Background and Objectives Despite recent insights on abnormalities of blood B cell subsets in human systemic lupus erythematosus (SLE), a peripheral blood biomarker with useful clinical information about the occurrence of an active disease period hasn’t yet been achieved. Moreover, the clinical relevance of anti-dsDNA antibodies and their utility for monitoring an individual patient remains a matter of debate. In this sense, we attempt to determine whether the degree of abnormalities of circulating B cell subsets correlates with SLE disease activity and constitute an useful tool for SLE patients monitoring.

Materials and Methods We analysed by flow cytometry the major circulating B cell subsets (immature, naïve, memory and plasmablast) and their expression profile of B cell related molecules (CD19, CD20, CD81 and BAFFR) in 43 SLE patients, 18 with active and 25 with inactive disease, according to the SLE Disease Activity Index 2000 (SLEDAI, 2k), as well as in 30 healthy individuals.

Results The results pointed to the existence of significant alterations on B cell homeostasis that are significantly correlated with disease activity. An overall decrease in absolute numbers of all B cell subsets was observed in SLE patients, with the exception of IgGplasmablast that remained equal or even higher than in the control group, particularly in active disease. Additionally, a higher number of plasmablast expressing each Ig-heavy chain isotypes was found in patients with mucocutaneous involvement. Moreover, among memory B cells, an increased IgG and decreased IgM positive cellswas observed in both SLE groups.

Furthermore, a decreased expression of CD19 observed in active disease and an increased BAFFR expression in inactive disease in the majority of B cell subsets, may contribute not only for breaking tolerance during B cell development, but also for enhancing plasmablast survival.

Conclusions In conclusion, flow cytometric monitoring of circulating B cell subsets, particularly focused on relative and absolute numbers of IgG plasmablasts, could provide a useful tool for monitoring disease activity, but also the therapy efficacy in patients with SLE.