SDC1 and systemic lupus erythematosus: Active SLE is associated with naive CD19+CD27- B cell lymphopenia, while transitional CD19+CD24hiCD38hi B cells, switched memory CD19+CD27+IgD- B cells, double negative CD19+CD27-IgD- B cells, plasmablasts/plasma cells CD27hiCD38+CD19+sIglowCD20-CD138+ B cells are increased which correlate with SLE disease activity (134, 135).