CD19 and systemic lupus erythematosus: To define variations in Bregs from lupus-prone mice at different stages of disease progression, we carried out single-cell RNA sequencing (scRNA-seq) on IL-10+ CD19+ B cells generated from spleens of female MRL/lpr mice at the pre-disease stage (6-8 weeks old) or active-disease stage (10-12 weeks old).