High-Resolution Imaging Flow Cytometry Reveals Impact of Incubation Temperature on Labeling of Extracellular Vesicles with Antibodies.

Extracellular vesicles (EVs) are released from basically all cells. Over the last decade, small EVs (sEVs; 50-150 nm) have gained enormous attention in diagnostics and therapy. However, methodological limitations coupled to the lack of EV standards leave many questions in this quickly evolving field unresolved. Recently, by using enhanced green fluorescent protein (eGFP)-labeled sEVs as biological reference material, we systematically optimized imaging flow cytometry for single sEV analysis. Furthermore, we showed that sEVs stained with different fluorescent antibodies can be analyzed in a multiparametric manner. However, many parameters potentially affecting the sEV staining procedure still require further evaluation and optimization. Here, we present a concise, systematic evaluation of the impact of the incubation temperature (4°C, room temperature and 37°C) during sEV antibody staining on the outcome of experiments involving the staining of EVs with fluorescence-conjugated antibodies. We provide evidence that both the staining intensity and the sample recovery can vary depending on the incubation temperature applied, and that observed differences are less pronounced following prolonged incubation times. In addition, this study can serve as an application-specific example of parameter evaluation in EV flow cytometry.