Association of BAFF, APRIL serum levels, BAFF-R, TACI and BCMA expression on peripheral B-cell subsets with clinical manifestations in systemic lupus erythematosus

Objective B-cell-activating factor (BAFF) and a proliferation-inducing ligand (APRIL) signaling pathways regulate B-cell survival through interactions with their receptors BAFF-R, TACI and BCMA. We evaluated the association of these ligands/receptors on B-cell subsets according to clinical manifestations of systemic lupus erythematosus (SLE). Methods BAFF and APRIL serum concentrations were measured in 30 SLE patients by enzyme-linked immunosorbent assay. The BAFF-R, TACI and BCMA expression was analyzed on each B cell subset (CD19+CD27-CD38-/+naive; CD19+CD27+CD38-/+memory; CD19+CD27-CD38++immature and CD19+CD27+CD38++plasma cells) by flow cytometry, and compared among patients with different clinical manifestations as well as healthy controls (HCs). Results Serum BAFF and APRIL levels were high in SLE patients and correlated with the Mex-SLEDAI disease activity index (r=0.584; p=0.001 and r=0.456; p=0.011, respectively). The SLE patients showed an increased proportion of memory and plasma B cells (p<0.05). BAFF-R, TACI and BCMA expression in SLE patients was decreased in almost all B cell subsets compared to HCs (p<0.05). A lower BCMA expression was associated with severe disease activity, glomerulonephritis, serositis and hemolytic anemia (p<0.01). BCMA expression showed a negative correlation with Mex-SLEDAI score (r=-0.494, p=0.006). Conclusions Decreased BCMA expression on peripheral B cells according to severe disease activity suggests that BCMA plays an important regulating role in B-cell hyperactivity and immune tolerance homeostasis in SLE patients.