Table 1 Common exosomal components and their main biofunctions

Proteins

Proteins involved in exosome biogenesis

Alix; Tsg101

MVB biogenesis

[36]

Adhesion molecules

Integrins-α and -β; P-selectin; lactadherin; ICAM-I

Cell anchorage, adhesion and uptake

[42, 45]

Tetraspanins

CD9; CD63; CD81; CD82

CD9 and CD81: mediates direct fusion between exosomes and cell membranes of target cells

CD63: exosomal cargo sorting

[49]

Membrane transport and fusion proteins

Annexin; Flotillin; Rab GTPase

Responsible for membrane transport and fusion. Exosome secretion into the extracellular environment

[50]

Cytoskeletal proteins

Actin; tubulin; myosin; cofilin

Cytosolic proteins involved in exosome formation and secretion

[42, 45]

Heat shock proteins

Hsp70; Hsp90

Exosomes secretion and signaling processes

[34]

Immune escaping proteins

“Self-marker” CD47; GPI-anchored CD55 and CD59

CD47: protection against macrophage clearance

CD55 and CD59: protection against complement lysis

[41, 44, 51]

Antigen-presenting proteins

MHC class I; MHC class II

Antigen presentation for immune activation

[52]

Lipids

Ceramides

Regulates cargo sorting into MVBs and exosome biogenesis

[45, 53]

Cholesterol

Involved in exosome secretion

[45, 54]

Sphingomyelin

Exosome structure and rigidity

[45, 55]

Phosphatidylserine

Exosome biogenesis

[45, 46]

Phosphatidylcholine

Exosome biogenesis and structure

[45, 46]

Phosphatidylinositol

Exosome biogenesis and structure

[45, 46]

Nucleic acids

DNA fragments

Mitochondrial DNA and chromosomal DNA

The genetic material of exosomes can modulate the phenotype of the recipient cells, and influence various biological processes. They have been used as non-invasive tools for clinical diagnosis of various diseases

[45]

Coding and non-coding RNAs

mRNA and miRNA