Analysis of B-cell subpopulations in systemic lupus erythematosus

Abnormalities in humoral immunity play a significant role in systemic lupus, mandating further studies in B-cell autoimmunity in this entity. Disease activity in systemic lupus erythematosus (SLE) is usually assessed with complex disease activity scores composed of a variety of different parameters. To determine whether SLE disease activity correlated with abnormal B-lymphocyte activity, B-cell subsets were analyzed and related to clinical measures. The distribution of B-cell subsets was determined by fluorescence-activated cell sorting analysis and compared with the autoantibody profile, with the disease activity measured by the SLE disease activity index (SLEDAI) and the European Consensus Lupus Activity Measurement (ECLAM), disease duration and therapy. The number and frequency of CD27^high plasma cells were significantly correlated with the SLE disease activity indices (SLEDAI and ECLAM) and the titer of anti-dsDNA autoantibodies. Circulating B-cell subsets were not influenced by age or gender, but appeared to relate to the duration of disease and the therapeutic regimen, with the numbers and frequencies of CD27^high plasma cells increasing and those of CD27-naïve B cells decreasing over time. Patients were divided into those with a SLEDAI score of 0–8 (low activity) and those with a SLEDAI score > 8 patients (high activity). High-activity patients were found to have an increased frequency of CD19⁺B cells as well as CD27^high plasma cells. Using a nonparametric data sieving algorithm, these B-cell abnormalities exhibited predictive values for nonactive and active disease of 78.0% and 78.9%, respectively. The predictive value of the B-cell abnormalities was greater than that of the humoral/clinical data pattern, including anti-DNA antibody levels, circulating immune complexes, increased erythrocyte sedimentation rate, mucocutaneous and acute renal involvement, which showed predictive values of 77.8% and 70.0% for active and nonactive disease. Flow cytometric monitoring of B-cell subsets in the peripheral blood provides new insights into the abnormalities in B-cell function in SLE, and may also be a diagnostically valuable option to follow disease activity in this autoimmune disease.