Exosomes derived from synovial fibroblast (SFB)-conditioned medium. (A) The size distribution of the particles in the ultracentrifugation pellet was measured with the qNano system. The major peak in particle size was at 60 to 80 nm and overall size distribution ranged between 60 and 200 nm. (B) The numbers of nanoparticles, including exosomes, isolated from IL-1β-stimulated SFB were significantly higher than the numbers in non-stimulated SFB (NSFB). Data are the means ± standard error of the mean. Comparison of mean values was performed by Mann-Whitney U-test; *P <0.05 versus non-stimulated SFB. (C) Immunoblotting of exosome markers, CD9, CD81, and flotillin-1, in isolated exosomes from IL-1β-stimulated SFB or non-stimulated SFB. Flot, flottilin-1; GAPDH, glyceraldehyde-3-phosphate dehydrogenase.