The expression of cluster of differentiation (CD)31 on NHAECs was analyzed by flow cytometry using appropriated primary and fluorescein isothiocyanate-labelled secondary antibodies (25 (link)). Samples were analyzed using a FACSCalibur/LSR II flow cytometer (BD Biosciences, Franklin Lakes, NJ, USA), and cell sorting was performed with a FACSVantage cell sorter (BD Biosciences). Data were analyzed using FACSDiva™ software (version 8.0.1; BD Biosciences). Gates were set according to isotype controls.