Objective To investigate the mRNA expression of a proliferation inducing ligand (APRIL) and its receptors including B cell maturation antigen (BCMA),transmembrane activator.calcium modulator and cyclophilin ligand interactor (TACI) in the peripheral blood mononuclear cells (PBMCs) of patients with systemic lupus erythematosus (SEE).Methods APRIL mRNA、BCMA mRNA and TACI mRNA in PBMCs were detected by real-time quantitative PCR in 66 SLE patients and 25 normal controls.Gene expression level was measured as 2-AACT.Results The expression levels of APRIL mRNA、BCMA mRNA and TACI-mRNA were significantly increased in both active SLE group and stable SLE group compared with those in the normal controls(P<0.01 for all).The expression levels of APRIL mRNA and TACI mRNA in active SLE group were significantly higher than those in stable SLE group(P<0.01,P<0.05,respectively).But there was no significant difierence in the expression levels of BCMA mRNA between the SLE stable and active groups-Beside,the expression levels of APRIL mRNA and TACI mRNA were significantly increased in patients with lupus nephritis (LN) compared to patients with non-LN (P<0.01 for all).Conclusion The expression levels of APRIL and its receptors are significantly elevated in SLE patients.It may suggest that APRIL and its receptors play an important role in the pathogenesis of SLE.