A new CD21low B cell population in the peripheral blood of patients with SLE.

A hallmark of systemic lupus erythematosus (SLE) is the production of autoantibodies. Recent reports suggest an abnormal peripheral blood B cell homeostasis in SLE patients without being conclusive. We analyzed by four color flow-cytometry peripheral blood B cell subpopulations of SLE patients, healthy donors, and patients with other systemic autoimmune diseases. IgM memory but not switched memory B cells of SLE patients were significantly decreased compared to healthy donors, whereas transitional B cells, characterized by CD19+IgMhiIgD+CD24hiCD38hi, were significantly expanded in SLE patients but also found in other autoimmune disorders. The population of plasmablasts (CD19loCD21loCD27++CD38++) was increased in active disease. Most interestingly, B cells in autoimmune disorders contain a so far uncharacterized subpopulation with an activated phenotype (CD19hiCD21loCD38loCD86int). None of the identified subpopulations was associated with current or previous therapy and therefore may represent different aspects of the disturbed B cell homeostasis in patients with SLE.