Objective    To analyze the expression level of serine-threonine kinase receptor-associated protein (STRAP) in peripheral blood mononuclear cells of patients with systemic lupus erythematosus (SLE) and to investigate the possible application of STRAP test in evaluation of SLE.    Methods     Peripheral blood mononuclear cells were collected from 6 stable and 6 active SLE patients and 6 healthy controls

respectively. STRAP was first identified and quantified with isobaric tagging for relative and absolute protein quantification (iTRAQ) in combination with tandem mass spectrometry

and then confirmed by Western blotting in a larger independent sample size.    Results    Initial mass spectrometry-based proteomic analysis revealed that the STRAP level was significantly lower in active SLE patients than in healthy controls with a relative ratio of 0.290 6

which was further confirmed by Western blotting (P0.05). Clinical data analysis disclosed that the expression level of STRAP in active SLE patients was negatively correlated with the SLE activity index (r=-0.607

P0.05).    Conclusion     STRAP may be involved in the pathogenic process of SLE and can be used as a potential condition-specific indicator of active SLE.