CD19 and systemic lupus erythematosus: The MSC-EV-treated groups had a significantly lower proportion of plasmablasts (CD19+CD27hiCD38hi) than the PBS group (PBS: 3.56 ± 1.42 %, FBS-EV: 2.61 ± 1.27 %, Rapa-FBS-EV: 1.62 ± 0.35 %, SLE-EV: 2.28 ± 0.83 %, Rapa-SLE-EV: 1.14 ± 0.27 %).