Background Background: neutrophil extracellular traps (NETs) are released by activated neutrophils. It has been shown that NETs play a role in the pathogenesis of different autoimmune diseases, including systemic lupus erythematosus (SLE) and primary antiphospholipid syndrome (PAPS). The aim: evaluate levels of NETs observed in blood smears and their association with clinical variables in SLE, SLE+APS, and PAPS.

Methods The study included 54 patients with SLE (SLICC criteria, 2012), 37 with PAPS (Sydney criteria, 2006), 42 with SLE+APS, and 27 healthy controls without acute infections. NETs were investigated in standardized thin blood smears produced from citrated whole blood and stained by the Giemsa method. NETs percentage to the number of neutrophils was calculated (%NETs).

Results Neutrophils in PAPS, SLE+APS, and SLE released significantly more NETs than neutrophils in the control group (p=0.023). When comparing the groups in pairs, we found that the level of NETs% was higher in PAPS, SLE+APS, and SLE compared to controls (p<0.05). There were no significant differences between the levels of NETs among patients (p>0.05). NETs levels was not associated with SLE activity. Patients with glomerulonephritis in SLE and SLE+APS had significantly lower NETs capacity (4 [2.6; 5.6] versus 6.6 [2.6; 11.1], p=0.04). The levels of NETs did not differ significantly in patients with PAPS and SLE+APS depending on antiphospholipid (aPL) positivity (single, double, triple positivity), history of thrombosis or obstetric pathology.

Conclusions NETs levels were higher in SLE, SLE+APS, and PAPS compared to controls. SLE patients with renal involvement had significantly lower NETs levels. This study was prepared as a part of the fundamental scientific theme №1021051402790.