ELISPOT analysis
ELISPOT was performed using the ELISpotPLUS Human IgM Kit (MABTECH AB, Sweden). Briefly, 1 × 104 flow cytometry-sorted CD27+IgD+ B cells as well as other B cell subsets from healthy individuals or SLE patients were subjected to IgM detection in the presence of anti-CD40 (3 µg/ml, eBioscience) and CpG (10 µg/ml, Invivogen, San Diego, CA, USA) for 24h. The results were analyzed on an ImmunoSpot Analyzer (Cellular Technology Ltd., Shaker Heights, OH, USA)