CD19 and systemic lupus erythematosus: This review focuses on ABC and ABC-like sub-populations found in Systemic Lupus Erythematosus (SLE) patients (such as the double negative 2;DN2 population: CD19+,IgD−,CD27−, CXCR5−,T-bet+) and broaches the subject of their potential use as prognostic and/or diagnostic markers.