Objective: This research aimed to explore the correlation between antiphospholipid antibodies (aPLs) and complement activation in lupus nephritis (LN) patients.
Methods: A retrospective analysis was carried out on patients diagnosed with LN based on renal biopsy from June 2019 to June 2022. The study assessed levels of IgM, IgA, and IgG subtypes of anticardiolipin antibodies (aCLs) and anti-β 2-glycoprotein I (anti-β 2-GPI) antibodies. Pathological and clinical data were collected concurrently with the renal biopsy.
Results: The analysis included 76 LN patients, with 44.7% testing positive for aPLs. LN patients with positive aPLs exhibited increased hematuria, higher SLEDAI scores, reduced serum C3 and C4 levels, and more C1q deposits in the glomerulus compared to those with negative aPLs (P< 0.05). Correlation analysis demonstrated the inverse relationships between IgG-aCL levels and serum C3 and C4 levels (r=− 0.29, P=0.005; r=− 0.24, P=0.016, respectively), as well as a positive correlation with C4 deposits in the glomerulus (r=0.20, P=0.041).
Conclusion: This investigation suggests that aPLs, particularly IgG-aCLs, may be associated with the severity of LN and could contribute to the activation of classical complement pathways.

Keywords: anticardiolipin antibodies, aCLs, anti-β 2GPI antibodies, complement activation, lupus nephritis, LN