CD27 and systemic lupus erythematosus: Compared with each other, cluster 1 (n = 191) displayed higher proportions of CD19+CD24b+CD27+ regulatory B cells (mean ± SD: 35.9%±12.6%), CD19+CD20+CD27+ bulk memory B cells (32.2%±9.9%), CD19+CD20+CD69+ activated B cells (0.2%±0.3%), CD19+CD20−CD138+ long-lived plasma cells (0.7%±1.0%) and CD19+CD38b+CD27b+ SLE-associated plasma cells (6.6%±7.0%).