Interleukin-21 is increased in active systemic lupus erythematosus patients and contributes to the generation of plasma B cells.

OBJECTIVES: Excessive interleukin- (IL-) 21 production by T cells has been implicated in the pathogenesis of systemic lupus erythematosus (SLE). We explored the expression and function of IL-21 in human SLE. METHODS: IL-21 and IL-21 receptor (IL-21R) expression was assessed by real-time PCR and flow cytometry in peripheral blood mononuclear cells (PBMCs) of SLE patients and healthy controls. PBMCs, purified CD19+CD27- naive and CD19+CD27+ memory B cells were stimulated with IL-21 and CpG-ODN2006 (TLR-9 agonist) to examine generation of memory and plasma (CD19+CD38highIgD-) B cells. Apoptosis was assessed by 7AAD staining. RESULTS: Active SLE patients had 4-fold higher IL-21 mRNA and increased levels of intracellular IL-21 in peripheral blood CD4+ T cells (mean±SD fluorescence intensity, 1.7±0.1 in active versus 0.9±0.3 in inactive SLE and controls, p=0.035). IL-21R mRNA was comparable between SLE and healthy controls. Stimulation of PBMCs with IL-21 increased the proportion of memory and plasma cells; addition of CpG-ODN2006 enhanced these effects. Both naive and memory B cells responded to IL-21/TLR-9 by increased generation of memory and plasma B cells, respectively; an anti-apoptotic effect was observed. In active SLE, PBMCs stimulation with IL-21 and/or CpG-ODN increased memory and plasma B cells, comparable to healthy controls. Addition of IL-21 to lupus autologous mixed lymphocyte cultures induced significant IgG production, and treatment with IL-21R.Fc to block IL-21/IL-21R interaction reduced the proportion of plasma cells. CONCLUSIONS: Increased IL-21 may synergise with TLR-9 signalling and contributes to generation of plasma cells in active SLE patients.