[Effect of serum interleukin-21 on B cell secretory capacity and apoptosis in patients with systemic lupus erythematosus]

Objective: To investigate the secretory capacity and apoptosis of interleukin (IL)-21 induced normal B cells by co-culture with serum from patients with systemic lupus erythematosus (SLE). Methods: Serum from twenty new-onset SLE patients and 20 healthy donors were collected. CD(19)(+) B cells from the normal controls were co-cultured with serum from SLE patients in the presence or absence of IL-21-R-FC(4 μg/ml). Supernatant IgG and IgM concentration were measured by immunoturbidimetric assay on day 5. Supernatant anti-dsDNA level was determined by ELISA. The percentage of apoptotic cells was detected by flow cytometer. Results: IgG, IgM and anti-dsDNA levels in normal B cells with SLE serum were significantly higher than those in the serum of SLE patients alone [(5.84±1.79)g/L vs (4.25±1.48)g/L, P=0.000; (0.46±0.21)g/L vs (0.43±0.21)g/L, P=0.003; (127.76±70.24)IU/ml vs (115.15±63.88) IU/ml, P=0.014 respectively]. However, no significant differences were found in the group of normal B cells with non-homologous serum from normal controls (P>0.05). Supernatant IgG, IgM and anti-dsDNA levels in normal B cells with SLE serum significantly decreased while IL-21R-fusion protein was added [(5.26±1.62)g/L vs (5.84±1.79)g/L, P=0.006; (0.42±0.20)g/L vs (0.46±0.21)g/L, P=0.002; (118.00±69.62)IU/ml vs (127.76±70.24)IU/ml, P=0.012 respectively]. The apoptotic rate of B cells with SLE serum was significantly higher than that with normal serum [(47.88±12.65)% vs (38.86±10.32)%, P=0.004]. But adding IL-21R-fusion conversed the apoptotic rates [(42.08±12.52)% vs (47.88±12.65)%, P=0.001]. Conclusions: SLE serum could induce normal B cells to form immunoglobulin secreting cells and producing autoantibodies, or apoptosis in pathological conditions. IL-21 might be considered as a potential therapeutic target of SLE.