Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with a wide spectrum of clinical manifestations and immunological abnormalities. Because of its heterogeneous presentation and unpredictable course, clinical management of SLE remains difficult.1 High numbers of CD27++ CD20− B lymphocytes, identified as plasma cells (PCs), in peripheral blood have been reported in patients with increased SLE disease activity.2 3 This is the first prospective study to evaluate PCs as a biomarker for SLE disease activity.

A heterogeneous population of patients with SLE (n=17) were followed up for a period of 2–7 years (172 total clinic visits). The cohort included 14 clinically quiescent patients with previously diagnosed SLE treated with immunosuppressive drugs and three patients with newly diagnosed SLE admitted to our hospital with active disease (SLE disease activity index (SLEDAI) 16–32).4

Thirty-one peaks, defined as a PC value >3.6×10^{6 …}