin 3.

Exosomes also contain heat- shock proteins Hsp70 and Hsp90, which can facilitate peptide loading onto major

histocompatibility complex (MHC)I and MHCII ( Gastpar et al., 2005). One of the characteristic features of exosomes is the

tetraspanins, which include CD9, CD63, CD81 and CD82. Exosomes also carry some cell -specific proteins like

MHCII and CD86 present only on exosomes isolated from antigen-presenting cells (APCs) ( Segura et al., 2005) and

MFG-E8/lactadherin present on exosomes from immature DCs (Veron et al., 2005). Exosomes are also enriched in

proteins that participate in vesicle formation and trafficking like the lyso- bisphosphatidic acid (LBPA)-binding protein

Alix (Futter et al., 2007). Other proteins detected on exosomes are the metabolic enzymes such as peroxidases, pyruvate

and lipid kinases and eno- lase-1 (Hegmans et al., 2004). Consistent with their endosomal origin, exo- somes typically do

not contain endoplasmic reticulum, mitochondria or nuclear proteins. Similar to proteins, lipids present on exosomes

are char- acteristic of the cell origin, with most of the lipid analytical work being performed on exosomes derived from

reti- culocytes (Vidal et al., 1989), mast cells (Laulagnier et al., 2004), B lymphocyte cell lines (Wubbolts et al., 2003) and human

DCs (Laulagnier et al., 2004). The typical lipid composition of mast cell-derived exosomes includes

lysophosphatidylcholine, sphingomyelin, phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine,

cholesterol and diglyceride (Laulagnier et al., 2004).

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