CD27 and systemic lupus erythematosus: As the DN B cell population was the only one with an increased percentage within B lymphocytes, we calculated the ratio of (IgD-CD27-)/[(IgD+CD27-) + (IgD-CD27+) + (IgD+CD27+)] in SLE patients and controls and found a significant difference of 0.14 (0.02–2.9) vs. 0.08 (0.02–0.54), respectively; p = 0.04.