Elevated Production of B Cell Chemokine CXCL13 is Correlated with Systemic Lupus Erythematosus Disease Activity

B lymphocyte chemoattractant (BLC/CXCL13), a CXC chemokine, is involved in B1 and B2 cell trafficking for the activation of autoreactive T helper (Th) cells and autoantibody production in target organs during the development of lupus. CXCL13 can induce the trafficking of CXCR5+ T lymphocyte subset designated as follicular helper T lymphocytes (T-FH) which are specifically involved in autoantibody production. We herein measured the plasma concentrations of CXCL13, B-cell-activating factor of the TNF family (BAFF), and T-FH-cells-related cytokine IL-21 and cell surface expression of T-FH-related receptor CXCR5 and IL-21R on CD4+Th and CD19+B cells in 35 systemic lupus erythematosus (SLE) patients and 23 sex- and age-matched control subjects (NC) using enzyme-linked immunosorbent assay and flow cytometry, respectively. Plasma CXCL13, BAFF, and IL-21 concentrations were significantly higher in SLE patients than NC group (all p < 0.0001). Increase in CXCL13 concentration correlated positively and significantly with SLEDAI score in SLE patients (r = 0.399, p = 0.032). Cell surface expression of CXCR5 on Th and B cells and IL-21R on B cells was however significantly lower in SLE patients than controls (both p < 0.01). It may indicate that most differentiated T-FH cells migrate out from circulation into lymphoid organ upon activation during the disease development of SLE. The above results suggest that the elevated production of CXCL13, BAFF, and IL-21 may be associated with the function of T-FH for the immunopathogenesis in SLE, and CXCL13 may serve as a potential disease marker of SLE.