Detection of synovial fibroblast-derived microvesicles and microvesicle-associated GusB activity. (a) Synovial fibroblast (SF)-derived microvesicles (MVs) were isolated from serum-free 24-hour fibroblast supernatants by centrifugation and subsequent ultracentrifugation at 100,000 × g. Electron micrographs show different MVs varying in size and morphology. The dominant microvesicle type appears to be ectosome (diameter between 100 and 800 nm). (b) Flow cytometric scatter plots of 24-hour supernatants of SFs with cell-derived microvesicles. SSC-H (side scatter), FSC-H (forward scatter). (c), (d) Histogram plots show that the majority of rheumatoid arthritis (RA) and osteoarthritis (OA) SF-derived microvesicles are β-D-glucuronidase (GusB)-positive when stained with a lipophilic fluorogenic substrate. OA synovial fibroblast-derived MVs are characterized by stronger mean fluorescence intensity values than those derived from RA SFs. FL1-H (histogram of the green fluorescence).