Background B lymphocytes derived from patients with systemic lupus erythematosus (SLE) displayed abnormal activation and overexpression of auto-antibodies. It was reported that leptin was elevated in the sera of SLE patients and lupus mice, and blockade of leptin also remarkably improved the disease activity and renal pathology of lupus mice. Therefore, our study is to explore whether leptin in SLE regulates the activation and function of B cells.

Objectives Our study is to explore whether leptin in SLE regulates the activation and function of B cells.

Methods The sera and peripheral blood monocyte cells (PBMC) were isolated from healthy controls and SLE patients with Ficoll, then B cells were acquired through magnetic activated cell sorting (MACS). The sera were incubated in 56° for 30 min (complement inactivation). B cells were cultured in normal or SLE serum, with or without recombinant leptin. Anti-leptin antibody or inhibitions of the signalling pathways were added in SLE sera in order to observe the effects of B cells induced by leptin. Cell proliferation was detected by flow cytometry and carboxyfluorescein diacetate succinimdyl ester (CFSE), and the levels of auto-antibodies and inflammatory cytokines were examined by ELISA. The total and phosphorylated protein was tested with Western Blot analysis.

Results Leptin R on B cells showed increased levels in SLE patients [(3.33±1.28)% v.s. (2.76±1.06)%, p<0.01]. Leptin could upregulate the activated markers (CD80, CD86), also increase the proliferation (CFSE) of B cells. Recombinant leptin promotes IgG/IgM production [ IgG: leptin 0 (45.50±3.87)ng/ml vs. leptin 100 (61.24±3.66)ng/ml, p<0.01; IgM: leptin 0 (60.75±19.60)ng/ml vs. leptin 100 (118.90±26.16)ng/ml, p<0.01], as well as inflammatory cytokines (IL-6, IL-10, TNF-a) secreted by B cells derived from SLE patients. [IL-10: leptin 0 (20.45±5.17)pg/ml vs. leptin 100 (23.81±5.45)pg/ml, p<0.01; IL-6: leptin 0 (156.10±32.64)pg/ml vs. leptin 100 (244.20±54.23)pg/ml, p<0.05; TNF-a: leptin 0 (13.33±2.38)pg/ml vs. leptin 100 (18.85±2.69)pg/ml, p<0.001.] Compared with Nor serum, SLE serum enhanced the levels of IgG/IgM and inflammatory cytokines, such as IL-6, IL-10, TNF-a. Moreover, blockade of leptin could partially reverse these effects. SLE serum or recombinant leptin could activate p38 MAPK, ERK1/2, and Jak/stat3,5 pathways, but not PI3K/Akt or Jak/stat1 pathways. In addition, blocking ERK1/2 and Jak/stat3,5 pathways could partially reverse the effects of enhanced secretion of autoantibodies and inflammatory cytokines induced by recombinant leptin or SLE serum.

Conclusions Leptin promote the activation and proliferation of B cells in SLE. Recombinant leptin or serum leptin from SLE patients both enhanced the expression of autoantibodies and inflammatory cytokines (IL-6, IL-10, TNF-a) of B lymphocytes. Additionaly, ERK1/2, and Jak/stat3,5 signalling pathways might play a vital role in this process.

Disclosure of Interest None declared