The study was performed at the V.A. Nasonova Research Institute of Rheumatology within the framework of the fundamental topic FURS-2022–003

The immunological criteria for systemic lupus erythematosus (SLE) include antiphospholipid antibodies (aPL), the value of IgA remains unclear whether they are a marker of SLE activity or the risk of thrombotic complications.

Aim to analyze the correlation between SLE activity and its clinical manifestations with IgA antibodies to cardiolipin (aCL) and IgA antibodies to beta-2 glycoprotein 1 (aß2-GP1) levels.

Method There were 112 patients with SLE (94 women and 18 men), of which 50 (45%) patients with SLE and antiphospholipid syndrome (APS) and 62 (55%) patients with SLE. Mean age was 36.0 [26.5–44.5], disease duration was 7.6 [2.7–17.5]. All patients had more than 4 criteria for the diagnosis of SLE (ACR, 1997). The study of immunological parameters in addition to SLE-mediated antibodies included IgA-aCL and IgA-aß2-GP1 by chemiluminescence analysis (CLA). The activity of SLE was assessed on a scale SLE Disease Activity Index-2000 (SLEDAI-2K). The control group consisted of 100 healthy donors of comparable age.

Results Based on the mean values of the control group in the determination of IgA-aCL, IgA-aß2-GP1, the levels of positivity were distinguished according to the formulas: arithmetic mean (M) + 3 or 5 standard deviations (SD): M+3SD and M+5SD. We also used the values suggested by the reagent manufacturer (>20 CU). In determining the diagnostic accuracy of the above values, it was determined that values >18.9 CU (M+5SD) for IgA-aCL are diagnostically more accurate, and values >20.0 (reagent manufacturer data) for IgG-aß2-GP1.

IgA-aCL were detected in 35 (31%) of 112 patients with SLE, of whom 27 (77%) were with SLE with APS and 8 (13%) with SLE without APS. IgA-aß2-GP1 was detected in 30 (26%) of 112 patients with SLE, including 22 (73%) with SLE with APS and 8 (27%) with SLE without APS.

Clinical manifestations of SLE and APS in patients with SLE are shown in Table 1. As can be seen from the table, patients with positive IgA-aCL values have significantly less kidney damage compared to patients with negative IgA-aCL values (χ2=4,77; p=0,02). Serositis occurs less frequently in patients with positive IgA-aß2-GP1 values compared to patients with negative values of these antibodies (χ2=4,21; p=0,04). APS manifestations are not associated with IgA-aCL and IgA-aß2-GP1 in patients with SLE (Table 1).

Conclusions APS manifestations are not associated with IgA-aCL and IgA-aß2-GP1 in patients with SLE. IgA-aCL positivity reduces the risk of kidney damage by 4.77 times, and IgA-aß2-GP1 positivity reduces the risk of serositis by 4.21 times.