Anti-beta-2-glycoprotein I domain 1 identifies antiphospholipid antibodies-related injuries in patients with concomitant lupus nephritis

Background: In this study we aimed to evaluate the usefulness of domain profiling of Beta-2-glycoprotein I(β2GPI)-Domain-1 (D1) antibodies in relation to antiphospholipid antibodies (aPL)-related nephropathy (aPL-N) in patients with biopsy-proven lupus nephritis (LN). Methods: Of 124 consecutive patients (96 women, mean age 45.5 ± 12.3 years, mean disease duration 14.7 ± 9.6 years) fulfilling the 1982 criteria for systemic lupus erythematosus (SLE), we identified 39 patients (mean age 39.84 ± 8.6 years, mean disease duration 11.3 ± 7.7 years) with the following characteristics: (a) biopsy-proven LN; (b) no previous diagnosis of antiphospholipid syndrome (APS) according to the current classification criteria. Results: Patients with both LN and aPL-N had higher median aβ2GPI-D1 antibody titres (220.1 CU, 25–75th IQ 29.1–334.2) as compared those with LN alone (46.5 CU, 25–75th IQ 12.5–75.1) (p = 0.0087). Median aβ2GPI-D1 antibody titres were higher in patients with acute thrombotic microangiopathy (aTMA) (N = 7) (250.1 CU, 25–75th IQ 61.2–334.2) vs. with LN alone (46.5 CU, 25–75th IQ 12.5–75.1 CU) (p = 0.0009). Having a Global Antiphospholipid Syndrome Score > 10 confers an increased probability of having acute features of aTMA (OR 6.25, 95%CI 1.2–31.8). As compared to other aPL, aβ2GPI-D1 antibodies have the best diagnostic accuracy for aTMA as evaluated by performances in Area Under the Curves in a ROC analysis. Conclusions: aβ2GPI-D1 antibodies detection might provide a second-line assay to be performed in aβ2GPI positive patients with LN, allowing more accurate stratification of the renal vascular involvement risk, thus potentially leading to a more tailored management.