Objective To investigate the expression level and clinical application value of G-protein coupled receptor 15 ligand (GPR15L) in patients with systemic lupus erythematosus (SLE).

Methods In a retrospective cohort, real-time fluorescent quantitative polymerase chain reaction (RT-qPCR) was used to detect the expression levels of G-protein coupled receptor 15 (GPR15) mRNA and GPR15L mRNA in peripheral blood from 63 SLE patients (SLE group) and 57 healthy controls (control group). Enzyme-linked immunosorbent assay was employed to measure the serum GPR15L protein expression levels in the SLE group, control group, and 50 rheumatoid arthritis (RA) patients (disease control group). The relationship between serum GPR15L and laboratory indicators as well as therapeutic efficacy in SLE patients was analyzed. Receiver operating characteristic (ROC) curves were used to assess the diagnostic efficacy of serum GPR15 alone and combination with common autoantibody indicators for SLE. Multivariate Logistic regression analysis was conducted to explore the independent risk factors for SLE onset.

Results Compared with the control group, the SLE group exhibited increased levels of GPR15 mRNA and GPR15L mRNA in peripheral blood (P=0.016 4, P < 0.000 1, respectively). The serum GPR15L expression in the SLE group was higher than that in the disease control group (P < 0.000 1). The serum GPR15L protein expression level in SLE patients was positively correlated with GPR15L mRNA and disease activity (r=0.301 3, P=0.016 4; r=0.361 7, P=0.003 6) and negatively correlated with complement C3 and C4 levels (r=-0.341 2, P=0.006 2; r=-0.338 4, P=0.006 7). The ROC curves showed that the area under the curve (AUC) for serum GPR15L in distinguishing the SLE group from the control group was 0.870 8, and the AUC for distinguishing the SLE group from the control group was 0.765 5. The diagnostic efficacy of serum GPR15L combined with anti-SSA for SLE was significantly improved, with an AUC of 0.895 2. Multivariate Logistic regression analysis revealed that elevated GPR15L protein and GPR15L mRNA were independent risk factors for SLE onset (P < 0.05).

Conclusion The significant increase in serum GPR15L protein levels in SLE patients is closely related to SLE disease activity, and abnormal expression of GPR15L may play an important role in the pathogenesis of SLE.