CD19 and systemic lupus erythematosus: Data from prospective studies [33–35] showed that addition of belimumab to usual treatment in SLE patients was associated with (1) decreased disease activity measured by the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score (up to 70%) and (2) lower absolute CD19 + B cell count and/or anti-DNA antibody levels.