CD19 and systemic lupus erythematosus: Cluster 2 (n = 366) displayed higher proportions of CD19+CD24bbrightCD38bbrightCD27− transitional B cells (6.3%±9.0%) and CD19+CD20+CD27− naïve B cells (85.4%±7.2%), and lower proportions of CD19+CD20−CD138+ peripheral long-lived plasma cells (0.2%±0.3%) and CD19+CD38b+CD27b+ SLE-associated plasma cells (1.6%±2.0%).