Circulating B Lymphocyte Subsets in Patients with Systemic Lupus Erythematosus.

: Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the abnormal activation of autoreactive T and B cells, autoantibody production, complement activation, and immune-complex deposition, resulting in tissue damage. However, data on immunologic disturbances in SLE, particularly regarding flares, are scarce. : We investigated 35 patients with SLE: 12 (34.3%) with disease exacerbation (SLE disease activity index [SLEDAI] ≥ 5 points) and 23 (65.7%) in remission (SLEDAI < 5 points). All patients met the 2019 EULAR/ACR SLE criteria. Flow cytometry was used to identify B cell subsets, including memory B cells. : In the whole patient group, SLEDAI was positively related to the percentage of transitional/regulatory B cells (r = 0.38, = 0.034). Some lymphocyte subsets correlated with complement levels, e.g., the percentage of naïve and memory B cells showed associations with C3c complement (r = 0.43, = 0.018 and r = -0.45, = 0.016, respectively). Furthermore, regarding inflammatory markers, we found associations between C-reactive protein and the percentage of plasmablasts (r = 0.40, = 0.026) and plasmocytes (r = 0.44, = 0.017). Finally, the percentage of plasmablasts correlated with SLE duration (r = 0.42, = 0.016). In the follow-up analysis, during a median observation of 5 years, 5 out of the initially 23 inactive SLE patients developed a disease flare. They were characterized by longer disease duration stated in the beginning compared to patients who remained in remission ( = 0.019). : Our study highlights significant associations between various B cell subsets and SLE disease activity. A more personalized approach to indicate patients with SLE at a higher risk of lupus flares is crucial for better management.