Identification and analysis of exosomes secreted from macrophages

Exosomes were small vesicles secreted by many cells, and they can play an important role in cell signal transductions. Because the diameter of exosomes is about 30-100 nm, it is so difficult to collection them. In this paper, three kinds of exosomes purifying methods (density gradient ultracentrifugation method, the ultracentrifugation and ultrafiltration method, ExoQuick™ Extraction kit method) were used to collected exosomes in culture supernatants of macrophages. The morphologies of three kinds of exosomes were analyzed by transmission electron microscopy (TEM), and the characteristic molecules such as CD86, LAMP-1, HSP-70 on exosomes were analyzed with Western blot. In addition, the biological activities of exosomes purified by three kinds of methods in vitro were analyzed by ELISA and flow cytometry methods. All experimental results show that the purity and quality of exosomes collected by ExoQuick™ extraction kit and ultracentrifugation and ultrafiltration method were better, and they could enhance the expression of MHC-I in macrophages and promote cells to secrete more TNF-α to cause inflammatory response of macrophages. The analysis pointed out that the advantages and disadvantages of the three methods by biological activities or components of exosomes. Therefore, the ultracentrifugation and ultrafiltration method or the ExoQuick™ Extraction kit method were more suitable to be applied in the scientific research.

Analysis of exosomes purified by three kinds of methods. Results are presented as means ± S.D of three independent experiments. All data were analyzed by SPSS 16.0. Tests were 2-sided and P values < 0.05 were considered as significant.